Solvothermal Synthesis and Diverse Coordinate Structures of a Series

Oct 5, 2009 - Kayla M. Miller , Shannon M. McCullough , Elena A. Lepekhina , Isabelle J. Thibau , and Robert D. Pike , Xiaobo Li , James P. Killarney ...
0 downloads 0 Views 4MB Size
Download PDF
DOI: 10.1021/cg900079p

Solvothermal Synthesis and Diverse Coordinate Structures of a Series of Luminescent Copper(I) Thiocyanate Coordination Polymers Based on N-Heterocyclic Ligands

2009, Vol. 9 4626–4633

Ming-Xing Li,*,† Hui Wang,† Sheng-Wen Liang,† Min Shao,‡ Xiang He,† Zhao-Xi Wang,† and Shou-Rong Zhu† †

Department of Chemistry, College of Sciences, Shanghai University, Shanghai 200444, China, and Instrumental Analysis and Research Center, Shanghai University, Shanghai 200444, China

‡

Received January 22, 2009; Revised Manuscript Received September 19, 2009

ABSTRACT: Solvothermal reactions of CuSCN with 4-amine-3,5-bis(3-pyridyl)-1,2,4-triazole (3-Abpt), 5-(4-pyridyl)tetrazole (4-Ptz), and 2-(n-pyridyl)benzimidazole (n-PyHBIm, n = 4, 3, 2) in acetonitrile afford six novel coordination polymers: [Cu5(SCN)5(3-Abpt)2]n (1), [Cu(SCN)(3-Abpt)]n (2), [Cu(SCN)(4-Ptz)]n (3), [Cu2(SCN)2(4-PyHBIm)]n (4), [Cu2(SCN)2(3-PyHBIm)]n (5), and [Cu2(SCN)2(2-PyBIm)(2-PyHBIm)]n (6). All these complexes were structurally characterized by X-ray diffraction analysis. 1 is the first example of a 1,1,1,3-μ4-tetradentate thiocyanate complex which displays a three-dimensional (3D) polymeric framework constructed from thiocyanate and tetradentate 3-Abpt. 2 exhibits a two-dimensional (2D) 4.82 network constructed from unidentate thiocyanate and tridentate 3-Abpt. 3 is a one-dimensional (1D) ladder-like double-chain polymer assembled by bidentate thiocyanate and 4-Ptz ligands. 4 shows a 2D 1,1,3-μ3-thiocyanate copper 4.82 network where bidentate 4-PyHBIm locates at both sides of the 2D layer. 5 displays a 2D 63 network constructing from 1,1,3-μ3-thiocyanate and bidentate 3-PyHBIm. 6 is a 1D 21 helical chain polymer constructing from 1,3-μ2-thiocyanate and 2-PyBIm anion. Bond valence sum (BVS) analysis and magnetic susceptibility indicate that 6 is a mixed-valence compound. The coordinate diversity of thiocyanate is discussed. 1-6 are all thermally stable up to 230-290 °C. They exhibit yellow or blue luminescence originating from ligandto-metal charge transfer or ligand-centered emission.

Scheme 1

Introduction The crystal engineering of metal-organic coordination polymers has attracted enormous interest because of their intriguing structural motifs and potential applications as functional materials.1 Much effort has been focused on the rational design and controlled synthesis of coordination polymers using multidentate ligands such as poly-carboxylate and N-heterocyclic ligands.2 Recently, there is a growing interest in the construction of coordination polymers based on triazole, tetrazole, and imidazole derivates.3 4-Amine-3,5- bis(3-pyridyl)-1,2,4-triazole and 5-(4-pyridyl)tetrazole (Scheme 1) possess five potential N-donors and exhibit diverse coordinate modes. 2-(n-Pyridyl)benzimidazole has three N-donors, which can play a neutral uni-, bidentate ligand, or an anionic tridentate ligand.4 These N-heterocyclic ligands are good molecular building blocks and coligands in constructing metal-organic frameworks with interesting structures and properties. Transition metal cyanides have been studied extensively over the past two decades due to their great importance in magnetism, luminescence, and porous material.5 Analogous to cyanide, thiocyanate is a linear triatomic pseudohalide and a worthy connector in constructing coordination polymer. Thiocyanate is a highly versatile ambidentate ligand. It can coordinate through either the nitrogen or the sulfur atom, or both, giving rise to linkage isomers or polymers. A number of transition metal thiocyanate-containing coordination polymers have been documented, which show interesting structural diversity and properties.6 Copper(I) tends toward *Corresponding author. E-mail: [email protected]. pubs.acs.org/crystal

Published on Web 10/05/2009

trigonal or tetrahedral coordination geometry in the presence of N-heterocyclic ligands and thiocyanate. This gives the possibility of promoting the formation of polymeric frameworks because of the strong coordinate nature of these multidentate ligands and their ability to act as connectors between different copper(I) ions. A series of copper(I) coordination polymers incorporating N-heterocyclic ligands have been synthesized and structurally characterized.7 These copper(I) complexes usually display varied luminescence in the solid state. Recently, we have synthesized and structurally characterized a series of thiocyanate-copper(I) coordination polymers based on N-heterocyclic ligands. Herein, we report their synthesis, crystal structures, and thermal and luminescent properties. The coordinate diversity of thiocyanate is further discussed. r 2009 American Chemical Society

Article

Crystal Growth & Design, Vol. 9, No. 11, 2009

4627

Table 1. Crystal Data and Structure Refinement for Complexes 1-6 formula fw cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V [A˚3] Z Dc (g cm-3) μ (mm-1) reflections GOF on F2 R1 (I >2σ(I)) wR2 (all data)

1

2

3

4

5

6

C29H20Cu5N17S5 1084.62 triclinic P1 8.453(3) 14.656(6) 15.651(6) 95.895(5) 102.855(5) 90.786(6) 1879.0(12) 2 1.917 3.112 9795/6496 1.038 0.0534 0.1272

C13H10CuN7S 359.88 monoclinic P21/n 9.6339(9) 14.4436(13) 10.0795(9) 90 101.732(1) 90 1373.2(2) 4 1.741 1.749 6986/2409 1.048 0.0303 0.0798

C7H5CuN6S 268.77 monoclinic P21/c 5.7243(7) 17.842(2) 9.1778(11) 90 99.999(2) 90 923.14(19) 4 1.934 2.562 4733/1632 1.060 0.0401 0.0977

C14H9Cu2N5S2 438.46 triclinic P1 8.7767(13) 9.0022(14) 9.3592(14) 80.617(2) 88.527(2) 88.527(2) 725.61(19) 2 2.007 3.222 3804/2528 1.060 0.0298 0.0719

C14H9Cu2N5S2 438.46 monoclinic P21 5.8910(9) 14.382(2) 8.6385(12) 90 95.156(2) 90 728.95(18) 2 1.998 3.207 3782/2461 1.024 0.0312 0.0621

C26H17Cu2N8S2 632.68 orthorhombic Pbca 18.1048(14) 10.3065(8) 26.212(2) 90 90 90 4891.0(7) 8 1.718 1.945 24094/4325 1.056 0.0544 0.1464

Experimental Section Materials and Methods. 3-Abpt, 4-Ptz, and n-PyHBIm were prepared according to the literature methods.8 Other chemicals were of reagent grade and used without further purification. Elemental analyses for C, H, and N were carried out on a Vario EL III elemental analyzer. IR spectra (KBr pellets) were recorded with a Nicolet A370 FT-IR spectrometer. Thermal analyses were performed on a Netzsch STA 449C thermal analyzer from 20 to 800 °C at a heating rate of 10 °C min-1 in air. The powder X-ray diffraction data were collected on a Rigaku DLMAX-2550 diffractometer. Magnetic susceptibilities were measured on a Quantum Design PPMS-9 apparatus. Luminescent spectra of crystalline samples were recorded on a Shimadzu RF-5301 PC spectrophotometer. Synthesis of [Cu5(SCN)5(3-Abpt)2]n (1) and [Cu(SCN) (3-Abpt)]n (2). A mixture of CuSCN (0.3 mmol), 3-Abpt (0.3 mmol), and acetonitrile (5 mL) was sealed in a 15 mL Teflon-lined stainless-steel reactor. The reactor was held at 140 °C for 72 h. Upon cooling to room temperature at a rate of 10 °C h-1, a mixture of brown block crystals of 2 (25% yield) and light-yellow rod crystals of 1 as a byproduct were obtained, which was separated manually. Complex 1: Anal. Calcd for C29H20Cu5N17S5: C, 32.11; H, 1.86; N, 21.95%. Found: C, 32.67; H, 1.88; N, 21.82%. IR: 3351m, 2105s, 1603m, 1462m, 1407m, 811w, 701s cm-1. Complex 2: Anal. Calcd for C13H10CuN7S: C, 43.39; H, 2.80; N, 27.24%. Found: C, 43.34; H, 2.71; N, 26.99%. IR: 3375m, 3249m, 2084s, 1599m, 1457m, 1400m, 885w, 811m, 701s cm-1. Synthesis of [Cu(SCN)(4-Ptz)]n (3). A mixture of CuSCN (0.2 mmol), 4-Ptz (0.2 mmol), and acetonitrile (6 mL) was sealed in a 15 mL Teflon-lined stainless-steel reactor. The reactor was held at 140 °C for 72 h. Upon cooling to room temperature at a rate of 10 °C h-1, red cubic crystals were obtained in 45% yield. Anal. Calcd for C7H5CuN6S: C, 31.28; H, 1.87; N, 31.26%. Found: C, 31.03; H, 1.80; N, 30.43%. IR: 3448m, 2108s, 1506m, 1419s, 844s, 772m, 726s cm-1. Synthesis of [Cu2(SCN)2(4-PyHBIm)]n (4). A mixture of CuSCN (0.2 mmol), 4-PyHBIm (0.2 mmol), and acetonitrile (6 mL) was sealed in a 15 mL Teflon-lined stainless-steel reactor. The reactor was held at 170 °C for 72 h. Upon cooling to room temperature at a rate of 10 °C h-1, yellow needle crystals were obtained in 60% yield. Anal. Calcd for C14H9Cu2N5S2: C, 38.35; H, 2.07; N, 15.97%. Found: C, 38.33; H, 2.04; N, 15.76%. IR: 3313m, 2114m, 2095s, 1610m, 1431s, 831m, 749m, 601m cm-1. Synthesis of [Cu2(SCN)2(3-PyHBIm)]n (5). A mixture of CuSCN (0.2 mmol), 3-PyHBIm (0.2 mmol), and acetonitrile (6 mL) was sealed in a 15 mL Teflon-lined stainless-steel reactor. The reactor was held at 140 °C for 72 h. Upon cooling to room temperature at a rate of 10 °C h-1, yellow rod crystals were obtained in 85% yield. Anal. Calcd for C14H9Cu2N5S2: C, 38.35; H, 2.07; N, 15.97%. Found: C, 38.66; H, 2.08; N, 15.66%. IR: 3264m, 2106s, 1629m, 1445s, 748m, 692m, 600m cm-1. Synthesis of [Cu2(SCN)2(2-PyBIm)(2-PyHBIm)]n (6). A mixture of CuSCN (0.2 mmol), 2-PyHBIm (0.2 mmol), and acetonitrile

(6 mL) was sealed in a 15 mL Teflon-lined stainless-steel reactor. The reactor was held at 140 °C for 72 h. Upon cooling of the sample to room temperature at a rate of 10 °C h-1, dark brown cubic crystals were obtained in 70% yield. Anal. Calcd. for C26H17Cu2N8S2: C, 49.36; H, 2.71; N, 17.71%. Found: C, 48.79; H, 2.62; N, 17.42%. IR: 3050m, 2091s, 1602m, 1442m, 745s, 674m cm-1. X-ray Crystallography. The single crystals of 1-6 were selected for X-ray diffraction study. Data collections were performed on a Bruker Smart Apex-II CCD diffractometer with graphite-monochromatic Mo KR radiation (λ = 0.71073 A˚) at room temperature. Determinations of the crystal system, orientation matrix, and cell dimensions were performed according to the established procedures. Lorentz polarization and absorption correction were applied. The structures were solved by the direct method with SHELXS-97 program, and refined by full matrix least-squares on F2 with SHELXL-97 program.9 All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were located and included at their calculated positions except H atoms in complex 1 had restraints employed and refined isotropically. The crystal data and structural refinement results are summarized in Table 1. The selected bond distances and angles are listed in Table 2. The measured and simulated powder X-ray diffraction patterns of 2-6 are shown in Figure S2, Supporting Information.

Results and Discussion Synthesis and Infrared Spectra. Complexes 1-6 were successfully prepared by solvothermal reactions in acetonitrile. No solvent molecule or lattice water was found in them. In all the reactions the molar ratio of CuSCN with N-heterocycles was kept at 1:1. However, the resulting products show different CuSCN/N-heterocycle ratios. The reaction of CuSCN with 3-Abpt afforded a mixture of [Cu5(SCN)5(3-Abpt)2]n (1) and [Cu(SCN)(3-Abpt)]n (2). Both complexes show characteristic vibration absorption of thiocyanate at 2105 and 2084 cm-1, respectively. The amino N-H stretching vibrations of 3-Abpt appear near 3351 cm-1. The reaction of CuSCN with 4-Ptz afforded 3, which exhibits characteristic absorption of thiocyanate at 2108 cm-1. The reactions of CuSCN with n-PyHBIm (n = 4, 3, 2) afforded copper(I) complexes 4, 5, and mixed-valence copper(I,II) complex 6. The thiocyanate characteristic absorption appears at 2095, 2106, and 2091 cm-1, respectively. The N-H stretching vibration of n-PyHBIm appears at 3313, 3264 cm-1, in 4 and 5, respectively. However, the spectrum of 6 has no N-H stretching vibration. It should be mentioned that partial 2-PyHBIm was deprotonated and partial copper(I) was oxidized in the synthetic process of 6. The formulas of 1-6 have been confirmed by

4628

Crystal Growth & Design, Vol. 9, No. 11, 2009

Li et al.

Table 2. Selected Bond Distances (A˚) and Angles (deg) for Complexes 1-6a 1 Cu(1)-N(13) Cu(1)-N(12) Cu(2)-N(1) Cu(3)-N(14) Cu(4)-N(11) Cu(4)-S(2) Cu(5)-S(4) N(13)-Cu(1)-N(8) N(16)-Cu(3)-N(14) N(11)-Cu(4)-S(2)

1.982(6) 2.124(5) 2.051(5) 1.931(6) 2.063(5) 2.339(2) 2.494(2) 116.0(2) 131.6(2) 108.89(17)

Cu(1)-N(2) Cu(2)-N(7) Cu(2)-S(5) Cu(3)-N(6) Cu(4)-S(1) Cu(5)-N(17) Cu(5)-S(4) N(2)-Cu(1)-N(12) N(6)-Cu(3)-S(4) N(17)-Cu(5)-N(15)

2.017(5) 2.018(5) 2.363(2) 2.081(5) 2.331(3) 1.911(7) 2.438(2) 116.9(2) 89.60(16) 129.0(3)

Cu(1)-N(8) Cu(2)-N(5) Cu(3)-N(16) Cu(3)-S(4) Cu(4)-S(3) Cu(5)-N(15)

2.049(5) 2.048(5) 1.922(6) 2.695(2) 2.337(3) 1.933(7)

N(7)-Cu(2)-N(1) S(1)-Cu(4)-S(3) S(4)-Cu(5)-S(4A)

115.5(2) 98.10(11) 95.73(7)

Cu(1)-N(2) C(13)-N(7) Cu(1)-N(7)-C(13)

2.087(2) 1.146(4) 144.7(2)

2 Cu(1)-N(3) Cu(1)-N(1) N(7)-Cu(1)-N(1)

2.021(2) 2.101(2) 105.1(1)

Cu(1)-N(7) C(13)-S(1) N(3)-Cu(1)-N(2)

2.029(3) 1.616(3) 113.81(8) 3

Cu(1)-N(1A) Cu(1)-S(1) S(1)-Cu(1)-N(6)

2.051(3) 2.4316(15) 105.55(12)

Cu(1)-N(1) Cu(1)-S(1) Cu(2)-S(1) N(1)-Cu(1)-S(1) S(1)-Cu(2)-S(2C)

2.028(2) 2.3462(9) 2.4603(9) 118.97(7) 112.86(4)

Cu(1)-N(6)

1.937(4)

Cu(1)-N(2)

2.056(3)

N(1A)-Cu(1)-N(2) 4

108.81(12)

Cu(1)-S(1)-C(7)

98.81(17)

Cu(1)-N(5A) Cu(2)-N(4B) Cu(2)-S(2C) N(5A)-Cu(1)-S(2) Cu(1)-S(1)-Cu(2)

1.978(3) 1.961(3) 2.3541(9) 104.00(8) 128.33(4)

Cu(1)-S(2) Cu(2)-N(3)

2.4625(10) 2.028(3)

N(4B)-Cu(2)-N(3) Cu(1)-S(2)-Cu(2C)

129.53(11) 147.42(4)

5 Cu(1)-N(1) Cu(1)-S(2) Cu(2)-N(3C) N(1)-Cu(1)-S(2) N(5B)-Cu(2)-S(2D)

Cu(1)-N(1) Cu(1)-N(5) Cu(2)-N(8) N(2)-Cu(1)-N(4) N(7)-Cu(1)-N(1) N(6)-Cu(2)-S(1)

2.044(3) 2.4561(14) 2.020(4) 104.20(11) 111.17(13)

2.343(5) 1.988(5) 1.928(5) 171.6(2) 105.6(2) 115.86(14)

Cu(1)-N(4A) Cu(2)-S(1) Cu(2)-N(5B) N(4A)-Cu(1)-S(1) Cu(1)-S(1)-Cu(2) 6

1.952(4) 2.6062(14) 1.913(4) 102.58(13) 104.19(5)

Cu(1)-S(1) Cu(2)-S(2D)

2.4187(13) 2.3568(14)

N(3C)-Cu(2)-S(1)

107.70(11)

Cu(1)-N(2) Cu(1)-N(7) Cu(2)-S(1) N(5)-Cu(1)-N(7) N(2)-Cu(1)-N(1) N(6)-Cu(2)-N(8)

1.978(5) 1.991(6) 2.3411(18) 148.3(2) 76.8(2) 123.0(2)

Cu(1)-N(4) Cu(2)-N(6)

2.007(5) 2.000(5)

N(5)-Cu(1)-N(1) N(4)-Cu(1)-N(5) N(8)-Cu(2)-S(1)

105.69(18) 81.14(19) 115.08(16)

a Symmetry transformations used to generate equivalent atoms. For 1: (A) 1 - x, -y, 1 - z. For 3: (A) 1 þ x, y, z. For 4: (A) 1 - x, 1 - y, 1 - z; (B) -x, 1 - y, 2 - z; (C) -x, 1 - y, 1 - z. For 5: (A) -1 þ x, y, z; (B) 1 - x, -0.5 þ y, -z; (C) 1 þ x, y, z; (D) 2 - x, -0.5 þ y, -z.

elemental analysis data and single crystal X-ray diffraction analysis. Structure of [Cu5(SCN)5(3-Abpt)2]n (1). Complex 1 is a 3D coordination polymer in which thiocyanate and 3-Abpt act as bridging ligands. As shown in Figure 1, the asymmetric unit consists of five crystallographically independent copper(I) ions, five thiocyanates, and two 3-Abpt ligands. All the copper centers are four-coordinated. Among them, four copper(I) ions are tetrahedrally coordinated, whereas Cu3 is trigonal-pyramidally coordinated. Cu1 is coordinated by thiocyanate N13, pyridyl N12, and two triazole N atoms. Cu1-N bond distances vary from 1.982(6) to 2.124(5) A˚. Cu2 is coordinated by thiocyanate S5, pyridyl N5, and two triazole N atoms. Cu2-N distances vary from 2.018(5) to 2.051(5) A˚, while Cu2-S5 is 2.363(2) A˚. Cu3 is in a distorted trigonal-pyramidal geometry. The basal plane is constructed by the coordination of pyridyl N6, thiocyanate N14, and N16 terminals. Cu3-N distances vary from 1.922(6) to 2.081(5) A˚. The N14-Cu3-N16 bond angle is 131.6(2)°. The apical position is occupied by S4 with a Cu3-S4 distance of 2.695(2) A˚, which is obviously longer than other Cu-S distances in 1. Cu4 is coordinated by

pyridyl N11 and three thiocyanate S donors. The Cu4-S bond distances are similar, from 2.331(3) to 2.339(2) A˚. Cu5 is coordinated by two thiocyanate N and two thiocyanate S donors. The average Cu5-N distance is 1.922 A˚, and Cu5-S is 2.466 A˚. The angle of N17-Cu5-N15 is 129.0(3)°. In the complex 1, five thiocyanates display two types of coordinate modes. Among them, four thiocyanates act as 1,3-μ2-bidentate bridge to coordinate copper(I) ions using both N and S terminals. The Cu-S-CN angles are from 98.9(3) to 118.0(3)°. Generally, metal thiocyanate complexes show a bent M-S-CN angle around 100°. Interestingly, the complex 1 contains a 1,1,1,3-μ4-tetradentate thiocyanate ligand, which coordinates to four copper(I) ions using a tridentate S4-donor and N16-terminal. S-donor is a soft base and tends to combine with a soft acid Cu(I) ion. To our knowledge, no structurally characterized example of such tetradentate thiocyanate complex has been documented. In 1, both 3-Abpt ligands are tetradentate and coordinate to four copper(I) ions through two triazole nitrogens and two pyridyl nitrogens. They adopt different conformations. The pyridyl N11 and N12 are in cis-conformation, whereas N5 and N6 are in trans-conformation. The amino group of

Article

Crystal Growth & Design, Vol. 9, No. 11, 2009

4629

Figure 2. Views of asymmetric unit and 2D polymeric network of 2.

Figure 1. Views of the asymmetric unit and packing diagram of 1.

3-Abpt is free. The complex 1 displays a complicated 3D polymeric framework constructed from bi-, tetradentate thiocyanates and tetradentate 3-Abpt ligands as shown in the packing diagram. For reason of classifying the net, we define four-coordinate copper(I) ions, μ4-tetradentate thiocyanate, and 3-Abpt ligands as 4-connected nodes, then complex 1 can be simplified as a four-nodal net. The Schafli symbol for this 4-connected uniform network is (3.4.72.82)(3.42.5.6.7)2(42.6.83)4(43.62.7) (Figure S3a, Supporting Information). Structure of [Cu(SCN)(3-Abpt)]n (2). The complex 2 displays a 2D polymeric network. As shown in Figure 2, the asymmetric unit contains an independent copper(I) ion, a thiocyanate, and a 3-Abpt ligand. Cu1 is in a distorted tetrahedral environment and coordinated by four nitrogen atoms. The thiocyanate is unidentate and binds to copper(I) through N terminal. 3-Abpt as a tridentate ligand coordinates to three copper(I) ions through triazole N3 and two pyridyl N donors. Two pyridyl nitrogens are in trans-conformation. The triazole N4 and amino group are uncoordinated. The Cu1 and Cu1A are connected by two 3-Abpt ligands to form a 14-numbered ring. The pyridyl groups connect the rings to form a 2D polymeric network, which belongs to 4.82 topology where 3-Abpt plays a 3-connector (Figure S3b, Supporting Information). Comparing the structures of 1 and 2, it is surprising that copper(I) ions are in six independent coordinate

environments, and thiocyanates act as uni-, bi-, and tetradentate ligands in both coordination polymers prepared in same solvothermal reaction. 3-Abpt ligand is tetradentate in 1 and tridentate in 2. The pyridyl groups are arranged in cis- or transconformation, which influence the coordinate structures. The amino group of 3-Abpt is uncoordinated in both complexes. To date, only three 3-Abpt coordination polymers, assembled by a [Ag(3-Abpt)]þ cation with ClO4-, PF6- and SiF62- anions, have been structurally characterized.10 In them, the 3-Abpt is tetradentate, and the coordination mode is similar to 1. Structure of [Cu(SCN)(4-Ptz)]n (3). Inspired by the work of Sharpless and in situ synthetic technology, the preparation of 5-substituted 1H-tetrazoles is now a safe and convenient route.11 However, the coordination polymers based on tetrazole derivatives have not been extensively studied. Several complexes containing neutral or anionic 5-(4-pyridyl)tetrazole have been reported, which show coordinate flexibility of the tetrazole group.12 The complex 3 is a 1D ladder-like double chain coordination polymer constructed from thiocyanate and a neutral 5-(4-pyridyl)tetrazole ligand. As shown in Figure 3, the asymmetric unit contains an independent copper(I) ion, a thiocyanate, and a 4-Ptz ligand. Cu1 adopts a distorted tetrahedral geometry and coordinates by S1 and three N donors. The angles of N2-Cu1-N1A and S1-Cu1-N6 are 108.81(12) and 105.55(12)°, respectively. Thiocyanate as a bidentate ligand links copper(I) ions through both N and S terminals, which leads to the formation of a 1D infinite copper-thiocyanate chain. 4-Ptz ligand is bidentate and connects to two copper(I) ions through adjacent tetrazole N donors with an average Cu-N distance of 2.054 A˚. The planes of pyridyl group and tetrazole ring are twisted by 8.3° with respect to one another. Two parallel 1D copper-thiocyanate chains are connected by 4-Ptz bidentate ligands to form a 1D ladder-like double-chain.

4630

Crystal Growth & Design, Vol. 9, No. 11, 2009

Li et al.

Figure 3. Views of the 1D double-chain and packing diagram of 3.

Such 1D ladder-like chains are parallel packed along the a-axis. The hydrogen bond of N4-H4 3 3 3 N5B is 2.820(5) A˚. Even though the parallel pyridyl rings have a vertical interplane distance of 3.544(2) A˚, the centroid-to-centroid distance of 4.704 A˚ indicates that not a real π-π stacking interaction exists between the neighboring pyridyl rings. Instead, the centroid-tocentroid distance of 3.716 A˚ between neighboring pyridyl and tetrazole rings indicates a weak π-π interaction. Thus, the ladder-like chains are connected by the hydrogen bond and π-π interaction into a 3D supramolecular network. Structure of [Cu2(SCN)2(4-PyHBIm)]n (4). The complex 4 is a 2D coordination polymer. As shown in Figure 4a, the asymmetric unit contains two independent copper(I) ions, two thiocyanates, and a 4-PyHBIm. Both copper(I) ions adopt distorted tetrahedral geometry and are coordinated by two N and two S donors. Each thiocyanate as a 1,1,3-μ3-tridentate ligand coordinates to three copper(I) ions using a bridging S atom and N terminal. This leads to the formation of an interesting 2D copper-thiocyanate polymeric network (Figure 4b), which belongs to 4.82 topology where tridentate thiocyanate acts as a connector (Figure S3c, Supporting Information). The average Cu-N distance is 1.970 A˚. Cu-S distances vary from 2.3462(9) to 2.4625(10) A˚. The S-bridging angles of Cu1-S1-Cu2A and Cu2-S2A-Cu1A are 128.33(4) and 147.42(4)°, respectively. 4-PyHBIm plays a neutral bidentate ligand to link two interval copper(I) ions through Nim and Npy donors. The pyridyl group and benzimidazole aromatic plane are twisted by a dihedral angle of 35.698(2)°. The 4-PyHBIm ligands locate at both sides of the 2D copper-thiocyanate network (Figure 4c). The 2D polymeric layers are parallel packed with 4-PyHBIm interdigitated. Adjacent planes of 4-PyHBIm ligands are parallel with an interplane distance of 3.724(8) A˚, indicating the existence of weak π-π interaction.

Figure 4. (a) Asymmetric unit of 4, (b) 2D copper-thiocyanate network; 4-PyHBIm is omitted for clarity, (c) view of packing diagram.

Structure of [Cu2(SCN)2(3-PyHBIm)]n (5). The complex 5 is a 2D coordination polymer. As shown in Figure 5a, the asymmetric unit contains two independent copper(I) ions, two thiocyanates, and a 3-PyHBIm. Similar to the structure of 4, both copper(I) ions in 5 are in a distorted tetrahedral coordination environment and coordinated by two N and two S donors. The Cu-S bond distances vary from 2.3568(14) to 2.6062(14) A˚, while the Cu-N distances are from 1.913(4) to 2.044(3) A˚. Both thiocyanates act as a 1,1,3-μ3-tridentate ligand to coordinate three copper(I) ions through a bridging S donor and N terminal. The Cu2-S1-Cu1A and Cu1-S2-Cu2B angles are 104.19(5)

Article

Crystal Growth & Design, Vol. 9, No. 11, 2009

4631

Figure 5. (a) Asymmetric unit of 5, (b) 2D copper-thiocyanate network; 3-PyHBIm is omitted for clarity, (c) view of packing layers.

and 138.49(7)°, respectively. 3-PyHBIm is bidentate and binds to two adjacent copper(I) ions through Nim and Npy donors. The pyridyl group is nearly coplanar with a benzimidazole aromatic plane (dihedral angle 5.36°). The copper-thiocyanate network in 5 is obviously different than the network in 4. The bridging sulfur atoms of thiocyanates link copper(I) ions to form a 1D infinite chain. The 1D copper-sulfur chains are further connected by thiocyanate N terminal to form a wave-like 2D copper-thiocyanate polymeric network (Figure 5b), which belongs to 63 topology with tridentate thiocyanate as a connector (Figure S3d, Supporting Information). Such polymeric layers are further parallelly packed together. Bidentate 3-PyHBIm ligands locate at both sides of the 2D layer alternately (Figure 5c). Adjacent 3-PyHBIm ligands are not parallel and have a dihedral angle of 68.5°. Structure of [Cu2(SCN)2(2-PyBIm)(2-PyHBIm)]n (6). The complex 6 is a mixed-valence 1D 21 helical chain coordination polymer. As shown in Figure 6a, the asymmetric unit contains two independent copper ions, two thiocyanates, a neutral 2-PyHBIm, and an anionic 2-PyBIm ligand. Two copper centers show obviously different coordinate geometry. Cu1 adopts a distorted square-pyramidal geometry and coordinated by five N donors. The Cu-N bond distances in the basal plane vary from 1.978(5) to 2.006(5) A˚, while the apical position is occupied by N1 with a bond distance of 2.343(5) A˚. Cu2 adopts planar trigonal geometry and is coordinated by S1A and two N donors. The Cu2-S1A bond distance is 2.341(18) A˚. Interestingly, charge balance indicates that the complex 6 is a copper(I,II) mixed-valence compound, although copper(I) salt was used in the preparation reaction. This is confirmed by the bond valence sum (BVS) analysis.13 The BVS value of Cu1 is 2.16, which is consistent with a Cu2þ oxidation state. While the BVS value of Cu2 is 1.04, which is exactly consistent with a Cuþ oxidation state. Magnetic

Figure 6. (a) Asymmetric unit of 6, (b) view of 1D 21 helical chain; 2-PyHBIm is omitted for clarity, (c) left- and right-hand helical chains are alternately arranged in ABAB fashion.

susceptibility determination further confirmed that the complex 6 is a mixed-valence compound (Figure S4, Supporting Information). The effective magnetic moment (μeff) per Cu2 unit at 300 K is 1.89 μB, which is close to the spinonly value of one Cu2þ ion (1.73 μB, S = 1/2). This result indicates that the asymmetric unit of 6 contains both Cu(II) and Cu(I) ions. By lowering the temperature from 300 to 75 K, the μeff value decreased gradually from 1.89 to 1.83 μB, indicating a very weak antiferromagnetic interaction between Cu(II) ions. Both thiocyanates exhibit different coordinate modes. One is a 1,3-μ2-bidentate ligand, which links Cu2 and Cu1A with a Cu2-S1A-C25A angle of 103.1(2)°. The other one is unidentate, which binds to cuprous Cu2 through N terminal. The S2 atom has a weak interaction with Cu2A. The Cu2A 3 3 3 S2 distance is 2.927 A˚. The neutral 2-PyHBIm ligand is bidentate and chelates to Cu1. The Cu1-N1 distance of 2.343(5) A˚ is longer than that of Cu1-N2 1.978(5) A˚. The other 2-PyHBIm is deprotonated. The resulting 2-PyBIm anion is tridentate, which chelates to Cu1 through Npy, Nim, and coordinates to Cu2 through another Nim donor. Cu-N distances vary from 1.988(5) to 2.007(5) A˚. Obviously, 2-PyBIm anion chelates to Cu1 stronger than neutral 2-PyHBIm. Interestingly, 2-PyBIm anion and 1,3-μ2-thiocyanate connect the copper(I) and copper(II) ions to form a 1D 21 helical chain along the b-axis (Figure 6b). Such left- and right-hand helical chains are alternately arranged in ABAB fashion to form supramolecular layers (Figure 6c), which are further parallel stacked to form a supramolecular architecture.

4632

Crystal Growth & Design, Vol. 9, No. 11, 2009

Li et al.

Scheme 2

Figure 7. Emission spectra of 1-6.

Comparing the structures of 4-6, the rigid n-PyHBIm ligands exhibit different coordinate features due to varied pyridyl nitrogen positions. 4-PyHBIm ligand tends to bridge two interval copper(I) ions in the copper-thiocyanate chain, whereas 3-PyHBIm as bridging ligand coordinates to two adjacent copper(I) ions. 2-PyHBIm or 2-PyBIm anion tends to chelating coordination.14 Thiocyanate ligands adopt unidentate, 1,3-μ2-bidentate, and 1,1,3-μ3-tridentate coordinate modes in these complexes, which lead to diverse structural features. Comparison of Thiocyanate Coordinate Modes. An account of metal thiocyanate complexes has been reported which show versatile coordinate structural diversity.15 Thiocyanate can act as a terminal or bridging ligand. Except for two types of terminal coordinate modes, Teo and co-workers have depicted that there are theoretically 13 multidentate bridging modes, ranging from bi- to hexadentate as simplified in Scheme 2. However, not all of these coordinate modes have been observed. The most commonly observed modes are the uni-, bi-, and tridentate coordination. The ambidentate nature and the highly versatile bridging modes of the thiocyanate ligand also allow the formation of a wide variety of 1D, 2D, and 3D polymeric metal-thiocyanate coordinate structures. We ran a CCDC search and found 2250 cases reported for various thiocyanate complexes so far, of which 1639 thiocyanate complexes are unidentate and 611 thiocyanate complexes adopt bridging coordinate modes. Interestingly, the thiocyanate complexes using S-coordination are obviously more than those using N-coordination. This can be understood that S-donor is a soft base and N-donor is a hard base. The 1,1,1-μ3-, 1,1,1,3-μ4-, and 1,1,1,3,3-μ5-thiocyanate coordinate modes have not been observed to date. In our work, the thiocyanate ligands display uni-, bi-, tri-, and tetradentate coordinate modes, leading to the formation of diverse structural features. In particular, the complex 1 contains four 1,3-μ2-bidentate and one 1,1,1,3-μ4- tetradentate thiocyanate ligands. This is the first example of 1,1,1, 3-μ4-thiocyanate complex using S-donor as the bridging atom. The thiocyanate in 2 is unidentate N-coordinate. The 1D double-chain of 3 is constructed by 1,3-μ2-thiocyanates. In three n-PyHBIm complexes, 4 and 5 both contain 1,1,3-μ3-tridentate thiocyanate ligands, which bind to copper(I) centers through a bridging S atom and N terminal. The mixed-valence complex 6 possesses a 1,3-μ2-bidentate thiocyanate and an unidentate thiocyanate, and the latter binds to the Cu(II) ion through N-terminal.

Thermal Analysis. Thermal stability is an important parameter for metal-organic coordination polymers. When considering the coordination polymers as functional materials, we desire them to be thermal stable. Thermogravimetric analysis revealed that the coordination polymers 1, 2, 3, 4, 5, and 6 are stable under 230, 230, 250, 280, 290, and 280 °C, respectively. Then they start to decompose, releasing N-heterocyclic ligands up to 400 °C. The Cu2(SCN)2(py) or Cu(SCN) intermediates decompose continuously from ca. 400 to 800 °C. The final residues are CuO (Figure S5, Supporting Information). Photoluminescence. It is well-known that d10 transition metal complexes possess varied luminescent properties. Organic ligands and their coordinate modes obviously affect their emission wavelengths and luminescent mechanisms.16 The luminescent properties of the copper(I) complexes 1-6 were investigated (Figure 7). When excited with 358 nm light, the complexes 1 and 2 are strong yellow fluorescent emitters with an emission maximum at 559 and 570 nm, respectively. The free 3-Abpt ligand contains pyridyl and triazole conjugated groups, which shows a narrow emission peak at 388 nm and a broad shoulder peak centered at 441 nm (Figure S6, Supporting Information). The energy of the luminescence suggests that the most possible assignment for the emissions of 1 and 2 originates from ligand-to-metal charge transfer (LMCT). This phenomenon is also observed in reported copper(I) thiocyanate complexes such as [Cu2(SCN)2(dmpz)]n (582 nm) and [Cu2(SCN)2(dps)]n (538 nm).17 Similarly, the complexes 4 and 5 are also yellow fluorescent emitters with emission maximum at 569 and 530 nm, respectively, when excited with 380 nm light. The free 4-PyHBIm and 3-PyHBIm ligands show a narrow emission peak at ca. 387 nm and a broad shoulder peak near 413 nm. The most possible mechanism for above complex luminescence is also assigned to be LMCT emission. The complex 6 exhibits obviously different luminescent behavior. In contrast to the free 2-PyHBIm ligand emitted at 430 nm, the complex 6 shows a blue fluorescent emission maximum at 440 nm when excited with 380 nm light. The narrow peak and similar wavelength of the complex luminescence indicate that the mechanism is ligand-centered emission.18 Unlike the neutral 4/3-PyHBIm ligands in 4 and 5, one 2-PyHBIm ligand in 6 is deprotonated which may influence the complex luminescence. When excited with 358 nm light, complex 3 shows a blue fluorescent emission peak at 435 nm, which is near the emission maximum of free 4-ptz ligand at 463 nm. The luminescence of 3 is assigned to ligand-centered emission.

Article

Crystal Growth & Design, Vol. 9, No. 11, 2009

Conclusions The solvothermal reactions of CuSCN with N-hetrocycle ligands led to the assembly of six coordination polymers: 3D [Cu5(SCN)5(3-Abpt)2]n (1), 2D [Cu(SCN)(3-Abpt)]n (2), 1D [Cu(SCN)(4-Ptz)]n (3), 2D [Cu2(SCN)2(4-PyHBIm)]n (4), 2D [Cu2(SCN)2(3-PyHBIm)]n (5), and 1D [Cu2(SCN)2(2-PyBIm)(2-PyHBIm)]n (6). The thiocyanate ligands display diverse coordinate structural features, which adopt uni-, bi-, tri-, and tetradentate coordinate modes in 1-6. 1 is the first 1,1,1,3-μ4-tetradentate thiocyanate complex. 6 is an interesting 21 helical chain mixed-valence complex. 1-6 are all thermally stable up to 230-290 °C. These copper(I) complexes exhibit yellow or blue luminescence originating from ligand-to-metal charge transfer or ligand-centered emission.

(4)

(5) (6)

(7)

Acknowledgment. Project supported by the Leading Academic Discipline Project of Shanghai Municipal Education Commission (J50102), and the Research Foundation for Returned Chinese Scholars Overseas of Chinese Education Ministry (7A14219).

(8)

Supporting Information Available: Crystallographic data for 1-6 in CIF format, and additional characterization data (IR spectra, powder XRD, topologic nets, TG curves, luminescence of free ligands, and magnetic susceptibilities of 6) are presented. This information is available free of charge via the Internet at http://pubs.acs.org/.

(10)

References

(11)

(1) (a) Ferey, G. Chem. Soc. Rev. 2008, 37, 191–214. (b) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O'Keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127–1129. (c) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem. Res. 2005, 38, 371–380. (d) Rao, C. N. R.; Natarajan, S.; Vaidhyanathan, R. Angew. Chem., Int. Ed. 2004, 43, 1466–1496. (e) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334–2375. (f) James, S. L. Chem. Soc. Rev. 2003, 32, 276–288. (2) (a) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature 2003, 423, 705–714. (b) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O'Keefe, M.; Yaghi, O. M. Science 2002, 295, 469–472. (c) Furukawa, H.; Kim, J.; Ockwig, N. W.; O'Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2008, 130, 11650– 11661. (d) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972– 983. (e) Hong, M. C. Cryst. Growth Des. 2007, 7, 10–14. (f) Li, M. X.; Miao, Z. X.; Shao, M.; Liang, S. W.; Zhu, S. R. Inorg. Chem. 2008, 47, 4481–4489. (3) (a) Niu, C. Y.; Wu, B. L.; Zheng, X. F.; Zhang, H. Y.; Hou, H. W.; Niu, Y. Y.; Li, Z. J. Cryst. Growth Des. 2008, 8, 1566–1574. (b) Wang, X. W.; Chen, J. Z.; Liu, J. H. Cryst. Growth Des. 2007, 7, 1227–1229. (c) Zhou, L. J.; Wang, Y. Y.; Zhou, C. H.; Wang, C. J.; Shi, Q. Z.; Peng, S. M. Cryst. Growth Des. 2007, 7, 300–306. (d) Zhang, J. P.; Lin, Y. Y.; Huang, X. C.; Chen, X. M. J. Am. Chem. Soc. 2005,

(9)

(12)

(13) (14) (15) (16)

(17) (18)

4633

127, 5495–5506. (e) Klingele, M. H.; Brooker, S. Coord. Chem. Rev. 2003, 241, 119–132. (a) Chen, L. J.; He, X.; Xia, C. K.; Zhang, Q. Z.; Chen, J. T.; Yang, W. B.; Lu, C. Z. Cryst. Growth Des. 2006, 6, 2076–2085. (b) Xia, C. K.; Lu, C. Z.; Zhang, Q. Z.; He, X.; Zhang, J. J.; Wu, D. M. Cryst. Growth Des. 2005, 5, 1569–1574. (c) He, X. F.; Vogels, C. M.; Decken, A.; Westcott, S. A. Polyhedron 2004, 23, 155–160. (a) Ohba, M.; Okawa, H. Coord. Chem. Rev. 2000, 198, 313–328. (b) Zhang, J. M.; Batten, S. R.; Du, M. Inorg. Chem. 2005, 44, 3371– 3373. (a) Jaremko, L.; Kirillov, A. M.; Smolenski, P.; Lis, T.; Pombeiro, A. J. L. Inorg. Chem. 2008, 47, 2922–2924. (b) Sekiya, R.; Nishikiori, S. I.; Ogura, K. J. Am. Chem. Soc. 2004, 126, 16587–16600. (c) Uemura, K.; Kitagawa, S.; Fukui, K.; Saito, K. J. Am. Chem. Soc. 2004, 126, 3817–3828. (d) Zhang, W. J.; Wu, X. T.; Wu, B.; Yu, S. Y.; Santoni, G.; Rehder, D. Inorg. Chem. 2003, 42, 1130–1134. (e) Zhang, X. M.; Hao, Z. M.; Wu, H. S. Inorg. Chem. 2005, 44, 7301– 7303. (f) Sekiya, R.; Nishikiori, S. I.; Ogura, K. Inorg. Chem. 2006, 45, 9233–9244. (a) He, X.; Lu, C. Z.; Yuan, D. Q.; Chen, S. M.; Chen, J. T. Eur. J. Inorg. Chem. 2005, 2181–2188. (b) Lang, J. P.; Xu, Q. F.; Chen, Z. N.; Abrahams, B. F. J. Am. Chem. Soc. 2003, 125, 12682–12683. (c) Lenthall, J. T.; Anderson, K. M.; Smith, S. J.; Steed, J. W. Cryst. Growth Des. 2007, 7, 1858–1862. (a) Cheng, L.; Zhang, W. X.; Ye, B. H.; Lin, J. B.; Chen, X. M. Inorg. Chem. 2007, 46, 1135–1143. (b) Detert, H.; Schollmeier, D. Synthesis 1999, 6, 999–1004. (c) Schiffmann, R.; Neugebauer, A.; Klein, C. D. J. Med. Chem. 2006, 49, 511–522. (a) Sheldrick, G. M. SHELXS-97, Program for the Solution of Crystal Structures; University of G€ottingen: Germany, 1997. (b) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structures; University of G€ottingen: Germany, 1997. Dong, Y. B.; Wang, H. Y.; Ma, J. P.; Huang, R. Q.; Smith, M. D. Cryst. Growth Des. 2005, 5, 789–800. (a) Himo, F.; Demko, Z. P.; Noodleman, L.; Sharpless, K. B. J. Am. Chem. Soc. 2003, 125, 9983–9987. (b) Xue, X.; Wang, X. S.; Wang, L. Z.; Xiong, R. G.; Abrahams, B. F.; You, X. Z.; Xue, Z. L.; Che, C. M. Inorg. Chem. 2002, 41, 6544–6546. (a) Luo, T. T.; Tsai, H. L.; Yang, S. L.; Liu, Y. H.; Yadav, R. D.; Su, C. C.; Ueng, C. H.; Lin, L. G.; Lu, K. L. Angew. Chem., Int. Ed. 2005, 44, 6063–6067. (b) Jiang, C.; Yu, Z. P.; Wang, S. J.; Jiao, C.; Li, J. M.; Wang, Z. Y.; Cui, Y. Eur. J. Inorg. Chem. 2004, 3662–3667. (c) Lin, P.; Clegg, W.; Harrington, R. W.; Henderson, R. A. Dalton Trans. 2005, 2388–2394. (a) Liu, W.; Thorp, H. H. Inorg. Chem. 1993, 32, 4102–4105. (b) Thorp, H. H. Inorg. Chem. 1998, 37, 5690–5692. Wang, H.; Li, M. X.; Shao, M.; He, X. Polyhedron 2007, 26, 5171– 5176. Zhang, H.; Wang, X. M.; Zhang, K. C.; Teo, B. K. Coord. Chem. Rev. 1999, 183, 157–195. (a) Colacio, E.; Kivekas, R.; Lloret, F.; Sunberg, M.; Suarez-Varela, J.; Bardaji, M.; Laguna, A. Inorg. Chem. 2002, 41, 5141–5149. (b) Phillips, D. L.; Che, C. M.; Leung, K. H.; Mao, Z.; Tse, M. C. Coord. Chem. Rev. 2005, 249, 1476–1490. (a) Hao, Z. M.; Zhang, X. M. Cryst. Growth Des. 2007, 7, 64–68. (b) N€ather, C.; Greve, J.; Jeb, I.; Wickleder, C. Solid State Sci. 2003, 5, 1167–1176. Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Chem. Soc. Rev. 2009, 38, 1330–1352.