Tuning the Supramolecular Structure through Variation of the Ligand

Article pubs.acs.org/crystal

Tuning the Supramolecular Structure through Variation of the Ligand Geometry and Metal Substituents−Diorganotin Macrocycles and Coordination Polymers Derived from cis- and trans-1,2‑, 1,3‑, and 1,4-Cyclohexanedicarboxylic and cis,cis-1,3,5Cyclohexanetricarboxylic Acid Irán Fernando Hernández-Ahuactzi,†,‡ Jorge Cruz-Huerta,† Hugo Tlahuext,† Victor Barba,† Jorge Guerrero-Alvarez,† and Herbert Höpfl*,† †

Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca, México ‡ Instituto Tecnológico Superior de Tlaxco, Predio Cristo Rey Ex Hacienda de Xalostoc s/n, Carretera Apizaco Tlaxco Km. 16.8, C.P. 90250, Tlaxco, México ABSTRACT: cis- and trans-1,2-chdcaH2, 1,3-chdcaH2, and 1,4-chdcaH2 (chdcaH2 = cyclohexanedicarboxylic acid) as well as cis,cis-1,3,5-chtcaH3 (chtcaH3 = cyclohexanetricarboxylic acid) have been treated with dimethyl- and di-n-butyltin reagents, and for the case of 1,4-chdcaH2 additionally with ditert-butyltin dichloride, to determine whether macrocyclic or polymeric diorganotin dicarboxylates are formed dependent of the spatial orientation of the coordinating ligand functions and the organic substituents at the metal atom and to analyze conformational and topological variations in the resulting supramolecular aggregates. The single-crystal X-ray diffraction studies showed that besides the ligand geometry the substituents at the metal center are key elements for the formation of either monomeric, cyclo-oligomeric, or polymeric assemblies. Two of the compounds characterized by X-ray diffraction analysis exhibited macrocyclic ring structures, [{Me2Sn(cise,a-1,4-chdca)}2] and [{nBu2Sn(cis-e,a-1,4-chdca)}4]. For most of the remaining compounds, one-dimensional polymeric solidstate structures of composition [{R2Sn(1,x-chdca)(H2O)y}n] (R = Me, nBu, tBu; x = 2, 3, 4; y = 0, 1) were observed, which had varying topologies, and for the case of the Me2Sn and nBu2Sn derivatives were further linked to two- or three-dimensional supramolecular architectures, either through intermolecular Sn···O or O−H···O hydrogen-bonding interactions. modulation and fine-tuning of the target structure.12−20 So far, such modifications have been achieved mainly through the variation of the ligand structure but rarely through the alteration of the substituents attached to the metal ions.21−24 For the creation of architectures containing macrocyclic rings or cages, it is important to generate free coordination sites of given geometry at the metal ion and to provide ligands with the proper spatial distribution of the coordinating functions. While it is generally easy to control the bond angle between the coordination sites of a given metal ion, there are only a few series of ligands that allow for a continuous variation of the bond angle between the metal-coordinating functions. As shown in Scheme 1, the cis/trans derivatives of 1,2-, 1,3-, and 1,4-cyclohexanedicarboxylic acid (1,x-chdcaH2 with x = 2, 3, and 4) form an ideal series of ligands for a systematic

1. INTRODUCTION During the past few years, the number of publications related to the preparation and structural characterization of coordination oligo- and polymers has increased exponentially, mainly because metal-directed self-assembly is now envisioned as the method of choice for the generation of materials with applications related to magnetism, conductivity, optics, electronics, etc. Moreover, supramolecular aggregates having cavities, channels, or pores are of growing interest for selective molecular recognition, storage, absorption, separation, and catalysis.1−3 Nevertheless, the number of metallosupramolecular assemblies derived from main group elements and organometallic building blocks is still rare.4−8 For the successful design of discrete architectures or metal− organic frameworks (MOFs) with specific structural characteristics or physical properties (crystal engineering), it is, among other aspects, necessary (i) to understand the details of the dynamic processes occurring during the assembly process9−11 and (ii) to dipose of building blocks that allow for the © XXXX American Chemical Society

Received: November 5, 2014 Revised: December 19, 2014

A

DOI: 10.1021/cg501629n Cryst. Growth Des. XXXX, XXX, XXX−XXX

Article

Crystal Growth & Design

Scheme 1. cis/trans Derivatives of 1,2-, 1,3-, and 1,4-Cyclohexanedicarboxylic Acid Form an Ideal Series of Ligands for the Formation of Either Macrocyclic Assemblies or Coordination Polymers

studies of diorganotin 1,x-benzene-,37,38 1,x-naphtalene,39 and 2,x-pyridinedicarboxylates40−42 have shown that aside from the ligand structure the steric and electronic influence of organic substituents attached to the tin atoms and the presence of metal-coordinating solvents are important key elements in this regard. Moreover, organotin carboxylates have industrial applications as catalysts in transesterification reactions and for the stabilization of polymers.43 Other organotin complexes have antifungal, antibacterial, antioxidant, and cytotoxic properties.44−46 We report herein on a series of dimethyl-, di-n-butyl, and ditert-butyltin complexes derived from cis- and trans-1,x-cyclohexanedicarboxylic acid (x = 2, 3, and 4) and cis,cis-1,3,5cyclohexanetricarboxylic acid, whose structures are outlined in Scheme 3. Our findings on the supramolecular isomerism, selfassembly dynamics and carboxylate shift of one of the complexes, namely, di-n-butyltin cis-e,a-1,4-cyclohexanedicarboxylate, [{nBu2Sn(cis-1,4-chdca)}z] with z = 4 or ∞, have been described in a preliminary communication.47 In two related previous studies, Ma and co-workers have explored the chemistry of triorganotin chlorides and diorganotin dichlorides in combination with cis-4-cyclohexene-1,2-dicarboxylic acid, cis1,4-cyclohexanedicarboxylic acid, and cis-1,3-cyclohexanedicarboxylic acid, using 2:1 stoichiometries (herein: 1:1). The resulting complexes were mostly 1D and 2D coordination polymers having the compositions [{(R 3 Sn) 2 L} n ] and [{(R2Sn)2O(L)}n] (R = Me, nBu, Ph, Bz), in which the triorganotin and bis(tetraorganodistannoxane) nodes, respectively, were linked by the cycloaliphatic spacers of the dicarboxylate ligands.48,49 Furthermore, there is a previous report on the crystal structure of [{Me2Sn(trans-e,e-1,2chdca)}n] (1); however, in this report no spectroscopic data have been documented, and the supramolecular connectivity has not been analyzed.50

exploration of the factors responsible for the formation of either macrocyclic assemblies or coordination polymers. Considering that the carboxyl groups in 1,x-cyclohexanedicarboxylic acids can have equatorial or axial orientation, giving either the (e,e), (e,a), or (a,a)-isomer, a total number of nine ligand isomers with different spatial distributions of the carboxylate functions arises, if enantiomers are not considered (Scheme 1).25,26 The angles formed between the carboxyl groups vary from approximately 90 to 180°. That the thermodynamically less stable (a,a)-conformers indeed occur in supramolecular metal− ligand assemblies and lead to the formation of supramolecular isomers has been shown previously.14,27 While the 1,x-chdcaH2 ligands are susceptible for the generation of macrocyclic and one-dimensional (1D) polymeric structures, cis,cis-1,3,5-cyclohexanetricarboxylic acid (1,3,5chtcaH3) allows for the formation of two- and threedimensional (2D and 3D) coordination polymers and due to the trigonal distribution of the carboxyl groups in the (e,e,e)conformer, frequently the formation of honeycomb-type structures is favored.26 So far, complexes containing the (a,a,a)-confomer have not been observed (Scheme 2). When combined with properly designed difunctional ligands, diorganotin fragments are able to form macrocyclic structures,28−36 thus being ideal candidates for an exploration of the factors that drive the self-assembly process to the formation of macrocyclic rings instead of coordination polymers. Previous Scheme 2. Cis,cis-1,3,5-Cyclohexanetricarboxylic Acid Gives Generally 2D Coordination Polymers with HoneycombType Structure

2. EXPERIMENTAL SECTION 2.1. Instrumental. NMR studies were carried out with Varian Gemini 200 and Varian Inova 400 instruments. Standard references B


Article

Crystal Growth & Design Scheme 3. Overview of the Molecular Compositions for Compounds 1−13

were used: TMS (δ1H = 0 and δ13C = 0) and SnMe4 (δ 119Sn = 0). Two-dimensional HSQC and COSY correlation experiments showed that the solid formulated as compound 5 indeed contains both ligand isomers (trans-e,a-1,3-chdca and cis-e,e-1,3-chdca). IR spectra as KBr disc have been recorded on a Bruker Vector 22 FT spectrophotometer. Mass spectra were obtained on Jeol JMS 700 equipment. Elemental analyses have been carried on an Elementar Vario ELIII instrument. 2.2. Preparative Part. cis/trans-1,2-, 1,3-, and 1,4-Cyclohexanedicarboxylic acids, potassium hydroxide, cis,cis-1,3,5-cyclohexanetricarboxylic acid, Me2SnCl2, nBu2SnCl2, tBu2SnCl2, and nBu2SnO were commercially available and were used without further purification. Dimethyltin oxide was prepared from Me2SnCl2 according to a previously reported method.51 [{Me2Sn(trans-e,e-1,2-chdca)}n] (1). Method A: trans-e,e-1,2-Cyclohexanedicarboxylic acid (0.500 g, 2.90 mmol) and dimethyltin oxide (0.479 g, 2.90 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1 v/v, 35 mL) and heated to reflux for 8 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a 1:1 mixture of hexane and ethanol. Yield: 0.39 g (42%). Method B: A U-shaped glass tube equipped with a ceramic membrane filter disc was filled with a solution of trans-e,e-1,2cyclohexanedicarboxylic acid (0.050 g, 0.29 mmol) and KOH (0.033 g, 0.58 mmol) in ethanol (8 mL) at one side and a solution of dimethyltin dichloride (0.064 g, 0.29 mmol) dissolved in ethanol (8 mL) at the other side. After 5 days crystals suitable for single-crystal Xray diffraction analysis had formed. Yield: 0.011 g (12%). Mp: 317− 319 °C. IR (KBr): ṽ = 2934 (m), 2858 (m), 1599 (s), 1400 (s), 1339 (m), 1277 (m), 1227 (w), 1113 (w), 1036 (w), 974 (w), 912 (w), 780 (m), 726 (w), 673 (w), 579 (m), 517 (w), 489 (w), 452 (w) cm−1. C10H16O4Sn (318.92): calcd. C 37.7, H 5.0; found C 37.9, H 4.6. [{nBu2Sn(trans-e,e-1,2-chdca)}n] (2). trans-e,e-1,2-Cyclohexanedicarboxylic acid (0.500 g, 2.90 mmol) and dibutyltin oxide (0.722 g, 2.90 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1 v/v, 30 mL) and heated to reflux for 8 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a 1:1 mixture of hexane and ethanol. Yield 0.433 g (37%). Mp 160−162 °C. IR (KBr): ṽ = 2957 (s), 2929 (s), 2860 (s), 1605 (s), 1562 (s), 1454 (m), 1377 (s), 1269 (m), 1214 (m), 1111 (w), 1080 (w), 1025 (m), 960 (w), 877 (w), 778 (w), 680 (m), 629 (m), 457 (w) cm−1. 1H NMR (200 MHz, CDCl3, TMS, 20 °C): δ = 0.92 (t, 6H, δ-H), 1.27−1.67 (m, 20H, H3, H4, H5, H6, α-H, β-H, γ-H), 2.15 and 2.59 (s, 2H, H1, H2) ppm. 13C NMR (50 MHz, CDCl3, TMS, 20 °C): δ = 13.9 (Cδ), 25.3 (C4, C5), 25.8 (Cγ), 26.7 (Cβ), 27.2 (Cα), 29.8 (C3, C6), 45.2, 45.3 (C1, C2), 185.5 (COO) ppm. 119Sn NMR (74.5 MHz, CDCl3, SnMe4, 20 °C): δ = −143, −151, and −154 ppm. MS (FAB+): m/z (%) = 1210 ([Mtrimer + H]+, 12), 1153 ([Mtrimer − nBu]+,

31), 1096 (Mtrimer − 2nBu]+, 10), 807 ([Mdimer + H]+, 42), 750 ([Mdimer − nBu]+, 37), 693 ([Mdimer − 2nBu]+, 20), 404 ([Mmonomer + H]+, 38), 251 (100). C16H28O4Sn (403.10): calcd. C 47.7, H 7.0; found C 47.4, H 7.1. [{(Me2Sn)2O(cis-e,a-1,2-chdcaOEt)2}2] (3). cis-e,a-1,2-Cyclohexanedicarboxylic acid (0.500 g, 2.90 mmol) and dimethyltin oxide (0.479 g, 2.90 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1 v/v, 30 mL) and heated to reflux for 16 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a 1:1 mixture of hexane and ethanol. Crystals suitable for single-crystal X-ray diffraction analysis could be obtained upon recrystallization from chloroform. Yield 0.30 g (29%). Mp 217−219 °C. IR (KBr): ṽ = 2936 (m), 2862 (m), 1734 (s), 1618 (m), 1562 (s), 1455 (m), 1383 (m), 1309 (m), 1276 (m), 1215 (m), 1177 (m), 1099 (w), 1037 (m), 927 (w), 854 (w), 792 (m), 649 (m), 572 (m), 491 (m) cm−1. C48H84O18Sn4 (1423.91): calcd. C 40.5, H 5.9; found C 40.8, H 6.0. [{Me2Sn(cis-e,e-1,3-chdca)(H2O)}]n (4). Method A: cis/trans-1,3Cyclohexanedicarboxylic acid (0.500 g, 2.90 mmol) and dimethyltin oxide (0.479 g, 2.90 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1 v/v, 35 mL) and heated to reflux for 8 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a 1:1 mixture of hexane and ethanol. Yield: 0.306 g (31%). Method B: A U-shaped glass tube equipped with a ceramic membrane filter disc was filled with a solution of cis/trans1,3-cyclohexanedicarboxylic acid (0.040 g, 0.23 mmol) and KOH (0.026 g, 0.46 mmol) in ethanol (8 mL) at one side and a solution of dimethyltin dichloride (0.051 g, 0.23 mmol) dissolved in ethanol (8 mL) at the other side. After 4 days crystals suitable for single-crystal Xray diffraction analysis had formed. Yield: 0.016 g (20%). Mp 297−300 °C. IR (KBr): ṽ = 3429 (s), 2935 (s), 2858 (m), 1726 (m), 1591 (m), 1403 (s), 1349 (m), 1321 (m), 1269 (w), 1223 (m), 1182 (w), 1122 (w), 1033 (w), 932 (w), 781 (m), 732 (w), 698 (w), 664 (w), 582 (w) cm−1. C10H18O5Sn (336.93): calcd. C 35.6, H 5.4; found C 35.4, H 5.7. [(nBu2Sn)y+z(trans-e,a-1,3-chdca)y(cis-e,e-1,3-chdca)z] (5). cis/ trans-1,3-Cyclohexanedicarboxylic acid (0.500 g, 2.90 mmol) and dibutyltin oxide (0.722 g, 2.90 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1 v/v, 35 mL) and heated to reflux for 8 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a 1:1 mixture of hexane and ethanol. Yield: 0.562 g (48%). Mp 225−227 °C. IR (KBr): ṽ = 2956 (s), 2929 (s), 2861 (m), 1731 (w), 1596 (s), 1456 (m), 1398 (s), 1347 (s), 1292 (m), 1265 (m), 1224 (m), 1186 (m), 1080 (w), 1026 (w), 962 (w), 877 (w), 781 (m), 678 (m), 626 (w), 590 (w), 495 (w) cm−1. 1H NMR (400 MHz, CDCl3, TMS, 20 °C): δ = 0.90 (t, J = 7.4 C


Article

Crystal Growth & Design Hz, 6H, δ-H), 1.36−2.30 (m, 20H, H2, H4, H5, H6, α-H, β-H, γ-H), 2.37 and 2.75 (m, 2H, H1, H3) ppm. 13C NMR (100 MHz, CDCl3, TMS, 20 °C): cis complex δ = 13.7 (Cδ), 22.5, 25.0 (C5), 25.1 (Cγ), 26.4 (Cβ), 26.8 (Cα), 28.4, 28.8 (C4, C6), 30.0, 31.8 (C2), 39.3, 42.7 (C1, C3), 185.2, 185.5 (COO) ppm. 119Sn NMR (74.5 MHz, CDCl3, SnMe4, 20 °C): δ = −148 ppm. 119Sn NMR (74.5 MHz, C5D5N, 20 °C, SnMe4): δ = −355 ppm. MS (FAB+): m/z (%) = 1210 ([Mtrimer + H]+, 4), 1152 ([Mtrimer − nBu]+, 6), 1095 ([Mtrimer − 2nBu]+, 3), 807 ([Mdimer + H]+, 30), 749 ([Mdimer − nBu]+, 17), 692 ([Mdimer − 2nBu]+, 10), 404 ([Mmonomer + H]+, 38), 251 (100). C16H28O4Sn (403.10): calcd. C 47.7, H 7.0; found C 47.3, H 7.2. [{Me2Sn(cis-e,a-1,4-chdca)(H2O)}2] (6). Method A. cis-e,a-1,4Cyclohexanedicarboxylic acid (0.500 g, 2.90 mmol) and dimethyltin oxide (0.479 g, 2.90 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1 v/v, 30 mL) and heated to reflux for 8 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a 1:1 mixture of hexane and ethanol. Yield: 0.626 g (64%). Method B: 1,4-cis-e,a-cyclohexanedicarboxylic acid (0.050 g, 0.29 mmol), potassium hydroxide (0.033 g, 0.58 mmol), and dimethyltin dichloride (0.064 g, 0.29 mmol) were suspended homogeneously in water (12 mL). The suspension was then transferred to a pressure tube with PTFE bushing and heated to 120 °C for 4 days, after which compound 6 had precipitated as colorless crystalline material. Yield: 0.092 g (94%). Mp > 350 °C. IR (KBr): ṽ = 3011 (m), 2934 (s), 2861 (m), 1558 (m), 1415 (s), 1341 (s), 1278 (m), 1204 (m), 1136 (w), 1041 (w), 927(w), 787(f), 638(m), 575 (m), 505 (m) cm−1. C20H36O10Sn2 (673.87): calcd. C 35.6, H 5.4; found C 35.3, H 5.3. [{tBu2Sn(cis-e,a-1,4-chdca)}n] (8). A U-shaped glass tube equipped with a ceramic membrane filter disc was filled with a solution of cis-e,a1,4-cyclohexanedicarboxylic acid (0.050 g, 0.29 mmol) and KOH (0.033 g, 0.58 mmol) in ethanol (8 mL) at one side and a solution of di-tert-butyltin dichloride (0.088 g, 0.29 mmol) dissolved in ethanol (8 mL) at the other side. After 1 week crystals suitable for single-crystal X-ray diffraction analysis had formed. Yield: 0.046 g (39%). Mp 265− 267 °C. IR (KBr): ṽ = 2933 (m), 2857 (m), 1600 (s), 1458 (m), 1397 (s), 1343 (m), 1283 (w), 1242 (m), 1199 (w), 1158 (m), 1031 (w), 938 (w), 851 (w), 711 (m), 711(w), 609 (m), 549 (m) cm−1. MS (FAB+): m/z (%) = 807 ([Mdimer + H]+, 7), 749 ([Mdimer − tBu]+, 10), 404 ([Mmonomer + H]+, 5), 346 ([Mmonomer − tBu]+, 15), 289 (100). C16H28O4Sn (403.10): calcd. C 47.7, H 7.0; found C 47.5, H 7.1. [{Me2Sn(trans-e,e-1,4-chdca)}n] (9). Method A: trans-e,e-1,4-Cyclohexanedicarboxylic acid (0.500 g, 2.90 mmol) and dimethyltin oxide (0.479 g, 2.90 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1, 30 mL) and heated to reflux for 8 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a mixture of hexane and ethanol. Yield: 0.657 g (71%). Method B: A U-shaped glass tube equipped with a ceramic membrane filter disc was filled with a solution of trans-e,e-1,4cyclohexanedicarboxylic acid (0.050 g, 0.29 mmol) and KOH (0.033 g, 0.58 mmol) in ethanol (8 mL) at one side and a solution of dimethyltin dichloride (0.064 g, 0.29 mmol) dissolved in ethanol (8 mL) at the other side. After 1 week crystals suitable for single-crystal X-ray diffraction analysis had formed. Yield: 0.044 g (48%). Mp > 350 °C. IR (KBr): ṽ = 2935 (m), 2854 (m), 1600 (s), 1455 (m), 1397 (s), 1342 (m), 1242 (m), 1145 (m), 1099 (w), 1028 (w), 938 (w), 851 (w), 707 (m), 609 (m), 549 (m) cm−1. C10H16O4Sn (318.92): calcd. C 37.6, H 5.0; found C 37.5, H 4.9. [{tBu2Sn(Cl)}2(trans-e,e-1,4-chdca)] (10). A U-shaped glass tube equipped with a ceramic membrane filter disc was filled with a solution of trans-e,e-1,4-cyclohexanedicarboxylic acid (0.050 g, 0.29 mmol) and KOH (0.033 g, 0.58 mmol) in ethanol (8 mL) at one side and a solution of di-tert-butyltin dichloride (0.176 g, 0.58 mmol) dissolved in ethanol (8 mL) at the other side. After 1 week crystals suitable for single-crystal X-ray diffraction analysis had formed. Yield: 0.086 g (42%). Mp 254−256 °C. IR (KBr): ṽ = 2931 (m), 2858 (m), 1602 (s), 1458 (m), 1381 (s), 1276 (m), 1210 (m), 1161 (m), 1028 (w), 927 (w), 789 (m), 567 (m), 488 (m) cm−1. C24H46Cl2O4Sn2 (706.89): calcd. C 40.8, H 6.5; found C 41.1, H 6.5.

[{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (11) and [{Me2Sn(cis,cis-e,e,e1,3,5-chtca)(H2O)}n] (12). A U-shaped glass tube equipped with a ceramic membrane filter disc was filled with a solution of cis,cis-e,e,e1,3,5-cyclohexanetricarboxylic acid (0.050 g, 0.23 mmol) and KOH (0.026 g, 0.46 mmol) in ethanol (8 mL) at one side and a solution of dimethyltin dichloride (0.050 g, 0.23 mmol) dissolved in ethanol (8 mL) at the other side. After 1 week crystals of compounds 11 and 12 had formed, which could be separated manually under the microscope due to their different morphologies (11, rectangular prisms; 12, needles). Yields: 11, 0.031 g (37%); 12, 0.046 g (53%) respectively. IR (KBr) 11: ṽ = 2955 (s), 2928 (s), 1716 (m), 1630 (s), 1580 (m), 1399 (m), 1351 (m), 1297 (m), 1266 (m), 1200 (m), 1124 (w), 1020 (m), 893 (w), 809 (m), 669 (m), 628 (m), 601 (m), 538 (m), 464 (m) cm−1. 12: ṽ = 3949 (m), 3148 (m), 3048 (s), 2874 (w), 1712 (s), 1627 (m), 1578 (s), 1396 (s), 1347 (m), 1312 (m), 1265 (m), 1238 (m), 1196 (m), 1020 (w), 965 (w), 870 (w), 786 (m), 729 (w), 669 (w), 624 (w), 542 (w) cm−1. 12: C11H18O7Sn (380.96): calcd. C 34.7, H 4.8; found C 34.9, H 4.7. [{nBu2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (13). cis,cis-e,e,e-1,3,5-Cyclohexanetricarboxylic acid (0.500 g, 2.31 mmol) and dibutyltin oxide (0.575 g, 2.31 mmol) were dissolved in a solvent mixture of ethanol and toluene (1:1 v/v, 30 mL) and heated to reflux for 8 h in the presence of a Dean−Stark trap. A white powder precipitated that was filtered and washed with a 1:1 mixture of hexane and ethanol. Yield: 0.517 g (50%). Mp 294−295 °C. IR (KBr): ṽ = 2958 (s), 2929 (s), 2866 (s), 1707 (s), 1594 (m), 1456 (m), 1402 (s), 1340 (s), 1265 (m), 1205 (m), 1126 (w), 1074 (w), 1020 (m), 958 (w), 920 (w), 870 (w), 790 (m), 680 (w) cm−1. 1H NMR (400 MHz, DMSO-d6, 20 °C, TMS): δ = 0.81 (t, 6H, J = 7.2 Hz, δ-H), 1.22 (m, 4H, γ-H), 1.26 (m, 6H, H2, H4, H6), 1.46 (m, 4H, β-H), 2.04 (m, 4H, α-H), 2.20 (m, 3H, H1, H3, H5) ppm. 13C NMR (100 MHz, DMSO-d6, 20 °C, TMS): δ = 13.8 (C-δ), 26.0 (C-γ), 26.8 (C-β), 27.6 (C-α), 31.9 (C-2, C4, C6), 42.2 (C1, C3, C5), 178.2 (COO) ppm. 119Sn NMR (74.5 MHz, DMSO-d6, SnMe4, 20 °C): δ = −150 ppm. C17H28O6Sn (447.11): calcd. C 45.7, H 6.3; found C 44.9, H 6.2. 2.3. X-ray Crystallography. Single-crystal X-ray diffraction studies were performed on a Bruker-APEX diffractometer with a CCD area detector (λMoKα = 0.71073 Å, monochromator: graphite). Frames were collected at T = 293 K (compounds 1 and 3) and T = 100 K (compounds 4, 6, 8−12) via ω/ϕ-rotation at 10 s per frame (SMART).52 The measured intensities were reduced to F2 and corrected for absorption with SADABS (SAINT-NT).53 Corrections were made for Lorentz and polarization effects. Structure solution, refinement, and data output were carried out with the SHELXTL-NT program package.54,55 Non-hydrogen atoms were refined anisotropically, while hydrogen atoms were placed in geometrically calculated positions using a riding model. For compounds 4, 6, 11, and 12, the O−H hydrogen atoms have been located from iterative examination of difference Fourier maps following least-squares refinements of the previous models with dO−H = 0.84 Å and Uiso(H) = 1.5Ueq(O). The crystals of compound 4 presented merohedral twinning and have been refined using the instruction TWIN 010 100 00-1 (BASF = 0.407). DIAMOND was used for the creation of figures.56 Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications no. CCDC 1032526−1032534. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44)1223-336-033; email: [email protected], www: http://www.ccdc.cam.ac.uk).

3. RESULTS AND DISCUSSION 3.1. Preparation of Compounds 1−13. For the preparation of the dimethyl and di-n-butyltin dicarboxylates 1−7, 9, and 11−13 (Table 1), the carboxylic acids were combined with the corresponding diorganotin oxide in a refluxing toluene/ethanol solvent mixture (1:1, v/v) in the presence of a Dean−Stark trap. Since the insolubility of the dimethyltin complexes disabled the formation of crystals suitable for single-crystal X-ray diffraction analysis by D


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X-ray diffraction analysis. The di-n-butyltin complexes 2, 5, 7, and 13 were characterized additionally by NMR (1H, 13C, 119 Sn) spectroscopy and FAB+ mass spectrometry. 3.2. Spectroscopic and Mass Spectrometric Characterization. The formation of the diorganotin 1,x-cyclohexanedicarboxylate (x = 2, 3, and 4) and cis-cis-1,3,5cyclohexanetricarboxylate complexes can be evidenced easily by IR spectroscopy. Upon metal-coordination, the absorptions characteristic for the ligand O−H and CO groups disappear, and two intense bands for the asymmetric and symmetric stretching vibrations of the metal-coordinated carboxylate functions appear in the regions of 1562−1630 cm−1 and 1377−1455 cm−1, respectively.57 The difference between the wavenumbers for νas(COO) and νs(COO) allows one to distinguish between monodentate, anisobidentate, and isobidentate coordination modes of the ligand. For compounds 1−13, the Δ(νas−νs) differences are in the range of 163−231 cm−1 and indicate an anisobidentate coordination mode, which is typically found for diorganotin dicarboxylates having skewedtrapezoidal bipyramidal coordination geometries.58 A comparison of the 1H NMR spectra between the starting 1,x-cyclohexanedicarboxylic acid and the soluble di-n-butyltin products 2, 5, and 7 provides additional evidence for the formation of the diorganotin dicarboxylate complexes and allows for some conclusions on the dynamic behavior of the compounds in solution. In the 1H NMR spectra of 2, 5, and 7, the carboxylic acid hydroxyl groups at δ = 12.0, 10.5, and 12.1 ppm, respectively, are absent due to the formation of the carboxylate group. Further, the signals in the regions of the cyclohexylene hydrogen atoms and the di-n-butyltin moieties are broadened, which indicates the occurrence of at least one fast dynamic equilibrium.37,59−61 Possible processes are the (a,e)−(e,a) conformational motion of the disubstituted cyclohexane ligand and carboxylate exchange (shift) reactions between the diorganotin complex molecules present in solution.47 The 13C NMR spectra for compounds 2, 5, and 7 gave signals in the range of δ = 183.3−185.2 ppm for the COO− groups that are in the region typically observed for diorganotin dicarboxylates.28−34 These signals are low-field shifted when compared to the starting dicarboxylic acids (Δδ = 1.8−9.8 ppm). The 119Sn NMR spectra of compounds 2, 5, and 7 gave chemical shifts in a range typical for five-coordinate diorganotin complexes.62 However, whereas the complex with 1,2-chdca (2) gave three different signals (δ = −143, −153, and −154 ppm), indicating the presence of different species with slightly different tin coordination environments, the 1,3-chdca (5) and 1,4-chdca (7) derivatives showed each only one signal (δ = −148 ppm for 5; δ = −151 ppm for 7). In order to examine if the tin atoms can indeed enhance their coordination spheres and thus participate in the association−rearrangement−dissociation pathway required for the above-mentioned carboxylate exchange equilibria, for complexes 5 and 7 the Lewis acidity of the tin atoms was tested by 119Sn NMR spectroscopy using pyridine-d5 as solvent. In both cases the signals were upfield-shifted to δ = −355 ppm and are now in the range typical for hexacoordinated complexes.62 Finally, the IR and NMR (1H, 13C, and 119Sn) spectroscopic characterization of [{nBu2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (13) indicates a 1:1 stoichiometric composition of the products and a tin coordination environment similar to that found for 2, 5, and 7 (δ = −150 ppm). Therefore, it is suggested that the structure is closely related to that of the dimethyltin analogue

Table 1. Chemical Composition of Diorganotin Complexes 1−13a compound

chemical composition

1 2 3 4 5 6 7

[{Me2Sn(trans-e,e-1,2-chdca)}n] [{nBu2Sn(trans-e,e-1,2-chdca)}n] [{(Me2Sn)2O(cis-e,a-1,2-chdcaOEt)2}2] [{Me2Sn(cis-e,e-1,3-chdca)(H2O)}]n [(nBu2Sn)y+z(trans-e,a-1,3-chdca)y(cis-e,e-1,3-chdca)z] [{Me2Sn(cis-e,a-1,4-chdca)(H2O)}2] [{nBu2Sn(cis-e,a-1,4-chdca)}4 {nBu2Sn(cis-e,a-1,4-chdca)}n] [{tBu2Sn(cis-e,a-1,4-chdca)}n] [{Me2Sn(trans-e,e-1,4-chdca)}n] [{tBu2Sn(Cl)}2(trans-e,e-1,4-chdca)] [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)(H2O)}n] [{nBu2Sn(cis,cis-e,e,e-1,3,5-chtca)}n]

8 9 10 11 12 13 a

Note: n = polymeric, y, z = oligo- or polymeric.

recrystallization, a second preparative method was employed, which consisted of a slow, diffusion-controlled reaction. In this method a U-shaped glass tube equipped with a ceramic membrane filter disc was filled with a solution of the potassium salt of the corresponding cyclohexanedicarboxylic acid in ethanol at one side and a solution of dimethyltin dichloride in the same solvent at the other side. For the case of the dinuclear macrocyclic complex 6, crystals suitable for singlecrystal X-ray diffraction analysis could be grown using a hydrothermal protocol in water (120 °C, 4 day; see Experimental Section). Unfortunately, until now 1,3-chdcaH2 has been commercially available only in the form of a 1:1 cis/trans mixture, in which the isomers have very similar physical properties. For this reason, we were not able to separate them by column chromatography, neither in the form of carboxylic acids or in the form of the corresponding ethyl esters. As a consequence, product mixtures were formed upon reaction with this ligand, of which only in the case of the combination with Me2SnCl2 a pure product could be isolated via crystallization, [{Me2Sn(cise,e-1,3-chdca)(H2O)}]n (4). From the reaction with the nBu2Sn-containing starting materials, only a product mixture could be isolated, which is formulated as [(nBu2Sn)y+z(trans-e,a1,3-chdca)y(cis-e,e-1,3-chdca)z] (5) with 0 < y < 1 and y + z = 1. From the remaining carboxylic acids a total of 10 dimethyl and di-n-butyltin carboxylate complexes could be isolated with satisfactorily elemental analyses and further characterized. Althoguh all reactions have been carried out in 1:1 stoichiometric proportions and using similar reaction conditions, for the cis-e,a-1,2-chdcaH2 ligand it was only possible to isolate the bis(tetraorganodistannoxane) derivative [{(Me2Sn)2O(cis-e,a-1,2-chdcaOEt)2}2] (3). In order to examine the steric effects of the organic groups attached to the tin atoms on the resulting supramolecular structure, for cisand trans-1,4-chdcaH2 di-tert-butyltin derivatives have been also prepared (compounds 8 and 10). The reactions between the diorganotin species and cis,cis-1,3,5-chtcaH3 have been carried out also in a 3:2 stoichiometric proportion (method A) in order to prepare 2D or 3D coordination polymers; however, only 1:1 products could be isolated (compounds 11−13, see Table 1). The composition of the dimethyl- and di-tert-butyltin derivatives 1, 3, 4, 6, and 8−12 was established by elemental analysis, IR spectroscopy, and as far as possible by single-crystal E


Article


Figure 1. (a) Fragments of the crystal structure of [{Me2Sn(trans-e,e-1,2-chdca)}n] (1) showing (a) the 1D polymeric chain, and (b) the intermolecular connectivity giving rise to tetranuclear macrocycles, which are arranged into 2D herringbone-type layers. Note: In panel b hydrogens atoms have been omitted for clarity.

the six-coordinate tin atoms are bound to four oxygen atoms from two different carboxylate groups and two carbon atoms from the organic substitutents (Figure 1a). The metalcoordination geometry is skewed-trapezoidal bipyramidal, in which the basal plane is formed by the oxygen atoms and the apical positions are occupied by the carbon atoms. The carboxylate groups chelate in an anisobidentate manner (Sn− Ocov = 2.104(7) and 2.112(7) Å; Sn···Ocoord = 2.602(8) and 2.461(8) Å; Ocov−Sn−Ocov = 81.2(3)°, Ocoord−Sn−Ocoord = 168.1(3)°), thus confirming the observations from the IR data. The angle formed between the carbon atoms of the carboxylate groups and the centroid of the cyclohexylene ring (61.5°) and the C7−C1−C2−C8 torsion angle formed between the metalcoordinating functions (54.5(13)°) illustrate why in this case a macrocyclic ring is not formed. However, in the crystal structure neighboring polymeric strands are linked through intermolecular O···Sn interactions (Sn···O = 3.084(8) Å), giving rise to the formation of tetranuclear 28-membered macrocyclic rings of the composition {C16O8Sn4} and Sn···Sn distances of 5.84 and 7.82 Å (Figure 1b) that are arranged in the form of a 2D herringbone-type layer. The cyclotetramers shown in Figure 1b approximate the shape of a parallelogram with overall dimensions of 13.6 × 16.3 Å2. So far, mostly di-, tri-, hexa-, and octanuclear macrocyclic diorganotin carboxylates have been described.28−34,37−40 Since the tin atoms are involved in intermolecular O···Sn interactions, four-membered Sn2O2 distannoxane rings arise, which enhance the thermodynamic stability of the crystal lattice, thus explaining the low solubility of the complex. A similar arrangement has been determined previously for the corresponding dimethyltin 1,2-benzenedicarboxylate, in which the OOC···centroid···COO angle is 61.7°.37 Unfortunately, the corresponding di-n-butyltin derivative 2 could not be crystallized and examined by X-ray diffraction analysis; however, the IR and NMR spectroscopic and mass spectrometric data indicate that the structure is probably strongly related to that of compound 1. This would be also in agreement with the previously determined molecular structure of di-n-butyltin 1,2-benzenedicarboxylate (1,2-bdc). The most

11, which has been characterized by single-crystal X-ray diffraction analysis (vide infra). The FAB+ mass spectrometric analysis of the di-n-butyltin complexes with 1,2- and 1,3-chdca, 2 and 5, respectively, gave each peaks at m/z = 404, 807, and 1210, which indicate the presence of mono-, di-, and trinuclear species. For the di-nbutyltin carboxylate with 1,4-chdca (7), additionally a peak for a tetranuclear fragment was found at m/z = 1613. The singlecrystal X-ray diffraction analyses of compounds 2 and 5 revealed 1D polymeric structures, and for 7 the formation of a 1:1 mixture of supramolecular isomers consisting of a 1D polymeric chain and a macrocyclic tetranuclear species was observed.47 In view of the coexistence of a cyclo-oligomeric and a polymeric organotin complex in the solid state and based on the mass spectrometry data, it can be proposed that related assemblies exist in solution also for compounds 2 and 5, independently from the observation that for these complexes the solid-state structures exhibit only 1D polymeric chain structures. This is in agreement with the detection of various signals in the 119Sn NMR spectrum of 2 and with previous reports that have established rapid exchange equilibria and the coexistence of different supramolecular aggregates for organotin carboxylates in solution.37,47,59−61 3.3. Single-Crystal X-ray Diffraction Analysis. For compounds 1, 3, 4, and 6−12, crystals suitable for X-ray diffraction analysis could be grown, which revealed monomeric structures for 3 and 10, a dinuclear macrocyclic structure for 6, a mixture of a tetranuclear macrocyclic and a polymeric structure for 7, and polymeric structures for 1, 4, 8, 9, 11, and 12. Of these, the crystal structures of complexes 1 and 7 have been reported previously,47,50 but the data are included also herein for the purpose of comparison. The molecular structures and/or fragments from the polymeric aggregate are shown in Figures 1−11. The most relevant crystallographic data and selected geometric parameters are summarized in Tables 2 and 3. Diorganotin Carboxylates Derived from cis- and trans1,2-chdcaH2 (1−3). In the solid-state, [{Me2Sn(trans-e,e-1,2chdca)}n] (1) is a 1D zigzag coordination polymer, in which F


C48H84O18Sn4 1423.91 P1̅ 293(2) 7.509(2) 13.285(4) 16.230(4) 71.017(4) 82.217(4) 85.408(4) 1515.7(7) 1 1.691 1.560 0.058 0.134 1.002

C10H16O4Sn 318.92 P21/c 293(2) 10.6733(17) 10.8591(17) 11.0886(18) 90 102.446(2) 90 1225.0(3) 4 2.029 1.688 0.082 0.164 1.143

formula MW (g mol−1) space group temp (K) a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z μ (mm−1) ρcalcd (g cm−3) R c, d Rwe,f GOF

C10H18O5Sn 336.93 R3c 100(2) 26.2852(18) 26.2852(18) 10.0237(10) 90 90 120 5997.6(8) 18 1.920 1.679 0.046 0.103 1.040

4 C20H36O10Sn2 673.87 Pbca 100(2) 13.2366(9) 12.6384(8) 14.5715(10) 90 90 90 2437.7(3) 4 2.100 1.836 0.023 0.054 1.135

6 C96H168O24Sn6 2418.44 P1̅ 200(2) 11.291(3) 16.605(4) 31.562(7) 79.638(4) 88.669(4) 70.766(3) 5492(2) 2 1.407 1.462 0.059 0.167 0.974

7b C16H28O6Sn 403.07 P21/n 100(2) 13.5209(8) 9.0508(6) 14.4884(9) 90 103.680(1) 90 1722.72(19) 4 1.496 1.554 0.037 0.097 1.066

8 C10H16O4Sn 318.92 C2/c 100(2) 11.5712(17) 5.1018(8) 20.444(3) 90 103.498(3) 90 1173.6(3) 4 2.169 1.805 0.016 0.041 1.039

9 C24H46Cl2O4Sn2 706.89 P1̅ 100(2) 6.3263(7) 14.4732(17) 16.566(2) 87.099(2) 89.087(2) 79.421(2) 1489.0(3) 2 1.882 1.577 0.053 0.110 1.091

10 C11H16O6Sn 362.93 P21 100(2) 8.1979(8) 16.2506(15) 10.0947(10) 90 102.638(2) 90 1312.2(2) 4 1.964 1.837 0.047 0.094 1.034

11

C11H18O7Sn 380.94 P21/c 100(2) 9.4552(12) 17.316(2) 8.7500(11) 90 93.211(2) 90 1430.3(3) 4 1.811 1.769 0.027 0.061 1.078

12

a λMoKα = 0.71073 Å. bData for these compounds have been reported previously47,50 but are included for the purpose of comparison. cF0 > 4σ(F0). dR = ∑∥F0| − |Fc∥/∑|F0|. eAll data. fRw = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2.

3

1b

crystal dataa

Table 2. Selected Crystallographic Data for Compounds 1, 3, 4, 6, 7, 8, 9, 10, 11, and 12

Crystal Growth & Design Article

G


H

Sn···Owater Sn···Cl C−O

Sn···Ointermol.

1.275(13) 1.243(13) 1.295(13) 1.234(13)

3.084(8)

2.602(8) 2.461(8)

2.104(7) 2.112(7)

Sn−Ocov

Sn−(μ3-O) Sn···Ocoord

2.085(10) 2.105(11)

Sn−C

1

a

1.179(9) 1.259(10) 1.295(9) 1.223(9)

2.168(5), 2.036(4)/2.033(4) 2.893(7)/2.735(6)

2.238(6)/2.267(7) −/2.171(5)

2.105(8)/2.087(9) 2.111(7)/2.107(9)

endo/exo

3b

1.274(14) 1.262(14) 1.250(13) 1.270(13)

2.322(6)

2.456(16) 2.400(17)

2.203(7) 2.204(7)

2.087(9) 2.112(9)

4

1.289(3) 1.234(3) 1.292(3) 1.224(3)

2.9434(19)

2.9430(19) 3.1257(19)

2.1112(19) 2.0322(18)

2.098(3) 2.098(3)

6

1.277(10) 1.245(10) 1.248310) 1.234(10) 1.297(10) 1.233(11) 1.284(10) 1.242(10) 1.292(10) 1.253(10) 1.286(10)

2.464(6) 2.514(6) 2.526(6) 2.566(6) 2.492(6) 2.492(6) 2.528(6) 2.605(6) 3.040(6) 3.020(6) 2.982(6) 2.997(6)

2.111(8) 2.114(9) 2.088(9) 2.116(8) 2.092(8) 2.110(8) 2.092(8) 2.117(8) 2.118(5) 2.137(5) 2.117(6) 2.121(6) 2.119(5) 2.142(5) 2.109(6) 2.114(6)

tetramer

7c,d

1.295(10) 1.226(11) 1.304(9) 1.208(9) 1.294(10) 1.232(10) 1.307(10) 1.237(10)

3.208(6) 2.968(6)

2.552(6) 2.576(6) 2.525(6) 2.603(6)

2.111(6) 2.102(6) 2.110(5) 2.128(5)

2.098(9) 2.106(8) 2.096(8) 2.113(9)

polymer

1.303(5) 1.239(5) 1.294(5) 1.243(5)

2.506(3) 2.482(3)

2.115(3) 2.138(3)

2.179(4) 2.180(4)

8

Table 3. Selected Bond Lengths [Å] and Intramolecular Distances [Å] for Compounds 1, 3, 4, 6, 7, 8, 9, 10, 11, and 12

1.295(2) 1.234(2)

3.7395(13)

2.5239(16)

2.1009(13)

2.097(2)

9

2.419(2) 1.302(9) 1.250(9)

2.420(5)

2.107(5)

2.169(7) 2.168(7)

10e 11

1.292(10) 1.279(9) 1.250(11) 1.243(10) 1.292(9) 1.300(9) 1.234(10) 1.247(9)

2.773(6) 2.843(6)

2.479(5) 2.490(5) 2.564(5) 2.509(5)

2.135(5) 2.142(5) 2.135(5) 2.116(5)

2.087(7) 2.089(7) 2.087(8) 2.095(8)

12

1.290(3) 1.232(3) 1.289(3) 1.246(3)

2.276(2)

2.775(2) 2.884(2)

2.1350(19) 2.0806(19)

2.104(3) 2.107(3)



Article

4.73 5.84 Sn···Sn

1

Data for this compound have been reported also in ref 50. bBis(dicarboxyltetraorganodistannoxane). cCompound containing two supramolecular isomers. dThis compound has been reported in a previous communication (see ref 47). eDiscrete species.

8.69 10.02

4 endo/exo

3b

a

Table 3. continued

relevant difference between the solid-state structures of [{Me2Sn(1,2-bdc)}n] and [{nBu2Sn(1,2-bdc)}n] is that in the first case each tin atom is involved in intermolecular O···Sn interactions, while in the second case, for steric reasons, only every second tin atom can participate in such an interaction.37 Since the resulting decrease of the crystal lattice energy is in accordance with the elevated solubility of the di-n-butyltin derivative 2, it can be proposed that the structures of the diorganotin trans-1,2-cyclohexane- and 1,2-benzene dicarboxylates are indeed analogous. From the reactions with cis-e,a-1,2-chdcaH 2 , only [{(Me2Sn)2O(cis-e,a-1,2-chdcaOEt)2}2] (3) could be isolated in pure form, namely, from the reaction with dimethyltin oxide in a refluxing solvent mixture of ethanol and toluene. Interestingly, in this case the bis(tetramethyldistannoxane) dicarboxylate shown in Figure 2 has formed, in which the uncoordinated carboxyl groups have been transformed to the corresponding ethyl ester functions. Bis(tetraorganodistannoxane) dicarboxylates are well-known, and Tiekink has shown that there are four different structural classes for this type of compounds, which can be differentiated from each other by the bridging modes of the four carboxylate groups.58 Compound 3 belongs to class I that is characterized by the presence of both monodentate and bidentate carboxylate bridging. The complex is a centrosymmetric dimer built up around a planar cyclic Sn2O2 unit. The two oxygen atoms of this four-membered ring are tridentate and bound each to three tin centers, two endo-cyclic (Sn1−O1 = 2.168(5) Å; Sn1#1−O1 = 2.036(4) Å; symmetry operator: #1, 2 − x, −y, 1 − z) and one exo-cyclic (Sn2−O1 = 2.033(4) Å). Additional connections between the tin atoms are provided by bidentate-bridging (Sn2−O6 = 2.171(5) Å; Sn2−O7 = 2.735(6) Å; Sn1−O6 = 2.893(7) Å) and bidentate chelate-bridging carboxylates (Sn1− O2 = 2.238(6) Å; Sn2#1−O3 = 2.267(7) Å; symmetry operator: #1, 2 − x, −y, 1 − z) from the 1,2-cyclohexane dicarboxylate ligands. The coordination geometries of the endo and exo tin atoms are trigonal bipyramidal with the organic groups and one μ3-O atom in the equatorial positions, in concordance with previously reported examples.58 Recently, several research groups have started to explore the utility of these tetranuclear species as secondary building blocks for the generation of porous 2D and 3D coordination polymers.48,49,63−67 Diorganotin Carboxylate Derived from cis-1,3-chdcaH2 (4). From the reaction with the mixture of cis/trans-1,3chdcaH2, two diorganotin complexes could be prepared (4 and 5), of which [{Me2Sn(cis-e,e-1,3-chdca)(H2O)}]n (4) could be isolated in pure form by fractional crystallization and analyzed by single-crystal X-ray diffraction analysis. Previous studies with 1,3-benzenedicarboxylic acids (1,3bdcH2) have shown that [{nBu2Sn(1,3-bdc)}3] has a trinuclear macrocyclic structure.37 Since the angle formed between the carboxylate groups in cis-e,e-1,3-chdc is practically identical to that found in 1,3-bdc (120°), one possible structure for compound 4 would be that of an analogous cyclotrimer. However, the formation of a 1D polymer is also possible as seen from the experimentally determined solid-state structure shown in Figure 3a. In compound 4, the tin atoms have distorted pentagonal bipyramidal coordination environments, in which the equatorial positions are occupied by the oxygen atoms from two anisobidentate chelating carboxylate groups (Sn−Ocov = 2.203(7) and 2.204(7) Å; Sn···Ocoord = 2.456(16) and 2.400(17) Å; Ocov−Sn−Ocov = 80.3(2)°, Ocoord−Sn−Ocoord

a

10.10 10.10 10.80 8.79 8.91 8.81 9.11 1.243(10) 1.284(10) 1.246(10) 1.297(10) 1.222(10) 8.45 9.24 8.46 9.50

6

tetramer

7c,d

polymer

8

10.99

9

10e

11

9.46

12


I


J

168.1(3)

Ocoord···Sn···Ocoord

125.3(9) 119.8(7)

119.7(12) 118.0(12)

168.15(18)

55.8(3) 55.7(3)

−/51.2(2)

−/−

80.3(2)

168.5(4)

4

−/−

142.9(4)/141.7(4)

endo/exo

122.1(2) 122.7(2)

111.83(7)

48.44(7) 44.74(7)

83.17(7)

132.87(11)

6 147.5(4) 146.4(4) 151.2(3) 147.3(3) 83.9(2) 82.3(2) 82.4(2) 82.4(2) 56.20(19) 55.1(2) 54.8(2) 55.3(2) 56.15(18) 55.47(19) 53.9(2) 55.3(2) 164.91(19) 167.6(2) 166.19(18) 168.4(2) 119.6(8) 119.2(7) 121.6(8) 119.2(7) 119.2(8) 119.4(8) 119.3(8) 119.5(8)

tetramer

7c,d

121.3(8) 122.1(7) 118.3(7) 120.1(8)

168.4(2) 168.3(2)

55.3(2) 54.1(2) 54.3(2) 56.0(2)

81.9(2) 81.1(2)

141.4(4) 147.3(3)

polymer

119.4(3) 120.0(4)

163.27(9)

56.23(10) 55.94(10)

84.57(10)

137.95(15)

8

119.34(17)

169.80(7)

55.42(5)

79.69(7)

137.07(13)

9

117.7(7)

57.20(18)

133.1(3)

10e 11

119.0(8) 119.5(7) 119.9(7) 118.5(7)

167.0(2) 165.36(18)

56.10(19) 55.5(2) 54.5(2) 55.72(18)

82.4(2) 83.4(2)

153.0(3) 151.9(3)

12

120.8(3) 121.3(3)

125.8(2)

50.0(2) 51.5(2)

84.99(7)

134.31(12)

Data for this compound have been reported also in ref 50. bBis(dicarboxyltetraorganodistannoxane). cCompound containing two supramolecular isomers. dThis compound has been reported in a previous communication (see ref 47). eDiscrete species.

a

54.1(3) 56.2(3)

O−Sn−O (chelate)

120.4(11) 118.8(11)

81.2(3)

Ocov−Sn−Ocov

O−C−O

142.1(5)

C−Sn−C

1a

3b

Table 4. Selected Bond Angles [°] for Compounds 1, 3, 4, 6, 7, 8, 9, 10, 11, and 12



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coordinating carboxylate functions is approximately 90° (Scheme 1), which makes this ligand highly prone to the formation of either dinuclear or tetranuclear macrocyclic structures. Interestingly, compounds 6−8 have different solidstate structures. While the dimethyltin complex 6 is composed of discrete dinuclear macrocyclic rings (Figure 5a), the di-nbutyltin analogue 7 is a 2D coordination polymer containing within the same crystal lattice a mixture of tetranuclear macrocycles and 1D polymeric double chains (Figure 6), and the di-tert-butyltin complex 8 consists of isolated 1D zigzag chains (Figure 7). The macrocycles in the solid-state structure of compound 6 are 18-membered and have the composition {C12O4Sn2}. However, the transannular Sn···Sn distances of 8.69 Å indicate that the cavities are too small for the inclusion of guest atoms or molecules. The tin atoms are seven-coordinated by five oxygen atoms from two carboxylate ligands and one water molecule, and two carbon atoms from the organic substituents. The coordination geometry is probably best described as distorted bicapped trigonal bipyramidal (Figure 5b), since the anisobidentate character of the chelating carboxylates is more pronounced than in most of the remaining structures (Sn−Ocov = 2.1112(19) and 2.0322(18) Å; Sn···Ocoord = 2.9430(19) and 3.1257(19) Å; Ocov−Sn−Ocov = 83.17(7)°, Ocoord−Sn−Ocoord = 111.83(7)°). The equatorial plane of the coordination polyhedron is composed of the organotin substituents and one of the carboxylate oxygens, while the apical positions are formed by the water molecule and the covalently bound oxygen from the second carboxylate group. A revision of the Cambridge Structural Database (version 5.35)68 showed only two entries for organotin carboxylates of the composition [R2Sn(OOCR)2(R′OH)] having this unusual coordination geometry (REFCODES: GIJPUL69 and SAPLUR).70 Within the crystal lattice, each macrocycle interacts with eight neighboring specimens through hydrogen bonding interactions formed between the tin-coordinated water molecules and the pending CO groups that form only relatively weak secondary interactions with the metal atoms (O5−H52···O2#1: 0.84, 1.86, 2.698(3) Å, 173°; O5−H51·· O4#2: 0.84, 1.88, 2.708(3) Å, 171°; symmetry operators: #1, x, −y + 1/2 + 1, +z + 1/2; #2, −x + 1/2, +y − 1/2, +z). In such a way, a 3D hydrogen bonded supramolecular structure arises. As already reported in ref 47, in the crystal structure of the di-n-butyltin derivative 7 two supramolecular isomers coexist within the same crystal structure, namely, the 36-membered macrocyclic tetranuclear complex [{nBu 2 Sn(cis-e,a-1,4chdca)}4] and the analogous polymeric form [{nBu2Sn(cis-e,a1,4-chdca)}n] (Figure 6a,b). Of these, the cyclotetramer skeleton is approximately rectangular with transannular Sn··· Sn distances of 10.7 and 14.1 Å, and overall dimensions of 25.2 × 25.6 Å2 (Figure 6a). The cavities within the {C24O8Sn4} macrocycles are occupied by part of the nBu groups attached to the tin atoms. Interestingly, Ma and co-workers described more recently the same macrocyclic complex, which they were able to crystallize separately from the polymer.49 When comparing the molecular structures, the most important difference is a change in the overall molecular symmetry. While the macrocycles in Ma’s crystal structure exhibited crystallographic inversion symmetry, they had no symmetry in the crystal structure of 7.47 The polymeric chains in [{nBu2Sn(cis-e,a-1,4-chdca)}n] have zigzag topology and contain two crystallographically independent tin atoms and 1,4-chdca ligands (Figure 6b). The supramolecular arrangement consists of alternating macrocycle

Figure 2. Perspective view of the molecular structure of [{(Me2Sn)2O(cis-e,a-1,2-chdcaOEt)2}2] (3). Note: Hydrogens atoms have been omitted for clarity.

= 168.15(18)°) and a metal-coordinated water molecule (Sn− Ow = 2.322(6) Å). Due to the reduced steric strain in the dimethyltin moiety, it is quite common to find that the coordination number of the central metal atom increases from six to seven.40,41 The observation that compound 4 did not crystallize in the form of the expected trinuclear macrocycle might be explained by the favorable intermolecular hydrogen bonding interactions occurring between neighboring 1D polymer strands in the crystal structure (Figure 3b). Groups of three chains each are linked through two crystallographically different intermolecular O−H···OCO interactions (O5−H52··· O2#1: 0.84, 1.92, 2.720(16) Å, 160°; O5−H51···O4#2: 0.84, 1.88, 2.706(10) Å, 169°; symmetry operators: #1, −x + y − 2/ 3, −x + 2/3, +z − 1/3; #2, −y + 2/3, +x − y + 1/3 + 1, +z + 1/ 3) to give columnar hydrogen bonded assemblies with 31 symmetry (Figures 3c and 4) that extend along the c-axis (space group R3c). Diorganotin-Carboxylates Derived from cis- and trans1,4-chdcaH2 (6−10). In combination with dimethyl-, di-nbutyl- and di-tert-butyltin, the cis-e,a-isomer of 1,4-chdcaH2 gave three crystalline compounds of the compositions [{Me2Sn(cis-e,a-1,4-chdca)(H2O)}2] (6) and [{R2Sn(cis-e,a1,4-chdca)}4] (7, R = nBu, z = 4 and ∞; 8, R = tBu, z = ∞). In cis-e,a-1,4-chdcaH2, the angle formed between the K


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Figure 3. (a) Fragments of the crystal structure of [{Me2Sn(cis-e,e-1,3-chdca)(H2O)}]n (4) showing a) the 1D polymer strand, and (b, c) the intermolecular hydrogen bonding connectivity, giving rise to columnar assemblies with 31 symmetry. Note: In panel c, part of the hydrogen atoms have been omitted for clarity.

Figure 4. Fragment of the crystal structure of [{Me2Sn(cis-e,e-1,3chdca)(H2O)}]n (4), providing a top view of the columnar hydrogen bonded assembly with 31 symmetry along the c-axis.

Figure 5. Perspective view of (a) the molecular structure of [{Me2Sn(cis-e,a-1,4-chdca)(H2O)}2] (6) and (b) the coordination geometry of the tin atoms.

and polymer strands with different patterns of Sn···O interactions in the range of 2.968(6)−3.208(6) Å that give rise to a total of four different types of supramolecular macrocyclic assemblies (Figure 6c). This arrangement probably resembles local environments in solution and allowed a plausible mechanistic pathway to be proposed for the ring−

chain rearrangement dynamics, through which the macrocycle molecules are transformed into other cyclo-oligomeric and polymeric molecules.47 L


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Figure 6. (a) Fragments of the crystal structure of [{nBu2Sn(cis-e,a-1,4-chdca)}4·{nBu2Sn(cis-e,a-1,4-chdca)}n] (7) showing (a) the tetranuclear macrocycles, (b) the 1D polymer strands, and (c) part of the intermolecular connectivity giving rise to different macrocyclic assemblies. Note: Hydrogen atoms and in panel c additionally part of the n-butyl groups have have been omitted for clarity.

The di-tert-butyltin derivative 8 is a 1D polymer with zigzag strands (Figure 7), in which the tin atoms are embedded in the usual skewed-trapezoidal bipyramidal coordination environ-

ment (Sn−Ocov = 2.115(3) and 2.138(3) Å; Sn···Ocoord = 2.506(3) and 2.482(3) Å; Ocov−Sn−Ocov = 84.57(10)°, Ocoord− Sn−Ocoord = 163.27(9)°). Contrary to the dimethyl- and di-nbutyltin derivatives 6 and 7, in this case the tin atoms do not participate in intermolecular Sn···O interactions, which can be attributed to the volume of the tert-butyl substituents, thus evidencing that the organic group attached to the metal atoms strongly influences the supramolecular structure of the resulting assembly. In the trans-isomer of 1,4-chdcaH2, the carboxyl groups are oriented in opposite directions of the space (180°); therefore, the formation of 1D diorganotin coordination polymers can be expected. This was indeed observed for compound 9 having the composition [{Me2Sn(trans-e,e-1,4-chdca)}n]. However, for the di-tert-butyltin derivative only the monomeric complex [{tBu2Sn(Cl)}2(trans-e,e-1,4-chdca)] (10) could be crystallized from a solution of the starting materials in ethanol. A perspective view of the polymeric chains of compound 9 is given in Figure 8a. The coordination geometry is skewedtrapezoidal bipyramidal (Sn−Ocov = 2.1009(13) Å; Sn···Ocoord = 2.5239(16) Å; Ocov−Sn−Ocov = 79.69(7)°, Ocoord−Sn−Ocoord = 169.80(7)°). The molecular and supramolecular structures are strongly related to the previously reported phthalate derivative [{nBu2Sn(1,2-bdc)}n], where 1,2-bdc = 1,2-benzene-

Figure 7. Fragment of the crystal structure of [{tBu2Sn(cis-e,a-1,4chdca)}n] (8), showing the 1D polymeric chain. M


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Figure 8. (a) Fragments of the crystal structure of [{Me2Sn(trans-e,e-1,4-chdca)}n] (9) showing (a) the 1D polymeric chain, and (b) the intermolecular connectivity giving rise to an overall 2D coordination polymer with 18-membered macrocycles. Note: In panel b hydrogen atoms have been omitted for clarity.

dicarboxylate.37 In the crystal structure, neighboring polymeric strands are linked through weak intermolecular Sn···O contacts (Sn···Ocoord = 3.7395(13) Å), thus giving an overall 2D coordination polymer containing 18-membered macrocycles of the composition {C12O4Sn2} (Figure 8b). The molecular structure of compound 10 is shown in Figure 9. In this case, the tin atoms are five-coordinated and embedded in a monocapped tetrahedral coordination environment. The Sn−Ocov and Sn···Ocoord bond distances are 2.107(5) and 2.420(5) Å, respectively, thus confirming the capping interaction.

Diorganotin Carboxylates Derived from cis,cis-1,3,5chdcaH3 (11−13). In analogy to 1,3,5-benzenetricarboxylic acid (trimesic acid), it can be expected that cis,cis-e,e,e-1,3,5chtcaH3 forms 2D coordination polymers when combined with di- or triorganotin moieties.71 Reaction of cis,cis-e,e,e-1,3,5chtcaH3 with potassium hydroxide and dimethyltin dichloride in a 1:2:1 stoichiometric ratio and using a solvent mixture of water/methanol (1:1, v/v) gave two crystalline products of the compositions [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (11) and [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)(H2O)}n] (12), which could be separated manually because of their different crystal shapes. When realizing the reaction in a 2:6:3 stoichiometric ratio with the purpose to achieve the coordination of all three ligand carboxylate groups to tin atoms, the same product mixture was obtained. Perspective views of the molecular structures of compounds 11 and 12 are shown in Figures 10a and 11a. Both complexes consist of 1D polymeric chains, in which the metal atoms have distorted skewed-trapezoidal bipyramidal (11) and bicapped trigonal bipyramidal (12) geometries. In the first case, the trapezoidal plane is formed by four oxygen atoms originating from two anisobidentae chelating carboxylate groups (Sn−Ocov = 2.116(5)−2.142(5) Å; Sn···Ocoord = 2.479(5)−2.564(5) Å; O cov −Sn−O cov = 82.4(2) and 83.4(2)°, Ocoord−Sn−Ocoord = 167.0(2) and 165.36(18)°) with the organic groups attached to the tin atoms in axial position. In the second case, the equatorial plane of the trigonal bipyramidal polyhedron is comprised of the carbon atoms from the organotin groups and an oxygen from a carboxylate group

Figure 9. Perspective view of the molecular structure of [{tBu2Sn(Cl)}2(trans-e,e-1,4-chdca)] (10). Note: only one of two crystallographically independent molecules is shown. N


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Figure 10. Fragments of the crystal structure of [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (11), showing (a) the 1D polymer strands, (b) the 1D double chains formed through Sn···O interactions, and (c) the intermolecular hydrogen bonding connectivity giving rise to 2D layers. Note: For clarity, in panel c C−H hydrogen atoms have been omitted.

adopts also an anisobidentate coordination (Sn−Ocov = 2.1350(19) Å; Sn···Ocoord = 2.775(2) Å) and a metalcoordinated water molecule (Sn−Ocov = 2.276(2) Å). The

(Sn−Ocov = 2.0806(19) Å), which shows an additional weak interaction with the tin atom (Sn···O = 2.884(2) Å). The apical positions are occupied by the second carboxylate group that O


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Figure 11. Fragments of the crystal structure of [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)(H2O)}n] (12), showing (a) the 1D polymer strands, and (b) the intermolecular hydrogen bonding connectivity giving rise to 2D layers. Note: For clarity, in panel b C−H hydrogen atoms have been omitted.

layers in the crystal structure of compound 12 contain 14- and 20-membered hydrogen bonded macrocycles of the compositions {C6H2O5Sn} and {C10H2O6Sn2} (Figure 11b). In the third dimension, these 2D layers are connected still further through Ow−H···OC interactions formed between the tincoordinated water molecules and the uncoordinated CO groups to give an overall 3D hydrogen bonded network (Ow− H71···O2#1: 0.84, 1.79, 2.626(3) Å, 175°; symmetry operator: #1, x, −y + 1/2, +z + 1/2). 3.4. Discussion. The above description of the solid-state structures has shown that diorganotin compounds derived from cis/trans-1,x-cyclohexanedicarboxylates exhibit preferentially either cyclo-oligomeric or polymeric structures depending on the following factors: (i) the angle θ formed between the carboxylate functions, (ii) the spatial orientation of the coordination functions in relation to the conformational isomers of the ligand, and (iii) the steric effect of the organic groups attached to the tin atoms. As outlined in Scheme 4, the diorganotin carboxylates derived from cis-e,a-1,4-cyclohexanedicarboxylic acid (θ ≈ 90°) are either dinuclear macrocyclic (6), a mixture of tetranuclear macrocyclic and polymeric species (7), or only polymeric (8), depending essentially on the size of the organic group attached the tin atom. While the dimethyltin moiety in 6 favored the formation of only a small macrocycle (Sn···Sn = 8.7 Å) and the di-n-butyltin group in 7 induced the coexistence of a tetranuclear macrocyclic (Sn···Sn = 10.7 and 14.1 Å) and a polymeric species (Sn···Snrepeating unit = 16.6 Å) within the same crystal lattice (supramolecular

bicapped coordination mode generates a significant distortion from the ideal trigonal-bipyramid, which can be seen from the bond angle formed between the apical substituents (O3−Sn− Ow = 158.71(9)°). Thus, the coordination geometry of the tin atom in compound 12 is similar to that observed for compound 6. In the crystal structure of [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (11), neighboring 1D polymer strands are interconnected through intermolecular Sn···O contacts (Sn···O = 2.773(6) and 2.843(6) Å) to double chains, which exhibit 16-membered dinuclear macrocycles of the composition {C10O4Sn2} (Figure 10b). These double chains are further linked to a 2D layer-type structure (Figure 10c) through hydrogen bonding interactions between the uncoordinated carboxyl groups and one of the carboxylate oxygen atoms (O5−H···O4#1: 0.84, 1.88, 2.706(7) Å, 170°; O35−H···O32#2: 0.84, 1.93, 2.756(6) Å, 170°; symmetry operators: #1, x − 1, +y, +z − 1; #2, x − 1, +y, +z). In [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)(H2O)}n] (12), neighboring polymer strands interact solely through hydrogen bonding interactions formed between the tin-coordinated water molecules, the perpendicular oriented carboxyl group, and the carbonyl oxygen of the remaining carboxylate function (O5− H50···O4#1: 0.84, 1.86, 2.670(3) Å, 162°; Ow−H72···O6#2: 0.84, 1.84, 2.672(3) Å, 174°; symmetry operators: #1, x, +y, +z − 1; #2, x, +y, +z + 1). The change in the tin coordination geometry in compound 12 results in a smaller C−Sn−C bond angle when compared to 11 (153.0(3)/151.9(3) versus 134.31(12)°). The overall resulting 2D hydrogen bonded P


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Scheme 4. Graphical Illustration of the Broad Structural Variety in the Metal Directed Self-Assembly of 1,x-chdcaH2 (x = 2, 3, and 4) with Diorganotin Reactants

isomerism), the di-tert-butyltin group in 8 gave only a polymeric assembly (Sn···Snrepeating unit = 17.3 Å). Ligands with θ-values that are different from 90°, such as trans-e,e-1,2cyclohexanedicarboxylic acid (θ ≈ 61°), cis-e,e-1,3-cyclohexanedicarboxylic acid (θ ≈ 122°), and trans-e,e-1,4-cyclohexanedicarboxylic acid (θ ≈ 180°), gave polymeric structures having different topologies in combination with the dimethyltin fragment (1, 4, 9). The topological variations result from changes in the symmetry of the polymer strands, which generate changes in the mutual orientation of neighboring Me2Sn moieties. In [{Me2Sn(trans-e,e-1,2-chdca)}n] (1), the polymers extend along c having glide reflection symmetry and in [{Me2Sn(cis-e,e-1,3-chdca)(H2O)}]n (4), they extend in the same direction, but have only translational symmetry. In [{Me2Sn(trans-e,e-1,4-chdca)}n] (9), the polymer strands along c have glide plane symmetry and, additionally, the repeating units are related by inversion symmetry. As a consequence, the mutual orientation of neighboring Me2Sn groups within the polymer strands is approximately gauche in 1, syn in 4, and anti in 9. These topological changes influence also the extension of the repating units, as seen from the Sn···Sn distances (1, 11.1 Å; 4, 10.0 Å; 9, 20.4 Å). The influence of the organic group on the resultant supramolecular structure can be deduced further from the comparison of compounds 9 and 10, which were both obtained from trans-e,e-1,4-cyclohexanedicarboxylic acid (θ ≈ 180°).

With dimethyltin (9) a polymer structure was formed, but in the presence of the di-tert-butyltin moiety (10) the steric effect inhibited the coordination of a second carboxylate function to the tin atom, giving the dinuclear monochlorinated species, which is an intermediate for the formation of a polymeric chain. Because of the variation of the metal coordination environment, the torsion angle formed between the carboxyl group and the cyclohexylene spacer (O1−C1−C2−C3) changed from −83.0(2)° in 9 to −35.4(10)° in 10. On the basis of the above, in the case of compound 3, which was prepared from cis-e,a-1,2-cyclohexanedicarboxylic acid (θ ≈ 61°) and the dimethyltin fragment, the formation of a polymeric compound was expected, but, interestingly, the tetraorganodistannoxane derivative 3 was favored. This seems to indicate that certain θ-values disfavor both the macrocyclic and the polymeric assembly, giving rise to complexes of different metal-to-ligand stoichiometry. With cis,cis-1,3,5-cyclohexanetricarboxylic acid, only two of the three carboxyl groups could be coordinated to the tin atoms under the reaction conditions explored herein. Thus, [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (11) and [{Me2Sn(cis,cis-e,e,e-1,3,5chtca)(H2O)}n] (12) were polymeric, despite having θ-values (θ ≈ 116°) with a close proximity to 120° that might have enabled also the formation of trinuclear macrocyclic species (vide supra). This can be explained by the formation of Q


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tendency to organize either into macrocyclic ring structures or infinite ccordination polymers. The conformation and topology of the resulting structure depend strongly on the substituents attached to the tin atoms, which could be evidenced most clearly for the complexes derived from cis-e,a1,4-chdcaH2 that gave rise to three quite different assemblies. With the smaller dimethyltin moiety, a dinuclear macrocyclic species was formed, albeit at the cost of an apparently less stable tin coordination environment (cis instead of trans coordination of the organic substituents and carboxylate groups). The larger n-butyl group induced the formation of arquitectures with larger, tetranuclear aggregates, in which the organic substituents can be accommodated. Furthermore, in both cases the tin atoms could enhance their coordination number from 6 to 7 through coordination to a water molecule capable of forming strong hydrogen bonds in the first case and through intermolecular Sn···O interactions in the second case, thus enhancing the thermodynamic stability of the resulting crystal structure. With the sterically more demanding tert-butyl groups, the cyclotetrameric assembly and intermolecular contacts seem not to be favored anymore, giving a 1D polymeric chain. Overall, these results show that organometallic building blocks are powerful tools for the purposes of supramolecular synthesis and crystal engineering, since they permit the finetuning of the structural properties through the variation of the organic substituents attached to the metal atom. In this context, it is important to notice that this purpose cannot be achieved as straightforward for metals without directly attached organic susbtituents.

additional noncovalent Sn···O and O−H···O interactions between neighboring chains in the solid-state structure. In this context, it is important to visualize that the coordination geometry and Lewis acidity of the metal center play an additional significant role for the supramolecular aggregation. In the molecular structures of the six-coordinate dimethyl-, di-n-butyltin, and di-tert-butyltin derivatives 1, 7, 8, 9, and 11, the tin atoms have skewed-trapezoidal bipyramidal geometries, in which both the organic and the carboxylate functions are trans-oriented. In contrast, in the sevencoordinate dimethyltin compounds 4, 6, and 12, where additionally water is coordinated to the metal center, the coordination polyhedra of the tin atoms are pentagonal bipyramidal (4) or bicapped trigonal bipyramidal (6 and 12), and, interestingly, only in these cases the carboxylate functions are cis-oriented. Finally the coordination geometry for the metal center in the discrete di-tert-butyltin complex 10 is distorted tetrahedral. For the compounds without water molecules coordinated to the tin atoms and carrying sterically less demanding groups (Me and nBu) (1, 7, 9, and 11), intermolecular O···Sn interactions occur, giving generally distannoxane units (Sn2O2). These interactions involve all tin atoms present in the respective structure with distances varying from 2.773(6) to 3.7395(13) Å that are all significantly shorter or close to the sum of the van der Waals radii for oxygen and tin (3.70 Å). For [{Me2Sn(trans-e,e-1,2-chdca)}n] (1) and [{nBu2Sn(cis-e,a-1,4chdca)}4·{nBu2Sn(cis-e,a-1,4-chdca)}n] (7), these intermolecular interactions between adjacent chains gave 2D layers with 28membered macrocycles (1) and a coassembly of cyclotetramers and polymer strands that coexist in the same crystal lattice (7). In this rare example of a cocrystallized supramolecular pair of ring−chain isomers, the intermolecular O···Sn distances varied from 2.968(6) to 3.208(6) Å, giving a total of four different types of macrocyclic aggregates that can be distinguished in the overall two-dimensional layer structure. As already mentioned and previously reported, the coexistence of supramolecular isomers and the complex interconnectivity between the specimens found in this particular structure show nicely that the energy barriers for a mutual transformation should be relatively small, thus explaining the presence of dynamic equilibria in solution between cyclo-oligomeric and polymeric species. 47 For [{Me 2 Sn(trans-e,e-1,4-chdca)} n ] (9) and [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (11), the O···Sn interactions favored infinite aggregates containing 18- and 16membered macrocycles, respectively. In compounds 4, 6, and 12 with metal-coordinated water molecules, the dimension of the supramolecular aggregates was enhanced further through Ow−H···O hydrogen-bonding interactions involving the acidic Sn−OH2 water molecules. These interactions gave a triplestranded polymer for [{Me2Sn(cis-e,e-1,3-chdca)(H2O)}]n (4), and complex hydrogen bonded networks for the cyclodimeric species [{Me2Sn(cis-e,a-1,4-chdca)(H2O)}2] (6) and the coordination polymer [{Me 2 Sn(cis,cis-e,e,e-1,3,5-chtca)(H2O)}n] (12). The 2D and 3D supramolecular structures of [{Me2Sn(cis,cis-e,e,e-1,3,5-chtca)}n] (11) and [{Me2Sn(cis,cise,e,e-1,3,5-chtca)(H2O)}n] (12) are accomplished by additional intermolecular COOH···O hydrogen bonds.

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AUTHOR INFORMATION

Corresponding Author

*Fax: (+52) 777 329 79 97. E-mail: hhopfl@uaem.mx. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work received financial support from Consejo Nacional de Ciencia y Tecnologia (CONACyT) through Grant Nos. CB2004-47347 and CB2010-158098.

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REFERENCES

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4. CONCLUSIONS The comparative structural analysis of diorganotin 1,x-cyclohexanedicarboxylates and 1,3,5-cyclohexanetricarboxylates has shown that diorganotin complexes exhibit a pronounced R


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