Lanthanide Ion Complexes with 2-, 3-, or 4-Sulfobenzoate and

Article pubs.acs.org/crystal

Lanthanide Ion Complexes with 2-, 3-, or 4-Sulfobenzoate and Cucurbit[6]uril Pierre Thuéry* CEA, IRAMIS, UMR 3299 CEA/CNRS, SIS2M, LCCEf, Bât. 125, 91191 Gif-sur-Yvette, France S Supporting Information *

ABSTRACT: The reaction of lanthanide nitrate, trifluoromethanesulfonate, or chloride salts with the three positional isomers of sulfobenzoic acid (SBH2) in the presence of cucurbit[6]uril (CB6) under hydrothermal conditions yielded 13 complexes which were crystallographically characterized. The ortho isomer gave a series of one-dimensional polymeric complexes of columnar shape, {[Ln(2-SB)(NO3)(H2O)2]2CB6}·xH2O [isomorphous for Ln = La (1) and Ce (2), x = 10 or 11], {[Nd(2SB)(H2O)3][Nd(2-SB)(H2O)4]CB6}·2NO3·7.5H2O (3), and {[Ln(2-SB)(H 2O) 4]2 CB6}·2NO3·xH2O [isomorphous for Ln = Eu (4), Dy (5), Er (6), and Yb (7), x = 5 or 6]. These compounds all comprise carboxylate-bridged dinuclear units connecting the CB6 molecules through lanthanide−carbonyl coordination, and they differ by sulfonate bonding and formation of a chelate ring being only present in 1−3. In contrast, [Lu(2-SB)(H2O)7]2·CB6·2NO3·7H2O (8) does not display sulfonate and carbonyl coordination, the carboxylate group being monodentate and the complex species being held as a lid over the CB6 portal by hydrogen bonding. The complexes obtained from erbium trifluoromethanesulfonate and chloride salts, {[Er(2-SB)(H 2 O) 4 ] 2 CB6}·2CF 3 SO 3 ·2.5H 2 O (9) and [Er(2-SB)(H2O)7]2·CB6·2Cl·6H2O (10), present the same features as 4−7 and 8, respectively. The meta isomer is in the form of the carboxybenzosulfonate 3-SBH−, with the carboxylic acid retaining its proton, in the isomorphous complexes {[Ln(3SBH)(H2O)4]2CB6}·4NO3 [Ln = Ce (11) or Nd (12)]. These complexes display the feature, unusual in this series, of coordination by the monodentate sulfonate group only. A columnar assembly is formed by coordination of each metal ion to two CB6 molecules, the 3-SBH− ligand having no role in the polymer formation. Finally, the para isomer is only coordinated by the chelating carboxylate group in [Nd1.5(4-SB)(CB6)(NO3)(H2O)6.5]·4-SBH·4-SBH1.5·15H2O (13).

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INTRODUCTION The three positional isomers of sulfobenzoic acid are versatile heterodifunctional ligands displaying two sites of very different geometry and coordination ability, which are well adapted to the synthesis of coordination polymers or frameworks. While carboxylates are among the coordinating groups most commonly used, sulfonates are relatively weak ligands, less efficient in particular than their phosphonate counterparts, and deemed to possess a quite unpredictable behavior.1 Numerous sulfonate complexes of rare-earth ions have been studied, as shown by the crystal structures reported in the Cambridge Structural Database (CSD, Version 5.32),2 a large proportion of which involve however the very common trifluoromethanesulfonate anion, and supramolecular arrangements or extended, polymeric structures have been described.3 In particular, lanthanide complexation by the three positional isomers of sulfobenzoic acid, often with auxiliary ligands such as 1,10-phenanthroline, oxalate, or benzene-1,4-disulfonate, yielded several polynuclear species and coordination polymers or frameworks.4 In these complexes, the sulfonic/ate groups are found to be either bridging bidentate, monodentate, or uncomplexed, and they are always involved in the formation of seven-membered chelate rings with the © 2012 American Chemical Society

carboxylate group in the case of the ortho isomer. It was shown recently that uranyl ion complexes with different sulfonates, notably the three sulfobenzoate isomers, and cucurbit[6]uril5 (CB6, Scheme 1) could be obtained, while crystals could not Scheme 1. Cucurbit[6]uril

be grown in the absence of CB6.6 These compounds display a wide spectrum of structures, from molecular species to Received: December 21, 2011 Revised: January 24, 2012 Published: February 24, 2012 1632

dx.doi.org/10.1021/cg2016808 | Cryst. Growth Des. 2012, 12, 1632−1640

Crystal Growth & Design

Article

introduced into glass capillaries with a protecting “Paratone-N” oil (Hampton Research) coating. The unit cell parameters were determined from 10 frames, then refined on all data. The data (combinations of φ- and ω-scans giving complete data sets up to θ = 30.5° for all compounds except 8 (28.7°) and 13 (25.7°) and a minimum redundancy of 4 for 90% of the reflections) were processed with HKL2000.9 Absorption effects were corrected empirically with the program SCALEPACK.9 The structures were solved by direct methods or Patterson map interpretation with SHELXS-97 (except when an isomorphous model could be used as a starting point), expanded by subsequent Fourier-difference synthesis and refined by full-matrix least-squares on F2 with SHELXL-97.10 All non-hydrogen atoms were refined with anisotropic displacement parameters, with restraints for some atoms in the disordered parts and/or solvent molecules. Some lattice water molecules were given partial occupancy factors in order to retain acceptable displacement parameters and/or to account for too close contacts. The chlorine counterion in 10 is disordered over two positions which have been refined with occupancy parameters constrained to sum to unity. Two nitrate ions in 11 and 12 are disordered around inversion centers. In compound 13, Nd2 was given an occupancy factor of 0.5 in order to retain an acceptable displacement parameter and to account for its closeness to its image by symmetry; the water molecules bound to Nd2 were given occupancy parameters of 0.5 accordingly (except for O26 which can be bound to both Nd2 positions); for charge equilibrium, the proton of the sulfonic acid group pertaining to one of the two uncoordinated molecules was given an occupancy factor of 0.5, although the true location of charges is quite uncertain in this case. The hydrogen atoms bound to oxygen atoms were found on Fourier-difference maps in all compounds, except for those of some water 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. Crystal data and structure refinement parameters are given in Table 1 and selected bond lengths are in Table 2. The molecular plots were drawn with ORTEP-311 and the views of the packings with VESTA.12

three-dimensional frameworks, and, since CB6 is also a good complexant for lanthanide ions,7 it appeared worthwhile to investigate the complexes formed with these cations under similar conditions. While, in contrast with the case of the uranyl ion, no crystal could be obtained with ethanedisulfonic acid or 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron), several lanthanide complexes involving the three sulfobenzoic acid isomers could be obtained and their structure determined by singlecrystal X-ray diffraction. These results, which display some original features, are reported herein.

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EXPERIMENTAL SECTION

Synthesis. Lanthanide nitrates (hexa- or penta-hydrates) were purchased from either Prolabo, Aldrich, Strem, or Fisher Scientific, erbium trifluoromethanesulfonate, erbium chloride hexa-hydrate, 2-sulfobenzoic acid cyclic anhydride (2-SBA), sodium 3-sulfobenzoate (3-SBNaH), and potassium 4-sulfobenzoate (4-SBKH) were from Aldrich, and cucurbit[6]uril pentahydrate was from Fluka. Elemental analyses were performed by Analytische Laboratorien GmbH at Lindlar, Germany. {[La(2-SB)(NO3)(H2O) 2]2CB6}·11H2O (1), {[Ce(2-SB)(NO3)(H2O)2]2CB6}·10H2O (2), {[Nd(2-SB)(H2O)3][Nd(2-SB)(H2O)4]CB6}·2NO3·7.5H2O (3), {[Eu(2-SB)(H2O)4]2CB6}·2NO3·6H2O (4), {[Dy(2-SB)(H2O)4]2CB6}·2NO3·5H2O (5), {[Er(2-SB)(H2O)4]2CB6}·2NO3·5H2O (6), {[Yb(2-SB)(H2O)4]2CB6}·2NO3·5H2O (7), and [Lu(2-SB)(H2O)7]2·CB6·2NO3·7H2O (8). CB6·5H2O (11 mg, 0.01 mmol), a 10-fold excess of Ln(NO3)3·xH2O (Ln = La, Ce, Nd, Eu, Dy, Er, Yb, or Lu; x = 5 or 6, 0.10 mmol) and 2-SBA (18 mg, 0.10 mmol), and demineralized water (1.5 mL) were placed in a 15 mL tightly closed glass vessel and heated at 180 °C under autogenous pressure. Colorless or very lightly colored crystals of the complexes appeared within one week. For 2: 7 mg, 34% yield on the basis of CB6. Anal. Calcd for C50H72Ce2N26O42S2: C, 29.24; H, 3.53; N, 17.73; S, 3.12. Found: C, 28.81; H, 3.42; N, 17.52; S, 2.97%. For 3: 10 mg, 48% yield on the basis of CB6. Anal. Calcd for C50H73N26Nd2O42.5S2: C, 29.00; H, 3.55; N, 17.58; S, 3.10. Found: C, 29.21; H, 3.67; N, 17.77; S, 3.04%. For 5: 9 mg, 43% yield on the basis of CB6. Anal. Calcd for C50H70Dy2N26O41S2: C, 28.87; H, 3.39; N, 17.50; S, 3.08. Found: C, 28.45; H, 3.32; N, 17.18; S, 2.93%. {[Er(2-SB)(H2O)4]2CB6}·2CF3SO3·2.5H2O (9). CB6·5H2O (11 mg, 0.01 mmol), a 10-fold excess of Er(CF3SO3)3 (61 mg, 0.10 mmol) and 2-SBA (18 mg, 0.10 mmol), and demineralized water (1.5 mL) were placed in a 15 mL tightly closed glass vessel and heated at 180 °C under autogenous pressure. Light pink crystals of complex 9 appeared within 24 h (15 mg, 68% yield on the basis of CB6). Anal. Calcd for C52H65Er2F6N24O38.5S4: C, 28.15; H, 2.95; N, 15.15; S, 5.78. Found: C, 27.98; H, 3.00; N, 15.18; S, 5.86%. [Er(2-SB)(H2O)7]2·CB6·2Cl·6H2O (10). CB6·5H2O (11 mg, 0.01 mmol), a 10-fold excess of ErCl3·6H2O (38 mg, 0.10 mmol) and 2-SBA (18 mg, 0.10 mmol), and demineralized water (1.5 mL) were placed in a 15 mL tightly closed glass vessel and heated at 180 °C under autogenous pressure, giving colorless crystals of complex 10 in low yield within two weeks. {[Ce(3-SBH)(H2O)4]2CB6}·4NO3 (11) and {[Nd(3-SBH)(H2O)4]2 CB6}·4NO3 (12). CB6·5H2O (11 mg, 0.01 mmol), a 10-fold excess of Ln(NO3)3·6H2O (0.10 mmol) and 3-SBNaH (22 mg, 0.10 mmol), and demineralized water (1.5 mL) were placed in a 15 mL tightly closed glass vessel and heated at 180 °C under autogenous pressure. Colorless crystals of the complexes appeared in low yield within three days. [Nd1.5(4-SB)(CB6)(NO3)(H2O)6.5]·4-SBH·4-SBH1.5·15H2O (13). CB6·5H2O (11 mg, 0.01 mmol), a 10-fold excess of Nd(NO3)3·6H2O (44 mg, 0.10 mmol) and 4-SBKH (24 mg, 0.10 mmol), and demineralized water (1.5 mL) were placed in a 15 mL tightly closed glass vessel and heated at 180 °C under autogenous pressure. Colorless crystals of complex 13 appeared in low yield within one month. Crystallography. The data were collected at 150(2) K on a Nonius Kappa-CCD area detector diffractometer8 using graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). The crystals were

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RESULTS AND DISCUSSION The reaction between the anhydride 2-SBA, which generates 2-SB2− in situ under hydrothermal conditions, CB6, and lanthanide nitrates has been investigated for La, Ce, Nd, Eu, Dy, Er, Yb, and Lu, which have been chosen as representative examples of the whole lanthanide series. In the case of Er, the synthesis has also been done with the trifluoromethanesulfonate and chloride salts for the sake of comparison. The compounds obtained can be separated into four groups: the La and Ce complexes are isomorphous, the Eu−Yb complexes constitute also an isomorphous group, with unit cell parameters close to those of the two previous compounds, but a different bonding scheme, and the Nd complex can be seen as intermediate between these two groups, while the Lu complex is very different from the others. The content in lattice water molecules determined during structure refinement was found to vary slightly within the two isomorphous groups. The two complexes involving the cations with the largest ionic radii, {[La(2SB)(NO3)(H2O)2]2CB6}·11H2O (1) and {[Ce(2-SB)(NO3)(H2O)2]2CB6}·10H2O (2), differ by one solvent water molecule, but they are otherwise identical, and only the cerium complex 2 is represented in Figure 1. The cation is chelated by one carboxylate and one sulfonate oxygen atoms from the same 2-SB2− molecule to form a seven-membered ring, as usual with lanthanide ions and also as in the uranyl ion complexes reported previously.6b The carboxylate group chelates a second cation, related to the first by an inversion center, which results in the formation of a dinuclear unit, with atom O1 being bridging. It is notable that the carboxylate groups only are involved in the 1633


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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 reflns collcd indep reflns obsd reflns [I > 2σ(I)] Rint params refined R1 wR2 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 reflns collcd indep reflns obsd reflns [I > 2σ(I)] Rint params refined R1 wR2 Δρmin (e Å−3) Δρmax (e Å−3)

C50H86Lu2N26O49S2 2249.51 monoclinic P21/c 13.5294(4) 19.5106(6) 15.6824(6) 90 103.460(2) 90 4025.9(2) 2 117017 10371 8545 0.047 596 0.047 0.138 −1.94 2.25

C50H74La2N26O43S2 2069.29 monoclinic P21/n 15.1305(5) 17.3114(6) 15.8534(5) 90 114.182(2) 90 3788.1(2) 2 135165 11548 9045 0.034 604 0.039 0.113 −1.30 1.87 8

1

3

10

4

11

5

6 C50H70Er2N26O41S2 2089.96 monoclinic P21/n 14.6535(5) 17.4352(6) 15.3977(3) 90 114.691(2) 90 3574.3(2) 2 127233 10877 8561 0.071 577 0.039 0.105 −1.48 1.52 12 C50H62N28Nd2O42S2 2079.88 triclinic P1̅ 10.5336(3) 12.7121(4) 13.8550(5) 72.483(2) 82.584(2) 80.408(2) 1738.32(10) 1 95925 10598 9719 0.029 592 0.026 0.072 −1.15 1.48

C50H70Dy2N26O41S2 2080.44 monoclinic P21/n 14.6276(2) 17.4349(3) 15.4430(2) 90 114.6458(6) 90 3579.66(9) 2 120020 10900 9595 0.024 577 0.027 0.076 −1.44 1.26

C50H62Ce2N28O42S2 2071.64 triclinic P1̅ 10.5886(2) 12.7178(5) 13.8515(7) 72.399(2) 82.545(3) 80.328(3) 1746.50(12) 1 97086 10659 9083 0.069 592 0.036 0.089 −1.75 1.36

C50H72Eu2N26O42S2 2077.38 monoclinic P21/n 14.6450(3) 17.4413(6) 15.4932(5) 90 114.636(2) 90 3597.17(19) 2 97870 10958 8291 0.038 570 0.037 0.099 −1.48 1.61

C50H84Cl2Er2N24O42S2 2162.95 monoclinic P21/c 13.7752(3) 19.3137(5) 15.5268(3) 90 104.392(2) 90 4001.27(16) 2 135733 12207 9911 0.060 578 0.042 0.122 −2.32 2.27

C50H73N26Nd2O42.5S2 2070.94 monoclinic P21/c 25.4539(8) 17.1496(5) 16.3153(5) 90 94.102(2) 90 7103.8(4) 4 229818 21675 17833 0.030 1108 0.036 0.097 −1.38 1.85

C52H65Er2F6N24O38.5S4 2219.04 monoclinic P21/n 15.1723(4) 17.3255(5) 15.1843(3) 90 112.784(2) 90 3680.01(17) 2 78511 11207 9032 0.049 577 0.036 0.097 −1.34 1.85

C50H72Ce2N26O42S2 2053.70 monoclinic P21/n 15.1318(3) 17.3172(6) 15.8969(5) 90 114.284(2) 90 3797.1(2) 2 138262 11581 8791 0.040 577 0.041 0.120 −1.32 1.94 9

2

Table 1. Crystal Data and Structure Refinement Details 7

C57H93.5N25Nd1.5O51.5S3 2265.61 triclinic P1̅ 15.7142(9) 16.0724(7) 19.3805(8) 96.914(3) 110.422(3) 106.722(4) 4258.2(4) 2 210976 16115 14094 0.066 1297 0.078 0.229 −1.63 2.73

C50H70N26O41S2Yb2 2101.52 monoclinic P21/n 14.6399(2) 17.4055(2) 15.4042(2) 90 114.660(2) 90 3567.24(10) 2 124705 10866 9312 0.023 577 0.027 0.075 −1.30 1.24 13

Crystal Growth & Design Article



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Table 2. Environment of the Metal Atoms in Compounds 1−13: Selected Bond Lengths (Å)a 1

2

3

4

a

La−O1 La−O1i La−O2i La−O3 La−O6 La−O8 La−O12 La−O13 La−O15 La−O16 Ce−O1 Ce−O1i Ce−O2i Ce−O3 Ce−O6 Ce−O8 Ce−O12 Ce−O13 Ce−O15 Ce−O16 Nd1−O1 Nd1−O3 Nd1−O6 Nd1−O11 Nd1−O13 Nd1−O23 Nd1−O24 Nd1−O25 Nd2−O2 Nd2−O7 Nd2−O17 Nd2−O19 Nd2−O26 Nd2−O27 Nd2−O28 Nd2−O29 Eu−O1 Eu−O2i Eu−O6 Eu−O8 Eu−O12 Eu−O13 Eu−O14 Eu−O15

2.5398(17) 2.7713(18) 2.6236(19) 2.5657(18) 2.5224(18) 2.6038(17) 2.690(2) 2.626(2) 2.4909(19) 2.555(2) 2.512(2) 2.812(2) 2.590(2) 2.552(2) 2.5025(19) 2.598(2) 2.666(2) 2.596(2) 2.475(2) 2.512(2) 2.3868(19) 2.5543(19) 2.4230(19) 2.3871(18) 2.5353(17) 2.4731(19) 2.4590(19) 2.4620(19) 2.4122(19) 2.3747(19) 2.5010(19) 2.4837(18) 2.486(2) 2.422(2) 2.543(2) 2.4731(19) 2.3332(19) 2.3373(19) 2.3926(18) 2.421(2) 2.416(2) 2.443(3) 2.445(2) 2.4343(19)

5

6

7

8

9

Dy−O1 Dy−O2i Dy−O6 Dy−O8 Dy−O12 Dy−O13 Dy−O14 Dy−O15 Er−O1 Er−O2i Er−O6 Er−O8 Er−O12 Er−O13 Er−O14 Er−O15 Yb−O1 Yb−O2i Yb−O6 Yb−O8 Yb−O12 Yb−O13 Yb−O14 Yb−O15 Lu−O1 Lu−O6 Lu−O7 Lu−O8 Lu−O9 Lu−O10 Lu−O11 Lu−O12 Er−O1 Er−O2i Er−O6 Er−O8 Er−O12 Er−O13 Er−O14 Er−O15

2.2947(15) 2.3015(14) 2.3558(15) 2.3883(15) 2.3777(16) 2.406(2) 2.406(2) 2.3920(15) 2.276(2) 2.2849(19) 2.344(2) 2.369(2) 2.349(2) 2.374(3) 2.386(3) 2.368(2) 2.2615(16) 2.2603(16) 2.3195(16) 2.3506(17) 2.3257(18) 2.358(2) 2.350(2) 2.3473(16) 2.297(3) 2.288(3) 2.328(3) 2.287(3) 2.301(3) 2.284(4) 2.346(4) 2.360(4) 2.3001(19) 2.2584(19) 2.3323(18) 2.3538(19) 2.358(2) 2.405(3) 2.365(2) 2.375(2)

10

11

12

13

Er−O1 Er−O6 Er−O7 Er−O8 Er−O9 Er−O10 Er−O11 Er−O12 Ce−O3 Ce−O6 Ce−O7i Ce−O8 Ce−O12 Ce−O13 Ce−O14 Ce−O15 Nd−O3 Nd−O6 Nd−O7i Nd−O8 Nd−O12 Nd−O13 Nd−O14 Nd−O15 Nd1−O1 Nd1−O2 Nd1−O6 Nd1−O8 Nd1−O10 Nd1−O18 Nd1−O19 Nd1−O20 Nd1−O21 Nd2−O13 Nd2−O15 Nd2−O24 Nd2−O25 Nd2−O26 Nd2−O26i Nd2−O27 Nd2−O28 Nd2−O29

2.325(2) 2.321(2) 2.345(3) 2.329(2) 2.352(2) 2.327(3) 2.347(3) 2.396(2) 2.4624(18) 2.4721(15) 2.4903(15) 2.4870(15) 2.4902(18) 2.4831(17) 2.476(2) 2.4637(17) 2.4250(14) 2.4375(13) 2.4569(13) 2.4515(13) 2.4584(15) 2.4489(14) 2.4421(16) 2.4325(15) 2.479(5) 2.571(4) 2.517(5) 2.451(4) 2.514(4) 2.515(5) 2.459(5) 2.523(5) 2.496(5) 2.305(6) 2.698(7) 2.446(5) 2.524(16) 2.491(10) 2.802(14) 2.361(14) 2.530(13) 2.575(12)

Symmetry codes: 1 and 2: i = 2 − x, 2 − y, 1 − z; 4−7 and 9: i = 1 − x, 1 − y, 2 − z; 11 and 12: i = x + 1, y, z; 13: i = −x − 1, −y, −z.

stabilization of the complex. A one-dimensional coordination polymer parallel to the a axis is thus formed (Figure 2), the columns being stacked so that, in the bc plane, the dinuclear units in one column are surrounded by the CB6 molecules in its closest neighbors. Such columnar arrangements, with matching of bumps and hollows between neighboring columns, are a very frequent feature in CB6 complexes, notably with lanthanide ions.7k,m The asymmetric unit in the neodymium complex {[Nd(2SB)(H2O)3][Nd(2-SB)(H2O)4]CB6}·2NO3·7.5H2O (3) contains two crystallographically independent metal ions, the dinuclear unit being no longer centrosymmetric, and two independent CB6 centrosymmetric molecules (Figure 3). The environment of the two metal ions is different from that in 1 and 2, with some differences also between the two cations. Both are bound to two adjacent carbonyl groups from the CB6

building of the dimeric unit. Each cation is also bound to two carbonyl groups from CB6, a chelating nitrate ion and two water molecules, which gives a 10-coordinate environment of bicapped square antiprismatic geometry with the two sets of atoms (O1, O2i, O12, O15) and (O3, O6, O13, O16) defining the two square bases [dihedral angles 5.92(9) and 5.76(10)° in 1 and 2, respectively]. The coordination polyhedra of the two metal ions in the dinuclear unit share the O1−O1i edge. The Ln−O bond lengths (Table 2) are unexceptional; in particular, the Ln− O(sulfonate) bond lengths of ca. 2.57 Å in 1 and 2.55 Å in 2, and the average Ln−O(carbonyl) bond lengths of 2.56(4) Å in 1 and 2.55(5) Å in 2 are comparable to the values from the CSD, 2.52(5) and 2.55(7) Å, respectively (averages including both La and Ce). Hydrogen bonds connecting the water ligands to carbonyl and sulfonate oxygen atoms contribute to the 1635



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Figure 1. View of the cerium complex 2. Displacement ellipsoids are drawn at the 30% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry codes: i = 2 − x, 2 − y, 1 − z; j = 1 − x, 2 − y, 1 − z.

Figure 3. View of the neodymium complex 3. Displacement ellipsoids are drawn at the 30% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry codes: i = 1 − x, 1 − y, −z; j = −x, 1 − y, 1 − z.

to Nd1 and Nd2, respectively. The formation of similar carboxylate-bridged dinuclear units, with additional coordination of one sulfonate oxygen atom, was previously encountered in complexes of 2-SB2− with lanthanide ions in the presence of 1,10-phenanthroline.4c,f Both cations in 3 are in eight-coordinate environments of square antiprismatic geometry sharing no common element, with the square faces defined by the sets of atoms (O1, O3, O6, O23) and (O11, O13, O24, O25) for Nd1 [dihedral angle 3.42(9)°], and (O2, O26, O27, O28) and (O7, O17, O19, O29) for Nd2 [dihedral angle 6.64(7)°]. The Nd−O(sulfonate) bond length, 2.5543(19) Å, is close to its counterparts in 1 and 2, while the average Nd−O(carbonyl) bond length of 2.48(6) Å is in agreement with the value of 2.450(6) Å recently measured in another bidentate neodymium complex with CB6.7m As a consequence of these differences in metal ion bonding, the distance between the two cations in the dimeric unit is larger in 3 than in 1 and 2, with values of 5.3995(2), 4.5899(3), and 4.6186(3) Å, respectively. The overall arrangement is however analogous, with one-dimensional chains running along the [1 0 1]̅ axis in 3 (Figure 4). The isomorphous complexes obtained with Eu, Dy, Er, and Yb, {[Eu(2-SB)(H2O)4]2CB6}· 2NO3·6H2O (4), {[Dy(2-SB)(H2O)4]2CB6}·2NO3·5H2O (5), {[Er(2-SB)(H2O)4]2CB6}· 2NO3·5H2O (6), {[Yb(2-SB)(H2O)4]2CB6}·2NO3·5H2O (7), crystallize in the same space group as 1 and 2, and with only slightly different unit cell parameters. However, the trends observed with Nd are found here also, and both sulfonate groups and nitrate counterions are uncoordinated, as shown in

Figure 2. View of the packing down the columns axis in complex 2. Solvent molecules and hydrogen atoms are omitted. The cerium coordination polyhedra are represented.

molecules, as in 1 and 2, but the carboxylate groups are bridging bidentate instead of bridging and chelating and no nitrate ion is coordinated; further, while Nd1 is chelated by the sulfonate and carboxylate group of one 2-SB2− ligand, the sulfonate group of the ligand bound to Nd2 is uncoordinated, with, as a consequence, three and four additional water molecules bound 1636



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antiprismatic environment. The dihedral angles between the two square faces defined by (O1, O12, O13, O14) and (O2i, O6, O8, O15) are in the range 2.16(5)−3.10(5)°. The individual Ln−O(carbonyl) bond lengths [corresponding to average values of 2.407(14), 2.372(16), 2.357(12), and 2.335(16) Å in 4−7, respectively], together with those in the three former complexes [2.56(4), 2.55(5), and 2.48(6) Å in 1−3, respectively], are in agreement with lanthanide contraction, as well as the average Ln−O(carboxylate) bond lengths, which decrease regularly from 2.335(2) Å in 4 to 2.261(1) Å in 7. The intermetallic distance in the dimeric unit also regularly decreases from 5.4329(3) Å for Eu to 5.3684(2) Å for Yb. Each sulfonate group is hydrogen bonded to two coordinated water molecules, with other bonds linking the water and carbonyl groups. The onedimensional coordination polymer formed is analogous to those in the previous compounds. Finally, the complex with the smallest lanthanide ion, [Lu(2-SB)(H2O)7]2·CB6·2NO3·7H2O (8), displays a structure radically different from those of the previous complexes. As shown in Figure 6, the cation is bound neither to the sulfonate,

Figure 4. View of the packing of columns in complex 3. Counterions, solvent molecules, and hydrogen atoms are omitted. The neodymium coordination polyhedra are represented.

Figure 5 for Eu. This is at variance with the consistent sulfonate coordination observed in the complexes of 2-SB with a wide

Figure 6. View of the lutetium complex 8. Displacement ellipsoids are drawn at the 40% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry code: i = 1 − x, −y, 1 − z.

CB6, or nitrate groups, but only to one carboxylate oxygen atom and seven water molecules, with a square antiprismatic environment geometry [dihedral angle of 1.54(17)° between the (O1, O6, O7, O8) and (O9, O10, O11, O12) faces]. Two hydrogen bonds link the sulfonate group to two water ligands, while another water molecule is bound to the uncoordinated carboxylate oxygen atom. In addition, five water ligands are connected to the CB6 molecule through six hydrogen bonds, all the carbonyl groups being thus involved. The CB6 molecule being centrosymmetric, both its portals are thus covered by a hydrogen bonded lid. The nitrate ions are coordinated in compounds 1 and 2 only, while they are simply acting as counterions in compounds 3−8. In order to check if other arrangements could be obtained with other counterions, the trifluoromethanesulfonate and chloride salts were investigated as starting materials in the case of

Figure 5. View of the europium complex 4. Displacement ellipsoids are drawn at the 30% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry codes: i = 1 − x, 1 − y, 2 − z; j = 1 − x, 1 − y, 1 − z.

range of lanthanide ions previously reported.4c,f Only one cation is present in the asymmetric unit, which has the same surroundings as Nd2 in 3, with two carboxylate, two carbonyl, and four water ligands giving an eight-coordinate, square 1637



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erbium. The complex {[Er(2-SB)(H2O)4]2CB6}·2CF3SO3· 2.5H2O (9) was obtained in the former case, which displays an arrangement essentially similar to that in complex 6, obtained from erbium nitrate. Both compounds crystallize in the same space group, with unit cell parameters which differ but little, the difference being due to the replacement of nitrate by bulkier trifluoromethanesulfonate counterions. The metal ion environment and the polymeric arrangement are similar and will not be further described. More surprisingly, the use of erbium chloride resulted in the isolation of the complex [Er(2SB)(H2O)7]2·CB6·2Cl·6H2O (10), which is isomorphous to the lutetium complex 8. This indicates that this particular form is not uniquely a consequence of the small size of lutetium, as the series obtained from the nitrate salts would seem to show, since it can also be obtained with a larger cation, possibly due to unpredictable structure-directing effects of the counterions. While crystalline materials are quite readily isolated with the ortho isomer of sulfobenzoic acid, two complexes only could be obtained in single crystal form with the meta isomer, used as its sodium salt, both of them with elements at the beginning of the lanthanide series. These compounds, {[Ln(3-SBH)(H2O)4]2CB6}·4NO3 with Ln = Ce (11) and Nd (12), are isomorphous. Only one metal atom is present in the asymmetric unit, the latter corresponding to half a formula unit. These complexes display a feature unusual in this series of compounds, which is the coordination of the carboxybenzosulfonate 3-SBH− by one sulfonate oxygen atom only, while the carboxylic acid group retains its proton and is uncoordinated, as shown in Figure 7 in the case of Nd. This is in contrast to

CB6 molecule, and one from the other portal of this molecule translated along the a axis, each centrosymmetric CB6 molecule being thus bound to four metal atoms, an arrangement already found with lanthanide ions.7a,k The average Ln−O(carbonyl) bond length amounts to 2.483(8) Å for Ce and 2.449(8) Å for Nd. The cation is further bound to one sulfonate oxygen atom, with a bond length of ca. 2.46 Å for Ce and 2.43 Å for Nd, shorter by about 0.1 Å than the values with the chelating 2-SB2− ligand, likely as an effect of the removal of geometric constraints. Four water molecules complete the coordination sphere, giving an eight-coordinate environment of square antiprismatic geometry, with a dihedral angle of 2.14(9)° (11) or 2.30(7)° (12) between the square faces defined by the sets of atoms (O3, O6, O8, O12) and (O7i, O13, O14, O15). Several hydrogen bonds link the water ligands to carbonyl oxygen atoms, while the carboxylic proton is bonded to nitrate oxygen atoms. The polymeric arrangement is once more columnar, and directed along the a axis, with the equatorial plane of CB6 nearly perpendicular to the column axis in this case, and not tilted as in compounds 1−7 and 9, which is due to the two neighboring cations being independent from one another, with each of them being bound to the two surrounding CB6 molecules, instead of being part of a dinuclear subunit bound to one CB6 only by each of its two halves. When viewed down the a axis, the 3-SBH− ligands protrude along two sides of the columns (Figure 8), while, in contrast to the previous complexes, the

Figure 7. View of the neodymium complex 12. Displacement ellipsoids are drawn at the 30% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry codes: i = x + 1, y, z; j = −x, 2 − y, −z; k = 1 − x, 2 − y, −z.

Figure 8. View of the packing down the columns axis in complex 12. Counterions and hydrogen atoms are omitted. π-Stacking interactions are represented as dashed lines. The neodymium coordination polyhedra are represented.

the bonding scheme in the only other lanthanide (Tb) complex with 3-SB2− reported, in which both acid groups are deprotonated, with sulfonate groups being either monodentate or uncoordinated.4g As will be seen below, both acid functions are deprotonated in the para isomer, as in the ortho. This seems to indicate that, in the conditions used, the apparent acidity of the carboxylic group is lower in the meta isomer than in the others, although the pKa values for the second deprotonation reported in the literature do not indicate such a difference between the meta and para isomers.13 The lanthanide cation in 11 and 12 is bound to two carbonyl groups from one portal of a

neighboring columns are not offset with respect to one another, but are related by translations along the b and c axes. Adjacent columns along the [0 1 1]̅ direction are linked by π-stacking interactions between the aromatic rings of the 3-SBH− ligands [centroid···centroid distances 3.6768(14) and 3.6674(12) Å, dihedral angle 0°, offset distances 0.79 and 0.77 Å in 11 and 12, respectively], which gives rise to the formation of sheets of columns held together by weak interactions, parallel to the (0 1 1) plane. Finally, only the neodymium complex [Nd1.5(4-SB)(CB6)(NO3)(H2O)6.5]·4-SBH·4-SBH1.5·15H2O (13) could be ob1638



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uranyl ion complex including CB6, in which the sulfonate groups of the two molecules present are either uncoordinated or bound to a potassium cation.6b Two uncoordinated 4-SBHx molecules (x = 1 or 1.5) are also present in 13, an occurrence not yet encountered in this family of compounds. The complex molecules are stacked so as to form columns directed along the [1 1 1] axis.

tained in crystal form, although in low yield, with the para isomer 4-SB. The crystals of this compound were of quite low quality and the structure, plagued by disorder effects, could not be determined with an accuracy matching that of the other complexes in this series (see Experimental Section). However, if the details remain somewhat dubious, particularly concerning the protonation scheme, the overall arrangement is determined unambiguously and the effect of the modification in the position of the sulfonate substituent is clearly apparent. Two independent metal ions are present (Figure 9), but one of them

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CONCLUSION

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ASSOCIATED CONTENT

The crystal structures of the lanthanide ion complexes formed by the ortho, meta, and para isomers of sulfobenzoic acid in the presence of CB6 were investigated. The series obtained with the ortho isomer 2-SB2− ligand is the most complete since it comprises eight cations spanning the whole lanthanide row, from La to Lu. In contrast, only the complexes of Ce and Nd could be characterized with the partially deprotonated meta isomer 3-SBH−, and only that of Nd with the para isomer 4-SB2−. The series with 2-SB2− displays two isomorphous families, one comprising La and Ce and the other Eu, Dy, Er, and Yb, with the Nd complex being intermediate. In all the cases, a dimeric, dinuclear unit is formed by bridging carboxylate groups, the sulfonate being coordinated, in monodentate fashion, only for the larger cations for which the coordination number is 10, instead of eight for the smaller ones. Although analogous dinuclear moieties were also observed in lanthanide complexes with 2-SB2− and 1,10-phenanthroline,4c,f the overall arrangement is different, and, in the present cases, bonding to CB6 molecules yields a one-dimensional polymeric arrangement. The Lu complex is completely different since the cation is only bound to one carboxylate oxygen atom and water molecules, one complex being hydrogen bonded to each CB6 portal as a lid. However, this different structure is not solely an effect of the smaller size of the cation since it is also obtained with Er, when the chloride salt is used as a starting material instead of the nitrate. The case of 3-SBH− is particularly unusual since, in contrast to what is observed in all lanthanide complexes with sulfobenzoates, the carboxylic group retains its proton and is uncoordinated, the cation being only bound to one sulfonate oxygen atom. A polymeric one-dimensional arrangement is formed in this case also. Finally, 4-SB2− is only bound by the chelating carboxylate group. The columnar architecture found in most compounds in this series is very frequent in CB6 complexes. In the present cases, the sulfobenzoate ligand 2-SB2− plays a structural role in the building of the assembly since it connects the two cations which are each bound to one CB6 only, while the carboxybenzosulfonate 3-SBH− is only an auxiliary ligand with no structural function, except that of linking adjacent columns by π-stacking interactions.

Figure 9. View of the neodymium complex 13. Displacement ellipsoids are drawn at the 30% probability level. Carbon-bound hydrogen atoms are omitted. Hydrogen bonds are shown as dashed lines. Symmetry code: i = −x − 1, −y, −z.

(Nd2), being close to its image by the inversion center, was given an occupancy factor of 0.5 (see Experimental Section). Nd1 is bound to three and Nd2 to two carbonyl groups, with an unexceptional average bond length of 2.50(13) Å. Nd1 is further bound to the asymmetrically chelating carboxylate of the 4-SB2− ligand [average bond length 2.53(5) Å], to one monodentate nitrate ion (the latter being included in the CB6 cavity) and three water molecules. Its nine-coordinate environment is capped square antiprismatic with O1 in the capping position and a dihedral angle of 4.39(17)° between the two square faces defined by the sets of atoms (O2, O8, O10, O18) and (O6, O19, O20, O21). Nd2 is bound to seven water molecules, most of them being disordered, and its nine-coordinate environment can best be viewed as capped square antiprismatic with O27 in the capping position and a dihedral angle of 3.7(5)° between the two square faces defined by (O15, O24, O26i, O29) and (O13, O25, O26, O28). The sulfonate group of the 4-SB2− ligand is uncoordinated, which is to be compared with the situation in the lanthanide ion complexes previously reported, in which the sulfonate group is either coordinated4a,d,e or free,4b and in the

S Supporting Information *

Tables of crystal data, atomic positions and displacement parameters, anisotropic displacement parameters, and bond lengths and bond angles in CIF format. This information 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. 1639



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(10) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112. (11) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (12) Momma, K.; Izumi, F. J. Appl. Crystallogr. 2008, 41, 653. (13) Zollinger, H.; Büchler, W.; Wittwer, C. Helv. Chim. Acta 1953, 36, 1711.

ACKNOWLEDGMENTS Pr. Bernardo Masci is thanked for fruitful discussions, and the Direction de l’Energie Nucléaire of the CEA for its financial support through the Basic Research Program RBPCH.

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REFERENCES

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Lanthanide Ion Complexes with 2-, 3-, or 4-Sulfobenzoate and

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