Coordination Polymers with Bulky Bis (imidazole) and Aromatic

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Coordination Polymers with Bulky Bis(imidazole) and Aromatic Carboxylate Ligands: Diversity in Metal-Containing Nodes and ThreeDimensional Net Topologies Chun-Hung Ke, Guan-Ru Lin, Bing-Chiuan Kuo, and Hon Man Lee* Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan, R.O.C. S Supporting Information *

ABSTRACT: Five new three-dimensional transition metal coordination polymers (CPs) with dia and different aromatic carboxylates, [Cd(oba)(dia)0.5] (1), [Cd(Hbtc)(dia)]·3H2O (2), and [M3(2-stp)2(dia)6(H2O)2] (3a, M = Cd; 3b, M = Co; 3c, M = Ni) were synthesized under hydrothermal condition (dia = 9,10-di(1H-imidazol-1-yl)anthracene; oba = 4,4′-oxybis(benzoate); btc = benzene-1,3,5-tricarboxylate; 2-stp = 2-sulfoterephthalate). Compounds 3a−c are isostructural. The coordination geometries at cadmium in 1, 2, and 3a are capped trigonal prism, pentagonal bipyramid, and octahedron, respectively. This diversity in coordination geometry is in sharp contrast to 3c and previously reported nickel complexes of a similar ligand set. The difference in metal-containing node geometries and carboxylate structures results in diverse network connectivity, including a tcs topology for 1, an unprecedented binodal topology of (42.63.85)(42.6) for 2, and a rare trinodal topology of (4.64.8)2(43.63)2(44.610.8) for 3. Based on secondary building units, the networks in 2 and 3 can be, alternatively, described as rob and pcu (or ilc) nets, respectively. This work shows the effect of the specific ion and the rich potential of using bulky bis(imidazole) and aromatic carboxylate as ligands in the construction of CPs with unusual topologies.

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3D bnn topology.30 The formation of these two topologically different structures can be rationalized by their relative orientations to a common square-pyramidal 5-connected node. Encouraged by the accessibility of novel CP topologies using dia and carboxylate as connecting ligands, we therefore sought to extend our efforts into the synthesis of more novel divalent metal CPs employing dia and a set of relevant carboxylates. Herein, we report the synthesis, structural characterization, and topological analysis on five new materials: [Cd(oba)(dia)0.5] (1), [Cd(Hbtc)(dia)]·3H2O (2), and [M3(2stp)2(dia)6(H2O)2] [btc = benzene-1,3,5-tricarboxylate; 2-stp =2-sulfoterephthalate;31 M = Cd (3a), M = Co (3b), M = Ni (3c)]. Compound 1−3 manifest diverse coordination geometries at metals, leading to subsequent diversity in 3D frameworks with unusual topologies, including a tcs topology for 1, an unprecedented binodal topology of (42.63.85)(42.6) for 2, and a rare trinodal topology of (4.64.8)2(43.63)2(44.610.8) for 3.

INTRODUCTION The use of crystal engineering to synthesize rational coordination polymers (CPs) or metal−organic frameworks (MOFs) attracts considerable interest, not only because of their potential applications as functional materials,1−11 but also because of their fascinating architectures and topologies.12−16 The combination of nitrogen donor ligands and aromatic carboxylate as connecting ligands is widely used for the construction of CPs. For example, the use of bis(imidazole) and aromatic carboxylates has led to a wide range of CPs with numerous interesting topologies.17−22 In contrast to the flexible bis(imidazole) ligands commonly reported in the literature,20−26 we have utilized 9,10-di(1H-imidazol-1-yl)anthracene (dia) bearing a flat anthracenyl ring as the ditopic nitrogen donor ligand.27 Along with 1,4-benzenedicarboxylate (bdc) as a connecting ligand, [Co(bdc)(dia)(H2O)·Co(bdc)(dia)2·H2O]n which manifests an intriguing 2D+3D interpenetrated array of (4,4) + pcu nets was obtained. Recently, we explored the replacement of bdc with structurally different aromatic carboxylates for the construction of novel CPs. In contrasting to bdc (structurally long and rigid), 4,4′-oxybis(benzoate) (oba),28,29 which is long but flexible, and 5-sulfoisophthalate (sip), which is a rigid and potentially tritopic anionic linker were chosen. We successfully obtained two new nickel CPs, namely, [Ni(oba)(dia)1.5(H2O)]·H2O, which is a rare (2D→ 3D) polycatenated array with (48.62) topology, and [Ni(Hsip)(dia)1.5(H2O)]·H2O which features a 2-fold interpenetrating © 2012 American Chemical Society

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EXPERIMENTAL SECTION

General Information. Solvents were dried with standard procedures. Starting chemicals were purchased from commercial source and used as received. The infrared spectra were acquired from a Received: April 24, 2012 Revised: June 7, 2012 Published: June 7, 2012 3758

dx.doi.org/10.1021/cg300559p | Cryst. Growth Des. 2012, 12, 3758−3765

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Table 1. Crystallographic Data empirical formula formula weight crystal system space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 T, K D, g/cm3 Z no. of unique data no. of params refined R1a [I > 2σI] R2b (all data) a

1

2

3a

3b

3c

C24H15CdN2O5 523.78 triclinic Pi ̅ 7.694(3) 12.172(5) 12.337(5) 80.08(3) 75.94(3) 86.75(3) 1103.9(8) 150(2) 1.576 2 5712 289 0.0500 0.1356

C29H18CdN4O6·3H2O 684.93 monoclinic C2/c 16.7010(3) 12.0214(2) 26.9900(6) 90 96.448(2) 90 5384.49(18) 150(2) 1.680 8 6976 406 0.0433 0.1055

C76H52Cd3N12O16S2 1790.62 triclinic Pi ̅ 9.6879(10) 13.4937(15) 14.8574(16) 80.996(8) 72.805(7) 83.954(7) 1829.0(3) 150(2) 1.626 1 9635 493 0.0503 0.1170

C76H52Co3N12O16S2 1630.21 triclinic Pi ̅ 9.388(3) 13.353(5) 14.644(5) 80.535(8) 72.638(6) 84.240(7) 1725.8(11) 150(2) 1.569 1 7144 493 0.0675 0.1996

C76H52Ni3N12O16S2 1629.55 triclinic Pi ̅ 9.393(2) 13.330(3) 14.569(4) 80.389(19) 73.261(17) 83.787(18) 1719.0(7) 150(2) 1.574 1 8873 493 0.0709 0.1917

R1 = Σ(||Fo| − |Fc||)/Σ|Fo|. bR2 = [Σ(||Fc|2 − |Fc|2)2/Σ(Fo2)]1/2. 2726 (w), 2381 (s) 2354 (s), 2316 (w), 1714 (w), 1650 (w), 1575 (w), 1504 (s), 1375 (s br), 1332 (w), 1197 (s br), 1108 (s), 1085 (s), 1029 (s), 993 (w), 962 (w), 935 (s), 912 (w), 894 (w), 816 (w), 863 (w), 833 (s), 779 (s), 732 (s). 684 (s), 653 (s), 632 (w), 609 (s). Synthesis of [Co3(2-stp)2(dia)6(H2O)2] (3b). Co(NO3)2·6H2O (0.281 g, 0.966 mmol), dia (0.100 g, 0.322 mmol) and NaH2(2-stp) (0.173 g, 0.644 mmol) were placed in H2O (5 mL) in a 20 mL Teflonlined stainless reactor. The reactor was tightly closed and heated up according to the same temperature program as that of 1. Red crystals were separated by filtration, washed with deionized water, dichloromethane, and DMF and dried in air. Yield: 0.077 g, 44%. Anal. Calcd for C76H52Co3N12O16S2: C, 55.99; H, 3.21; N, 10.31. Found: C, 55.92; H, 3.07; N, 9.96. IR (KBr/pellet cm−1): 3174 (br), 1733 (w), 1602 (s), 1527 (s) 1524 (s), 1450 (s), 1446 (s), 1390 (s), 1340 (s), 1294 (w), 1255 (s), 1193 (s), 1132 (s), 1087 (s), 1041 (s), 954 (w br), 875 (w), 842 (s), 788 (s), 757 (s), 676 (w), 669 (s), 572 (w), 528 (w), 476 (w), 457 (w). Synthesis of [Ni3(2-stp)2(dia)6(H2O)2] (3c). Ni(NO3)2·6H2O (0.281 g, 0.966 mmol), dia (0.100 g, 0.322 mmol) and NaH2(2-stp) (0.173 g, 0.644 mmol) were placed in H2O (5 mL) in a 20 mL Teflon-lined stainless reactor. The reactor was tightly closed and heated up according to the same temperature program as that of 1. Green crystals were separated by filtration, washed with deionized water, dichloromethane, and DMF, and dried in air. Yield: 0.092 g, 53%. Anal. Calcd for C76H52Ni3N12O16S2: C, 56.02; H, 3.22; N, 10.31. Found: 55.51; H, 3.35; N, 10.14. IR (KBr/pellet cm−1): 3180 (br), 3114 (s), 1600 (s), 1544 (s) 1446 (s), 1427 (s), 1388 (s), 1340 (w), 1294 (w), 1257 (w), 1255 (s), 1191 (s), 1132 (s), 1087 (s), 1045 (s), 950 (w br), 887 (s), 873 (w), 844 (s), 794 (s), 755 (w), 730 (s), 632 (w), 644 (s), 570 (s), 505 (w). X-ray Diffraction Studies. Single-crystal X-ray diffraction data were collected on a Bruker APEX II equipped with a CCD area detector and a graphite monochromator utilizing Mo Kα radiation (λ = 0.71073 Å) at 150(2) K. The unit cell parameters were obtained by least-squares refinement. The data were integrated via SAINT.32 Lorentz and polarization effect and multiscan absorption corrections were applied with SADABS.33 The structures were solved by direct methods and refined by full-matrix least-squares methods against F2 with SHELXTL.34 All non-H atoms were refined anisotropically. All H-atoms, except those of water, were fixed at calculated positions and refined with the use of a riding model. H-atoms upon O7 in 2 were located in a different Fourier map. Some H-atoms of the water solvent molecule in 2 was not located but included in the molecular formula. CCDC-872940 (1), -872941 (2), -872942 (3a), −874313 (3b), and

Varian Cary 640 infrared spectrophotometer. The emission spectra were measured on a Varian Cary Eclipse spectrometer. Elemental analyses were performed on a Thermo Flash 2000 CHN-O elemental analyzer. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer Pyris 6 thermogravimetric analyzer under flowing N2 gas (20 mL/min), and the heating rate was 20 °C/min. Synthesis of [Cd(oba)(dia)0.5] (1). Cd(NO3)2·4H2O (0.198 g, 0.644 mmol), dia (0.100 g, 0.322 mmol), and H2oba (0.0833 g, 0.322 mmol) were placed in H2O (10 mL) in a 20 mL Teflon-lined stainless reactor. The reactor was tightly closed and heated up to 140 °C in 12 h and maintained at the same temperature for 60 h. Afterward, the reaction mixture was allowed to cool down to room temperature at a rate of −5.83 °C/h. Red-orange crystals were separated by filtration, washed with deionized water, dichloromethane, and DMF, and dried in air. Yield: 0.085 g, 50%. Anal. Calcd for C24H15CdN2O5: C, 55.03; H, 2.88; N, 5.34. Found: C, 54.69; H, 3.01; N, 5.22. IR (KBr/pellet cm−1): 3536 (s br), 2370 (w), 1600 (s br), 1521 (s br), 1409 (s br), 1340 (w), 1268 (w), 1234 (s), 1159 (m), 1105 (m), 1081 (s), 1033 (m), 1012 (m), 937 (m), 881 (s), 854 (w), 854 (w), 806 (w), 777 (s), 732 (w), 663 (s), 647 (m), 620 (w). Synthesis of [Cd(Hbtc)(dia)]·3H2O (2). Cd((NO3)2·4H2O (0.0994 g, 0.322 mmol), dia (0.100 g, 0.322 mmol) and H3btc (0.0677 g, 0.322 mmol) were placed in H2O (10 mL) in a 20 mL Teflon-lined stainless reactor. The reactor was tightly closed and heated up to 140 °C in 12 h and maintained at the same temperature for 72 h. Afterward, the reaction mixture was allowed to cool down to room temperature at a rate of −11.6 °C/h. Yellow crystals were separated by filtration, washed with deionized water, dichloromethane, and DMF and dried in air. Yield: 0.0937 g, 43%. Anal. Calcd for C29H24CdN4O9: C, 50.85; H, 3.53; N, 8.18. Found: C, 51.04; H, 3.27; N, 8.15. IR (KBr/pellet cm−1): 3484 (s br), 3158 (w), 2894 (w), 2667 (w) 2364 (s), 2331 (w), 2223 (w), 1857 (w), 1731 (s), 1698 (s br), 1612 (s br), 1552 (s), 1500 (s), 1442 (s), 1413 (w), 1367 (s br), 1297 (w br), 1213 (w), 1172 (s br), 1105 (s br), 1033 (s), 933 (s br), 858 (w br), 744 (s br), 700 (s), 657 (s). 588 (s), 559 (s), 520 (s). Synthesis of [Cd3(2-stp)2(dia)6(H2O)2] (3a). Cd(NO3)2·4H2O (0.298 g, 0.966 mmol), dia (0.100 g, 0.322 mmol) and NaH2(2-stp) (0.173 g, 0.644 mmol) were placed in H2O (5 mL) in a 20 mL Teflonlined stainless reactor. The reactor was tightly closed and heated up according to the same temperature program as that of 1. Orange crystals were separated by filtration, washed with deionized water, dichloromethane, and DMF and dried in air. Yield: 0.062 g, 42%. Anal. Calcd for C76H52Cd3N12O16S2: C, 50.98; H, 2.92; N, 9.39. Found: C, 50.60; H, 3.06; N, 9.35. IR (KBr/pellet cm−1): 3496 (br), 2859 (w), 3759

dx.doi.org/10.1021/cg300559p | Cryst. Growth Des. 2012, 12, 3758−3765

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−874314 (3c) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/ cif. Powder X-ray diffraction (PXRD) measurements were recorded on Shimadzu Lab-X XRD-6000 diffractometer with Cu Kαλ = 1.54060 Å. Topological Analyses. Topological analyses were performed using TOPOS software. The new topology in 2 (standard simplification) has been deposited in TTD database as hml1.

mode, align Cd atoms in chains along the direction of the a-axis with alternating Cd···Cd distances of 3.779(2) and 4.039(2) Å, and further connect them into 2D layers parallel to the ab plane (Figure S6, in Supporting Information). These layers are linked by the dia ligands along the c-axis to form a 3D coordination network (Figure 2a). To understand the topology of this framework, the dia ligands in 1 can be considered as simple linkers. Each ditopic oba ligand, operating in μ2-η2:η1-bridging mode to connect four Cd atoms, can be regarded as a 4connected node. Each Cd atom connects four oba ligands and one dia ligand and can therefore be considered as a 5connected node. Thus, the coordination network in 1 can be simplified as a 4,5-connected binodal net. Under this simplification scheme, topological analysis by the TOPOS software36 reveals a tcs topology of the underlying net of 1. The point symbol37 is (44.62)(44.66) and the vertex symbols for the 4- and 5-connected nodes are (4.4.4.4.6.6) and (4.4.4.4.6.6.6.6.102.102), respectively. CPs with such 3D framework are rarely found in the literature. The only examples are the recently reported structures: [Cd2(pht)2(bpfp)(H2O)2];38 [Cd2(hmph)2(4-bpfp)], where pht = phthalate, hmph = homophthalate and bpfp = bis(4-pyridylformyl)piperazine);39 {[Zn2(Hpyro) 2(H2O) 2(H2-3-bpmp)]·H2O}, where [3-bpmp = bis(3-pyridylmethyl)piperazine and H4pyro = pyromellitic acid];40 {[La(trans-DAM)(cis-DAM)(H2O)2](ClO4)·3H2O}, where HDAM = N,N′-diacetic acid imidazolium);41 and [Ba(C2O4)(H2O)2].42 Structural Description of [Cd(Hbtc)(dia)]·3H2O (2). The Cd atom in 2 is also seven-coordinated, but unlike that of 1, the coordination geometry of the metal center can be described as a distorted pentagonal pyramid (Figure 3). Such metal coordination geometry is commonly found in the cadmium CPs reported in the literature.43−46 The coordination sphere consists of five O atoms from three Hbtc ligands, and two cis N atoms from two dia ligands. N(4) and O6#2 are the axial atoms with N···Cd···O bond angle of 175.5(1)°. The N···Cd···N angle is almost perpendicular [91.0(1)°]. The μ-O6 atoms from a pair of Hbtc ligands link two Cd atoms together to form a dimeric cluster unit with a Cd···Cd distance of 4.0216(4) Å. The center of this cluster unit sits on a special position of inversion center and can be regarded as a secondary building unit (SBU) of the framework (vide infra). Only double deprotonation of H3btc occurred. There is a proton attached to the carboxylate O3 atom and its C28−O3 single bond distance is 1.278(4) Å, which is considerably longer the C28−O4 double bond distance of 1.251(5) Å. This carboxylate group is not involved in metal coordination but rather hydrogen bonding interactions. In fact, each Hbtc ligand connects to three Cd atoms with the carboxylate group involving O5 and O6 connecting to two of them (μ2-η2:η1-bridging mode) and that involving O1 and O2 coordinating to one Cd atom only (η2-chelation mode). As a result of these carboxylate coordinations, infinite 1D ladder chains of Cd atoms are formed running approximately along the [110] direction (Figure S7). These 1D chains running parallel to the ab plane form stacks, with the upper and lower stacks containing chains that run at right angles to those in the middle stack. These stacks, arranged in an AB fashion, are further bridged by the dia ligands to form a 3D coordination network. To understand the topology of the 3D coordination network in 2, the Hbtc ligand can be considered as a 3-connected node connecting three Cd atoms, each Cd atom as a distorted 5connected node, and the dia ligand as a simple linker. Based on

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RESULTS AND DISCUSSION Synthesis and Characterization of CPs. The novel compound, [Cd(oba)(dia)0.5] (1), was prepared under hydrothermal condition from a mixture of Cd(NO3)2·4H2O, dia, and H2oba. [Cd(Hbtc)(dia)]·3H2O (2) and [M3(2stp)2(dia)6(H2O)2] (3) were similarly prepared by replacing the H2oba with H3btc and NaH2(2-stp), respectively. Each compound was characterized by elemental analysis, IR spectroscopy, PXRD studies, and X-ray crystallographic analysis (Table 1−3). As shown in Figures S1−5 in the Supporting Table 2. Important Bond Distances (Å) and Angles (deg) of 1 and 2 1 Cd1−N1 Cd1−O1 Cd1−O2 Cd1−O1#1 Cd1−O3#2 Cd1−O3#4 Cd1−O4#2 N1−Cd1−O1 N1−Cd1−O1#1 N1−Cd1−O2 N1−Cd1−O3#2 N1−Cd1−O3#4 N1−Cd1−O4#2 O1−Cd1−O1#1 O1−Cd1−O4#2 O2−Cd1−O1 O2−Cd1−O1#1 O2−Cd1−O3#2 O2−Cd1−O3#4 O2−Cd1−O4#2 O3#2−Cd1−O1 O3#2−Cd1−O1#1 O3#2−Cd1−O3#4 O3#2−Cd1−O4#2 O3#4−Cd1−O1 O3#4−Cd1−O1#1 O3#4−Cd1−O4#2 O4#2−Cd1−O1#1

2 2.282(4) 2.469(4) 2.299(4) 2.531(4) 2.331(3) 2.394(3) 2.474(4) 88.8913 79.9813 121.1914 100.7813 86.5913 146.3913 72.2613 107.0812 54.6213 119.6113 131.6313 85.0913 91.6713 156.6513 88.4112 73.7713 54.4612 128.4612 155.3012 104.4712 77.2813

Cd1−N4 Cd1−N1#4 Cd1−O1 Cd1−O2 Cd1−O5#3 Cd1−O6#2 N1#4−Cd1−N4 N1#4−Cd1−O1 N1#4−Cd1−O2 N1#4−Cd1−O6#2 N4−Cd1−O1 N4−Cd1−O2 N4−Cd1−O6#2 O1−Cd1−O2 O1−Cd1−O6#2 O5#3−Cd1−N1#A O5#3−Cd1−N4 O5#3−Cd1−O1 O5#3−Cd1−O2 O5#3−Cd1−O6#2 O6#2−Cd1−O2

2.319(3) 2.291(3) 2.332(3) 2.498(3) 2.280(2) 2.382(2) 91.03(11) 142.23(10) 88.09(10) 91.29(9) 88.45(10) 83.88(10) 175.53(10) 54.30(9) 87.38(9) 129.29(10) 85.00(10) 88.28(9) 141.10(9) 96.47(8) 92.38(8)

Information, the phase purities of 1−3 were confirmed by comparing their PXRD patterns with those simulated from single-crystallographic studies. Structural Description of [Cd(oba)(dia)0.5] (1). As shown in Figure 1, the Cd atom is seven-coordinated with six O atoms from four oba ligands and one N atom from dia taking up the coordination sites. The coordination geometry at cadmium can be described as a distorted monocapped trigonal prism.35 The basal edge consists of O2 and O3#4, whereas O1, O3#2, O4#2, and N1 form the 4-atom plane, which is capped by O1#1. The two carboxylate groups of oba, functioning in μ2-η2:η1-bridging 3760

dx.doi.org/10.1021/cg300559p | Cryst. Growth Des. 2012, 12, 3758−3765

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Table 3. Important Bond Distances (Å) and Angles (deg) of 3a−c M1−N5#4 M1−N5 M1−O8 M1−O8#4 M1−O5#4 M1−O5 O5#4−M1−O5 O8−M1−O8#4 N5#4−M1−N5 N5#4−M1−O8#4 N5−M1−O8 N5#4−M1−O5#4 N5−M1−O5 O8#4−M1−O5#4 O8−M1−O5 O8#4−M1−O5 O8−M1−O5#4 N5#4−M1−O5 N5−M1−O5#4 N5−M1−O8#4 N5#4−M1−O8

3a

3b

3c

2.293(3) 2.293(3) 2.297(3) 2.297(3) 2.384(3) 2.384(3) 180.00(14) 180 180.00(15) 80.66(12) 80.66(12) 87.79(12) 87.79(12) 90.43(11) 90.43(11) 89.57(11) 89.57(11) 92.21(12) 92.21(12) 99.34(12) 99.34(12)

2.124(3) 2.123(3) 2.104(3) 2.104(3) 2.164(3) 2.164(3) 180 180 179.999(1) 83.67(12) 83.67(12) 88.37(12) 88.37(12) 89.75(11) 89.75(11) 90.25(11) 90.25(11) 91.63(12) 91.63(12) 96.33(12) 96.33(12)

2.065(4) 2.065(4) 2.087(4) 2.087(4) 2.177(4) 2.177(4) 179.999(1) 180.00(8) 180.00(19) 84.85(17) 84.85(17) 88.44(16) 88.44(16) 90.41(14) 90.41(14) 89.59(14) 89.59(14) 91.56(16) 91.56(16) 95.15(17) 95.15(17)

M2−N1 M2−N3 M2−O1 M2−O2 M2−O3 M2−O4 N1−M2−N3 N1−M2−O1 N1−M2−O2 N3−M2−O1 N3−M2−O2 O2−M2−O1 O3−M2−N1 O3−M2−N3 O3−M2−O1 O3−M2−O2 O4−M2−N1 O4−M2−N3 O4−M2−O1 O4−M2−O2 O4−M2−O3

3a

3b

3c

2.274(4) 2.323(4) 2.335(3) 2.334(3) 2.224(3) 2.204(3) 93.72(15) 94.31(12) 93.73(13) 82.31(12) 165.32(13) 84.53(11) 170.09(12) 94.57(13) 81.46(10) 77.01(11) 87.76(13) 92.65(14) 174.66(12) 100.27(12) 97.25(11)

2.092(4) 2.118(4) 2.131(3) 2.145(3) 2.025(3) 2.045(3) 91.61(14) 92.93(12) 91.86(13) 85.05(12) 171.54(13) 87.08(11) 172.14(13) 96.09(13) 86.19(11) 80.30(12) 90.28(13) 92.02(13) 175.70(11) 95.68(12) 91.02(11)

2.056(4) 2.057(4) 2.093(4) 2.114(4) 2.000(4) 2.039(4) 92.40(19) 91.92(16) 90.59(17) 86.86(16) 174.12(18) 87.98(15) 172.19(16) 95.37(17) 87.80(14) 81.60(16) 89.60(16) 93.61(17) 178.39(15) 91.48(15) 90.63(15)

(imidazol-1-ylmethyl)benzene) is a recent example of a CP with rob topology.48 Structural Description of [M3(2-stp)2(dia)6(H2O)2] (3). The cadmium (3a), cobalt (3b), and nickel (3c) compounds are isostructural. Therefore we described the structure of 3a representatively. In this structure, the asymmetry unit contains two independent Cd atoms with the Cd1 atom residing on an inversion center. Unlike for 1 and 2, the two independent Cd atoms in 3a adopt an octahedral coordination geometry (Figure 6).43,44 The Cd1 atom is ligated by two trans-N atoms of two dia ligands, and four carboxylate O atoms from four 2-stp ligands. Contrastingly, the Cd2 atom is ligated by two cis-N atoms of two dia ligands, and two cis-carboxylate O atoms of two 2-stp ligands. An aqua ligand and a sulfonate O atom in cis disposition complete the coordination sphere. Whereas structures 1 and 2 featured μ2-η2:η1-bridging carboxylate groups, the two carboxylate groups of the 2-stp ligand in 3a operate in μ2-η1:η1-bridging mode only, linking three Cd atoms together to form a trimeric SBU (vide infra). The sulfonate O1 and carboxylate O3 are coordinated to Cd2 in a bidentate fashion. Thus, each 2-stp connects to four Cd atoms via O4, O5, O8, and the bidentate coordination of O1 and O3. The trimeric unit forms infinite 1D chains along the a-axis (Figure S8), with adjacent chains being connected by strong classical hydrogen bonds between the aqua ligands and uncoordinated sulfonate O6 and O7 atoms (Table 4), forming layers parallel to the ac plane. These layers stack in AAA fashion and are connected by dia ligands along the b-axis to form a 3D coordination network. As clearly depicted in Figure 7, infinite 1D channels are present along the a-axis. However, the resulting solvent-accessible space is just 51.9 Å3 (2.8% per unit cell volume) according to PLATON.49 In the middle of these channels are strong hydrogen bonds, which provide extra stabilization for the 3D network. To analyze the topology of the 3D framework, nodes simplification was applied. Since each 2-stp ligand connects to four Cd atoms, it can be considered as a 4-connected node. Regarding dia as a simple linker, each Cd1 atom can connect to

Figure 1. Local coordination environment in 1 with thermal ellipsoids shown at 50% probability. Symmetry code: #1 = −x, −y, 1 − z; #2 = −1 + x, −1 + y, z; #3 = −1 − x, −y, 1 − z; #4 = −x, 1 − y, 1 − z.

such simplification, topological analysis by TOPOS reveals the new 3D (3,5)-connected binodal topology of 2 (Figure 4). This net does not appear in TOPOS, nor in the RCSR database. The point symbol for the 3D net is (42.63.85)(42.6) and the vertex symbols for the 3- and 4-connected nodes are (4.4.6) and (4.4.6.6.84.84.84.84.812.*), respectively. Alternatively, the dimeric [Cd2(CO2)4] unit can be considered as a SBU and the dia ligand as a simple connector. Based on such cluster simplification, the underlying net of 2 shows a uninodal 6connected rob topology (Figure 5). The vertex symbol for the cluster node is (4.4.4.4.4.4.4.4.64.64.68.68.68.68.*) and the point symbol for the rob net is (48.66.8). Examples of CPs with 6connected rob topology are relatively unusual in comparison with 6-connected nets based on pcu topology.47 {[Mn(Fbix)3]·(ClO4)2·CHCl2} (Fbix =2,3,5,6-tetrafluoro-1,4-bis3761

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Figure 2. (a) Polyhedral representation for the 3D coordination network in 1. (b) Network perspective of the tcs topology in 1. The 4-connected oba and 5-connected Cd nodes are drawn in red and yellow spheres, respectively.

Based on such simplification, the topological analysis of the 4,6,6-connected net using TOPOS software, revealed a rare 3D trinodal net topology of 3a (Figure 8a). The point symbol is (4.64.8)2(43.63)2(44.610.8) and the vertex symbol for the 4connected node is (4.4.4.63.6.6). Those for the Cd1 and Cd2 are (4.4.4.4.6.6.6.6.64.64.64.64.*.*.*) and (4.86.6.65.6.65), respectively. To our knowledge, the only example of such a topology was observed for the 4,4,6T107 underlying net of coordination polymer, [Zn3(C14H8O4)3(C12H10N2)2].50 Alternatively, the trimeric [Cd3(2-stp)2(H2O)2] unit shown in Figure 9 can be considered as a secondary building unit (SBU), which consists of one Cd1 and two Cd2 atoms. Based on such cluster simplification, the underlying net of 3a can be described as a uninodal pcu topology, which is commonly observed for CPs (Figure 8b).47 The point symbol for pcu net is (412.63} and the vertex symbol for the cluster node is (4.4.4.4.4.4.4.4.4.4.4.4.*.*.*). Intriguingly, when the classical hydrogen bonds along the a-axis are also taken into consideration (see Figure 7), the cluster node becomes 8connected, giving rise to an ilc net topology with point symbol (424.5.63) (Figure 8c). Reports on CPs or MOFs with ilc topology are extremely scarce in the literature.51−53 Role of Metal Ions and Bridging Ligands. Diverse coordination geometries at Cd atoms are achieved with different coordination modes of aromatic carboxylate (μ2-

Figure 3. Local coordination environment in 2 with thermal ellipsoids shown at 50% probability. Symmetry code: #1 = −x, −y, 1 − z; #2 = 0.5 − x, −0.5 − y, 1 − z; #3 = −0.5 + x, 0.5 + y, z; #4 = 0.5 − x, −0.5 + y, 1.5 − z.

four 2-stp ligands and two Cd atoms, and each Cd2 atom can connect to two Cd atoms and two 2-stp ligands. Thus Cd1 and Cd2 can be treated as 6- and 4-connected nodes, respectively.

Figure 4. Polyhedral representation of the 3D coordination network in 2. 3762

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Figure 5. (a) Network perspective of the (42.63.85)(42.6) topology in 2 (standard representation). The 3-connected btc node and 5-connected Cd nodes are drawn in red and yellow spheres, respectively. (b) Network perspective of rob topology in 2 (cluster representation). The 6-connected SBUs are shown in purple color.

Figure 7. Polyhedral representation of the 3D coordination network in 3a. Classical hydrogen bonds are shown in broken red lines.

different carboxylate ligands (oba, Hsip, and 2-stp), three nickel CP topologies were achieved. However, the atoms at inner coordination spheres in [Ni(oba)(dia)1.5(H2O)]·H2O and [Ni(Hsip)(dia)1.5(H2O)]·H2O are essentially the same, only the difference in the relative orientation of the resultant common square-pyramidal 5-connected nodes leads to the two topologically different structures (vide supra). All these results imply that it is possible to produce a wider range of topological frameworks by varying the carboxylate structures when a cadmium ion (the second row of transition metals in general) is used. This difference can be attributed to the ionic size effects of metal ions (6- vs 7- coordination, carboxylate bridging vs chelation modes, cluster formation, etc). Despite a large variation in the carboxylate ligand structure, a common feature in these frameworks is the alignment of Cd atoms in sheets by the bridging aromatic carboxylates. These sheets are further bridged by dia ligands to furnish their 3D frameworks. Notably, in the frameworks of 1−3, the anthracenyl rings of the bulky dia ligand are neatly aligned along the same direction, minimizing unfavorable steric hindrance. The noninterpenetrating nature of these frameworks may also be attributed to the use of such bulky ligands. Thermal and Emission Studies. TGA was conducted to understand the thermal stability of 1, 2, and 3a (Figure S9). Among them, 1 is most thermally robust. The network in 1 is stable up to ca. 430 °C but those in 2 and 3a commence to decompose at ∼348 and 292 °C, respectively. The least stability of 3a can be attributed to the facile thermal decomposition of sulfonate group. The emission properties of 1, 2, and 3a at ambient temperature, together with the free ligands, in solidstate were studied. The free H3btc ligand is weakly emissive showing a band at 380 nm (λex = 334 nm), attributable to the π* → n transitions.54 The free H2oba ligand is emissive with

Figure 6. Local coordination environment in 3a with thermal ellipsoids shown at 50% probability. Symmetry code: #1 = −x, −y, −z; #2 = −1 + x, y, z; #3 = 1 − x, 1 + y, −z; #4 = −x, 1 − y, 1 − z.

Table 4. Classical Hydrogen Bonds in 3a−c (Å and deg)a D−H···A

d(D−H)

d(D···A)

∠(DHA)

2.05 2.02

2.751(4) 2.823(4)

161.6 170.6

1.97 1.89

2.777(4) 2.824(4)

172.6 156.4

1.83 2.02

2.767(5) 2.885(6)

166.5 126.6

d(H···A) 3a

O2−H39···O6$A O2−H40···O7$B

0.73 0.81

O2−H39···O6$A O2−H40···O7$B

0.81 0.99

O2−H39···O6$A O2−H40···O7$B

0.96 1.18

3b

3c

Symmetry transformations used to generate equivalent atoms: #1: − x, −y + 1, −z; #2: x + 1, y, z. a

η2:η1-, μ2-η1:η1-bridging mode, and η2-chelation mode) and nitrogen coordination (single N atom coordination in 1, cis-N atom coordination in 2, and cis- and trans-N atom coordination in 3a). These include the capped trigonal prism in 1, the pentagonal bipyramid in 2, and the octahedron in 3a. This is in sharp contrast to 3c and our previously reported nickel CPs, [Ni(oba)(dia)1.5(H2O)]·H2O and [Ni(Hsip)(dia)1.5(H2O)]·H2O, which exhibit only the octahedron coordination geometry around the Ni atoms. Using three 3763

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Figure 8. (a) Network perspective of the (4.64.8)2(43.63)2(44.610.8) topology in 3a (standard representation). The 4-connected 2-stp, 4-connected Cd and 6-connected Cd nodes are drawn in red, green, and yellow spheres, respectively. (b) Network perspective of pcu topology in 3a (cluster representation). The 6-connected SBUs are shown in purple color. (c) Network perspective of ilc topology in 3a (cluster representation with classical hydrogen bonds taken into consideration). The 8-connected SBUs are shown in purple color.

coordination geometries at cadmium are very different. A variety of carboxylate structures allowed for the assembly of 3D frameworks with unusual topologies, including the rare tcs topology of 1, the unprecedented topology of (42.63.85)(42.6) of 2, and the unusual topology of (4.64.8)2(43.63)2(44.610.8) of 3. Based on SBUs, the underlying nets of 2 and 3 can be alternatively described as rob and pcu, respectively. The pcu net of 3 transforms into a highly uncommon ilc net when classical hydrogen bonds are also taken into consideration. This work demonstrates the importance of the metal ion effect, and the rich potential of using bulky bis(imidazole) ligand and aromatic carboxylates as connecting ligands, in the construction of 3D CPs with intriguing topologies.

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Figure 9. Trinuclear [Cd3(2-stp)2(H2O)2] SBU unit in the pcu net of 3.

ASSOCIATED CONTENT

S Supporting Information *

the emission band located at about 318 nm upon excitation at 303 nm.29 The emission maxima for the free NaH2(2-stp) ligand are at 473 and 515 nm.55 The emission intensities from these carboxylic acids are much weaker than that from the dia ligand, which exhibits a very intense emission band at 479 nm upon excitation at 336 nm.27 Previously, we showed that [Ni(oba)(dia)1.5(H2O)]·H2O and [Ni(Hsip)(dia)1.5(H2O)]·H2O bearing some of these ligands are, however, nonemissive, which can be related to the quenching behavior of the paramagnetic octahedral Ni(II) ions.27 In the case of diamagnetic Cd(II) compounds bearing the similar set of ligands, 1 is very weakly emissive (see Figure S10, in Supporting Information) and 2 and 3a did not obviously display emission, implying that the significant fluorescence quenching should be related to the intramolecular energy transfer in their 3D frameworks.

PXRD patterns, TGA traces, and additional drawings for 1−3, and X-ray crystallographic information files (CIF) for compounds 1−3. This information is available free of charge via the Internet at http://pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +886 4 7232105, ext. 3523. Fax: +886 4 7211190. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the National Science Council of Taiwan for financial support of this work. We also thank the National Center for High-performance Computing of Taiwan for computing time and financial support of the Conquest software. We thank Dr. Amitabha Datta for the partial preparation of 3b.

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CONCLUSIONS In sharp contrast to the nickel structures 3c, [Ni(oba)(dia) 1.5 (H 2O)]·H 2 O, and [Ni(Hsip)(dia) 1.5 (H 2 O)]·H 2 O, which share the same octahedron coordination geometry, the 3764

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