Complexation of Uranyl and Rare-Earth Ions by a Fluorinated

Article pubs.acs.org/crystal

Complexation of Uranyl and Rare-Earth Ions by a Fluorinated Tetracarboxylate. Formation of a Layered Assembly and ThreeDimensional Frameworks Pierre Thuéry,*,† Bernardo Masci,‡ and Jack Harrowfield§ †

CEA, IRAMIS, UMR 3299 CEA/CNRS, SIS2M, LCCEf, Bât. 125, 91191 Gif-sur-Yvette, France Dipartimento di Chimica and IMC−CNR, Sapienza − Università di Roma, P.le Aldo Moro 5, 00185 Roma, Italy § Institut de Science et d′Ingénierie Supramoléculaires, Université de Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France ‡

S Supporting Information *

ABSTRACT: The reaction of uranyl and rare-earth nitrates with 4,4′(1,1,1,3,3,3-hexafluoroisopropylidene)diphthalic acid (H4L) under hydro-/ solvo-thermal conditions (2:1 water/acetonitrile at 180 °C) gives a series of complexes, most of which have been crystallographically characterized. In the lattice of the uranyl complex [(UO2)2(L)(H2O)2]·2H2O (1), the metal atoms are chelated by two adjacent carboxylate groups, each of the latter being bridging bidentate, and the resulting coordination polymer is two-dimensional. The ∼14 Å thick layers comprise two uranyl-covered faces linked to one another by L4− pillars, a claylike architecture likely due to the hydrophobic interactions between the organic ligands. The complexes [Ce(HL)(H2O)]·1.5H2O (2) and [Nd(HL)(H2O)]·2.5H2O (3) are isomorphous and they display a high degree of connectivity, with the metal atoms in ten- or eleven-coordinate environments being bound to five or six HL3− ligands. The three-dimensional (3D) framework formed contains one-dimensional subunits of adjacent metal ions with each coordination polyhedron sharing two triangular faces with its neighbors. The hydrophobic CF3 groups are oriented divergently from the exterior of wide channels (∼22 × 8 Å), which are occupied by the solvent water molecules. The complexes with rare-earth ions of smaller ionic radii, [M4(L)3(H2O)9]·7H2O with M = Er (4), Yb (5), and Y (6), are isomorphous to the previously reported terbium(III) complex, and they crystallize as 3D frameworks containing di- and tetra-nuclear subunits. In the visible region, only the uranyl and europium (and terbium) complexes display significant solid-state luminescence.

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INTRODUCTION Most metal−organic assemblies involving f elements make use of polycarboxylate ligands and, among the latter, those built around an aromatic skeleton constitute a particularly notable subset.1 In the very commonly used benzene polycarboxylates, up to six functional groups are held in a quite rigid arrangement in a manner suitable to act as divergent nodes in metalcontaining networks, as recently beautifully exemplified in the case of mellitate (benzenehexacarboxylate) with both uranyl and lanthanide cations.2 Ligands possessing a smaller number of carboxylate groups, such as benzenetricarboxylate, phthalate, and isophthalate, also underpin a rich structural chemistry, as evidenced by the many crystal structures reported in the Cambridge Structural Database (CSD, version 5.34).3 An interesting variation upon these molecules consists of introducing a higher degree of geometric freedom, which can be done, for example, by replacing carboxylate by methylenecarboxylate units4 or by using molecules comprising two linked benzene(poly)carboxylate moieties. Relatively few examples of the latter approach are to be found in f-element chemistry; in particular, those in which two dicarboxylatebearing rings are linked in a bent fashion by a single sp2 or sp3 © XXXX American Chemical Society

carbon atom are limited to the uranyl and lanthanide complexes of benzophenone-3,3′,4,4′-tetracarboxylate5 and lanthanide complexes of 4,4′-(hexafluoroisopropylidene)diphthalate6 and methylenediisophthalate,7 while known examples with monocarboxylate-substituted rings comprise lanthanide complexes of benzophenone-4,4′-dicarboxylate 8 and 4,4′-(hexafluoroisopropylidene)dibenzoate.9 The uranyl ion complex with benzophenone-3,3′,4,4′-tetracarboxylate forms a two-dimensional (2D) assembly with a bilayer geometry made possible by the twisting of the two aromatic rings around the central bonds.5a Whereas the coordination geometry of the uranyl ion is well-defined, with an array of three to six donors in the equatorial plane, the 4f ions are notorious for their high coordination numbers and variable bonding geometry, which result in quite diverse network topologies. The complexes formed by trivalent europium, gadolinium, and terbium ions with benzophenone-3,3′,4,4′-tetracarboxylate crystallize as 2D arrays,5b while the lanthanide ion complexes of the other Received: April 22, 2013 Revised: May 29, 2013

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dx.doi.org/10.1021/cg400606z | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Table 1. Crystal Data and Structure Refinement Details chemical formula M (g mol−1) crystal system 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) reflections collected independent reflections obsd reflections [I > 2σ(I)] Rint parameters refined R1 wR2 S Δρmin (e Å−3) Δρmax (e Å−3)

1

2

3

4

5

6

C19H14F6O16U2 1088.36 monoclinic P2/c 15.9819(10) 6.6086(2) 12.5145(7) 90 107.808(3) 90 1258.43(11) 2 2.872 12.978 988 50433 3838 3293 0.040 195 0.031 0.078 1.018 −3.45 1.60

C19H12CeF6O10.5 662.41 monoclinic P21/c 7.3524(2) 29.1642(14) 23.1750(11) 90 90.772(3) 90 4968.9(4) 8 1.771 1.928 2576 144266 12790 9891 0.050 695 0.054 0.158 1.059 −1.02 1.68

C19H14F6NdO11.5 684.54 monoclinic P21/c 7.3654(3) 29.0284(17) 23.4808(14) 90 90.969(3) 90 5019.6(5) 8 1.812 2.169 2672 147293 9497 7671 0.057 712 0.055 0.163 1.093 −1.64 2.03

C57H50Er4F18O40 2386.01 triclinic P1̅ 8.0722(2) 21.2247(7) 22.7899(8) 82.622(2) 82.404(2) 80.079(2) 3790.1(2) 2 2.091 4.523 2292 200674 23142 18480 0.057 1090 0.031 0.082 1.018 −1.77 2.11

C57H50F18O40Yb4 2409.13 triclinic P1̅ 8.0659(4) 21.2621(14) 22.7182(16) 82.919(3) 82.369(4) 80.025(4) 3783.1(4) 2 2.115 5.039 2308 172557 19501 12702 0.076 1090 0.046 0.107 0.965 −1.53 2.11

C57H50F18O40Y4 2072.61 triclinic P1̅ 8.0954(3) 21.2590(12) 22.8149(12) 82.520(2) 82.394(3) 79.972(3) 3809.3(3) 2 1.807 3.156 2060 222493 23255 15047 0.066 1110 0.045 0.114 0.955 −0.66 1.74

trinitrates for complexes 2−6. 4,4′-(1,1,1,3,3,3-Hexafluoroi s o p r o p y l i d e n e ) d i p h t h a l i c a c i d ( 2 4 m g , 0. 0 5 m m o l ) , UO2(NO3)2·6H2O (50 mg, 0.10 mmol), acetonitrile (0.5 mL), and demineralized water (1.0 mL) were placed in a 15 mL tightly closed glass vessel and heated at 180 °C under autogenous pressure. Light yellow, platelet-shaped crystals of complex 1 appeared within two days (27 mg, 50% yield). Anal. Calcd for C19H14F6O16U2: C, 20.97; H, 1.30. Found: C, 20.93; H, 2.08%. The crystals of complexes 2−6 are colorless or very slightly colored (light blue-violet for 3, light pink for 4) and platelet- or needle-shaped. For 2: 18 mg, 54% yield (on the basis of H4L, as in the following cases). For 3: 22 mg, 64% yield. For 4: 26 mg, 65% yield. Anal. Calcd for C57H50Er4F18O40: C, 28.69; H, 2.11. Found: C, 28.29; H, 2.80%. Complexes 5 and 6 were obtained in low yield, and no improvement resulted from prolonged heating. Repeated efforts to obtain the Eu(III) complex resulted only in microcrystalline products unsuitable for structure determinations; however, X-ray powder diffraction (Supporting Information) indicated that this complex is not isomorphous to either of the two forms which have been found for other lanthanide ions. Crystallography. The data were collected at 150(2) K on a Nonius Kappa-CCD area detector diffractometer12 using graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). The crystals were introduced into glass capillaries with a protecting “Paratone-N” oil (Hampton Research) coating. The unit cell parameters were determined from ten frames, then refined on all data. The data (combinations of φ- and ω-scans with a minimum redundancy of 4 for 90% of the reflections) were processed with HKL2000.13 Absorption effects were corrected empirically with the program SCALEPACK.13 The structures were solved by direct methods, except when an isostructural model was available, expanded by subsequent Fourierdifference synthesis, and refined by full-matrix least-squares on F2 with SHELXL-97.14 All non-hydrogen atoms were refined with anisotropic displacement parameters, with restraints for some atoms, particularly in the solvent molecules. Some of the latter were given partial occupancy factors in order to retain acceptable displacement parameters and/or to account for too close contacts. Most hydrogen atoms bound to oxygen atoms were found on Fourier-difference maps in all compounds, except for those of almost all solvent water

ligands cited above display various three-dimensional (3D) architectures. The latter complexes have been investigated in particular for their photoluminescence6,7b,9 and their magnetic6,7b,9 or catalytic7a properties, which make them interesting as multifunctional materials. The terbium(III) complex only has been reported in the case of 4,4′-(hexafluoroisopropylidene)diphthalic acid (denoted H4L hereafter),6 a ligand possessing four functional groups and the notable feature of a hydrophobic fluorous bridge. While fluorous groups are hydrophobic, they are also lipophobic,10 thus providing a novel means of influencing solid-state (crystal) structures, although this has, to date, found only limited application with coordination complexes.11 In the present work, we report the synthesis and crystal structures of the complexes of H4L with the uranyl ion and several trivalent rare-earth ions (Ce, Nd, Er, Yb, and Y) with the particular objective of exposing the influence of the fluorous groups within the crystal lattices. Preliminary studies of the luminescence in the solid state of the uranyl and Eu(III) complexes (crystals suitable for a structure determination could not be obtained for the latter) are also reported.

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EXPERIMENTAL SECTION

Synthesis. Because uranium is a radioactive and chemically toxic element, uranium-containing samples must be handled with suitable care and protection. Caution is also warranted for the manipulation of glass vessels under pressure. UO2(NO3)2·6H2O (depleted uranium, R. P. Normapur, 99%) was purchased from Prolabo, rare-earth nitrates (hexa- or penta-hydrates) from either Prolabo, Aldrich, or Strem, and 4,4′-(1,1,1,3,3,3hexafluoroisopropylidene)diphthalic acid from Aldrich. Elemental analyses were performed by MEDAC Ltd. at Chobham, U.K. [(UO2)2(L)(H2O)2]·2H2O (1), [Ce(HL)(H2O)]·1.5H2O (2), [Nd(HL)(H2O)]·2.5H2O (3), [Er4(L)3(H2O)9]·7H2O (4), [Yb4(L)3(H2O)9]·7H2O (5), and [Y4(L)3(H2O)9]·7H2O (6). The same experimental procedure was followed for all complexes, as exemplified below in the case of the uranyl complex 1, with uranyl dinitrate being changed for rare-earth B



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molecules, 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 to 1.2 times that of the parent atom. The number of solvent water molecules was adjusted in each case within the two groups of isomorphous compounds, which accounts for one more water molecule being present in 3 than in 2, while, although 6 has the same overall number of lattice water molecules as 4 and 5, their distribution over different sites is not the same, resulting in a slightly different number of refined parameters. Crystal data and structure refinement parameters are given in Table 1 and selected bond lengths in Tables 2, 3, and 4. The molecular plots were drawn with ORTEP-315 and the views of the packings with VESTA.16 The topological analyses were done with TOPOS.17

Table 4. Environment of the Metal Atoms in the Isomorphous Compounds 4−6: Selected Bond Lengths (Å)a M1−O1 M1−O2 M1−O9 M1−O13i M1−O23 M1−O25 M1−O26 M1−O27 M2−O2 M2−O3 M2−O3j M2−O4j M2−O10 M2−O14i M2−O15k M2−O16k M2−O28 M3−O5l M3−O6l M3−O11 M3−O17 M3−O21m M3−O29 M3−O30 M3−O31 M4−O5l M4−O7l M4−O18 M4−O19n M4−O20n M4−O22m M4−O32 M4−O33

Table 2. Environment of the Uranium Atom in Compound 1: Selected Bond Lengths (Å) and Angles (deg)a U−O1 U−O2 U−O3 U−O4i U−O5 U−O6j U−O7 a

1.752(3) 1.756(3) 2.391(3) 2.363(3) 2.377(3) 2.366(3) 2.450(3)

O1−U−O2 O3−U−O5 O5−U−O4i O4i−U−O6j O6j−U−O7 O7−U−O3

179.18(13) 70.82(10) 72.78(10) 73.18(9) 71.86(10) 71.73(10)

Symmetry codes: i = x, y − 1, z; j = x, −y, z − 1/2.

Table 3. Environment of the Metal Atoms in the Isomorphous Compounds 2 and 3: Selected Bond Lengths (Å)a M1−O1 M1−O2 M1−O3i M1−O4i M1−O7j M1−O9 M1−O10 M1−O11k M1−O12k M1−O15l M1−O17 M2−O2 M2−O3 M2−O7m M2−O8m M2−O9k M2−O11k M2−O13n M2−O15l M2−O16l M2−O18

M = Ce (2)

M = Nd (3)

2.545(5) 2.921(4) 2.702(4) 2.613(4) 2.571(5) 2.861(4) 2.495(5) 2.742(4) 2.647(4) 2.464(4) 2.550(8) 2.538(4) 2.506(4) 2.866(4) 2.498(5) 2.558(4) 2.494(4) 2.513(4) 2.881(4) 2.507(4) 2.539(5)

2.509(6) 3.024(5) 2.698(5) 2.571(6) 2.515(6) 2.785(5) 2.464(6) 2.776(6) 2.608(6) 2.412(6) 2.517(10) 2.475(5) 2.476(5) 2.900(6) 2.446(6) 2.554(6) 2.470(6) 2.488(6) 2.922(6) 2.464(5) 2.483(6)

M = Er (4)

M = Yb (5)

M = Y (6)

2.370(3) 2.615(2) 2.280(2) 2.256(2) 2.256(2) 2.361(2) 2.401(3) 2.353(2) 2.439(2) 2.347(2) 2.537(2) 2.387(3) 2.288(2) 2.323(2) 2.442(2) 2.395(2) 2.423(2) 2.513(2) 2.420(3) 2.244(2) 2.286(3) 2.309(2) 2.330(2) 2.342(3) 2.376(3) 2.394(3) 2.286(3) 2.325(2) 2.401(2) 2.430(3) 2.216(2) 2.356(2) 2.350(3)

2.337(5) 2.621(4) 2.255(4) 2.235(4) 2.239(4) 2.345(5) 2.394(5) 2.334(4) 2.420(4) 2.324(4) 2.546(4) 2.372(5) 2.261(4) 2.298(4) 2.427(5) 2.380(4) 2.412(4) 2.487(4) 2.389(5) 2.219(4) 2.269(5) 2.282(4) 2.291(5) 2.309(5) 2.363(5) 2.379(4) 2.245(5) 2.300(5) 2.383(4) 2.404(4) 2.203(4) 2.351(4) 2.320(5)

2.382(2) 2.619(2) 2.289(2) 2.267(2) 2.268(2) 2.375(2) 2.412(2) 2.370(2) 2.446(2) 2.357(2) 2.545(2) 2.401(2) 2.293(2) 2.339(2) 2.454(2) 2.404(2) 2.432(2) 2.519(2) 2.422(2) 2.254(2) 2.295(2) 2.320(2) 2.333(2) 2.353(2) 2.396(2) 2.411(2) 2.286(2) 2.331(2) 2.415(2) 2.438(2) 2.233(2) 2.347(2) 2.352(2)

Symmetry codes: i = x − 1, y, z; j = 1 − x, 1 − y, 1 − z; k = 2 − x, 1 − y, 1 − z; l = 1 − x, 1 − y, 2 − z; m = x + 1, y, z; n = 1 − x, 2 − y, 2 − z. a

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RESULTS AND DISCUSSION S y n t h e s i s . T h e v e r y l o w s o l u bi l it y o f 4 , 4 ′ (hexafluoroisopropylidene)diphthalic acid in water under normal conditions can be overcome by the use of pressure and temperature in hydro- or solvo-thermal procedures. Although the Tb(III) complex, [Tb4(L)3(H2O)9]·7H2O, has been successfully prepared6 under hydrothermal conditions from the sodium salt of the ligand formed by the rapid reaction between NaOH and the acid anhydride, we considered that crystal growth might be superior under conditions where the anionic (carboxylate) forms of the ligand were of more restricted availability and where the possibility of forming metal-hydroxo species might be avoided. Thus, for the present syntheses, we used a hydro-/solvo-thermal procedure involving a 2:1 mixture of water and acetonitrile as the solvent for the acid form of the ligand (and the metal salts). This combination of solvents is not unprecedented among those used for hydro-/ solvo-thermal synthesis18 (solvothermal conditions with pure acetonitrile have also been reported19), although the synthesis temperature used in the present work (180 °C) was higher than those generally adopted when acetonitrile is present (100−160 °C). Interestingly, no crystalline materials were deposited in the absence of acetonitrile, indicating that the present reactions

a Symmetry codes: i = x − 1, y, z; j = 1 − x, y + 1/2, 1/2 − z; k = x + 1, y, z; l = x, 3/2 − y, z − 1/2; m = 2 − x, y + 1/2, 1/2 − z; n = x + 1, 3/2 − y, z − 1/2.

Luminescence Measurements. Emission spectra were recorded on solid samples using a Hiroda−Jobin−Yvon Fluolog spectrofluorimeter. The powdered complex was pressed between two silica plates which were mounted such that the faces were oriented vertically and at 45° to the incident excitation radiation. An excitation wavelength of 300 nm was used in all cases and the emissions monitored between 400 and 800 nm, with a 400 nm bandpass filter used to block transmission of the excitation radiation. C



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may provide examples of so-called “homogeneous precipitation”,20 resulting from the slow decrease of solution acidity caused by the hydrolysis, probably metal-ion catalyzed,21 of acetonitrile ultimately to ammonium acetate. In the case of the species presently characterized, the procedure used has led to the formation of compounds containing either triply or quadruply deprotonated ligand units, although solubility factors are presumably of some importance also in determining the nature of the crystalline deposits. A change in crystal phase across the lanthanide series is well-known for various carboxylates22 and does appear to be the case for 4,4′(hexafluoroisopropylidene)diphthalate, although from the present results it can only be surmised that it may occur between Sm and Gd (with the possibility of a third phase, as indicated by the X-ray powder diffraction data for the Eu(III) species; see the Supporting Information). Attempts were made at the synthesis of uranyl−lanthanide heterometallic complexes, but, under the present conditions, they gave only crystals of the uranyl complex 1. Crystal Structures. The complex with the uranyl ion, [(UO2)2(L)(H2O)2]·2H2O (1), crystallizes in the space group P2/c, with one uranyl ion and only half the tetraanionic ligand in the asymmetric unit, and the carbon atom bridging the two aromatic rings located on a 2-fold rotation axis (f site), as shown in Figure 1. The uranyl ion is chelated by the two carboxylate groups attached to one aromatic ring, thus forming a seven-membered ring, and its equatorial coordination is completed by two carboxylate oxygen atoms from two other ligands and a water molecule to give the usual pentagonal bipyramidal uranium coordination geometry. The average U− O(carboxylate) bond length of 2.374(11) Å is unexceptional [average bond length from the CSD 2.42(7) Å]; the bond length to the chelating donors [2.384(7) Å] is slightly larger (although not quite significantly) than that to the other two donors [2.365(2) Å]. Each carboxylate group is bridging bidentate, in a μ-1κO:2κO′ syn−anti fashion, a coordination mode also encountered in the uranyl ion complex of benzophenone-3,3′,4,4′-tetracarboxylate.5a The dihedral angles between the carboxylate groups and the aromatic ring are 45.8(3) and 51.4(3)° [72.5(4)° between the carboxylates, so as to minimize steric interactions], and the two aromatic rings are themselves nearly orthogonal, with a dihedral angle of 83.00(11)°. Each uranyl ion thus connects three ligands, while each ligand is bound to six metal ions, with the bonding mode represented in Scheme 1. The resulting polymeric assembly is 2D and parallel to the bc plane, the ∼14 Å thick layers comprising two uranyl-covered faces linked to one another by L4− pillars. The binodal network, which is represented in simplified form in Scheme 2, has the total point symbol {43}2{46.66.83} (first symbol for uranium and second for L4−). As a consequence of this arrangement, the inner spaces of the layers are hydrophobic, and the water solvent molecules are located in the interlayer spaces. The water ligand is a hydrogen donor toward the solvent water molecule [O7···O8, 2.709(5) Å; O7−H···O8, 172°], and although the protons of the latter have not been found, it is likely, from the interatomic distance of 2.872(5) Å, that it forms a hydrogen bond with the carboxylate oxygen atom O3 of another layer. Adjacent layers along the a axis are thus connected to one another via the lattice water molecules. No significant π-stacking, F···π, or F···F interactions are present. The hydrophobic interactions between the organic ligands and the associated water exclusion may explain the peculiar, claylike

Figure 1. Top: view of the uranyl complex 1. Displacement ellipsoids are drawn at the 50% probability level. Solvent molecules and carbonbound hydrogen atoms are omitted. Symmetry codes: i = x, y − 1, z; j = x, −y, z − 1/2; k = x, y + 1, z; l = x, −y, z + 1/2; m = 1 − x, y, 5/2 − z; n = 1 − x, y + 1, 5/2 − z; o = 1 − x, −y, 2 − z. Bottom: view of the packing with the sheets viewed edge-on, showing the uranium coordination polyhedra and with solvent molecules and hydrogen atoms omitted.

Scheme 1. Coordination Modes of the Ligand H(4−x)Lx− in complexes 1−3. The coordination modes in complexes 4−6 are similar to those in the terbium complex.6

D



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aromatic rings along the bonds joining them to the central bridging carbon atom and of the carboxylate groups with respect to the aromatic rings. The dihedral angles between the two rings are 61.0(2) and 69.7(2)° for the two molecules in the cerium complex, while the dihedral angles between the carboxylate groups and the aromatic rings are extremely different, with either one carboxylate nearly coplanar with the ring [6.3(9) and 5.8(9)°] and the other nearly orthogonal to it [87.6(3) and 84.8(4)°] or both carboxylates tilted in an intermediate position [35.1(7) and 53.0(5)° in one molecule, 51.7(4) and 37.7(6)° in the other]. In each molecule, the carboxylate groups which chelate one metal atom are nearly orthogonal to one another [81.3(6) and 83.1(6)°], but those which do not share a complexed cation are less tilted [54.7(8) and 53.1(8)°]. The two ligands display nearly identical coordination modes, with the carboxylate groups attached to one ring being trichelating and one of those of the other ring being chelating and bridging; the main difference comes from the carboxylic group, which is uncoordinated in one case and monodentate in the other. These coordination modes are different from those reported for the two independent L4− ligands in the terbium complex6 and as a consequence from those in complexes 4−6. This quite intricate bonding scheme gives rise to the formation of a 3D framework, represented in Figure 2. In contrast to the framework formed in the terbium complex and in compounds 4−6, which comprise di- and tetranuclear metal clusters, this assembly contains one-dimensional arrays directed along the a axis, built from adjacent lanthanide ions with coordination polyhedra sharing two triangular faces (defined by atoms O2, O11k, O15l, and O3i, O9, O7j) with their neighbors. These chains are connected to one another along both the b and c axes by extended HL3− ligands, which gives a four-nodal network of total point symbol {410.65}{44.64.82}{47.67.8}{49.6} (first symbol for Ce1, second and third for the two ligands, and fourth for Ce2). When the framework is viewed along a (the chain axis), it appears that six out of the eight CF3 groups per ring are pointing toward the same direction and define extremely narrow hydrophobic channels (such CF3-lined channels have been dubbed “Teflonlike”9a). Much larger channels running along a are also present, which are nearly free of CF3 groups (two such groups only point at the periphery of the channel). These elongated channels, with a dimension of ∼22 × 8 Å, are occupied by the solvent water molecules. While no significant π-stacking or F···π interactions are present, six short intermolecular F···F contacts, in the range of 2.58−2.97 Å, are possibly indicative of halogen···halogen interactions.23 However, the stabilizing role of F···F interactions has been questioned, in contrast to that of the heavier halogens.23b Four short F···H(aromatic) contacts, in the 2.42−2.71 Å range, are also present. As in the case of the uranyl complexes, the structures of 2 and 3 are different from that in the lanthanide (Eu, Gd, and Tb) ion complexes with benzophenone-3,3′,4,4′-tetracarboxylic acid. The latter crystallize as 2D assemblies with one-dimensional (1D) subunits of closely packed metal ions with edge-sharing coordination polyhedra.5b The crystal structure of compounds 4−6, being isomorphous to that of the terbium complex which has been thoroughly studied previously,6 will not be described in detail. The asymmetric unit contains four independent metal ions and three L4− ligands, as illustrated in Figure 3 in the case of the ytterbium complex 5. Three metal ions are eight-coordinate (to carboxylates and two or three water ligands), with an

Scheme 2. Simplified View of the 2D Assembly in 1 down the a Axis and with the c Axis Horizontala

a

Yellow: uranium, red: oxygen, blue: centroid of L4−.

architecture of these layers. It is notable that the uranyl complex with benzophenone-3,3′,4,4′-tetracarboxylate,5a which only differs from the present ligand by the nature of the bridge which links the two aromatic rings, crystallizes also as a 2D assembly with a bilayer geometry, but in this case uranyl ions, and not organic molecules, act as pillars. The four complexes obtained with lanthanide ions (Ce, Nd, Er, and Yb) and the yttrium complex can be separated into two groups of isomorphous compounds. The complexes with the two lanthanide ions with the larger ionic radii, [Ce(HL)(H2O)]·1.5H2O (2) and [Nd(HL)(H2O)]·2.5H2O (3), constitute the first group, notwithstanding a difference in the number of refined solvent water molecules (see Experimental Section), while [Er4(L)3(H2O)9]·7H2O (4), [Yb4(L)3(H2O)9]·7H2O (5), and [Y4(L)3(H2O)9]·7H2O (6) are isomorphous with the terbium complex previously described.6 Complexes 2 and 3 crystallize in the space group P21/c, with two crystallographically independent metal ions and two trianionic HL3− ligands (Figure 2). The metal atom M1 is chelated by four carboxylate groups pertaining to four ligands, and it is also bound to two monodentate carboxylate oxygen atoms from two more ligands and a water molecule. The eleven-coordinate environment has a rather irregular geometry. The atom M2 is chelated by two carboxylates only and is bound to five monodentate carboxylate oxygen atoms and one water molecule, the ten-coordinate environment being bicapped square antiprismatic with the two sets of atoms (O2, O11k, O16l, O18) and (O3, O9k, O8m, O13n) defining the two faces [dihedral angle 1.73(7)°] and atoms O7m and O15l in the capping positions. The M−O(carboxylate) bond lengths span the ranges 2.464(4)−2.921(4) and 2.412(6)−3.024(5) Å for Ce and Nd, respectively. Atom M1 connects six ligands and M2 only five, while, conversely, the two ligands are bound to five and six metal atoms, with the bonding modes shown in Scheme 1. The planar representation of the ligands in this scheme does not properly account for the variable degree of rotation of the E



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Figure 2. Top: view of the cerium complex 2, isomorphous to the neodymium complex 3. Displacement ellipsoids are drawn at the 50% probability level. Solvent molecules and carbon-bound hydrogen atoms are omitted. Symmetry codes: i = x − 1, y, z; j = 1 − x, y + 1/2, 1/2 − z; k = x + 1, y, z; l = x, 3/2 − y, z − 1/2; m = 2 − x, y + 1/2, 1/2 − z; n = x + 1, 3/2 − y, z − 1/2; o = 1 − x, y − 1/2, 1/2 − z; p = 2 − x, y − 1/2, 1/2 − z; q = x − 1, 3/2 − y, z + 1/2; r = x, 3/2 − y, z + 1/2. Middle: view of the 3D framework, showing the cerium coordination polyhedra and with solvent molecules and hydrogen atoms omitted. Bottom: view of the 1D subunit of fused cerium polyhedra, showing the carboxylate bridges.

four or five ligands (the latter for the cation in a ninecoordinate environment), while each ligand is bound to five or six metal atoms. Due to the decrease in the coordination number, the degree of connectivity is thus somewhat reduced with respect to that in 2 and 3. The 3D framework in 4−6 displays metal clusters of lower dimensionality and smaller channels than 2 and 3. Luminescence Properties. The fluorescence spectrum of solid [(UO2)2(L)(H2O)2]·2H2O (Figure 4) shows the vibronic progression near 500 nm typical of uranyl species, with the

environment which has been described as distorted bicapped trigonal prismatic in the case of terbium but can also be viewed as distorted square antiprismatic, while the nine-coordinate environment of the last metal ion (with only one water ligand) is capped square antiprismatic. As in complexes 2 and 3, the M−O(carboxylate) bond lengths span large ranges, 2.216(2)− 2.615(2) Å for Er, 2.203(4)−2.621(4) Å for Yb, and 2.233(2)− 2.619(2) Å for Y [the ionic radii for these ions in their trivalent state and in eight-coordinate environments are 1.004, 0.985, and 1.019 Å, respectively24]. The metal atoms connect either F



Article

Figure 3. Top: view of the ytterbium complex 5, isomorphous to the terbium,6 erbium (4), and yttrium (6) complexes. Displacement ellipsoids are drawn at the 50% probability level. Solvent molecules and carbon-bound hydrogen atoms are omitted. Symmetry codes: i = x − 1, y, z; j = 1 − x, 1 − y, 1 − z; k = 2 − x, 1 − y, 1 − z; l = 1 − x, 1 − y, 2 − z; m = x + 1, y, z; n = 1 − x, 2 − y, 2 − z. Bottom: view of the 3D framework, showing the ytterbium coordination polyhedra and with solvent molecules and hydrogen atoms omitted.

weak and broad bands near 450 nm possibly associated with ligand-based emission. Although it has not been structurally characterized, the Eu(III) complex shows quite intense solidstate emission in the red (Figure 4b), consistent with its coordination sphere containing the small number (one) of water molecules seen in the complexes of the lighter rare earths. A detailed comparison with the Tb(III) complex, however, is not possible based on the presently known data.

pattern and positions of the bands (major peaks at 483, 500, 523, 547, 573, and 601 nm; Figure 4a) consistent with the observed pentagonal-bipyramidal form of the uranium atom coordination sphere.25 The crystals of the complex appear pale yellow, indicating that the perceived color is determined mainly by absorption and not by the emission in visible light, thus indicating the emission to be significantly weaker than in the greenish hexagonal-bipyramidal species obtained on binding pyridine-2,6-dicarboxylate to the uranyl ion.26 Unsurprisingly, given that they contain rare earths expected either to be nonemissive or to emit in the near-IR only,27 the structurally characterized rare earth complexes of the present work gave solid-state emission spectra showing at most some

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CONCLUSIONS The use of hydro-/solvo-thermal synthetic conditions enables the growth of single crystals suitable for X-ray structure determinations of the uranyl and rare-earth (Ce, Nd, Er, Yb, G



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Figure 4. Solid-state luminescence spectra of the complexes of 4,4′-(hexafluoroisopropylidene)diphthalate with (a) uranyl and (b) Eu(III). Excitation wavelength 300 nm. Horizontal scale, wavelength/nm; vertical scale, emission intensity (arbitrary units).

and Y) complexes with the fluorinated ligand 4,4′(hexafluoroisopropylidene)diphthalic acid. For other members of the rare-earth series, Eu(III) in particular, the procedure appears not to be so successful, although this may only be a consequence of the generation of a mixture of phases. Although the ligand has the same overall geometry as the previously used benzophenone-3,3′,4,4′-tetracarboxylic acid, the topology of the metal−organic assemblies formed is completely different. Obviously, these ligands are somewhat flexible, and together with the varying coordination modes of the eight donor atoms, the rotation of the different parts (aromatic rings and carboxylic groups) with respect to each other is of a nature to induce large variations of the final architectures by itself. However, a particularly prominent feature of the 4,4′-(hexafluoro-

isopropylidene)diphthalate ligand is the presence of the hydrophobic CF3 groups which appear, in these and in previously reported structures, to have a marked tendency to organize the ligands so as to form hydrophobic regions, which are either layers in complex 1 or channels in complexes 2−6. The sheet topology in 1 is likely due to the well-known tendency of uranyl ions to give rise to 2D arrangements, but the pillaring by L4− anions to give very thick layers with a hydrophobic inner part appears to be a consequence of the peculiar nature of the ligand. In the case of rare-earth ions, the coordination environment is closer to a spherical geometry and more adapted to the formation of 3D structures. The topology of the latter is, however, determined by the segregation of the hydrophobic groups, two different architectures being obtained H



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(17) (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. (18) See, for example: (a) Lu, J.; Yu, C.; Niu, T.; Paliwala, T.; Crisci, G.; Somosa, F.; Jacobson, A. J. Inorg. Chem. 1998, 37, 4637. (b) Huang, X. C.; Zheng, S. L.; Zhang, J. P.; Chen, X. M. Eur. J. Inorg. Chem. 2004, 1024. (c) Xie, Y. B.; Gao, Q.; Zhang, C. Y.; Sun, J. H. J. Solid State Chem. 2009, 182, 1761. (d) Yuan, X. Q.; Feng, M. L.; Li, J. R.; Huang, X. Y. J. Solid State Chem. 2010, 183, 1955. (e) Cui, J.; Huang, L.; Lu, Z.; Li, Y.; Guo, Z.; Zheng, H. CrystEngComm 2012, 14, 2258. (19) See, for example: (a) Satta, S.; Chang, Y. D.; Zubieta, J. J. Chem. Soc., Chem. Commun. 1994, 1039. (b) Hu, S.; Zhou, A. J.; Zhang, Y. H.; Ding, S.; Tong, M. L. Cryst. Growth Des. 2006, 6, 2543. (c) Li, L. L.; Liu, L. L.; Ren, Z. G.; Li, H. X.; Zhang, Y.; Lang, J. P. CrystEngComm 2009, 11, 2751. (20) See, for example: (a) Gordon, L.; Salesin, E. D. J. Chem. Educ. 1963, 40, A306. (b) Kratohvil, S.; Matijević, E. J. Mater. Res. 1991, 6, 766. (c) Candal, R. J.; Regazzoni, A. E.; Blesa, M. A. J. Mater. Chem. 1992, 2, 657. (d) Dixit, M.; Subbanna, G. N.; Kamath, P. V. J. Mater. Chem. 1996, 6, 1429. (21) Chin, J. Acc. Chem. Res. 1991, 24, 145. (22) See, for example: Junk, P. C.; Kepert, C. J.; Lu, W. M.; Skelton, B. W.; White, A. H. Aust. J. Chem. 1999, 52, 437 and 459. (23) (a) Sakurai, T.; Sundaralingam, M.; Jeffrey, G. A. Acta Crystallogr. 1963, 16, 354. (b) Desiraju, G. R.; Parthasarathy, R. J. Am. Chem. Soc. 1989, 111, 8725. (c) Pedireddi, V. R.; Reddy, D. S.; Goud, B. S.; Craig, D. C.; Rae, A. D.; Desiraju, G. R. J. Chem. Soc., Perkin Trans. 2 1994, 2, 2353. (24) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751. (25) (a) Burrows, H. D.; Miguel, M. da G. Adv. Colloid Interface Sci. 2001, 89−90, 485. (b) Formosinho, S. J.; Burrows, H. D.; Miguel, M. da G.; Azenha, M. E. D. G.; Saraiva, I. M.; Ribeiro, A. C. D. N.; Khudyakov, I. G.; Gasanov, R. G.; Sarakha, M. Photochem. Photobiol. Sci. 2003, 2, 569. (c) For a general overview of actinide photochemistry, see: Natrajan, L. S. Coord. Chem. Rev. 2012, 256, 1583. (26) Harrowfield, J. M.; Lugan, N.; Shahverdizadeh, G. H.; Soudi, A. A.; Thuéry, P. Eur. J. Inorg. Chem. 2006, 389. (27) (a) Døssing, A. Eur. J. Inorg. Chem. 2005, 1421. (b) Bünzli, J. C. B. Acc. Chem. Res. 2006, 39, 53. (c) Moore, E. G.; Samuel, A. P. S.; Raymond, K. N. Acc. Chem. Res. 2009, 42, 542.

according to the size and coordination number of the rare-earth ion. The readily detected solid-state luminescence in the visible region of the Tb(III)6 and Eu(III) complexes of 4,4′(hexafluoroisopropylidene)diphthalate indicates that the ligand serves as an adequate antenna for the absorption of near-UV radiation and transfer of energy to the states localized on the metal ions.

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ASSOCIATED CONTENT

S Supporting Information *

X-ray powder diffractograms for the Nd(III), Eu(III), and Er(III) complexes. Tables of crystal data, atomic positions, and displacement parameters; anisotropic displacement parameters; and bond lengths and bond angles in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Dr. N. Kyritsakas-Gruber (Strasbourg University) kindly recorded the powder X-ray diffractograms. The Direction de l′Energie Nucléaire of the CEA is thanked for its financial support through the Basic Research Program RBPCH.

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REFERENCES

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Complexation of Uranyl and Rare-Earth Ions by a Fluorinated

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