MetalâOrganic Coordination Polymers Generated from Chiral

DOI: 10.1021/cg900676x

Metal-Organic Coordination Polymers Generated from Chiral Camphoric Acid and Flexible Ligands with Different Spacer Lengths: Syntheses, Structures, and Properties

2009, Vol. 9 4872–4883

Xiao-Qiang Liang, Dong-Ping Li, Xin-Hui Zhou, Yan Sui, Yi-Zhi Li, Jing-Lin Zuo,* and Xiao-Zeng You* Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China Received June 18, 2009; Revised Manuscript Received August 27, 2009

ABSTRACT: A new family of coordination polymers, [{Cd(D-ca)(bte)} 3 H2O]n (1, D-H2ca = D-camphor acid, bte = 1,2bis(1,2,4-triazol-1-yl)ethane), [Cd4(D-ca)4(btp)2(H2O)4]n (2, btp=1,3-bis(1,2,4-triazol-1-yl)propane), [{Cd(D-ca)(btb)1.5} 3 3H2O]n (3, btb = 1,4-bis(1,2,4-triazol-1-yl)butane), [{Cd4(D-ca)4(bth)4} 3 2H2O]n (4, bth = 1,6-bis(1,2,4-triazol-1-yl)hexane), and [{Cd(D-Hca)2(bth)(H2O)} 3 H2O]n (5), have been prepared under hydrothermal conditions and characterized by elemental analyses, IR, thermogravimetric and X-ray structural analyses. The bis(triazole) ligands with different spacer lengths exhibit conformational flexibility and lead to the generation of diversified architectures. Complex 1 shows a two-dimensional (2D) rectangular network with (4,4) topology. Complex 2 displays the chiral three-dimensional (3D) framework with (32 3 4) (3 3 84 3 12) (83) (4 3 8 3 10) topology. The 2D honeycomb motif with one-dimensional (1D) nanosized channels is found in compound 3. Compound 4 is a 2D parallelogram sheet with (4,4) topology. Compound 5 shows a chiral 1D fish-bone chain, and the chains are further connected through hydrogen-bonding interactions to form a 3D supramolecular framework. Their luminescent, second-order nonlinear optical and ferroelectric properties have been investigated in the solid state.

Introduction The design and syntheses of functional metal-organic coordination polymers have attracted increasing attention in the field of coordination chemistry.1 Currently, a particular focus on this topic is on chiral metal-organic coordination polymers by virtue of their potential applications in enantioselective catalysis and separation, nonlinear optics, ferroelectrics, and magnetism.2-6 One of the most effective and direct approaches to prepare chiral metal-organic coordination polymers is to use enantiopure chiral ligands as starting materials. Among them, some naturally chiral carboxylate ligands, such as L-lactic acid, L-tartric acid, L-aspartic acid, L-glutamic acid, and D-camphoric acid, have been widely studied for chiral complexes.7-11 Recently, metal-organic coordination polymers constructed from mixed ligands of polycarboxylate groups and polyimine groups have been reported.12 However, chiral metal-organic coordination polymers with mixed ligands of naturally chiral polycarboxylate groups and polyimine groups have been less studied so far.13 For example, the reactions of zinc nitrate with D-camphoric acid and some rigid N-donor spacers form a series of homochiral and porous coordination polymers.14 The homochiral diamond networks are constructed from M2þ atoms, D-camphoric acid, and flexible 4,40 -trimethylenedipyridine.15 The flexible bis(pyridine), bis(imidazole), bis(triazole), and bis(tetrazole) ligands with different spacer lengths are useful for preparation of functional metal-organic coordination polymers.16-19 The characteristics of flexible bis(triazole) ligands are as follows: (1) Like the flexible bis(pyridine), the flexible bis(triazole) ligands can adopt different conforma-

tions on the basis of relative orientations of CH2 groups.20 (2) The flexible bis(triazole) ligands possess four potential coordination sites which connect metal ions to form high-dimensional frameworks. (3) Only a few coordination polymers of the flexible bis(triazole) ligands as the mixed ligands have been explored so far.21 In this paper, with the use of D-camphoric acid and different flexible bis(triazole) ligands as spacers, five new cadmium(II) coordination polymers, [{Cd(D-ca)(bte)} 3 H2O]n (1, D-H2ca = D-camphor acid, bte= 1,2-bis(1,2,4-triazol-1-yl)ethane), [Cd4(D-ca)4(btp)2(H2O)4]n Scheme 1. Molecular Structure of the Ligands Used in This Paper

*Corresponding authors. Tel.: þ86 25 83593893; fax: þ86 25 83314502; e-mail: [email protected]; [email protected]. pubs.acs.org/crystal

Published on Web 09/15/2009

r 2009 American Chemical Society

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Table 1. Crystallographic Data and Details of Refinements for Complexes 1-5 complexes

1

2

3

4

5

empirical formula Mr crystal system space group a (A˚) b (A˚) c (A˚) R (°) β (°) γ (°) V (A˚3) Z Dc (mg/m-3) μ (mm-1) θ range [ ° ] collected reflections unique reflections parameters F(000) T (K R1a, wR2b [I > 2σ(I)] R1a, wR2b [all data] GOF largest peak and hole (e 3 A˚-3) flack parameter

C16H24CdN6O5 492.81 orthorhombic Aba2 17.212(2) 13.6942(18) 18.955(2) 90 90 90 4467.6(10) 8 1.465 1.013 2.15 -26.00 11387 4288 273 2000 )291(2) 0.0471, 0.1098 0.0693, 0.1153 1.054 0.331, -1.043 0.01(5)

C54H84Cd4N12O20 1670.93 monoclinic P21 14.323(2) 11.679(3) 19.029(3) 90 91.131(3) 90 3182.6(11) 2 1.744 1.400 2.05-26.00 16039 11794 822 1688 291(2) 0.0522, 0.1167 0.0703, 0.1218 1.024 0.491, -0.855 0.04(3)

C22H38CdN9O7 653.01 monoclinic, C2/c 25.404(17) 17.119(11) 17.508(16) 90 102.505(16) 90 7433(10) 8 1.167 0.631 1.98-26.00 19619 7270 413 2696 291(2) 0.0419, 0.0809 0.0632, 0.0846 1.036 0.416, -1.024

C80H124Cd4N24O18 2159.63 monoclinic P21/c 19.941(12) 9.571(6) 13.145(8) 90 108.974(8) 90 2373(2) 1 1.512 0.960 2.16-26.00 12116 4648 296 1108 291(2) 0.0536, 0.1023 0.0762, 0.1063 1.033 0.790, -1.067

C30H50CdN6O10 767.16 triclinic P1 6.712(2) 12.100(4) 12.426(4) 113.727(4) 93.701(5) 100.604(5) 897.2(4) 1 1.420 0.669 1.81-26.00 4850 4126 430 400 291(2) 0.0479, 0.1155 0.0489, 0.1158 1.012 0.691, -0.841 0.01(4)

)

R1=Σ Fo| - |Fc /Σ|Fo|. b wR2=[Σw(|Fo2| - |Fc2|)2/Σw(|Fo2|)2]1/2. )

a

Table 2. Selected Bond Lengths (A˚) and Angles (°) for 1-5a Complex 1 N(1)-Cd(1) Cd(1)-O(1) Cd(1)-O(2) N(1)-Cd(1)-N(6b) N(6b)-Cd(1)-O(1) N(6b)-Cd(1)-O(3a) N(1)-Cd(1)-O(2) O(1)-Cd(1)-O(2) N(1)-Cd(1)-O(4a) O(1)-Cd(1)-O(4a) O(2)-Cd(1)-O(4a)

2.074(5) 2.299(6) 2.425(5) 89.2(2) 91.9(2) 108.1(2) 108.9(2) 54.9(2) 130.7(2) 98.2(2) 98.1(1)

Cd(1)-O(2) Cd(1)-O(6a) Cd(1)-O(1) Cd(1)-N(2b) Cd(2)-O(8) Cd(2)-O(18) Cd(2)-O(7) Cd(3)-O(14a) Cd(3)-O(19) Cd(3)-O(9) Cd(4)-N(6d) Cd(4)-O(20) Cd(4)-O(16) O(2)-Cd(1)-O(6a) O(6a)-Cd(1)-O(17) O(6a)-Cd(1)-N(1) O(2)-Cd(1)-O(1) O(17)-Cd(1)-O(1) O(2)-Cd(1)-O(5a) O(17)-Cd(1)-O(5a) O(1)-Cd(1)-O(5a) O(6a)-Cd(1)-N(2b) N(1)-Cd(1)-N(2b) O(5a)-Cd(1)-N(2b) O(4)-Cd(2)-N(7) O(4)-Cd(2)-O(18) N(7)-Cd(2)-O(18) O(8)-Cd(2)-O(3) O(18)-Cd(2)-O(3)

2.147(5) 2.229(5) 2.416(6) 2.596(7) 2.242(5) 2.366(5) 2.415(6) 2.310(5) 2.328(5) 2.537(6) 2.212(6) 2.310(6) 2.351(5) 154.4(2) 86.8(2) 119.3(2) 50.9 (2) 138.7(2) 141.9(2) 128.5(2) 91.2 (2) 80.8(2) 158.3(2) 117.2(2) 92.8(2) 109.0(2) 92.0(2) 122.7(2) 82.5(2)

Cd(1)-N(6b) Cd(1)-O(3a) Cd(1)-O(4a) N(1)-Cd(1)-O(1) N(1)-Cd(1)-O(3a) O(1)-Cd(1)-O(3a) N(6b)-Cd(1)-O(2) O(3a)-Cd(1)-O(2) N(6a)-Cd(1)-O(4a) O(3a)-Cd(1)-O(4a)

2.229(5) 2.323(5) 2.471(5) 131.1(2) 78.0(2) 145.8(2) 146.5(2) 103.2(1) 90.0(2) 55.7(2)

Cd(1)-O(5a) Cd(1)-N(1) Cd(1)-O(17) Cd(2)-O(4) Cd(2)-N(7) Cd(2)-O(3) Cd(3)-O(10) Cd(3)-N(12) Cd(3)-O(13a) Cd(3)-N(11c) Cd(4)-O(12) Cd(4)-O(15) Cd(4)-O(11) O(2)-Cd(1)-O(17) O(2)-Cd(1)-N(1) O(17)-Cd(1)-N(1) O(6a)-Cd(1)-O(1) N(1)-Cd(1)-O(1) O(6a)-Cd(1)-O(5a) N(1)-Cd(1)-O(5a) O(2)-Cd(1)-N(2b) O(17)-Cd(1)-N(2b) O(1)-Cd(1)-N(2b) O(4)-Cd(2)-O(8) O(8)-Cd(2)-N(7) O(8)-Cd(2)-O(18) O(4)-Cd(2)-O(3) N(7)-Cd(2)-O(3) O(4)-Cd(2)-O(7)

2.570(6) 2.308(6) 2.262(6) 2.238(5) 2.285(6) 2.373(5) 2.190(6) 2.318(6) 2.424(5) 2.682(8) 2.283(5) 2.328(6) 2.393(6) 88.1(2) 85.9(2) 91.2(2) 132.0(2) 81.6(2) 53.7 (2) 83.5(2) 73.6(2) 81.2(2) 90.6(2) 155.2(2) 94.5(2) 94.4 (2) 55.3(18) 142.7(2) 101.0(2)

Complex 2

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O(8)-Cd(2)-O(7) O(18)-Cd(2)-O(7) O(10)-Cd(3)-O(14a) O(14a)-Cd(3)-N(12) O(14a)-Cd(3)-O(19) O(10)-Cd(3)-O(13a) N(12)-Cd(3)-O(13a) O(10)-Cd(3)-O(9) N(12)-Cd(3)-O(9) O(13a)-Cd(3)-O(9) O(14a)-Cd(3)-N(11c) O(19)-Cd(3)-N(11c) O(9)-Cd(3)-N(11c) N(6d)-Cd(4)-O(20) N(6d)-Cd(4)-O(15) O(20)-Cd(4)-O(15) O(12)-Cd(4)-O(16) O(15)-Cd(4)-O(16) O(12)-Cd(4)-O(11) O(15)-Cd(4)-O(11)

55.5(2) 132.2(2) 153.6(2) 84.6(2) 88.4(2) 124.5(2) 84.3(2) 52.9(2) 80.4(2) 91.8(2) 73.3(2) 85.9(2) 119.4(2) 86.5(2) 146.7(2) 84.1(2) 161.6(2) 55.5(2) 53.2(2) 83.6(2)

N(7)-Cd(2)-O(7) O(3)-Cd(2)-O(7) O(10)-Cd(3)-N(12) O(10)-Cd(3)-O(19) N(12)-Cd(3)-O(19) O(14a)-Cd(3)-O(13a) O(19)-Cd(3)-O(13a) O(14)-Cd(3)-O(9) O(19)-Cd(3)-O(9) O(10)-Cd(3)-N(11c) N(12)-Cd(3)-N(11c) O(13a)-Cd(3)-N(11c) N(6d)-Cd(4)-O(12) O(12)-Cd(4)-O(20) O(12)-Cd(4)-O(15) N(6d)-Cd(4)-O(16) O(20)-Cd(4)-O(16) N(6d)-Cd(4)-O(11) O(20)-Cd(4)-O(11) O(16)-Cd(4)-O(11)

123.2(2) 85.2(2) 121.7(2) 88.3(2) 91.3(2) 55.3(2) 143.6(2) 145.2(2) 123.0(2) 80.4(2) 157.7(2) 84.9(2) 93.6(2) 91.7(2) 118.5(2) 96.5(2) 104.2(2) 126.0(2) 129.0(2) 108.7(2)

Complex 3 Cd(1)-O(4a) Cd(1)-O(2) Cd(1)-N(1) Cd(1)-O(3a) O(4a)-Cd(1)-N(9) N(9)-Cd(1)-O(2) N(9)-Cd(1)-N(6a) O(4a)-Cd(1)-N(1) O(2)-Cd(1)-N(1) O(4a)-Cd(1)-O(1) O(2)-Cd(1)-O(1) N(1)-Cd(1)-O(1) N(9)-Cd(1)-O(3a) N(6a)-Cd(1)-O(3a) O(1)-Cd(1)-O(3a)

2.242(2) 2.312(2) 2.343(3) 2.611(2) 133.62(8) 135.43(7) 92.05(9) 85.77(8) 95.5(1) 138.88(6) 52.73(7) 80.23(9) 83.58(8) 82.12(9) 168.00(6)

Cd(1)-N(9) Cd(1)-N(6a) Cd(1)-O(1)

2.291(3) 2.317(3) 2.585(2)

O(4a)-Cd(1)-O(2) O(4a)-Cd(1)-N(6a) O(2)-Cd(1)-N(6a) N(9)-Cd(1)-N(1) N(6a)-Cd(1)-N(1) N(9)-Cd(1)-O(1) N(6a)-Cd(1)-O(1) O(4a)-Cd(1)-O(3a) O(2)-Cd(1)-O(3a) N(1)-Cd(1)-O(3a)

90.95(7) 92.84(8) 84.8(1) 88.70(9) 178.58(8) 84.74(8) 101.05(8) 51.64(7) 139.27(7) 96.77(9)

Cd(1)-N(4) Cd(1)-O(2a) Cd(1)-O(4) N(1)-Cd(1)-O(3) N(1)-Cd(1)-O(2a) O(3)-Cd(1)-O(2a) N(4)-Cd(1)-O(1a) O(2a)-Cd(1)-O(1a) N(4)-Cd(1)-O(4) O(2a)-Cd(1)-O(4)

2.288(4) 2.331(4) 2.441(3) 105.2(2) 94.1(2) 142.3(1) 85.3(2) 55.7(2) 153.4(1) 95.6(1)

Complex 4 Cd(1)-N(1) Cd(1)-O(3) Cd(1)-O(1a) N(1)-Cd(1)-N(4) N(4)-Cd(1)-O(3) N(4)-Cd(1)-O(2a) N(1)-Cd(1)-O(1a) O(3)-Cd(1)-O(1a) N(1)-Cd(1)-O(4) O(3)-Cd(1)-O(4) O(1a)-Cd(1)-O(4)

2.233(4) 2.294(4) 2.395(4) 102.6(2) 99.0(2) 108.1(1) 149.5(2) 102.4(1) 87.3(2) 54.4(1) 98.7(1) Complex 5

Cd(1)-O(2) Cd(1)-N(1) Cd(1)-O(1) Cd(1)-O(9) O(2)-Cd(1)-N(6a) N(6a)-Cd(1)-N(1) N(6a)-Cd(1)-O(5) O(2)-Cd(1)-O(1) N(1)-Cd(1)-O(1) O(2)-Cd(1)-O(6) N(1)-Cd(1)-O(6) O(1)-Cd(1)-O(6) N(6a)-Cd(1)-O(9) O(5)-Cd(1)-O(9) O(6)-Cd(1)-O(9)

2.302(8) 2.321(8) 2.419(6) 2.450(5) 96.9(3) 162.2(2) 102.0(3) 52.5(2) 102.3(2) 167.4(2) 90.2(3) 140.1(2) 81.9(2) 139.4(2) 87.4(2)

Cd(1)-N(6a) Cd(1)-O(5) Cd(1)-O(6)

2.316(8) 2.382(6) 2.428(8)

O(2)-Cd(1)-N(1) O(2)-Cd(1)-O(5) N(1)-Cd(1)-O(5) N(6a)-Cd(1)-O(1) O(5)-Cd(1)-O(1) N(6a)-Cd(1)-O(6) O(5)-Cd(1)-O(6) O(2)-Cd(1)-O(9) N(1)-Cd(1)-O(9) O(1)-Cd(1)-O(9)

86.0(3) 137.8(2) 87.1(3) 93.2(3) 88.8(2) 83.3(3) 53.7(2) 80.2(2) 81.4(2) 131.6(2)

a Symmetry codes: (a) -x þ 3/2, y, z þ 1/2; (b) x - 1/2, -y þ 1/2, z for 1; (a) x, y, z - 1; (b) -x, y - 1/2, -z - 1; (c) -x þ 1, y -1/2, -z; (d) x þ 1, y - 2, z þ 1 for 2; (a) -x þ 1/2, y þ 1/2, -z þ 1/2 for 3; (a) x, y þ 1, z for 4; (a) x - 2, y - 1, z - 1 for 5.

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Figure 1. (a) View of the coordination environment of Cd(II) in complex 1; thermal ellipsoids are drawn at the 50% probability level. Lattice water molecules and hydrogen atoms are omitted for clarity. (b) The conformation of the bte ligand. (c) Two dimensional layer (black, C; blue, N; red, O; green, Cd). (d) Schematic description of the (4,4) topological 2D rectangular network.

(2, btp = 1,3-bis(1,2,4-triazol-1-yl)propane), [{Cd(D-ca)(btb)1.5} 3 3H2O]n (3, btb=1,4-bis(1,2,4-triazol-1-yl)butane), [{Cd4(D-ca)4(bth)4} 3 2H2O]n (4, bth=1,6-bis(1,2,4-triazol-1yl)hexane), and [{Cd(D-Hca)2(bth)(H2O)} 3 H2O]n (5), have been successfully synthesized and structurally characterized (Scheme 1). The role of the conformation of flexible bis(triazole) ligands on the resulting structures of polymers are discussed. In addition, the luminescent, nonlinear optic, and ferroelectric properties of these complexes are investigated in the solid state. Experimental Section General Procedures. The bridging bis(triazole) ligands were synthesized according to the literature method.22 All other reagents and solvents were commercially available and used without further purification. Elemental analyses for C, H, and N were measured on a CHN-O-Rapid analyzer and an Elementar Vario MICRO analyzer. The IR spectra were performed on a Bruker Vector 22 FT-IR spectrometer by using KBr pellets in the 4000-450 cm-1 range. Thermogravimetric analyses were collected on a Perkin-Elmer Pyris 1 TGA analyzer from room temperature to 750 °C with a heating rate of 20 °C/min under nitrogen. X-ray powder diffraction (XRPD) analysis was performed by a Philips X-pert X-ray diffractometer at a scanning rate of 4°/min in the 2θ range from 5° to 60°, with graphite monochromatized Cu KR radiation (λ=1.5418 A˚). Photoluminescence analyses for the solid samples were recorded on

an AMINCO Bowman Series2 luminescence spectrometer. The second-order nonlinear optical intensity was estimated by measuring a powder sample relative to urea. A pulsed Q-switched Nd:YAG laser at a wavelength of 1064 nm was used to generate a SHG signal from powder samples. The backscattered SHG light was collected by a spherical concave mirror and passed through a filter that transmits only 532 nm radiation. Electric hysteresis loop of a pellet of powders was measured by the Premier II ferroelectric tester at room temperature. Preparation. [{Cd(D-ca)(bte)} 3 H2O]n (1). A mixture of Cd(NO3)2 3 4H2O (45 mg, 0.15 mmol), D-H2ca (30 mg, 0.15 mmol), bte (49 mg, 0.30 mmol), and NaOH (8 mg, 0.20 mmol) in H2O (8 mL) was placed in a Teflon-lined stainless steel container, heated at 140 °C for 75 h and cooled to room temperature. Colorless crystals of 1 were obtained and washed with distilled water. Yield: 30%. Anal. Calc. for C16H24N6O5Cd: C, 38.99; H, 4.91; N, 17.06. Found: C, 38.78; H, 4.72; N, 17.42%. IR (KBr, cm-1): 3417(br), 3112(m), 2968(m), 1525(vs), 1462(m), 1398(s), 1367(m), 1319(w), 1278(s), 1127(s), 1008(m), 991(m), 891(w), 798(w), 702(m), 678(m), 653(m). [Cd4(D-ca)4(btp)2(H2O)4]n (2). Compound 2 was prepared by a method similar to 1 except for using btp instead of bte. Yield: 42%. Anal. Calc. for C54H84N12O20Cd4: C, 38.81; H, 5.07; N, 10.06. Found: C, 38.64; H, 5.35; N, 10.21%. IR (KBr, cm-1): 3415(br), 2969(m), 1617(m), 1529(vs), 1458(m), 1400(m),1385(s), 1278(m), 1200(w), 1172(w), 1028(s), 986(m), 882(w), 816(m), 698(w), 661(w), 630(m). [{Cd(D-ca)(btb)1.5} 3 3H2O]n (3). Compound 3 was prepared by a method similar to 1 except for using btb instead of bte. Yield: 64%.

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Figure 2. (a) View of the coordination environments of Cd(II) in complex 2, thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity. (b) The conformation of the btp ligand (symmetry codes: (e) - 1, y þ 2, z; (f) -x þ 1, y þ 1/2, -z). (c) Three dimensional framework (black, C; blue, N; red, O; green, Cd). (d) Schematic description of the 3D network with (32 3 4) (3 3 84 3 12) (83) (4 3 8 3 10) topology. Anal. Calc. for C22H38N9O7Cd: C, 40.46; H, 5.86; N, 19.31. Found: C, 40.84; H, 5.71; N, 19.63%. IR (KBr, cm-1): 3416(br), 3133(w), 2962(m), 1524(vs), 1463(m), 1395(s), 1667(m), 1279(s), 1210(m), 1133(s), 1010(m), 984(m), 813(w), 797(w), 746(w), 676(m), 652(w). [{Cd4(D-ca)4(bth)4} 3 2H2O]n (4). Compound 4 was prepared by a method similar to 1 except for using bth instead of bte. Yield: 40%. Anal. Calc. for C80H124N24O18Cd4: C, 44.48; H, 5.79; N, 15.57. Found: C, 44.73; H, 5.89; N, 15.34%. IR (KBr, cm-1): 3421(br), 3093(s), 2943(s), 1549(vs), 1462(m), 1400(s), 1366(m), 1268(s), 1212(w), 1125(s), 986(w), 908(w), 811(w), 749(w), 679(m). [{Cd(D-Hca)2(bth)(H2O)} 3 H2O]n (5). A mixture of Cd(NO3)2 3 4H2O (45 mg, 0.15 mmol), D-H2ca (30 mg, 0.15 mmol), bth (49 mg, 0.30 mmol), NaOH (4.5 mg, 0.113 mmol) in H2O (8 mL) was placed in a Teflon-lined stainless steel container, heated at 140 °C for 75 h, and cooled to room temperature. The reaction mixture was filtered and left to stand at room temperature. Colorless plate-like crystals suitable for X-ray analysis were obtained by slow evaporation of the solvent for 1 day. Yield: 56%. Anal. calc. for C30H50N6O10Cd: C, 46.97; H, 6.57; N, 10.96. Found: C, 47.73; H, 6.28; N, 11.34%. IR (KBr, cm-1): 3406(br), 3137(m), 2966(s), 1721(s), 1676(s), 1533(vs), 1460(m), 1399(m), 1364(m), 1280(s), 1206(m), 1135(s), 985(w), 880(w), 806(w), 675(m), 648(w).

X-ray Structure Determinations. X-ray intensity data of 1-5 were collected on a Bruker SMART APEX CCD diffractometer23 using graphite monochromatized Mo KR radiation (λ = 0.71073 A˚) at 291(2) K. The raw data were reduced and corrected for Lorentz and polarization effect using the SAINT program and for absorption using the SADABS program. The structures were solved by direct methods and refined with the full-matrix least-squares technique using SHELXTL version 5.1.24 Anisotropic thermal parameters were assigned to all non-hydrogen atoms. All hydrogen atoms were placed in calculated positions and refined using a riding model. The crystallographic data are shown in Table 1. Selected bond lengths and bond angles are given in Table 2. The corresponding H-bond data are listed in Table S1 (Supporting Information).

Results and Discussion Syntheses. Compounds 1-4 were synthesized under similar hydrothermal conditions by the reaction of Cd(NO3)2, D-H2ca, the corresponding bis(triazole) ligands (bte, btp, btb, and bth) and NaOH in a mole ratio of 3:3:6:4 in water. However, compound 5 was synthesized under similar hydrothermal

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Figure 3. (a) View of the coordination environment of Cd(II) in complex 3; thermal ellipsoids are drawn at the 50% probability level. Lattice water molecules and hydrogen atoms have been omitted for clarity. (b) The conformations of the btb ligands (Symmetry code: (h) -x þ 1, -y þ 1, z). (c) 1-D double-stranded chain. (d) Two dimensional layer. (e) Schematic description of the (6,3) topological 2D network. (f) The 3D supramolecular architecture via C-H 3 3 3 N hydrogen bonds. (g) The 3D architecture with 1D nanosized channels (Lattice water molecules have been omitted for clarity). (h) The 3D framework’s vacancy occupied by the guest water molecules and the existence of hydrogen-bonding interactions (black, C; blue, N; red, O; green, Cd; light gray, H).

conditions by treating Cd(NO3)2, D-H2ca, bth, and NaOH in a mole ratio of 4:4:8:3 in water. Actually, the amount of NaOH used for the preparation of compound 4 was approximately twice as that for compound 5. The different amount of NaOH used ultimately affects the crystal structures of compounds 4 and 5. All products are stable in air at ambient temperature and insoluble in common solvents such as water, methanol, ethanol, acetone, and acetonitrile. Description of Crystal Structures. Structure of [{Cd(Dca)(bte)} 3 H2O]n (1). Compound 1 crystallizes in the noncentrosymmetric space group Aba2, which belongs to the polar point group C2v. The asymmetrical unit of 1 contains one Cd atom, one D-ca2- ligand, one bte ligand, and a solvated water molecule. As shown in Figure 1a, the Cd(II) center lies in a distorted CdN2O4 octahedral environment, which is provided by two N atoms from two different bte ligands and four O atoms from two different D-ca2- ligands with chelating fashion. The bte ligand adopts a T conformation with the dihedral angles of 51.56° between two triazole rings (Figure 1b). The torsion angles N2-N3-C13-C14 and N5-N4-C14-C13 are 7.4(9) and 19.8(9)°, respectively. Each D-ca2- and bte ligands bridge the Cd atoms to afford a 2D sheet with (4,4) topology (Figure 1c,d). The 2D network structure consists of rectangular grids in which the Cd 3 3 3 Cd distances separated by D-ca2- and the bridging bte are 9.478 and 12.108 A˚, respectively. Structure of [Cd4(D-ca)4(btp)2(H2O)4] n (2). Compound 2 crystallizes in the chiral space group P21. In the asymmetrical unit, there are four Cd atoms, four D-ca2- ligands, two btp ligands, and four coordinated aqua molecules. As shown in Figure 2a, both Cd1 and Cd3 atoms are coordinated by two nitrogen atoms from two different btp ligands, four oxygen atoms from two different D-ca2- ligands, and one oxygen atom from a coordinated aqua molecule to give distorted CdN2O5 pentagonal bipyramidal geometries. Both Cd2 and Cd4 atoms adopt distorted octahedron spheres, being ligated by one nitrogen atom from a btp ligand, one oxygen atom from a coordinated aqua molecule, and four oxygen atoms from two different D-ca2- ligands. The btp ligands exhibit TG conformation, and the dihedral angles

between two triazole rings are 19.39 and 20.09°, respectively (Figure 2b). The torsion angles N2-N3-C3-C4, N5-N4-C5-C4, N8-N9-C10-C11, and N11-N10-C12-C11 are 92.1(8), 47.0(9), 49.3(9), and 77.5(8)°, respectively. It is noted that the coordination mode of one triazole ring of btp ligand adopts a μ2 bridging mode and btp acts as bridging tridentate ligand. The D-ca2- and btp ligands bridge Cd(II) atoms to lead to the generation of a 3D polymer, which is topologically equivalent to a (32 3 4) (3 3 84 3 12) (83) (4 3 8 3 10) framework (Figure 2c,d). In addition, lots of O-H 3 3 3 O hydrogen-bonding interactions are formed through oxygen atoms of carboxylate and coordinated aqua molecules. Structure of [{Cd(D-ca)(btb)1.5} 3 3H2O]n (3). In 3, the asymmetric unit consists of one Cd atom, one D-ca2- ligand, one and half of btb ligands, and three solvated water molecules. As shown in Figure 3a, each Cd(II) center sits in a distorted pentagonal bipyramidal environment which contains three nitrogen atoms (N1, N6a, N9) from three different btb ligands and four oxygen atoms (O1, O2, O3a, O4a) from two different D-ca2- ligands with chelating mode. The N9, O1, O2, O3a, and O4a atoms make up the equatorial plane, whereas the N1 and N6a atoms are located in the axial positions. Both btb ligands show TTG and GTG conformations, and the dihedral angles between the two pairs of triazole rings are 63.85 and 0°, respectively (Figure 3b). The torsion angles N2-N3-C14-C15, N5-N4-C17-C16, N8-N7-C21-C20, and N8h-N7h-C21h-C20h are 56.2(4), 62.1(4), 58.3(4), and 58.3(4)°, respectively. Each Cd(II) atom is linked by D-ca2- and btb ligands to form a 1-D double-stranded chain (Figure 3c), which is further connected by a btb ligand to form a 2-D (6,3) layer motif with the neighboring Cd 3 3 3 Cd distances of 9.737 and 12.814 A˚, respectively (Figure 3d,e). The 2D layers are further extended to a 3D architecture via hydrogen bonds (C17-H17A 3 3 3 N2i and C18-H18 3 3 3 N2i) (Figure 3f). The intriguing structural feature of the 3D architecture holds 1D nanosized channels with dimensions of ca. 14.2 12.3 A˚ (Figure 3f). The 1D channels are occupied by a large amount of water guest molecules which generate strong hydrogen bonding interactions (Figure 3g). After the removal of these

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Figure 4. (a) View of the coordination environment of Cd(II) in complex 4; thermal ellipsoids are drawn at the 50% probability level. Lattice water molecules and hydrogen atoms have been omitted for clarity. (b) The conformation of the bth ligand (Symmetry code: (b) -x, -y þ 1, -z þ 2). (c) The 1D S-shape chain of [Cd(bth)]n2þ. (d) Two dimensional layer (black, C; blue, N; red, O; green, Cd). (e) Schematic description of the (4,4) topological 2D parallelogram network.

guest solvents, PLATON calculations show that the volume of the effective void is 36.3% of the unit-cell volumes. Structure of [{Cd4(D-ca)4(bth)4} 3 2H2O]n (4). There is one Cd atom, one D-ca2- ligand, one bth ligand, and a half

water molecule in the asymmetric unit. As illustrated in Figure 4a, the coordination geometry of Cd(II) atom is surrounded by one nitrogen atom of the bth ligand and three carboxylate oxygen atoms of two D-ca2- ligands in the

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Figure 5. View of the coordination environment of Cd(II) in complex 5; thermal ellipsoids are drawn at the 50% probability level. Lattice water molecules and hydrogen atoms have been omitted for clarity. (b) The conformation of the bth ligand. (c) The 1D chiral fish-bone chain. (d) The 3D supramolecular architecture via hydrogen-bonding interactions (black, C; blue, N; red, O; green, Cd; light gray, H).

equatorial plane, and one nitrogen donor of the other bth ligand and one oxygen donor of D-ca2- ligand in the apical position, forming a distorted [CdN2O4] octahedron. The bth ligand shows GTTTG conformation, and the dihedral angle between the triazole rings is 0° (Figure 4b). The torsion angles N2-N3-C13-C14 and N2b-N3b-C13b-C14b are 84.5(7) and 84.5(7)°, respectively. The Cd

atoms are bridged by the bth ligands to give rise to the S-shape chain of [Cd(bth)]n2þ (Figure 4c). These chains are further linked by D-ca2- ligands to form a 2D parallelogram net with a 42-membered macrocylic ring (Figure 4d). In the macro-metallacycle, the neighboring Cd 3 3 3 Cd distances spanned by the D-ca2- and bth ligands are 9.571 and 13.147 A˚, respectively.

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materials (Figures S1-S5, Supporting Information). The differences in intensity are perhaps due to the preferred orientation of the powder samples. TGA measurements are performed for crystalline samples of 1-5 in the temperature range of 25-750 °C (Figure S6, Supporting Information). A weight loss of 3.32% in 25-130 °C corresponds to the release of the lattice water molecules (calculated 3.65%) for complex 1. The framework begins to collapse over 130 °C with several complicated weight losses. For 2, the weight loss in the range of 95-250 °C is related to the loss of four coordinated aqua molecules (4.48% weight loss observed; 4.31% calculated) and the further weight loss is ascribed to the decomposition of the compound. The loss of six guest water molecules for 3 occurs between 28 and 105 °C (8.57% weight loss observed; 8.27% calculated), and the decomposition of the material is observed at ca. 200 °C. Two solvated water molecules in 4 are lost in the temperature range of 40-323 °C with a weight loss of 1.95% (calcd, 1.67%). The further weight loss results from the decomposition of the product. The weight loss 5.00% (calcd, 4.70%) for 5 occurs between 33 and 160 °C, which is ascribed to the loss of one coordinated and one crystalline water molecule. Physical Properties

Figure 6. Electric hysteresis loop of a pellet of powders of compounds 1 (a) and 5 (b) (the different curves represent different hysteresis loops at different voltage measurements).

Structure of [{Cd(D-Hca)2(bth)(H2O)} 3 H2O]n (5). Compound 5 crystallizes in the chiral space group P1. The asymmetric unit consists of two D-Hca- ligands, one bth ligand, one coordinated aqua molecule, and one solvated water molecule. As illustrated in Figure 5a, the Cd atom adopts a distorted pentagonal bipyramidal sphere, in which the apical positions are completed by two nitrogen atoms (N1, N6a) from the bth ligands, and the basal plane is formed by four oxygen atoms (O1, O2, O5, and O6) from D-Hca- ligands and the other one oxygen atom (O9) from the coordinated aqua molecule. In contrast to 4, bth exhibits TTTGT conformation with the dihedral angle of 12.60° between the triazole rings (Figure 5b). The torsion angles N2N3-C23-C24 and N5-N4-C28-C27 are 58.4(1) and 67.0 (1)°, respectively. The D-Hca- ligand chelate to Cd(II) atom to form [Cd(D-Hca)2] basic unit. The basic units are further bridged by the bth ligand and lead to a chiral 1D fish-bone chain with Cd 3 3 3 Cd separation of 16.694 A˚ (Figure 5c). In addition, O-H 3 3 3 O hydrogen-bonding interactions from carboxylic and carboxylate oxygen atoms, coordinated or uncoordinated aqua molecule, connect the chains to give rise to a 3D supramolecular framework (Figure 5d). XRPD and Thermogravimetric Analyses. X-ray powder diffraction (XRPD) experiments have been carried out for all new complexes. All XRPD patterns measured for the assynthesized samples are in agreement with the results simulated from the respective single-crystal X-ray data, indicating that the crystal structures are truly representative of the bulk

Photoluminescence. The photoluminescent properties of compounds 1-5 and the free bis(triazole) ligands have been investigated in the solid state at room temperature. When excited at 270 nm, blue fluorescent emissions are observed at 383 and 400 nm for bte and btp respectively. Similar fluorescent emissions are at 400 nm for btb and bth with the excitation at 355 nm (Figure S7, Supporting Information). No obvious photoluminescence was observed for complexes 1 and 2. Complex 3 displays the intense emission maximum at 398 nm when excitated at 341 nm (Figure S8, Supporting Information), and compounds 4 and 5 exhibit emissions around 399 nm. They can be assigned to intraligand charge-transfer (LCT) emissions.25 Second Harmonic Generation Efficiency and Ferroelectricity. The noncentrosymmetric or chiral structure is confirmed by the observation of second-order nonlinear optical effect. The second harmonic generation (SHG) efficiency for compounds 1, 2, and 5 can be estimated using the methods proposed by Kurtz and Perry.26 Preliminary experimental results indicate that compounds 1, 2, and 5 display SHG intensities about 0.3, 0.8, and 0.4 times that of urea, respectively. It is noteworthy that the SHG efficiency of compound 2 is stronger than that of compound 5. The enhancement of the SHG efficiency is probably due to the strength and numbers of intermolecular hydrogen bondings.27 As shown in Figure 6, compounds 1 and 5 display ferroelectric features representing electric hysteresis loops with a remnant polarization (Pr) of ca. 0.059 μC 3 cm-2 for 1 and 0.036 μC 3 cm-2 for 5, and coercive field (Ec) of ca. 9.41 kV 3 cm-1 for 1 and 8.96 kV 3 cm-1 for 5. The saturation of the spontaneous polarizations (Ps) of 1 and 5 is about 0.143 μC 3 cm-2 and 0.103 μC 3 cm-2, respectively. The ferroelectric feature of 5 may be associated with the interaction of strong hydrogen bonding.28 Role of Conformational Flexibility of Bis(triazole) Ligands. As illustrated in Scheme 2, the diversity of architectures for compounds 1-5 mainly results from the bis(triazole) ligands with different spacer lengths and conformational

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Scheme 2. Schematic Showing the Diversified Structures in 1-5

flexibility. The flexible bte employ the T conformation to generate a 2D rectangular network with (4,4) topology in 1. The btp ligand in 2 adopts TG conformation and multiple coordination sites from one of triazole to extend other units into a 3D framework with (32 3 4) (3 3 84 3 12) (83) (4 3 8 3 10) topology. The 2D honeycomb motif with 1D nanosized channels for 3 is due to two different conformations (TTG and GTG) existing in the btb ligand. The bth ligands in both 4 and 5 adopt two different conformations of GTTTG and TTTGT, which generate two different structures. Moreover, different physical features are found in complexes 1-5. It is noteworthy that compounds 4 and 5 fall in centrosymmetric space group (P21/c) and chiral space group (P1), respectively. Complex 5 displays both second-order nonlinear optical effect and ferroelectric behavior, while no such properties are observed for compound 4. Therefore, the second-order nonlinear optical effect and ferroelectric behavior may result from the difference of molecular arrangements in the crystal, which depends on the conformations of the ligand. That is to say, the stereoeffect resulting from the conformational effect of the ligand affects ferroelectric and NLO properties of the solids. Conclusions and Perspectives In this paper, the systematic investigations on a series of coordination polymers generated from chiral camphoric acid and flexible ligands with different spacer lengths are presented. A diversity of architectures is found for these new complexes: the 2D rectangular network with (4,4) topology for 1, the 3D framework with (32 3 4) (3 3 84 3 12) (83) (4 3 8 3 10)

topology for 2, the 2D honeycomb motif with 1D nanosized channels for 3, the 2D parallelogram sheet with (4,4) topology for 4, and the 1D fish-bone chain for 5. These compounds exhibit different physical properties of luminescence, nonlinear optics, and ferroelectricity. Constructed from the same bth ligand, compounds 4 and 5 show different properties owing to the different conformations of the ligand. The results confirm that the stereoeffect (conformation effect) of the organic ligand play an important role in second-order nonlinear optical effect or/and ferroelectric behavior. Acknowledgment. This work was supported by the National Basic Research Program of China (2006CB806104 and 2007CB925100), and the National Natural Science Foundation of China (20531040, 20725104 and 20721002). Supporting Information Available: The XRPD patterns and TGA curves of 1-5, emission spectra of the free bis(triazole) ligands and 3-5. X-ray crystallographic file in CIF format for 1-5. This material is available free of charge via the Internet at http://pubs. acs.org.

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