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Modulation of the Structure and Properties of Uranyl Ion Coordination Polymers Derived from 1,3,5-Benzenetriacetate by Incorporation of Ag(I) or Pb(II) Pierre Thuéry*,† and Jack Harrowfield*,‡ †

NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France ISIS, Université de Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France

‡

S Supporting Information *

ABSTRACT: Reaction of uranyl nitrate with 1,3,5-benzenetriacetic acid (H3BTA) in the presence of additional species, either organic bases or their conjugate acids or metal cations, has provided 12 new crystalline complexes, all but one obtained under solvo-hydrothermal conditions. The complexes [C(NH2)3][UO2(BTA)]·H2O (1) and [H2NMe2][UO2(BTA)] (2) crystallize as one- or two-dimensional (1D or 2D) assemblies, respectively, both with uranyl tris-chelation by carboxylate groups and hydrogen-bonded counterions but different ligand conformations. One of the bound carboxylate units is replaced by chelating 1,10-phenanthroline (phen) or 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4phen) in the complexes [(UO2)3(BTA)2(phen)3]·4H2O (3) and [(UO2)3(BTA)2(Me4phen)3]·NMP·3H2O (4) (NMP = N-methyl-2-pyrrolidone), which are a 2D network with honeycomb topology and a 1D polymer, respectively. With silver(I) cations, [UO2Ag(BTA)] (5), a three-dimensional (3D) framework in which the ligand assumes various chelating/bridging coordination modes, and the aromatic ring is involved in Ag(I) bonding, is obtained. A series of seven heterometallic complexes results when lead(II) cations and N-chelating molecules are both present. The complexes [UO2Pb(BTA)(NO3)(bipy)] (6) and [UO2Pb2(BTA)2(bipy)2]·3H2O (7), where bipy is 2,2′-bipyridine, crystallize from the one solution, as 1D and 2D assemblies, respectively. The two 1D coordination polymers [UO2Pb(BTA)(HCOO)(phen)] (8 and 9), again obtained from the one synthesis, provide an example of coordination isomerism, with the formate anion bound either to lead(II) or to uranyl cations. Another 2D architecture is found in [(UO2)2Pb2(BTA)2(HBTA)(H2O)2(phen)2]·2H2O (10), which provides a possible example of a Pb−oxo(uranyl) “cation−cation” interaction. While [UO2Pb(BTA)(HCOO)0.5(NO3)0.5(Me2phen)] (11), where Me2phen is 5,6-dimethyl-1,10-phenanthroline, is a 1D assembly close to those in 6 and 8, [UO2Pb2(BTA)2(Me4phen)2] (12), obtained together with complex 4, crystallizes as a 2D network as a result of the high degree of connectivity provided by the chelating/bridging tricarboxylate ligand. Emission spectra measured in the solid state display vibronic fine structure attributable to uranyl luminescence (except for complex 5, in which emission is quenched), with variations in maxima positions associated with modifications of the uranyl ion environment.

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INTRODUCTION The formation of solid frameworks incorporating cavities suited to selective absorption of molecular species and involving uranyl ion centers within the framework1 has, as obvious potential applications, sensing due to changes in luminescence and catalytic photo-oxidation of any absorbed species.2 Although an isolated uranyl center is a one-electron photooxidant,2c,d the possibility of arranging multiple uranyl centers about a single cavity in a solid raises the prospect of performing a variety of multielectron oxidations. Despite the extensive characterization of uranyl−organic coordination polymers and frameworks, however, systems that might be suitable for such applications have been obtained more by chance than design, and in the majority of cases only those that can be considered polyuranate derivatives have uranium(VI) centers in close proximity. The remarkable family of peroxo-bridged polyuranates provides elegant examples of this situation.3 It is © XXXX American Chemical Society

known that uranyl luminescence is subject to numerous influences,4 including the presence of other uranyl centers and of a variety of transition metal ions,5,6 so that the systematic investigation of mixed-metal uranyl coordination polymers would seem a rational pathway to applications of uranyl ion photochemistry. Recent reports by us and other groups have dealt with the investigation of the crystal structure and luminescence properties of uranyl ion complexes, coordination polymers or frameworks including 3d block metal cations either as additional metal centers in the complex unit or as counterions, the ligands used being polycarboxylates or polyphosphonates.5,6 The present work is an extension of this survey to a poly(carboxylic acid), which has been little used in uranyl chemistry, 1,3,5-benzenetriacetic acid (H3BTA), the Received: May 12, 2016

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DOI: 10.1021/acs.inorgchem.6b01168 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

[(UO2)3(BTA)2(Me4phen)3]·NMP·3H2O (4) and [UO2Pb2(BTA)2(Me4phen)2] (12). H3BTA (13 mg, 0.05 mmol), UO2(NO3)2·6H2O (25 mg, 0.05 mmol), Pb(NO3)2 (17 mg, 0.05 mmol), 3,4,7,8-tetramethyl-1,10-phenanthroline (12 mg, 0.05 mmol), N-methyl-2-pyrrolidone (0.2 mL), and demineralized water (0.6 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 4 overnight, mixed with a smaller amount of light orange crystals of complex 12. Repeated attempts with varying conditions did not enable isolation of either complex in pure form. [UO2Ag(BTA)] (5). H3BTA (13 mg, 0.05 mmol), UO2(NO3)2·6H2O (25 mg, 0.05 mmol), AgNO3 (17 mg, 0.10 mmol), tetrahydrofuran (THF; 0.3 mL), and demineralized water (0.7 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 5 in low yield within one week. When N,N-dimethylacetamide (DMA) was used instead of THF, crystallization by slow evaporation of the solution at room temperature gave the homometallic complex [Ag2(HBTA)(H2O)] as the only product (9 mg, 37% yield). Anal. Calcd for C12H12Ag2O7: C, 29.78; H, 2.50. Found: C, 29.57; H, 2.40%. [UO2Pb(BTA)(NO3)(bipy)] (6) and [UO2Pb2(BTA)2(bipy)2]·3H2O (7). H3BTA (13 mg, 0.05 mmol), UO2(NO3)2·6H2O (25 mg, 0.05 mmol), Pb(NO3)2 (17 mg, 0.05 mmol), 2,2′-bipyridine (16 mg, 0.10 mmol), N,N-dimethylacetamide (0.2 mL), and demineralized water (0.6 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving a mixture of light yellow crystals of complexes 6 and 7 within 3 d. [UO2Pb(BTA)(HCOO)(phen)] (8 and 9). H3BTA (25 mg, 0.10 mmol), UO2(NO3)2·6H2O (50 mg, 0.10 mmol), Pb(NO3)2 (33 mg, 0.10 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), N,Ndimethylformamide (0.2 mL), and demineralized water (0.8 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving a mixture of light yellow-orange crystals of complexes 8 and 9 within one week (38 mg, 40% yield). Anal. Calcd for C25H18N2O10PbU: C, 31.55; H, 1.91; N, 2.94. Found: C, 30.90; H, 2.17; N, 2.88%. [(UO2)2Pb2(BTA)2(HBTA)(H2O)2(phen)2]·2H2O (10). H3BTA (13 mg, 0.05 mmol), UO2(NO3)2·6H2O (25 mg, 0.05 mmol), Pb(NO3)2 (17 mg, 0.05 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), N,Ndimethylacetamide (0.2 mL), and demineralized water (0.7 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 10 in low yield within 3 d. [UO2Pb(BTA)(HCOO)0.5(NO3)0.5(Me2phen)] (11). H3BTA (25 mg, 0.10 mmol), UO2(NO3)2·6H2O (50 mg, 0.10 mmol), Pb(NO3)2 (33 mg, 0.10 mmol), 5,6-dimethyl-1,10-phenanthroline (21 mg, 0.10 mmol), N,N-dimethylformamide (0.3 mL), and demineralized water (0.8 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 11 within 3 d (54 mg, 55% yield). Anal. Calcd for C26.5H21.5N2.5O10.5PbU: C, 32.21; H, 2.19; N, 3.54. Found: C, 32.06; H, 2.23; N, 3.73%. Crystallography. The data were collected at 150(2) K on a Nonius Kappa-CCD area detector diffractometer14 using graphitemonochromated Mo Kα radiation (λ = 0.710 73 Å). The crystals were introduced into glass capillaries with a protective coating of ParatoneN oil (Hampton Research). The unit cell parameters were determined from 10 frames, then refined on all data. The data (combinations of φand ω-scans with a minimum redundancy of at least four for 90% of the reflections) were processed with HKL2000.15 Absorption effects were corrected empirically with the program SCALEPACK.15 The structures were solved by intrinsic phasing with SHELXT,16 expanded by subsequent difference Fourier synthesis and refined by full-matrix least-squares on F2 with SHELXL-2014.17 All non-hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms bound to oxygen or nitrogen atoms were retrieved from difference Fourier maps (except for those of one lattice water molecule in each of complexes 4 and 7), and the carbon-bound hydrogen atoms were introduced at calculated positions; all hydrogen atoms were treated as riding atoms with an isotropic displacement parameter equal

additional metal cations employed being silver(I) and lead(II), both having a distinctive coordination chemistry7 quite different to that of uranyl ion and thus being expected, if indeed incorporated into a heterometallic coordination polymer with uranyl ion, to possibly place this last species in novel environments. Despite its resemblance to tripodal ligands known to be capable of enveloping a single uranyl ion in a tris(carboxylato) embrace,8 H3BTA appears to have arms that are too short to adopt such a coordination mode, while being more flexible than Kemp’s triacid9 with, in particular, the possibility of location of the functional groups on the same (cis,cis conformation) or opposite sides (cis,trans) of the aromatic ring; this property distinguishes it also from the more widely used 1,3,5-benzenetricarboxylic acid. Only four uranyl complexes of BTA3− have been reported up to now, [UO2(H2O)5][UO2(BTA)]2·5H2O,10 [NMe4][UO2(BTA)]· H2 O,11 [(UO 2 ) 3(BTA) 2 (NMP) 3 ]·0.5H 2 O, and [Hbipy][UO2(BTA)]·H2O,6a where NMP is N-methyl-2-pyrrolidone and bipy is 2,2′-bipyridine; these complexes crystallize as onedimensional (1D) polymer chains or as two-dimensional (2D) polymer networks. This system thus appears to be sensitive to changes in counterions or solvents and therefore to be a good candidate for an exploration of the effect of additional metal cations. Of the two cations used here, silver(I) is the more commonly found in known uranyl species,6i,12 and only three cases of heterometallic uranyl−lead(II) complexes have been described so far.12b,13 We report herein the syntheses, crystal structures, and (in most cases) emission spectra of 12 novel uranyl complexes, homo- and heterometallic, with H3BTA.

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EXPERIMENTAL SECTION

Syntheses. Caution! Uranium is a radioactive and chemically toxic element, and uranium-containing samples must be handled with suitable care and protection. UO2(NO3)2·6H2O (depleted uranium, R. P. Normapur, 99%), AgNO3, Pb(NO3)2, and [C(NH2)3]NO3 were purchased from Prolabo; 1,3,5-benzenetriacetic acid (H3BTA), 2,2′bipyridine (bipy), and 5,6-dimethyl-1,10-phenanthroline (Me2phen) were from Fluka; 1,10-phenanthroline (phen) and 3,4,7,8-tetramethyl1,10-phenanthroline (Me4phen) were from Aldrich. Elemental analyses were performed by MEDAC Ltd. at Chobham, U.K, and Service de Microanalyse of the CNRS at Gif-sur-Yvette, France. [C(NH2)3][UO2(BTA)]·H2O (1). H3BTA (25 mg, 0.10 mmol), UO2(NO3)2·6H2O (50 mg, 0.10 mmol), and guanidinium nitrate (12 mg, 0.10 mmol) were dissolved in a mixture of demineralized water (0.8 mL) and acetonitrile (0.2 mL). The solution was left to evaporate slowly at room temperature, and light yellow crystals of complex 1 appeared within two weeks (5 mg, 8% yield). Anal. Calcd for C13H17N3O9U: C, 26.14; H, 2.87; N, 7.03. Found: C, 26.64; H, 2.72; N, 6.92%. [H 2 NMe 2 ][UO 2 (BTA)] (2). H 3 BTA (25 mg, 0.10 mmol), UO2(NO3)2·6H2O (50 mg, 0.10 mmol), Pb(NO3)2 (17 mg, 0.05 mmol), 2,2′-bipyridine (16 mg, 0.10 mmol), N,N-dimethylformamide (0.2 mL), and demineralized water (0.8 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 2 within 3 d (40 mg, 71% yield). Anal. Calcd for C14H17NO8U: C, 29.75; H, 3.03; N, 2.48. Found: C, 30.48; H, 2.72; N, 2.68%. [(UO2)3(BTA)2(phen)3]·4H2O (3). H3BTA (13 mg, 0.05 mmol), UO2(NO3)2·6H2O (25 mg, 0.05 mmol), Pb(NO3)2 (17 mg, 0.05 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), N-methyl-2pyrrolidone (0.2 mL), and demineralized water (0.8 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 3 within 3 d (15 mg, 47% yield based on U). Anal. Calcd for C60H50N6O22U3: C, 37.51; H, 2.62; N, 4.37. Found: C, 37.89; H, 2.34; N, 4.30%. B


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Inorganic Chemistry Table 1. Crystal Data and Structure Refinement Details chemical formula M (g mol−1) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) μ(Mo Kα) (mm−1) F(000) reflns collcd indep reflns obsd reflns [I > 2σ(I)] Rint params refined R1 wR2 S Δρmin (e Å−3) Δρmax (e Å−3) chemical formula M (g mol−1) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) μ(Mo Kα) (mm−1) F(000) reflns collcd indep reflns obsd reflns [I > 2σ(I)] Rint params refined R1 wR2 S Δρmin (e Å−3) Δρmax (e Å−3)

1

2

3

4

5

6

C13H17N3O9U 597.32 monoclinic P21/n 11.5081(7) 11.4273(4) 13.2728(8) 90 91.889(3) 90 1744.51(16) 4 2.274 9.358 1120 64 495 4506 3967 0.036 235 0.026 0.066 1.069 −2.03 1.00 7

C14H17NO8U 565.31 orthorhombic Pbca 8.9860(3) 17.7983(4) 21.3159(7) 90 90 90 3409.17(18) 8 2.203 9.563 2112 126 662 3210 2983 0.010 227 0.020 0.050 1.130 −1.01 1.13 8

C60H50N6O22U3 1921.15 monoclinic C2/c 19.0486(5) 17.4121(6) 19.6753(5) 90 114.184(2) 90 5953.1(3) 4 2.144 8.228 3616 102 973 9092 7460 0.035 420 0.028 0.067 1.089 −1.45 1.09 9

C77H81N7O22U3 2170.57 triclinic P1̅ 13.9272(7) 17.5666(8) 17.9322(8) 99.490(3) 91.664(3) 100.672(3) 4244.3(3) 2 1.698 5.781 2088 221 377 16 039 13 067 0.062 1078 0.058 0.150 1.098 −2.67 2.19 10

C12H9AgO8U 627.09 monoclinic C2/c 18.6927(8) 8.0733(4) 19.9326(9) 90 115.851(3) 90 2707.1(2) 8 3.077 13.436 2272 52 482 4152 3572 0.037 199 0.026 0.064 1.037 −1.80 0.97 11

C22H17N3O11PbU 944.60 orthorhombic Pna21 22.0490(11) 9.3829(3) 11.5465(5) 90 90 90 2388.78(18) 4 2.627 13.878 1728 55 184 5910 5270 0.027 344 0.029 0.064 1.024 −1.59 0.71 12

C44H40N4O17Pb2U 1549.21 monoclinic C2/c 42.4808(13) 12.0108(3) 19.2498(6) 90 115.5883(15) 90 8858.5(5) 8 2.323 11.312 5792 255 366 11 425 9520 0.047 614 0.026 0.053 1.033 −1.89 2.76

C25H18N2O10PbU 951.63 monoclinic P21 9.2166(5) 11.5073(4) 24.1868(13) 90 100.550(3) 90 2521.8(2) 4 2.506 13.143 1744 94 167 12 998 10 655 0.044 704 0.038 0.087 1.044 −1.71 1.32

C25H18N2O10PbU 951.63 triclinic P1̅ 8.5007(4) 11.5247(7) 14.1610(8) 108.338(3) 97.398(3) 96.192(3) 1289.59(13) 2 2.451 12.851 872 68 689 6663 5491 0.067 352 0.030 0.069 1.057 −1.79 2.21

C60H52N4O26Pb2U2 2135.49 triclinic P1̅ 11.2775(9) 11.4481(6) 14.4258(13) 75.212(5) 84.831(4) 62.004(5) 1589.1(2) 1 2.232 10.449 996 88 486 6031 4918 0.068 457 0.036 0.096 1.028 −1.45 1.96

C26.5H21.5N2.5O10.5PbU 988.18 monoclinic P21/c 9.7286(4) 11.4674(3) 23.6531(9) 90 92.341(2) 90 2636.58(16) 4 2.489 12.578 1824 97 798 6819 5850 0.048 381 0.032 0.076 1.136 −3.12 1.00

C56H50N4O14Pb2U 1655.41 triclinic P1̅ 9.2139(4) 11.9645(7) 13.4876(6) 96.971(3) 109.499(3) 111.642(3) 1251.05(12) 1 2.197 10.016 782 61 929 4749 4383 0.044 372 0.038 0.083 1.218 −6.10 3.66

solvent molecules is disordered over two positions, which were given occupancy parameters of 0.5. Complex 4. The two solvent NMP molecules and all the water molecules but one were given occupancy factors of 0.5 to retain acceptable displacement parameters. Restraints were applied for two bond lengths and the displacement parameters of most atoms in the NMP molecules. Some voids in the lattice likely indicate the presence of other, unresolved solvent molecules. Twinning was detected with TwinRotMat18 and was taken into account.

to 1.2 times that of the parent atom (1.5 for CH3, with optimized geometry), except for those bound to N1 in complex 2, which were refined. Refined values of the Flack parameter are 0.500(10) for complex 6 and 0.002(9) for complex 8. Special details are as follows. Complex 3. Restraints on displacement parameters were applied for the carbon atoms of the phen molecule with twofold rotation symmetry, since they became strongly anisotropic during refinement otherwise, probably because of unresolved disorder. One of the water C


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Inorganic Chemistry

Figure 1. (top left) View of complex 1. Displacement ellipsoids are drawn at the 50% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry codes: i = 3/2 − x, y + 1/2, 3/2 − z; j = x, y + 1, z; k = 3/2 − x, y − 1/2, 3/2 − z; l = x, y − 1, z. (top right) View of the 1D assembly with uranium coordination polyhedra colored yellow. (bottom left) Packing with chains viewed end-on. Solvent molecules and hydrogen atoms are omitted. (bottom right) View of the hydrogen bonding pattern. Complex 10. The carboxylate ligand bound to Pb1 is disordered over two positions related by an inversion center and sharing two CH2COO− groups, and its aromatic ring was refined as an idealized hexagon with restraints on displacement parameters. Complex 11. One formate and one nitrate anion occupy the same coordination site on Pb1, and they were given occupancy factors of 0.5 each; the corresponding nitrogen and carbon atoms were constrained to have the same position and displacement parameters. Complex 12. The uranyl cation and part of its equatorial environment (atoms U1, O1, O2, and O3) display large and very anisotropic displacement parameters, but disorder could only be resolved for atoms O2 and O3, for which the two positions were given occupancy parameters constrained to sum to unity. Restraints on bond lengths, angles, and displacement parameters had to be applied for these disordered atoms, and the precise geometry of this part of the structure is thus somewhat uncertain. The highest residual electron density is located near the heavy atoms, probably as a result of both disorder and imperfect absorption corrections. Crystal data and structure refinement parameters are given in Table 1. The molecular plots were drawn with ORTEP-3,19 and the polyhedral representations were drawn with VESTA.20 The topological analyses were conducted with TOPOS.21 Luminescence Measurements. Emission spectra were recorded on solid samples using a Horiba−Jobin−Yvon Fluorolog spectrofluorometer. The powdered complex was pressed between two silica plates that were mounted such that the faces were oriented vertically and at 45° to the incident excitation radiation. An excitation

wavelength of 420 nm, a commonly used point2,4 although only part of a broad manifold, was used in all cases, and the emission was monitored between 450 and 650 nm.

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RESULTS AND DISCUSSION Synthesis. With the exception of complex 1, which was obtained at room temperature in water/acetonitrile and in the absence of an additional metal cation, all the compounds reported here were synthesized under solvo-hydrothermal conditions (140 °C) from mixtures of H3BTA with uranyl nitrate and either silver or lead nitrate plus, in all but one instance, an aza-aromatic chelate, either 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (Me 2 phen), or 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4phen). The organic solvents used in the solvo-hydrothermal syntheses were N,N-dimethylformamide (DMF; complexes 2, 8, 9, and 11), N,N-dimethylacetamide (DMA; complexes 6, 7, and 10), N-methyl-2-pyrrolidone (NMP; complexes 3, 4, and 12) and tetrahydrofuran (THF; complex 5). In general, an organic cosolvent is required to ensure the initial formation of a homogeneous solution, but it is presumed that it may also have an influence upon the solubility of the reaction products; in some instances (see below) its hydrolysis, probably catalyzed by the metal ions present, can have an influence upon the chemistry observed. Since the cosolvents D


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Inorganic Chemistry

Figure 2. (top left) View of complex 2. Displacement ellipsoids are drawn at the 40% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry codes: i = 1 − x, 1 − y, 1 − z; j = 3/2 − x, y + 1/2, z; k = 3/2 − x, y − 1/2, z. (top right) View of the 2D assembly with uranium coordination polyhedra colored yellow. (bottom left) Packing with layers viewed edge-on. Counterions and hydrogen atoms are omitted. (bottom right) Nodal representation of the 2D network. Yellow: uranium, red: oxygen, blue: tricarboxylate ligand.

chemistry.1 Any such hydrolysis was expected to be inhibited by the use of the ligand in its acid form, and this in turn may explain the presence of the incompletely deprotonated acid in complex 10. Quite clearly, the results of the present syntheses are the consequences of the operation of a multiplicity of factors. Crystal Structures. The structures of the homometallic complexes are described first, followed by those of the silverand lead-containing heterometallic complexes, although this order, based only on the ultimate characterization of the crystals, is adopted to facilitate the discussion and does not always reflect a logical progression of the synthetic procedures. In complex 1, [C(NH2)3][UO2(BTA)]·H2O, the uranyl cation is chelated by three carboxylate groups from separate BTA3− ligands (Figure 1), with unexceptional U−O bond lengths in the range of 2.443(3)−2.489(2) Å [average 2.461(16) Å]. The BTA3− ligand adopts a conformation in which two carboxylate groups are on the same side of the aromatic ring, the third being bisected by the mean plane of the ring (i.e., with the two carbon atoms of the CH2COO− group close to the plane and the two oxygen atoms on either side of it), as previously observed in other uranyl complexes.6a,10 Both uranyl ion and ligand are thus threefold nodes, and a 1D coordination polymer directed along the b axis is formed, which

employed varied considerably in volatility, the different pressures developed at the common temperature of 140 °C may also have been an influence upon the particular products formed. There is, of course, no guarantee that the use of mixed metal reactants must produce a heterometallic product, and the present work provides two further examples where such reaction mixtures provide only homometallic crystal products. Although numerous combinations of solvent/additional cation/ N-donor were tested systematically, a large number were unsuccessful in that they did not provide any crystalline material. Where crystals were obtained, the yields were mostly satisfactory, and the rather low yield of complex 1 may simply be due to the very slight extent of ionization of H3BTA at room temperature. NMP only was retained once as a lattice solvent in the final product (compound 4), but hydrolysis of DMF (frequently observed under conditions such as those used here22 and signaled by the strong odor of dimethylamine emitted by the final reaction mixtures) led to dimethylammonium cations being present in complex 2 and ligated formate anions in complexes 8, 9, and 11, although any consequences of hydrolysis of its homologue DMA were not observed. No instance was found of uranyl ion hydrolysis giving rise to oligomeric secondary building units containing oxo or hydroxo bridges, otherwise observed to be widespread in uranyl ion E


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Inorganic Chemistry is very similar to that in the complex [Hbipy][UO2(BTA)]· H2O,6a and displays a nanotubular shape, albeit extremely narrow and unsuited to any possible guest inclusion. While the Hbipy+ cation in the latter complex is only involved in a single hydrogen bond, the guanidinium cation in 1 fulfills its potential of six bonds (two of them chelating), the acceptors being oxo, carboxylate, or water oxygen atoms [O···O distances in the range of 2.852(5)−3.149(5) Å], and it is held at one side of the tubular unit, the bond with an oxo group involving a uranyl cation located on the other side. Considering only the hydrogen bonding of guanidinium and uranyl units, a helical array is apparent, with the helicity of tubes lying in sheets parallel to the ab plane being the same in a given sheet but alternating from one to the next. The lattice water molecule is itself a hydrogen bond donor toward two carboxylate groups, so that an intricate hydrogen bonding pattern unites the chains to form a 3D assembly, as illustrated in Figure 1. With a Kitaigorodski packing index (KPI, estimated with PLATON18) of 0.70, this compound has no significant free space left and thus cannot be regarded as a porous material. The dimethylammonium counterion in [H 2 NMe 2 ][UO2(BTA)] (2) was formed in situ from DMF hydrolysis. The uranyl cation is chelated by three carboxylate groups from separate BTA3− ligands, as in 1 [U−O bond lengths in the range of 2.416(2)−2.506(2) Å; average 2.46(3) Å], but, in spite of having identical formulas, the anionic assemblies are different (Figure 2). The ligand is here in its all-cis conformation, with the three carboxylate groups on the same side of the aromatic ring, thus assuming a tripodal shape, and it is tris-chelating (Scheme 1). The same coordination mode was previously found in [NMe4][UO2(BTA)]·H2O,11 and the resulting assembly formed in both cases is 2D (parallel to the ab plane in 2) with the total point (Schläfli) symbol {4.82} of the fes topological type,21 the thick sheets corresponding to bilayer arrangements. However, while the NMe4+ cation in the previous complex was encompassed by the three arms of the ligand, with possible cation−π interactions (an interesting point to be noted in relation to the heterometallic complexes involving Ag(I) and Pb(II) described herein) in addition to Coulombic forces, the H2NMe2+ counterion in 2 is somewhat similarly located and may again be involved in weak cation−π [CH(methyl)···C(aromatic)] interactions but is also involved in two strong hydrogen bonds with two carboxylate oxygen atoms [N1···O5 2.940(4) Å, N1···O7 2.987(4) Å], each hydrogen atom giving also a longer bond with two more carboxylate oxygen atoms of the same layer [N1···O4i 3.201(4) Å, N1···O6ii 3.280(4) Å; symmetry codes i = 1 − x, 1 − y, 1 − z; ii = x + 1/2, 1/2 − y, 1 − z]. Both hydrogen atoms are thus bound in an asymmetric bifurcated way, and they create fourmembered rings including one uranium atom, with the descriptor R21(4) in graph set notation.23 It is notable that the chains in 1 and the sheets in 2 look alike when the latter are viewed edge-on, as it appears in Figures 1 and 2, but the different orientation of the uranyl equatorial planes ensures the lateral propagation of the polymer in 2, as is apparent in the side-on view of the 2D network. The KPI of 0.68 is similar to that of 1. Like complex 2, [(UO2)3(BTA)2(phen)3]·4H2O (3) was obtained in the presence of lead(II) cations, which are absent from the crystallized species; changing the organic solvent from DMF to NMP prevents the hydrolytic formation of additional cations, and a very different architecture is formed. In the absence of Pb(II) in the lattice, the aza-aromatic base (here,

Scheme 1. Coordination Mode of the BTA Ligand in Complexes 1−12

a

(a) and (b) are the coordination modes in one of the complexes previously reported.6a

1,10-phenanthroline) is bound to uranium, restricting the equatorial coordination sphere to the binding of but two chelating carboxylate groups and engendering chirality at the uranium center, as seen in various related species.24 The asymmetric unit contains two independent uranium atoms, one of them (U1) located on a twofold rotation axis that bisects the phen molecule bound to it (Figure 3). The U−O(carboxylate) and U−N bond lengths are in the ranges of 2.440(2)−2.471(2) Å [average 2.457(13) Å] and 2.612(2)−2.651(2) Å [average 2.630(18) Å], respectively. The nitrogen atoms are displaced by 0.614(3), −0.449(4), and 0.867(4) Å (for N1, N2, and N3, respectively) from the mean uranyl equatorial planes defined by the uranium atom and the four carboxylate oxygen donors (root-mean-square deviations 0.12 and 0.09 Å for U1 and U2, respectively). The dihedral angles between these planes and the average planes of the phen molecules are 29.25(7) and 32.13(5)°, which are comparable to the largest values measured in a family of dicarboxylate complexes of uranyl with bipy and phen coligands.24 The BTA3− anion is in the cis,trans conformation, and it is once more a threefold node, being bound to three separate uranyl centers. An undulating 2D polymeric sheet lying parallel to the (2 0 1̅) plane is formed, in which the uranyl cations are merely edge-defining, due to the presence of the terminal phen ligands, and which is thus a distorted hexagonal honeycomb (hcb) network with the {63} point symbol. The rings are very large (60-membered in terms of bonds) and elongated in shape, with largest and smallest dimensions of ∼24 and ∼10 Å, the latter value being affected by the three phenanthroline units projecting into the interior. F


Article

Inorganic Chemistry

intricate interdigitation reveal the presence of parallel-displaced π-stacking interactions between each layer and its two neighbors [centroid···centroid distances in the range of 3.3497(18)−4.1724(17) Å, dihedral angles 0−9.25(15)°]. Among other interactions beyond dispersion, one CH···π contact may be significant, between a methylene hydrogen atom of the BTA3− ligand and the aromatic ring of another such ligand pertaining to a second layer, thus creating a dimeric motif, since the two ligands involved are related by an inversion center [H···centroid distance 2.86 Å, C−H···centroid angle 136°]. The estimated KPI is 0.66, with solvent water molecules excluded. The complex [(UO2)3(BTA)2(Me4phen)3]·NMP·3H2O (4), which was obtained together with the heterometallic complex 12 (see Experimental Section), has an overall formula analogous to that of 3 but for the replacement of phen by the bulkier Me4phen and different solvation; the structures of these two compounds are however quite different. The three independent uranyl ions in the asymmetric unit of 4 are all chelated by two carboxylate groups and one phen molecule, and the two BTA3− anions are in the cis,trans conformation (Figure 4), like their counterparts in 3. The U−O(carboxylate) bond lengths are in the range of 2.442(7)−2.491(7) Å [average 2.463(16) Å], and the U−N bond lengths are in the range of 2.612(8)−2.683(10) Å [average 2.64(2) Å]. The nitrogen atoms are differently displaced from the mean uranyl equatorial planes, by 0.659(14) and −0.725(14) Å for N1 and N2, by 0.672(17) and −0.624(17) Å for N3 and N4, and by 0.262(14) and −0.822(14) Å for N5 and N6. The dihedral angles between the average equatorial planes and the phen molecules are however not very different, at 34.1(2), 31.3(3), and 33.4(3)°, which are indicative of significant chirality at the uranium centers, this being identical for U1 and U2, and reverse for U3. 1D polymeric double-chain ribbons parallel to the [1 0 1]̅ axis are formed, with the point symbol {42.6} for the threefold tricarboxylate nodes. Unlike the 1D structure observed in complex 1, the presence of the blocking N-donor chelate results in a uninodal arrangement in which uranyl ions are edgedefining. The width of the polymer is thus enlarged so as to form planar ribbons with two lateral, linear chains involving BTA3− bridges between alternating U1 and U3 centers of opposite chirality, these chains being cross-linked by U2 centers, alternating in chirality, bound to the third carboxylate of each BTA3− unit. The Me4phen molecules are located on one or the other side of the ribbons so that the packing displays alternate sheets of side-by-side [(UO2)3(BTA)2] chains and of interdigitated Me4phen molecules. Parallel-displaced π-stacking interactions thus appear to play a prominent role in the cohesion of the solid, as witnessed by the short contacts present [centroid···centroid distances in the range of 3.688(7)− 4.147(6) Å, dihedral angles 0−5.6(5)°]. Some of the water hydrogen protons were not found, but the others are involved in hydrogen bonding with oxygen atoms of carboxylate groups, NMP, and water molecules [O···O distances in the range of 2.69(2)−2.933(19) Å], thus building weak links between the chains. Although in other instances,6a,b,e,g,i,9a NMP has been found as a ligand on U(VI), in the present species it does not appear capable of competing with chelating carboxylate or Me4phen. The KPI is 0.55, with solvent molecules (NMP and water) excluded. The complex [UO2Ag(BTA)] (5) is the only heterometallic species in the present series to involve silver(I) cations. The unique uranium atom is bound to four carboxylate groups from

Figure 3. (top) View of complex 3. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = 1 − x, y, 3/2 − z; j = 1/2 − x, y + 1/2, 1/2 − z; k = 1/2 − x, y − 1/2, 1/2 − z. (middle) View of the 2D assembly with the uranium coordination polyhedra colored yellow. (bottom) Packing with layers viewed edge-on and with one individual layer isolated in the lower part. Solvent molecules and hydrogen atoms are omitted in all views.

Within a given sheet, all uranyl centers have the same chirality, but this alternates from one sheet to the next. Partly disordered water molecules are also present that serve to link the sheets by hydrogen bonding interactions with both uranyl and carboxylate oxygen atoms and within themselves [O···O distances in the range of 2.692(7)−3.357(7) Å]. Several short contacts between phen molecules from adjacent layers resulting from G


Article

Inorganic Chemistry

Figure 4. (top) View of complex 4. Displacement ellipsoids are drawn at the 30% probability level. Symmetry codes: i = 1 − x, 1 − y, 1 − z; j = x − 1, y, z + 1; k = x + 1, y, z − 1. (middle) Packing of the chains with the uranium coordination polyhedra colored yellow. (bottom) Packing with the chains viewed end-on. Solvent molecules and hydrogen atoms are omitted in all views.

different ligands, one of them chelating and the three others monodentate (and involved in different bridging interactions), and its environment is thus pentagonal bipyramidal (Figure 5), a geometry unique in the present series but previously encountered in another complex of BTA.6a Bridging in a μ2η1:η1 fashion by O5 and O6 results in a centrosymmetric U(OCO)2U dimer unit. The U−O(carboxylate) bond lengths are 2.451(2) and 2.535(3) Å for the slightly unsymmetrical chelating group, and in the range of 2.309(3)−2.378(3) Å [average 2.34(3) Å] for the monodentate ones. The Ag(I) coordination environment is, as expected, quite different to that of the uranyl ion. The silver cation is chelated by two carboxylate groups (through one oxygen atom from each) of one BTA3− unit, one of these oxygen donors (O8) bridging to another Ag(I) and thus generating a centrosymmetric Ag2O2 motif. The other donor, O3, is also bridging, being part of the carboxylate group chelating the uranium atom, while O7, the carboxylate complement of O8, is also bound in a unidentate manner to a uranyl unit, so that chains in which dimeric uranyl

Figure 5. (top) View of complex 5. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = 1 − x, y − 1, 3/2 − z; j = x + 1/2, 1/2 − y, z + 1/2; k = 1 − x, 1 − y, 2 − z; l = 1 − x, y + 1, 3/2 − z; m = x − 1/2, 1/2 − y, z − 1/2. (middle and bottom) Two views of the 3D framework with the uranium coordination polyhedra colored yellow and silver atoms represented as blue spheres. Hydrogen atoms are omitted in all views.

units alternate with dimeric Ag(I) units can be discerned. The Ag−O bond lengths are in the range of 2.269(3)−2.299(2) Å [average 2.286(13) Å], and another, longer contact with the carbon atom C6 of the aromatic ring, at 2.407(3) Å, results in a metal environment that may be described as distorted square planar, although from the Hirshfeld surface calculated using CrystalExplorer (version 3.1)25 it appears that there is a weak axial interaction with the uranyl oxo atom O2 [2.789(3) Å], justifying an alternative description as distorted squarepyramidal. A similar situation arises in the hydrated Ag(I) complex of BTA3−,26 where all three inequivalent, approxH


Article

Inorganic Chemistry

Figure 6. (top left) View of complex 6. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = 1 − x, 1 − y, z − 1/2; j = 1 − x, 1 − y, z + 1/2. (top right) The 1D assembly viewed end-on with the uranium coordination polyhedra colored yellow and lead atoms represented as blue-green spheres. (bottom) View of the packing. Hydrogen atoms are omitted in all views.

larger than twice the van der Waals radius and thus probably not indicative of an intermetallic interaction), U···U 5.3452(3), and U···Ag 4.2542(4) Å. While arrays of parallel aromatic rings can be discerned in the lattice, the separations are much too great for significant interactions to be possible (no centroid··· centroid distance shorter than 5.5 Å). The framework does not contain solvent molecules, and it does not display significant free spaces either, the KPI value being 0.73. When the reaction leading to complex 5 is conducted with DMA in place of THF, the silver-only complex [Ag2(HBTA)(H2O)] is obtained as the sole product from crystallization at room temperature. The structure of this compound (Figure S1, Supporting Information) is different from that of [Ag3(BTA)]·1.5H2O, which involves the fully deprotonated BTA3− ligand.26 Nonetheless, in both cases, one silver ion occupies the same O2C coordination site, defined by two carboxylate arms and the aromatic ring of the ligand, as its counterpart in 5. [Ag2(HBTA)(H2O)] crystallizes as a 2D assembly, not a 3D framework as for [Ag3(BTA)]·1.5H2O, but in both these complexes, as well as in 5, chainlike structures in which different binuclear units alternate are apparent. Thus, to a large degree, Ag(I) imposes its coordination preferences, albeit ones that are quite flexible, in all three compounds, and this may be the reason for the pentagonal bipyramidal coordination of U(VI) found in 5. The two complexes [UO2Pb(BTA)(NO3)(bipy)] (6) and [UO2Pb2(BTA)2(bipy)2]·3H2O (7) were obtained together from a reaction using DMA as organic solvent. Complex 6 retains one nitrate anion and bipy chelates Pb(II) in both cases. The unique uranium atom in 6 is chelated by three carboxylate

imately planar Ag(I) coordination units have a relatively long contact to an extra O-donor, which is such in the case of the metal center (Ag3) bound to C [Ag3−C6 2.460(4) Å] that it can be considered a square pyramidal species. Also, an interesting consequence of the relatively short Ag−C contacts in this complex and in 5 is that they bring the aromatic carbon atoms adjacent to that considered bound to Ag(I) into contact distances to the metal near 2.9 Å, distances which, when considered in terms of the interaction seen of Ag(I) with benzene, for example,27 indicate that BTA3− may interact with Ag(I) in an η3 manner. The BTA3− ligand in complex 5 is in the cis,trans conformation, with the two groups on the same side being nearly coplanar with the mean plane defined by the silver O3C environment (rms 0.19 Å). The dihedral angle between the latter mean plane and the aromatic ring is 77.31(9)°, or 85.58(9)° if atom O8k, which is the most displaced from the mean plane, is omitted. Each ligand is bound to as many as six metal atoms with μ2-η2:η1, μ2-η1:η1, and μ3-η2:η1 coordination modes for the three carboxylate groups. This high degree of connectivity results in the formation of a 3D framework in which however the silver ions have no topological role, the uranium atoms and BTA3− ligands having the point symbols {3.4.84} and {32.42.84.92}, respectively. Sheets of closely packed uranium dimers (with no common coordination polyhedron edge) and silver dimers lie parallel to the (0 0 1) plane while, when viewed down the c axis, the framework displays an irregular pseudohexagonal arrangement of uranyl ions encompassing the silver cations. The shortest metal···metal separations within a sheet are Ag···Ag 3.4227(6) Å (slightly I


Article

Inorganic Chemistry

Figure 7. (top left) View of complex 7. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = x, y − 1, z; j = x, 1 − y, z + 1/2; k = x, 2 − y, z + 1/2; l = 1/2 − x, y + 1/2, 1/2 − z; m = x, y + 1, z; n = x, 1 − y, z − 1/2; o = x, 2 − y, z − 1/2; p = 1/2 − x, y − 1/2, 1/2 − z. (top right and bottom left) Two views of the packing with layers viewed edge-on. Uranium coordination polyhedra are colored yellow and lead atoms are represented as blue-green spheres. Solvent molecules and hydrogen atoms are omitted in all views. (bottom right) Nodal representation of the 2D network. Yellow: uranium, light blue-green: lead, red: oxygen, dark blue: tricarboxylate ligand, dark red: bipy.

and runs along the c axis. Like the silver(I) cations in complex 5, the lead(II) cations have no topological role here, and the Pb(NO3)(bipy)+ units are simply decorating groups pointing on two sides of the chains. Only if the two longer contacts with O4j and O5 are considered is a Pb(II)/BTA3− polymeric subunit discernible, and uranium and lead centers alternate in helical chains enveloped by the BTA3−, nitrate, and bipy ligands. The zigzag array of uranium centers in the helix is regular, with a U···U separation of 7.9349(5) Å, whereas the Pb···U distances alternate between 4.3731(5) and 4.6665(5) Å. The chains lie side by side to form tightly packed sheets parallel to (1 0 0), all units in one plane being of the same helicity but opposite to that in the adjacent plane. Only two rather weak parallel-displaced π-stacking interactions, intra- and interchain (but intralayer), may be present, both between bipy and BTA rings [centroid···centroid distances 4.162(5) and 4.193(5) Å, dihedral angles 4.7(5) and 10.3(4)°]. Interactions of chains both within and between sheets appear also to involve CH···O hydrogen bonds, connecting both aromatic and aliphatic hydrogen atoms to nitrate, carboxylate, and uranyl oxygen atoms. The KPI value of 0.73 indicates that no solventaccessible space is present. The asymmetric unit in complex 7 contains a unique uranium atom, which is chelated by three carboxylate groups, as in 6, and two independent lead atoms, both chelated by one carboxylate group and one bipy molecule (Figure 7). The U− O(carboxylate) bond lengths are unexceptional [2.458(2)− 2.498(3) Å, average 2.481(13) Å], as well as the Pb−N [2.507(3)−2.561(3) Å, average 2.536(19) Å] and Pb−O ones

groups [U−O bond lengths in the range of 2.461(6)−2.507(6) Å, average 2.481(17) Å] (Figure 6). The lead(II) cation is chelated by both bipy and NO3− [average Pb−N and Pb−O bond lengths 2.429(6) and 2.55(3) Å, respectively, to be compared with the average values of 2.57(8) and 2.7(2) Å determined from the Cambridge Structural Database (CSD, Version 5.37)28]. Pb(II) is also bound to two carboxylate oxygen atoms, which are thus bridging the two metal centers [Pb−O3 2.732(7) and Pb−O8j 2.860(6) Å, symmetry code: j = 1 − x, 1 − y, z + 1/2]; much longer contacts with O5 [3.249(6) Å] and with O4j [3.413(7) Å] may not be considered as bonding interactions, although distances as long as 3.2 Å are sometimes regarded as such.29 It is notable that the distribution of Pb−O(carboxylate) bond lengths calculated from the CSD is approximately Gaussian in shape, and, with a mean value of 2.61(17) Å, it contains very few values above ∼3.1 Å, a bonding distance which has, however, in some instances,30 been justified by bond valence estimates. In general, the assignment of the coordination sphere of Pb(II) in crystal lattices is a topic that has generated much discussion but not a complete resolution.7a,c,d,f−h The six-coordinate environment assigned here to Pb(II) is very irregular and somewhat umbrella-shaped with atom N1 on its axis, corresponding to what would be considered a clear case of hemidirected coordination due to the presence of a stereochemically active lone pair.7a,c,d,f−h,31 The BTA3− ligand is in the same conformation as in complex 1, with two carboxylate groups on the same side of the aromatic ring and the third one bisected by it (μ2-η2:η1 and η2 coordination modes), and the same 1D polymer as in this complex is formed J


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Inorganic Chemistry

Figure 8. (top) View of one of the two independent units in complex 8. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = 1 − x, y − 1/2, 1 − z; j = 1 − x, y + 1/2, 1 − z. (middle) View of the 1D polymer with the uranium coordination polyhedra colored yellow and lead atoms represented as blue-green spheres. (bottom) Packing with chains viewed end-on. Hydrogen atoms are omitted in all views.

[2.417(3)−3.120(3) Å, average 2.7(2) Å]. The coordination polyhedra of the eight-coordinate lead atoms assume very distorted square antiprismatic geometries, and they share one common edge (O7−O13l). Although their coordination numbers are equal, the two lead atoms are bound differently, with Pb1 attached to five and Pb2 to four BTA3− ligands, two of the oxygen donors in the latter case pertaining to two carboxylate groups of the same ligand (O6, O7), which is thus chelating twice, through either one or two carboxylate groups. This structure illustrates the subtlety of factors influencing the stereochemistry of Pb(II) complexes, since Pb1, for which all Pb−O contacts are shorter than 3.0 Å, appears to have a holodirected environment, whereas Pb2, especially if the long contact [3.120(3) Å] to O7 and the even longer contact [3.391(5) Å] to O11 are ignored, is hemidirected, like the lead center in 6. The two ligands themselves are in different conformations, one of them (containing atoms O3 to O8) having two carboxylate groups on one side of the

ring and the other bisected by it, and the other (O9 to O14) being in the cis,trans conformation; both connect six metal atoms (seven for the first ligand if the Pb2−O7 contact is considered a bond), but these are two U and four (or five) Pb for the first ligand [μ 2 -η 2 :η 1 (twice) and μ 3 -η 1 :η 2 :η 1 coordination modes], and one U and five Pb for the second [μ2-η2:η1 (twice) and μ2-η1:η1 coordination modes]. The fivenodal polymeric assembly formed is a thick 2D one, parallel to (1 0 0) and with the point symbols {43} for U1, {44.66} for Pb1, and {45.6} for Pb2. As shown in the nodal representation of Figure 7, the arrangement is very intricate, with two layers of uranyl and lead ions surrounding a central sheet of BTA3− and bipy molecules (the Pb1 atoms being outermost), the overall thickness being ∼20 Å (compared to ∼10 Å in complex 2). Ignoring the Pb(II) binding, the hexagonal bipyramidal U(VI) units do form chains with the bridges involving two carboxylate units from BTA3− resembling those seen in complexes 1 and 2, so that Pb(II) does not seem to have as great an influence upon K


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Inorganic Chemistry the binding of uranyl ion as does Ag(I) in complex 5. While the smallest U···U distance is 9.3365(4) Å, U···Pb and Pb···Pb are all in the range of 4.24−4.59 Å. As expected from the thick layer arrangement, both intra- and interlayer parallel-displaced π-stacking interactions between bipy molecules are probably present [centroid···centroid distances 3.466(3) and 3.508(3) Å, dihedral angle 3.0(2)° for both]. Longer intralayer contacts are also found between bipy and BTA3− anions [centroid···centroid distances of 4.219(2)−4.425(2) Å, dihedral angles of 6.7(2)− 35.69(19)°], but their significance is more uncertain. Three intralayer CH···π interactions are also detectable, two of them involving the two hydrogen atoms of a BTA methylene group and the other one bipy hydrogen atom, and the aromatic rings being from either bipy or BTA [H···centroid distances 2.53− 2.85 Å, C−H···centroid angles 138−144°]. Weak CH···O hydrogen bonds involving, in particular, bipy hydrogen atoms and either oxo or carboxylate oxygen atoms may also contribute to the cohesion of the layers (shortest H···O distance 2.44 Å). Although located at the periphery of the layers, the water molecules are only directly involved in hydrogen bonds with a single polymeric unit; however, although all water hydrogen atoms were not found, it may be surmised from O···O distances that water bridges exist between adjacent sheets. With a KPI of 0.73, the packing does not display significant free space. Two compounds of identical overall formula, but with structures that are different as a result of coordination isomerism, [UO2Pb(BTA)(HCOO)(phen)] (8 and 9), crystallized together from the same solution. In both cases, the complex integrates a formate coligand, generated from DMF hydrolysis, which chelates either the lead atom (in 8) or the uranium atom (in 9). In complex 8, represented in Figure 8, the asymmetric unit contains twice the formula unit, the two independent motifs being essentially identical. Each uranium atom is chelated by three carboxylate groups from BTA3− ligands [U−O bond lengths in the range 2.429(8)−2.520(8) Å, average 2.48(2) Å], while each lead(II) atom is chelated by both the formate [2.413(9)−2.558(9) Å, average 2.49(6) Å] and phen ligands [2.431(10)−2.464(10) Å, average 2.446(13) Å], with additional coordination to two BTA3− oxygen atoms [2.809(8)−3.077(8) Å] and two longer contacts with two more [3.209(9)−3.480(9) Å]. If the latter longer contacts are disregarded, the lead atoms are six-coordinate with a very irregular but clearly hemidirected environment. The ligands are in the cis/bisected conformation previously encountered, and the three carboxylate groups have the μ2-η2:η1 (twice) and η2 coordination modes. The 1D coordination polymer formed, parallel to the b axis, is analogous to those in complexes 1 and 6 with, as in the latter case, the lead atoms having no topological role. The chains are stacked into sheets parallel to (0 0 1), each containing only chains generated by one of the two crystallographically independent units (KPI 0.71). Paralleldisplaced π-stacking interactions may be present, uniting phen and BTA aromatic rings of the same or adjacent chains in the same layer [centroid···centroid distances 3.813(8)−4.366(8) Å, dihedral angles 0−5.0(6)°]. Several intra- and interlayer CH···π and CH···O interactions are also probably significant. The asymmetric unit in complex 9 contains only one uranium and one lead atom (Figure 9). The former is chelated by two carboxylate groups from BTA3− and by the formate anion [2.428(4)−2.507(5) Å, average 2.47(3) Å]; the latter is chelated by one carboxylate group from BTA3− [2.467(4) and 2.497(4) Å] and also by the phen molecule [2.503(4) and 2.580(4) Å], and it is bound to three more oxygen atoms

Figure 9. (top) View of complex 9. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = x, y − 1, z; j = 1 − x, 1 − y, 1 − z; k = x, y + 1, z. (middle) View of the 1D polymer with the uranium coordination polyhedra colored yellow and lead atoms represented as blue-green spheres, with phen molecules omitted for clarity. (bottom) Packing with chains viewed end-on. Hydrogen atoms are omitted in all views.

[2.702(3)−2.922(4) Å], among which one is from formate (which is thus bound in μ2-η2:η1 fashion). The Pb(II) center is hepta-coordinated, with an environment taking the trigonal base−tetragonal base geometry, with the former base defined by atoms O7, O8, and O10j, and the latter by N1, N2, O3j, and O7j (rms deviation 0.048 Å); the dihedral angle between the two bases is 10.3(3)°, and Pb1 is displaced by only 0.492(2) Å from the tetragonal one, thus leaving a coordination “hole” and conforming to a hemidirected array. Unlike the hemidirected species described above, however, in this case the “hole” is actually occupied by the phenyl ring of BTA3−. Hexahapto binding of ligand phenyl rings to Pb(II) has been suggested to explain the form of Pb(DBM)2 (DBM = dibenzoylmethanide ion),32 although other instances where Pb(II) lies above the face of a phenyl ring have been assigned as due to lone pair donation into the lowest unoccupied molecular orbital of the aromatic system7g (meaning that Pb(II) may act as a Lewis base as well as a Lewis acid). The Pb···C distances found in 9 [3.581(5)−3.693(6) Å] are similar to those in these various other instances. The BTA3− anion has the same conformation as in complex 8, and it is connected to four (two U and two L


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Inorganic Chemistry Pb) metal centers [μ2-η2:η1 (twice) and η2 coordination modes]. Here also, the assembly formed is 1D and directed along the b axis, but both metal ions contribute to the formation of the polymer. Two UO2(BTA)− strands mark out the two sides of the ribbon, which are unconnected to one another due to the occupancy of the uranyl coordination site directed inward by the formate anion; centrosymmetric dimers of Pb(II) cations located in the center of the ribbon link these two strands, as shown in Figure 9. Adjacent chains along the a axis are connected through parallel-displaced π-stacking interactions involving both BTA and phen rings [centroid··· centroid distances 3.700(3) and 3.844(3) Å, dihedral angles 3.2(3) and 2.7(3)°], and CH···π and CH···O interactions may also be present; the resulting packing has a KPI of 0.70. Classical examples of coordination isomers are found in ionic species in which the ligands of the complex cations and anions can be interchanged. The situation is different here, since the heterometallic complexes in compounds 8 and 9 are neutral, the isomerization resulting from an internal rearrangement of the different ligands. Obviously, because of the similar nature of the two donor groups involved, chelating formate and carboxylate from BTA3−, replacement of one by the other can proceed with minimal effect on the environment of the metal cations, notwithstanding the different resulting topologies. When the same reactants giving complexes 8 and 9 are used with DMA in place of DMF as organic cosolvent, the compound [(UO 2 ) 2 Pb 2 (BTA) 2 (HBTA)(H 2 O) 2 (phen) 2 ]· 2H2O (10), devoid of acetate coligands that would result from any hydrolysis, is obtained instead. The asymmetric unit corresponds to half the formula unit and contains one uranyl cation, one Pb(phen)2+ unit, one fully deprotonated BTA3− ligand (in the cis/bisected conformation), and a second, doubly deprotonated HBTA2− ligand (in an approximately trans/ bisected conformation) that is disordered around an inversion center (Figure 10). The uranyl ion is chelated by three carboxylate groups from three fully deprotonated ligands [U− O(carboxylate) bond lengths in the range 2.447(5)−2.497(5) Å, average 2.466(16) Å]. In addition to the phen molecule, Pb(II) is chelated by one carboxylate group from HBTA2− [Pb−O bond lengths 2.509(5) and 2.531(5) Å] and is bound in monodentate fashion to two oxygen atoms from BTA3− ligands [2.818(5) and 2.916(5) Å] and one water molecule [2.737(7) Å]. It may also be involved in a longer contact with the uranyl oxo atom O1, at 3.176(5) Å, which, to the best of our knowledge, would be the first instance of a Pb−oxo(uranyl) interaction (so-called “cation−cation” interaction). This Pb1− O1 distance is however large with respect to those generally observed in such interactions, and, in particular, larger than those involving lanthanide cations33 [2.822(4) Å for Ce(III) and 2.792(6) Å for Nd(III), while the ionic radius of Pb(II) is only ∼0.1 Å larger than that of Ce(III)]; distances comparable to that found here, 3.085(8)−3.269(8) Å, have been observed with Cs(I), which has an ionic radius larger by ∼0.4 Å.34 In the present case, the two UO bond lengths are nearly equal [1.766(5) and 1.759(5) Å] and show no lengthening associated with the interaction with Pb(II), thus indicating that the interaction is weak at best. Recent observation of a shorter Pb− oxo(uranyl) bond length [2.999(4) Å] shows however that such a cation−cation interaction is possible.35 The Pb(II) cation in 10 is in an eight-coordinate environment of very irregular geometry (if the Pb1−O1 interaction is taken into account, seven-coordinate otherwise), though not one that is

Figure 10. (top) View of complex 10. Displacement ellipsoids are drawn at the 30% probability level. Solvent molecules and carbonbound hydrogen atoms are omitted. Only one position of the disordered ligand is represented. Symmetry codes: i = x, y − 1, z; j = 1 − x, 1 − y, 1 − z; k = x, y + 1, z; l = −x, 2 − y, − z. (middle) View of the 2D assembly with the uranium coordination polyhedra colored yellow and lead atoms represented as blue-green spheres. (bottom) Packing with layers viewed edge-on. Solvent molecules and hydrogen atoms are omitted, and both positions of the disordered ligands are shown in the last two views.

markedly hemidirected. The uranium atoms are thus threefold nodes and, together with the BTA3− ligands [with carboxylate groups in the μ2-η2:η1 (twice) and η2 coordination modes], they give rise to the formation of 1D subunits running along the b axis, which are similar to the chains observed in complexes 1, 6, and 8. As in the two latter complexes, the Pb(II) cations are attached (albeit in a somewhat different manner than in the other complexes) on two sides of the chains. Considering only the direct oxygen bridges between U and Pb, there is no longer an infinite helical polymer but simply tetranuclear centrosymmetric U2Pb2 units lying, as a result of the BTA3− links, in chains along the b axis. Within these nearly square units, the diagonal distances are U···U 7.0047(7) and Pb···Pb 6.0983(8) Å, while the U···Pb separations are 4.5388(5) and 4.7463(6) Å. In contrast to complexes 6 and 8, the Pb-chelating, disordered HBTA2− ligands bridge the chains to generate a 2D network parallel to (1 0 1̅), so that, as in complex 9, the Pb(II) cations have a topological role here. Intrasheet hydrogen bonds contribute to the stabilization of these layers: the un-ionized M


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Inorganic Chemistry

bound to two carboxylate oxygen atoms in monodentate fashion, with the overall range 2.469(5)−2.812(4) Å for the Pb−O bond lengths. An additional longer contact with the carboxylate atom O5, at 3.297(4) Å, is not considered as a coordinate bond, and neither is an even longer contact to a symmetry equivalent of O4 at 3.750(4) Å, making the lead(II) environment six-coordinate, with the irregular, umbrella-shaped hemidirected geometry having atom N1 on its axis. The overall arrangement is very close to those in complexes 6 and 8, and the Pb(II) cations have no role in the building of the polymeric species. The packing is also closely related to those in complexes 6 and 8, and it will not be described further. Complex 12, [UO2Pb2(BTA)2(Me4phen)2], was obtained together with the homometallic uranyl complex 4 previously described. The absence of formate anions and the replacement of phen by the bulkier Me4phen result in a connectivity different from all those previously observed. The unique uranium atom is located on an inversion center, and its environment is partly disordered (see Experimental Section). It is chelated by two carboxylate groups and bound to two monodentate oxygen atoms from two other carboxylate groups, which gives a six-coordinate equatorial environment (Figure 12). The lead(II) cation is chelated by the Me4phen molecule and one carboxylate, and it is additionally bound to three more carboxylate oxygen atoms (one of them disordered), with Pb− O bond lengths spanning the range 2.441(5)−2.976(10) Å. As in complex 9, the heptacoordinate Pb(II) environment geometry can be viewed as being of the trigonal base− tetragonal base type, with the former base defined by atoms O6, O7, and O5m, and the latter by N1, N2, O3al, and O6l (rms deviation 0.081 Å); the dihedral angle between the two bases is 13.9(2)°, and Pb1 is displaced by 0.483(3) Å from the tetragonal one. A further similarity with complex 9 is that again the coordination sphere “hole” on Pb is actually occupied by a phenyl ring (of BTA), the Pb(II) center lying almost directly above the ring centroid at a distance of 3.38 Å, with Pb···C distances in the range of 3.617(7)−3.700(7) Å. The BTA3− ligand is in the cis,trans conformation, and its three functional groups are bound differently to the metal cations: the two that are on the same side of the aromatic ring are chelating either uranyl or Pb(II), and both are additionally bound to another Pb(II) cation (μ2-η2:η1 coordination mode), while the third carboxylate is bound to one uranyl and one Pb(II) cation in bridging bidentate fashion (μ2-η1:η1). Overall, BTA3− is thus bound to five metal centers, whereas the uranyl cation is bound to four and the Pb(II) cation to three carboxylate ligands. This connectivity results in the formation of a 2D assembly parallel to (0 1 0), but it is notable that each cation, if considered alone, only forms chains directed along the a axis, their combination being necessary to the dimensionality increase. In the case of Pb(II), the 1D subunits are based on the repetition of a centrosymmetric dinuclear motif with two carboxylate bridges, each cation being chelated by one carboxylate group of one ligand and also between two carboxylate groups of the other ligand. The Me4phen ligands protrude on both sides of the layers, but they are offset so that only one contact possibly indicative of a parallel-displaced π-stacking interaction between lateral rings is found [centroid···centroid distance 4.610(5) Å, dihedral angle 0°, large slippage value of 2.91 Å]; all other centroid···centroid distances are larger than 5.10 Å. As previously observed, the presence of numerous aromatic rings in a crystallized complex is not necessarily conducive to πstacking interactions being prominent in the packing,36 and the

carboxylic acid group (disordered over two opposed orientations) is hydrogen bonded to a water molecule [O···O distance 2.452(17) Å], which in turn is hydrogen bonded to two Pb-bound oxygen atoms, from carboxylate [O10, O···O distance 2.763(8) Å] and water [O13, O···O distance 2.961(11) Å] ligands; the latter water molecule is hydrogen bonded to a uranium-bound carboxylate group from the same sheet [O6, O···O distance 2.958(9) Å]. Adjacent sheets are juxtaposed such that stacked pairs of phen units are formed, with distances indicative of parallel-displaced π-stacking interactions [centroid···centroid distances 3.595(4)−4.525(4) Å, dihedral angles 0−6.6(4)°], and one other such intersheet interaction is also apparent between two rings of BTA3− ligands [centroid···centroid distance 3.620(4) Å, dihedral angle 0°]. Multiple intersheet CH···O, and in a lesser measure CH···π, contacts are also apparent. The last two heterometallic complexes contain methylated derivatives of phen. Complex 11, [UO2Pb(BTA)(HCOO)0.5(NO3)0.5(Me2phen)], was synthesized in DMF and, like complexes 8 and 9, it includes formate anions as coligands. The uranyl ion is chelated by three carboxylate groups from three BTA3− ligands in the cis/bisected conformation [U−O bond lengths in the range 2.459(4)−2.495(4) Å, average 2.472(13) Å], a now usual motif giving rise to the formation of a 1D chain running along the b axis (Figure 11). In addition to Me2phen, the lead(II) cation is chelated by a disordered formate/nitrate anion (see Experimental Section), and it is

Figure 11. (top) View of complex 11. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = 1 − x, y − 1/2, 1/2 − z; j = 1 − x, y + 1/2, 1/2 − z. (bottom) Packing of the chains with the uranium coordination polyhedra colored yellow and lead atoms represented as blue-green spheres. The formate ion only is represented in the disordered part, and hydrogen atoms are omitted in both views. N


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Inorganic Chemistry

possibly containing a very small amount of 12) and those of the heterometallic species 5−11 were recorded in the solid state at room temperature under excitation at a wavelength of 420 nm, a value suitable for excitation of the uranyl chromophore,37 and they are represented in Figure 13. The

Figure 13. Emission spectra of the homometallic uranyl complexes (top) and the heterometallic complexes (bottom). The excitation wavelength was 420 nm. Figure 12. (top) View of complex 12. Displacement ellipsoids are drawn at the 40% probability level. Symmetry codes: i = −x, −y, −z; j = x − 1, y, z; k = 1 − x, −y, −z; l = 1 − x, −y, 1 − z; m = 2 − x, −y, 1 − z; n = x + 1, y, z. (middle) View of the 2D assembly with the uranium coordination polyhedra colored yellow and lead atoms represented as blue-green spheres. (bottom) Packing with layers viewed edge-on. Only one position of the disordered atoms is represented, and hydrogen atoms are omitted in all views.

spectra of the couples of complexes 6/7 and 8/9 were recorded on mixtures of these complexes, which grow together and could not be separated in bulk. Uranyl emission is commonly considered characterized by the vibronic progression corresponding to the S11 → S00 and S10 → S0ν (ν = 0−4) electronic transitions,38 and it is common to observe only five peaks. However, the positions of the emission bands are sensitive to the nature and geometry of the uranyl coordination sphere,4 and the overall intensity of the spectra is often affected by quenching effects, in particular, when d-block transition metal ions are present as well.5b,6,12h,39 It is also well-established that the bandwidth of emission at room temperature can mask considerable complexity involving multiple, overlapping vibronic progressions resolvable only at low temperature,40 such measurements on some simple halouranates providing a recent example.41 In the present series, nearly complete quenching is only observed in the heterometallic silver(I)containing complex 5 (the complex of BTA3− with Ag(I) only giving itself no emission); such quenching has previously been found in other uranyl/Ag(I) complexes and attributed to

presence of the methyl substituents, in particular, may be an impediment to their formation in the present case. Two CH···π interactions involving these methyl groups are found, one of them being intrasheet with a BTA3− ring [H···centroid distance 2.70 Å, C−H···centroid angle 147°], and the other intersheet with another Me4phen molecule [2.78 Å, 137°]. Several CH··· O interactions, both intra- and intersheet, are also present, as in the previous complexes. The packing is quite compact, with a KPI of 0.73, and neither solvent molecules nor free spaces are present. Luminescence Properties. The emission spectra of the homometallic uranyl complexes 1−4 (the latter complex O


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Inorganic Chemistry silver(I) cations providing a nonradiative relaxation pathway,12h although this is by no means general,6i,12c,d presumably because the energy level structure of Ag(I) varies with its coordination environment and possibly because of a dependence upon the coordination environment of U(VI) (the two known cases of complete quenching occurring for pentagonal bipyramidal species). In all other present cases, either homo- or heterometallic, the spectra display either well-resolved or moderately well-resolved emission bands, showing, in particular, that Pb(II) centers do not have a major quenching effect upon the uranyl center luminescence. However, the maxima positions vary significantly within the series. The spectra of the uranyl-only complexes 1 and 2 are nearly superimposable, except for the lower resolution of the vibronic components in the spectrum of 1, which could be seen as the superposition of uranyl bands upon a broader single peak, and the positions of the maxima for 2 are 463 (m), 480 (s), 500 (s), 522 (s), 545 (m), and 571 (w) nm. The same maxima positions (with departures of 1 nm at most) are found in the heterometallic complexes 6/7, 8/9, and 11, and they are close to those in other uranyl carboxylate complexes with six equatorial Odonors.6a,c−e,g,h,22k,42 In contrast, although they retain the same overall shape, the spectra of complexes 3, 4, and 10 display maxima red-shifted by ∼7−10 nm, with values of 489 (s), 509 (s), 531 (s), and 555 (m) for the main bands in 3, and 487 (s), 507 (s), 529 (s), and 553 (m) in 10. In complexes 3 and 4, this shift is very probably due to the replacement of one chelating carboxylate by one N-chelating ligand in the uranyl coordination sphere, although values intermediate between the two sets observed here were recently found in uranyl complexes with carboxylate and bipy or phen donors.24 In the spectrum of 4, the vibronic bands are weak and appear to be superimposed on a broader emission (as in the case of 1 and verified for 4 in that the excitation spectrum showed two close low energy peaks with varying contributions depending upon the emission wavelength), which here could be that from the aza-aromatic ligand. The nature of the donors as well as the deformation of the equatorial garland may be operative here. In 10, the most conspicuous particularity possibly accounting for the shift is the involvement of one of the uranyl oxo groups in an interaction with Pb(II), but this observation is also further evidence of the difficulty of relating subtle changes in the emission band structure to that of the solid.

building of the polymeric species. The versatility of the BTA3− ligand, partly due to the different conformations it is able to assume, is revealed through modifications of the synthetic procedure, which provide complexes with different connectivities and, for some of them, higher dimensionalities. The use of DMF as an organic cosolvent leads to the generation of dimethylammonium cations and formate anions through hydrolysis in situ, and the former, acting as hydrogen bonded counterions in the uranyl-only compound 2, promote the formation of a bilayer 2D assembly of the fes topological type that was previously encountered with NMe4+ counterions. Formate anions are found as coligands in complexes 8, 9, and 11, the two former cases being particularly interesting in providing an example of coordination isomerism, with formate bound either to lead or uranium centers, which induces a different topology of the chains. Only in the uranyl-only complexes 3 and 4 is the N-chelating ligand (phen or Me4phen) bound to the uranyl cation, which leads to crystallization either of a 2D architecture with honeycomb topology and very large rings in 3, or of large ribbons covered with protruding Me4phen molecules in 4. The five-nodal 2D network in the Pb/U complex 7 is very intricate and displays both intra- and interlayer parallel-displaced π-stacking interactions, which, together with CH···O and CH···π interactions, play a significant role in this series of compounds, particularly in the case of the neutral complexes. Although BTA3− has a strong propensity to act as a triply chelating ligand toward uranyl cations, a coordination mode (very often associated with further bridging) observed in most complexes, it also acts as a doubly chelating bridge between lead(II) centers in complex 10, resulting in the formation of a 2D polymer. A different chelating and bridging coordination mode toward both uranyl and lead atoms gives another 2D assembly in complex 12. The quite remarkable variability in the coordination proclivities of Pb(II) is typical of this metal ion, and this flexibility may explain why, in the present heterometallic species, it appears to engender much less marked changes in the coordination sphere of the uranyl ion than does Ag(I). The only 3D framework in this series is found in the uranyl−silver(I) complex 5, with further reduction of chelation to only one carboxylate, the others being bridging bi- or tridentate, leading to an increase in dimensionality in which Ag(I) ions themselves have no direct part. In known U(VI)−Ag(I) complexes, however, excepting those where the Ag(I) has its own, independent primary coordination sphere,6i the presence of Ag(I) is in all but one case associated with a relatively low coordination number for U(VI) (either 6 or 7), and the pentagonal bipyramidal coordination of U(VI) in 5 is unique in the present series. But for the quenching of uranyl luminescence in the silvercontaining complex, all the other compounds display the usual uranyl emission vibronic fine structure, with various degrees of resolution and slight shifts in the maxima positions arising from small variations in the uranyl cation environment. The ability to turn uranyl ion luminescence on and off may be useful, but the multiplicity of factors seemingly influencing the form and intensity of the “on” state remains to be fully elaborated. In regard to the possibility that the coordination polymers described herein might find application as photocatalysts for reactions of absorbed molecules, the absence of major bodies of lattice solvent and high KPI values in most cases indicate that this is unlikely, except possibly for complexes 3 and 4.

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CONCLUSIONS Although many studies have now been devoted to the investigation of the heterometallic coordination polymers or frameworks containing both uranyl and d-block metal cations, few examples of such species in the uranyl−lead(II) family have been reported.12b,13 Following our previous results on uranyl ion complexes with 1,3,5-benzenetriacetic acid,6a,10,11 the present work further explores the structural chemistry of this system, particularly as to the effect of additional species such as organic counterions, N-chelating species, and metal cations, specifically Pb(II) and, in one case, Ag(I). There is a significant contrast in the influence of the two metal ions upon the coordination of cocrystallized uranyl ions. The formation of 1D polymeric chains, with both tris-chelated uranyl and BTA3− ligands as threefold nodes, occurs for complex 1, where only uranyl ion is present, as well as in the Pb/U complexes 6, 8, and 11, and, as a subunit, in the 2D assembly 10. In the cases of compounds 6, 8, and 11, the lead(II) cations are simple appendages on such chains, and they play no role in the P


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(h) Gourlaouen, C.; Parisel, O.; Gérard, H. Dalton Trans. 2011, 40, 11282−11288. (i) Eckhardt, S.; Brunetto, P. S.; Gagnon, J.; Priebe, M.; Giese, B.; Fromm, K. Chem. Rev. 2013, 113, 4708−4054. (8) (a) Sather, A. C.; Berryman, O. B.; Rebek, J., Jr. J. Am. Chem. Soc. 2010, 132, 13572−13574. (b) Sather, A. C.; Berryman, O. B.; Moore, C. E.; Rebek, J., Jr. Chem. Commun. 2013, 49, 6379−6381. (9) (a) Thuéry, P. Cryst. Growth Des. 2014, 14, 901−904. (b) Thuéry, P. Cryst. Growth Des. 2014, 14, 2665−2676. (10) Thuéry, P. CrystEngComm 2009, 11, 1081−1088. (11) Thuéry, P. Cryst. Growth Des. 2011, 11, 347−355. (12) (a) Yu, Z. T.; Liao, Z. L.; Jiang, Y. S.; Li, G. H.; Chen, J. S. Chem. - Eur. J. 2005, 11, 2642−2650. (b) Frisch, M.; Cahill, C. L. Dalton Trans. 2006, 4679−4690. (c) Luo, G. G.; Lin, L. R.; Huang, R. B.; Zheng, L. S. Dalton Trans. 2007, 3868−3870. (d) Yu, Y. Y.; Zhan, W.; Albrecht-Schmitt, T. E. Inorg. Chem. 2007, 46, 10214−10220. (e) Liao, Z. L.; Li, G. D.; Bi, M. H.; Chen, J. S. Inorg. Chem. 2008, 47, 4844−4853. (f) Adelani, P. O.; Albrecht-Schmitt, T. E. Angew. Chem., Int. Ed. 2010, 49, 8909−8911. (g) Adelani, P. O.; Albrecht-Schmitt, T. E. Cryst. Growth Des. 2012, 12, 5800−5805. (h) Kerr, A. T.; Cahill, C. L. Cryst. Growth Des. 2014, 14, 1914−1921. (i) Nelson, A. G. D.; Rak, Z.; Albrecht-Schmitt, T. E.; Becker, U.; Ewing, R. C. Inorg. Chem. 2014, 53, 2787−2796. (13) Serezhkina, L. B.; Vologzhanina, A. V.; Klepov, V. V.; Serezhkin, V. N. Crystallogr. Rep. 2011, 56, 132−135. (14) Hooft, R. W. W. COLLECT; Nonius BV: Delft, The Netherlands, 1998. (15) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307− 326. (16) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−8. (17) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (b) Sheldrick, G. M. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8. (18) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7−13. (19) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (20) Momma, K.; Izumi, F. J. Appl. Crystallogr. 2008, 41, 653−658. (21) (a) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. J. Appl. Crystallogr. 2000, 33, 1193. (b) Blatov, V. A.; O’Keeffe, M.; Proserpio, D. M. CrystEngComm 2010, 12, 44−48. (22) See, for example: (a) Buckingham, D. A.; Harrowfield, J. M.; Sargeson, A. M. J. Am. Chem. Soc. 1974, 96, 1726−1729. (b) Paulet, C.; Loiseau, T.; Férey, G. J. Mater. Chem. 2000, 10, 1225−1229. (c) Chen, W.; Wang, J. Y.; Chen, C.; Yue, Q.; Yuan, H. M.; Chen, J. S.; Wang, S. N. Inorg. Chem. 2003, 42, 944−946. (d) Ganesan, S. V.; Lightfoot, P.; Natarajan, S. Solid State Sci. 2004, 6, 757−762. (e) Harrowfield, J. M.; Skelton, B. W.; White, A. H.; Wilner, F. R. Inorg. Chim. Acta 2004, 357, 2358−2364. (f) Zhao, J.; Li, J.; Ma, P.; Wang, J.; Niu, J. Inorg. Chem. Commun. 2009, 12, 450−453. (g) Bilyk, A.; Dunlop, J. W.; Fuller, R. O.; Hall, A. K.; Harrowfield, J. M.; Hosseini, M. W.; Koutsantonis, G. A.; Murray, I. W.; Skelton, B. W.; Stamps, R. L.; White, A. H. Eur. J. Inorg. Chem. 2010, 2106−2126. (h) Thuéry, P. Cryst. Growth Des. 2011, 11, 2606−2620. (i) Thuéry, P. Cryst. Growth Des. 2011, 11, 3282−3294. (j) Thuéry, P. Cryst. Growth Des. 2012, 12, 499−507. (k) Thuér y, P.; Harrowfield, J. CrystEngComm 2015, 17, 4006−4018. (23) (a) Etter, M. C.; MacDonald, J. C.; Bernstein, J. Acta Crystallogr., Sect. B: Struct. Sci. 1990, 46, 256−262. (b) Bernstein, J.; Davis, R. E.; Shimoni, L.; Chang, N. L. Angew. Chem., Int. Ed. Engl. 1995, 34, 1555−1573. (24) Thuéry, P.; Harrowfield, J. CrystEngComm 2016, 18, 3905− 3918. (25) Wolff, S. K.; Grimwood, D. J.; McKinnon, J. J.; Turner, M. J.; Jayatilaka, D.; Spackman, M. A. CrystalExplorer; University of Western Australia, 2012. (26) Zhu, H. F.; Fan, J.; Okamura, T. A.; Zhang, Z. H.; Liu, G. X.; Yu, K. B.; Sun, W. Y.; Ueyama, N. Inorg. Chem. 2006, 45, 3941−3948. (27) Turner, R. W.; Amma, E. L. J. Am. Chem. Soc. 1966, 88, 3243− 3247.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01168. Crystal structure of the complex [Ag2(HBTA)(H2O)]. (PDF) X-ray crystallographic information. (CIF) X-ray crystallographic information. (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. (P.T.) *E-mail: harrowfi[email protected]. (J.H.) Notes

The authors declare no competing financial interest.

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REFERENCES

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