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Nov 24, 2010 - An efficient route to construct three-dimensional (3-D) M/S/Cu nest-cluster-based coordination polymers has been developed. By this met...
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DOI: 10.1021/cg1009779

Syntheses, Structural, Theoretical, and Nonlinear Optical Studies of Non-Interpenetrating Three-Dimensional Nest-Shaped-Cluster [MoOS3Cu3]-Based Coordination Polymers

2011, Vol. 11 100–109

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Jinfang Zhang,†,‡ Suci Meng,† Yinglin Song,§ Yimeng Zhou,†,# Yuan Cao,‡ Jianghua Li,† Huajian Zhao,‡ Jingchun Hu,† Jinhua Wu,† Mark G. Humphrey,*, and Chi Zhang*,†,‡ †

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Functional Molecular Materials Research Centre, Scientific Research Academy, School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, P. R. China, ‡Functional Molecular Materials Research Centre, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China, §School of Physical Science and Technology, Suzhou University, Suzhou 215006, P. R. China, #Liberal Arts College, Carleton College, Northfield, Minnesota 55057, United States, and Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 0200, Australia Received July 23, 2010; Revised Manuscript Received October 5, 2010

ABSTRACT: An efficient route to construct three-dimensional (3-D) M/S/Cu nest-cluster-based coordination polymers has been developed. By this method, cyanide bridges have been successfully introduced to build three new non-interpenetrating 3-D nest-shaped-cluster [MoOS3Cu3]-based coordination polymers, 3¥{[(NO3)⊂(Me4N)3]⊂[MoOS3Cu3(CN)3]} (1) and 3 0 ¥{[(NH4) 3 2DMF]⊂[Mo2O2S6Cu6(CN)3(L)4]} (L1 =bipy=4,4 -bipyridine, 2; L2 =bpee = 1,2-bis(4-pyridyl)ethene, 3). The structures of 1-3 have been established by elemental analysis, IR, UV-vis, and single-crystal X-ray crystallographic studies. 1 is the first non-interpenetrating 3-D 6-connected M/S/Cu coordination polymer and possesses an unprecedented dual-inclusive structure, rare “ACS” topology and huge free volume. 2 and 3 possess unusual non-interpenetrating 3-D pillar-layer-alternating honeycomb-like frameworks with diamondoid topologies. Nonlinear optical (NLO) properties of these clusters were investigated by Z-scan employing 5 ns pulses at 532 nm, with 1-3 showing strong third-order NLO properties. Time-dependent density functional theory (TD-DFT) studies have afforded insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials.

Introduction The last two decades have witnessed significant progress in the realm of coordination polymers (CPs).1 The extensive efforts devoted to such species have not only led to the fabrication of a large number of CPs with diverse topologies and aesthetic beauty, but also established some rational design strategies to construct functionalized molecular materials to target special applications.1-3 As an interesting category of CPs, heterothiometallic M/S/Cu (M = Mo, W) cluster-based CPs have attracted much attention for their intriguing structures and potential applications, such as nonlinear optical (NLO) materials, and as models of the active sites of various metalloenzymes and in catalytic reactions.4-9 Several methods have been successfully developed to construct M/S/Cu CPs with diverse frameworks (e.g., solvothermal reactions, solid-state reactions at low temperatures, cluster-based reactions, etc.).5 However, the existing synthetic methods suffer from the very low solubilities of M/S/Cu cluster-based CPs in polar solvents, rapid precipitation rendering structural characterization of these species very difficult. As a result of this problem, terminal halogen atoms or the large counterions are usually introduced into the starting materials or the preformed clusters when synthesizing M/S/Cu cluster-based CPs.6 Such halogen atoms or large counterions can improve, to some extent, the solubilities of M/S/Cu clusters in reaction *Corresponding authors: (C.Z.): Fax: þ86-511-88797815. E-mail: chizhang@ ujs.edu.cn; (M.G.H.): Fax: þ61-2-61250760. E-mail: mark.humphrey@ anu.edu.au. pubs.acs.org/crystal

Published on Web 11/24/2010

solutions, but impede their polymerization, heavily constraining the development of the chemistry of heterothiometallic M/S/Cu CPs; it is of crucial importance to develop effective methods for overcoming these difficulties. Only a few 3-D M/S/Cu CPs have been reported thus far,7,8 most of them possessing interpenetrating networks;8 in particular, all known 3-D nest [MOS3Cu3]-based species crystallize with interpenetrating nets and little variety in their topological structures.8a-c For example, {[NH4][W2O2S6Cu6I3(4,40 -bipy)4] 3 5H2O}n (a) has a 3-fold interpenetrating anionic diamondoid framework;8a {[W4O4S12Cu12Cl2(4,40 -bipy)12]Cl2 3 4H2O}n (b) exhibits a 3-fold interpenetrating cationic diamondoid network;8b and {[MoOS3Cu3(NCS)(4,40 -bipy)2.5] 3 3(aniline)}n (c) shows a 3-fold interpenetrating neutral diamondoid network.8c This may be because the driving force for the construction of these 3-D M/S/Cu cluster-based interpenetrating networks is the presence of long bridging ligands, such as 4,40 -bipy, which are sufficiently long that the resultant voids facilitate interpenetration. The aforementioned examples were obtained serendipitously; there are no design criteria for the control of the conformation of heterothiometallic M/S/Cu cluster-based CPs with interpenetrating or non-interpenetrating networks. We recently communicated the use of cyano bridges to link planar pentanuclear [MS4Cu4]2þ and T-shaped tetranuclear [WS4Cu3]þ building clusters, and the successful construction of non-interpenetrating three-dimensional (3-D) networks.7 Inspired by this idea, we report herein an interdiffusion method for the efficient construction of three new noninterpenetrating heterothiometallic 3-D M/S/Cu CPs based on r 2010 American Chemical Society

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Table 1. Crystallographic and Structure Refinement Data for 1-3 molecular formula formula weight temperature (K) wavelength (A˚) crystal system space group a (A˚) b (A˚) c (A˚) R () β () γ () V (A˚3) Z Fcalc (g cm-3) μ (mm-1) F (000) reflections collected unique reflections Rint no. parameters GOF R1 [I > 2σ(I )] wR2 [I > 2σ(I )] ΔFmax/ΔFmin (e A˚-3)

1

2

3

C15H36Cu3MoN7O4S3 761.31 213(2) 0.71070 hexagonal P63mc 13.5715(17) 13.5715(17) 8.7125(12) 90 90 120 1389.7(3) 2 1.819 2.964 768 13084 961 0.0307 68 1.117 0.0291 0.0785 0.736/-0.317

C49H50Cu6Mo2N14O4S6 1664.63 153(2) 0.71070 monoclinic C2/c 27.543(4) 13.7619(18) 17.350(2) 90 99.340(4) 90 6489.2(15) 4 1.704 2.544 3311 31213 5927 0.0773 315 1.226 0.0760 0.1536 0.759/-0.746

C57H58Cu6Mo2N14O4S6 1768.77 193(2) 0.71073 monoclinic C2/c 27.550(5) 13.281(3) 20.356(4) 90 97.03(3) 90 7392(3) 4 1.589 2.239 3535 33440 6457 0.0617 333 1.148 0.0653 0.1400 0.816/-0.646

nest-shaped [MoOS3Cu3]þ building clusters and CN- bridges. Single-crystal X-ray diffraction studies reveal 3¥{[(NO3)⊂(Me4N)3]⊂[MOS3Cu3(CN)3]} (1) to be the first 6-connected M/S/Cu CP exhibiting a novel non-interpenetrating 3-D honeycomb framework with an unprecedented dual-inclusive structure, rare “ACS” topology and huge free volume, and show that 3 ¥{[(NH4) 3 2DMF]⊂[M2O2S6Cu6(CN)3(L)4]} (L1 = bipy, 2; L2 = bpee, 3) have an unusual non-interpenetrating 3-D pillar-layer-alternating honeycomb-like framework and diamondoid topology. In addition, NLO studies on these clusters demonstrate that these new 3-D nest [MOS3Cu3]-based CPs exhibit strong third-order NLO properties. Finally, timedependent density functional theory (TD-DFT) studies provide insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials. Experimental Section The reactions and manipulations were conducted using standard Schlenk techniques under an atmosphere of argon. The starting material (NH4)2MoOS3 was prepared according to the literature procedure.10 The solvents were carefully dried and distilled prior to use; other chemicals were commercially available and used as received. Elemental analysis for carbon, hydrogen, and nitrogen were performed on a Perkin-Elmer 240C elemental analyzer. Infrared spectra were recorded with a Nicolet FT-170SX Fourier transform spectrometer (KBr pellets). Electronic spectra were measured on a Shimadzu UV-3100 spectrophotometer. The X-ray powder diffraction (XRPD) measurements were recorded on a Bruker D8 ADVANCE powder X-ray diffractometer (Cu KR = 1.5418 A˚). Preparation of 3¥{[(NO3)⊂(NMe4)3]⊂[MoOS3Cu3(CN)3]} 1. [NH4]2MoOS3 (0.24 g, 1 mmol) was added to 10 mL of DMF and the resultant solution was stirred for 5 min. CuCN (0.27 g, 3 mmol) was added to the black-red solution, the reacting system immediately turning black in color. Stirring was continued for an additional 2 h, after which the black solution was filtered and the black-red filtrate was carefully layered with 2 mL of DMF. Ten milliliters of a saturated solution of [NMe4]NO3 in methanol was in turn carefully layered on the top. Several days later, 1 was obtained as black-red hexagonal-prismatic crystals (yield: 0.32 g, 42% based on Mo). Anal. Calcd. for C15H36Cu3MoN7O4S3: C, 23.66; H, 4.77; N, 12.88%. Found: C, 23.82; H, 4.85; N, 12.94%. IR (KBr pellets, cm-1): 3028w, 2108vs, 1484vs, 1362vs, 954vs, 916vs, 447vs. UV/vis (DMF, λmax/nm, 103 ε/cm-1 mol-1 dm3): 387 (3.21), 267 (5.90).

Preparation of 3¥{[(NH4) 3 2DMF]⊂[Mo2O2S6Cu6(CN)3(bipy)4]} 2. The same procedure as in the preparation of 1 was applied to synthesize 2 except using a solution of bipy in methanol (0.3 mol dm-3) instead of the saturated solution of [NMe4]NO3 in methanol; 2 was obtained as black-red rhombic crystals (0.27 g, 32% based on Mo). Anal. Calcd. for C49H50Cu6Mo2N14O4S6: C, 35.35; H, 3.03; N, 11.78%. Found: C, 35.26; H, 3.15; N, 11.90%. IR (KBr pellets, cm-1): 2127vs, 1661vs, 1599vs, 915vs, 443vs. UV/vis (DMF, λmax/ nm, 103 ε/cm-1 mol-1 dm3): 402 (8.24), 273 (27.9). Preparation of 3¥{[(NH4) 3 2DMF]⊂[Mo2O2S6Cu6(CN)3(bpee)4]} 3. The same procedure as in the preparation of 1 was applied to synthesize 3 except using a solution of bpee in methanol (0.2 mol dm-3) instead of the saturated solution of [NMe4]NO3 in methanol; 3 was obtained as black-red rhombic crystals (0.28 g, 32% based on Mo). Anal. Calcd. for C57H58Cu6Mo2N14O4S6: C, 38.71; H, 3.31; N, 11.09%. Found: C, 38.68; H, 3.28; N, 11.12%. IR (KBr pellets, cm-1): 2129vs, 1603vs, 910vs, 827vs, 550vs, 444vs. UV/vis (DMF, λmax/nm, 104 ε/cm-1 mol-1 dm3): 399 (3.83), 299 (43.4), 289 (44.0), 226 (11.4). X-ray Structure Determinations. Crystals of 1-3 suitable for single-crystal X-ray analyses were obtained directly from the above preparations. All measurements were made on a Rigaku Mercury CCD X-ray diffractometer by using graphite monochromated Mo KR radiation (λ=0.71070 A˚). Single crystals of 1-3 were mounted with grease at the top of a glass fiber. Cell parameters were refined on all observed reflections by using the program CrystalClear (Rigaku and MSC, Ver. 1.3, 2001). The collected data were reduced by the program CrystalClear and an absorption correction (multiscan) was applied. The reflection data for 1-3 were also corrected for Lorentz and polarization effects. The crystal structures of 1-3 were solved by direct methods and refined on F2 by full-matrix least-squares methods using the SHELXTL software package.11 All non-hydrogen atoms in 1 and 2 were refined anisotropically, while some of the disordered atoms in 3 were refined isotropically. The hydrogen atoms were placed at calculated positions. After completing the initial structure solution for 2 and 3, many diffuse electron density peaks remained in the channels parallel to the c axis. No satisfactory disorder model could be found, and for further refinements, the contributions of the missing solvent molecules (DMF) and counter-cations ([NH4]þ) to the diffraction pattern were subtracted from the observed data by the “SQUEEZE” method as implemented in PLATON.12,13 The coexisting solvent molecules (DMF) and countercation ([NH4]þ) have also been confirmed by the elemental analysis and infrared spectral measurements on 2 and 3. A summary of the key crystallographic information and the selected bond lengths and bond angles for 1-3 are listed in Tables 1-4, respectively.

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Table 2. Selected Bond Distances (A˚) and Bond Angles () for 1a 3

¥{[(NO3)⊂(NMe4)3]⊂[MoOS3Cu3(CN)3]}

Mo(1)-O(1) 1.693(8) Cu(1)-C(1) 1.935(6) Cu(1)-S(1) 2.3418(8) O(1)-Mo(1)-S(1) 111.05(4) C(1)-Cu(1)-N(1)#3 112.4(2) N(1)#3-Cu(1)-S(1) 101.39(9)

1

Mo(1)-S(1) 2.2570(16) Cu(1)-N(1)#3 2.137(5) N(1)-C(1) 1.152(8) S(1)#1-Mo(1)-S(1) 107.85(5) C(1)-Cu(1)-S(1) 118.37(10) S(1)#1-Cu(1)-S(1) 102.33(7)

a Symmetry transformations used to generate equivalent atoms: #1 -y þ 1, x - y, z; #3 -x þ 1, -y, z - 1/2.

Table 3. Selected Bond Distances (A˚) and Bond Angles () for 2a 3 ¥{[(NH4) 3 2DMF]⊂[Mo2O2S6Cu6(CN)3(bipy)4]}

Mo(1)-O(1) Mo(1)-S(3) Cu(1)-C(2) Cu(1)-N(6) Cu(2)-C(1) Cu(2)-S(2) Cu(3)-N(1)#1 Cu(3)-S(2) Cu(3)-S(3) O(1)-Mo(1)-S(1) O(1)-Mo(1)-S(2) S(1)-Mo(1)-S(3) C(2)-Cu(1)-N(6) C(2)-Cu(1)-S(1) N(2)-Cu(1)-S(3) N(6)-Cu(1)-S(3) S(1)-Cu(1)-S(3) C(1)-Cu(2)-N(3) N(3)-Cu(2)-S(2) S(2)-Cu(2)-S(1) N(1)#1-Cu(3)-N(5)#2 N(5)#2-Cu(3)-S(2) N(5)#2-Cu(3)-S(3)

1.712(5) 2.265(2) 2.00(3) 2.098(7) 1.925(7) 2.287(2) 1.947(8) 2.278(2) 2.290(2) 110.8(2) 110.3(2) 107.78(8) 105.3(11) 113.3(10) 113.3(9) 109.4(2) 105.75(8) 103.8(3) 109.26(19) 106.32(8) 93.1(3) 106.14(18) 111.03(18)

Mo(1)-S(1) Mo(1)-S(2) Cu(1)-N(2) Cu(1)-S(1) Cu(1)-S(3) Cu(2)-N(3) Cu(2)-S(1) Cu(3)-N(5)#2 O(1)-Mo(1)-S(3) S(1)-Mo(1)-S(2) S(3)-Mo(1)-S(2) N(2)-Cu(1)-N(6) N(2)-Cu(1)-S(1) N(6)-Cu(1)-S(1) C(2)-Cu(1)-S(3) N(3)-Cu(2)-S(1) C(1)-Cu(2)-S(2) C(1)-Cu(2)-S(1) N(1)#1-Cu(3)-S(2) N(1)#1-Cu(3)-S(3) S(2)-Cu(3)-S(3)

2 2.261(2) 2.270(2) 1.90(3) 2.291(2) 2.295(2) 2.125(7) 2.317(2) 2.166(6) 110.8(2) 108.84(8) 108.14(8) 103.7(9) 118.5(8) 105.85(19) 116.7(10) 97.98(19) 118.1(2) 119.1(2) 123.0(2) 115.0(2) 107.03(8)

a Symmetry transformations used to generate equivalent atoms: #1 -x þ 1/2, y þ 1/2, -z þ 1/2; #2 -x þ 1/2, -y þ 1/2, -z þ 1.

Optical Measurements. The third-order NLO absorptive and refractive properties of clusters 1, 2 and 3 were determined by performing Z-scan measurements.14 DMF solutions of clusters 1 (1.0  10-4 mol dm-3), 2 (1.0  10-4 mol dm-3), and 3 (1.74  10-4 mol dm-3) were placed in a 5-mm quartz cuvette for the nonlinear optical measurements, which were performed with linearly polarized 5-ns pulses at 532 nm generated from a Q-switched frequencydoubled Nd:YAG laser. The clusters 1-3 are stable toward air and laser light under experimental conditions. The spatial profiles of the optical pulses were of nearly Gaussian transverse mode. The pulsed laser was focused onto the sample cell with a 30 cm focal length mirror. The spot radius of the laser beam was measured to be 55 μm (half-width at 1/e2 maximum). The energy of the input and output pulses were measured simultaneously by precision laser detectors (Rjp-735 energy probes), which were linked to a computer by an IEEE interface,15 while the incident pulse energy was varied by a Newport compensated attenuator. The interval between the laser pulses was chosen to be 1 Hz to avoid the influence of thermal and long-term effects. The samples were mounted on a translation stage that was controlled by computer to move along the axis of the incident laser beam (Z-direction) with respect to the focal point. To determine both the sign and magnitude of the nonlinear refraction, a 0.2 mm diameter aperture was placed in front of the transmission detector and the transmittance recorded as a function of the sample position on the Z axis (closed-aperture Z-scan). To measure the nonlinear absorption, the Z-dependent sample transmittance was taken without the aperture (open-aperture Z-scan).

Results and Discussion Synthetic Method. Solvothermal reactions, solid-state reactions at low temperatures, cluster-based reactions, etc. can

Table 4. Selected Bond Distances (A˚) and Bond Angles () for 3a 3 ¥{[(NH4) 3 2DMF]⊂[Mo2O2S6Cu6(CN)3(bpee)4]} 3 Mo(1)-O(1) 1.719(4) Mo(1)-S(1) 2.2526(17) Mo(1)-S(2) 2.2620(16) Mo(1)-S(3) 2.2668(17) Cu(1)-N(4) 1.962(7) Cu(1)-N(1) 2.159(5) Cu(1)-S(1) 2.2850(18) Cu(1)-S(3) 2.2930(17) Cu(2)-C(1)#1 1.938(6) Cu(2)-N(5) 2.155(5) Cu(2)-S(3) 2.3038(18) Cu(2)-S(2) 2.3182(17) Cu(3)-N(2) 1.95(2) Cu(3)-C(2) 1.96(3) Cu(3)-N(3) 2.073(5) Cu(3)-S(2) 2.2788(17) Cu(3)-S(1) 2.2884(19) O(1)-Mo(1)-S(1) 110.11(19) O(1)-Mo(1)-S(2) 110.76(17) S(1)-Mo(1)-S(2) 107.91(6) O(1)-Mo(1)-S(3) 111.09(19) S(1)-Mo(1)-S(3) 108.13(7) S(2)-Mo(1)-S(3) 108.74(6) N(4)-Cu(1)-N(1) 93.5(2) N(4)-Cu(1)-S(1) 114.31(17) N(1)-Cu(1)-S(1) 107.85(16) N(4)-Cu(1)-S(3) 124.90(17) N(1)-Cu(1)-S(3) 108.26(16) S(1)-Cu(1)-S(3) 106.13(7) C(1)#1-Cu(2)-S(3) 115.20(17) C(1)#1-Cu(2)-N(5) 104.6(2) N(5)-Cu(2)-S(3) 114.09(15) C(1)#1-Cu(2)-S(2) 120.70(18) N(5)-Cu(2)-S(2) 95.15(16) S(3)-Cu(2)-S(2) 105.58(6) N(2)-Cu(3)-N(3) 99.2(7) C(2)-Cu(3)-N(3) 102.6(8) N(2)-Cu(3)-S(2) 118.1(6) C(2)-Cu(3)-S(2) 121.5(8) N(3)-Cu(3)-S(2) 106.34(16) N(2)-Cu(3)-S(1) 116.6(6) C(2)-Cu(3)-S(1) 110.2(7) N(3)-Cu(3)-S(1) 109.65(17) S(2)-Cu(3)-S(1) 106.12(6) a Symmetry transformations used to generate equivalent atoms: #1 -x - 1/2, y þ 1/2, -z - 1/2.

be employed to construct M/S/Cu cluster-based CPs.5 However, heterothiometallic M/S/Cu CPs exhibiting new 3-D topological structures are still very scarce.7,8 This can be attributed to the fact that these reactions usually suffer from a low solubility of the 3-D M/S/Cu cluster-based CPs in common organic solvents, rendering structural characterization of these species quite difficult. The terminal halogen atoms or large counterions are usually introduced into the starting materials or the preformed clusters when synthesizing M/S/Cu cluster-based CPs. Such terminal halogen atoms or large counterions can significantly improve the solubilities of M/S/Cu clusters in reaction solutions but frequently impede their polymerization. This renders the obtention of 3-D frameworks highly problematic. As a result, there are no 3-D M/S/Cu CPs primarily linked by bridging halide ligands, and large [PPh4]þ cations have thus far only induced the formation of discrete, one- or two dimensional (1-D or 2-D) M/S/Cu clusters.4-8 Eliminating precipitation while avoiding terminal halide ligands or large counterions in reaction systems is critically important for the synthesis of heterothiometallic M/S/Cu CPs with unique 3-D structures. The interdiffusion procedure has been developed to overcome the current shortcomings. In this method, a buffer band is utilized to separate the two solutions, one of which contains the soluble M/S/Cu cluster, while the other contains a precipitating agent such as a counterion, bridging ligand, etc. When these two solutions diffuse into the buffer band and meet, the M/S/Cu CPs slowly form and crystallize in the buffer band. The rate of crystal growth can be conveniently controlled by adjusting the length of the buffer band. Through this approach, diverse M/S/Cu CPs can be designed by varying the solutions (i.e., using different M/S/Cu clusters and precipitating agents). For example, when two solutions containing nest-shaped [MOS3Cu3]þ clusters and either [NMe4]NO3, bipy or bpee, were separated by a DMF buffer band, three new 3-D heterothiometallic nest [MOS3Cu3]based CPs were successfully constructed. However, in contrast to this new interdiffusion method, when [NMe4]NO3, bipy, or bpee was added directly to a solution of nest-shaped

Article

Figure 1. Packing diagram of 1 (ball-and-stick representation), viewed along (a) the c-axis and (b) the a- or b-axis, showing the hexagonal channels occupied by [NMe4]þ cations and NO3- anions, and irregular shaped channels stacking in an ABAB manner, respectively (S yellow, C gray, N blue, Cu red, Mo green, O pink).

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[MOS3Cu3]þ clusters, a thick precipitate appeared immediately in the reaction solution. The interdiffusion approach is clearly very effective for the preparation of 3-D heterothiometallic M/S/Cu cluster-based CPs. Most 3-D M/S/Cu cluster-based CPs possess interpenetrating networks.8 In particular, all reported 3-D nest [MOS3Cu3]-based species exist as interpenetrating nets.8a-c This is likely to arise from their long bridging ligands, which can support M/S/Cu cluster-based networks with sufficient interbuilding-clusters space for interpenetration. For instance, the structures of a, b, and c (interpenetrating diamondoid networks: see Introduction) are driven by the long 4,40 -bipy bridging ligand, the average distances between M atoms in the connected nest-shaped [MOS3Cu3]þ clusters being 13.3082, 13.2842, and 14.0072 A˚ in their respective frameworks.8a-c Shorter bridging ligands would be expected to favor formation of non-interpenetrating 3-D M/S/Cu CPs. Cyanide bridges are shorter than 4,40 -bipy bridges, but longer than halide bridges. When CN- bridges are used in 1 for framework construction, non-interpenetrating 3-D anionic nets are generated that possess huge effective free volumes. Although 2 and 3 contain the longer bipy or bpee double bridges, their construction is dominated by the CNbridges because the CN- and bipy (bpee) bridges are in the molar ratio of 3:1, resulting in non-interpenetrating 3-D frameworks for 2 and 3 as well. Structural analysis reveals that the average distances between the Mo atoms in connected nest-shaped [MoOS3Cu3]þ clusters are 8.9650, 10.9104, and 11.4193 A˚ for 1-3, respectively, significantly shorter than those found in a, b and c with interpenetrating 3-D networks. This confirms that the CN- bridge is playing a key role in the construction of these non-interpenetrating 3-D nest [MOS3Cu3]-based coordination polymers. Crystal Structure of 3¥{[(NO3)⊂(NMe4)3]⊂[MoOS3Cu3(CN)3]} 1. X-ray crystallographic analysis reveals that 1 crystallizes in the hexagonal space group P63mc and exhibits a novel non-interpenetrating 3-D honeycomb framework (Figure 1). 1 is the first 3-D nest [MoOS3Cu3]-based coordination polymer constructed from single bridges. As shown in Figure 2a, each building cluster [MoOS3Cu3]þ exhibits C3v symmetry and connects another six crystallographically

Figure 2. (a) Partial view of the 3-D anionic ball-and-stick plot for 1, showing the 6-connected node of the nest-shaped building cluster [MoOS3Cu3]þ; (b) topological view of 1 with nodes highlighted in pink emphasizing the trigonal prismatic connectivity; (c) two groups of [NMe4]þ cations forming the inner channel; for clarity, only the central N atoms are shown for the [NMe4]þ cations (S yellow, C gray, N blue, Cu red, Mo green, O pink).

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Figure 4. (a) Partial view of the 3-D anionic ball-and-stick plot for 2, showing the 4-connected node of the nest-shaped building cluster [MoOS3Cu3]þ; all H atoms have been omitted for clarity (S yellow, C gray, N blue, Cu red, Mo green, O pink); (b) topological view of 2, yellow balls representing the [MoOS3Cu3]þ nodes. The distances between adjoining tetrahedral nodes are 8.810 (in pink), 9.384 (in green), and 12.605 (in blue) A˚.

Figure 3. (a) Packing diagram of 2 viewed along the c-axis, showing the honeycomb framework; (b) overall view of 2 down the b-axis, demonstrating the pillar-layer-alternating framework; (c) packing diagram of 2 along the a-axis, showing the corrugated sheets and bipy pillars stacking in an ABAB manner. A ball-and-stick model has been applied, and all H atoms and terminal bipy ligands have been omitted for clarity (S yellow, C gray, N blue, Cu red, Mo green, O pink).

equivalent [MoOS3Cu3]þ units through single cyanide bridges to furnish a trigonal prismatic coordination geometry. In each building cluster [MoOS3Cu3]þ, the Mo atom is linked by three μ3-S atoms and one terminal O atom, giving rise to a tetrahedral coordination geometry; the three Cu atoms have the same

four-coordinate environment, each formed by two μ3-S and two cyanide bridges. From a topological viewpoint, each building cluster [MoOS3Cu3]þ in 1, linked by another six equivalent units (Figure 2a), can be regarded as a 6-connected node, the first example in Mo/S/Cu cluster-based coordination polymers. The topology of 1 is an unusual six-connected 4966 network, termed an “ACS” net (Figure 2b); this is the first example of an “ACS” net found in the field of Mo/S/Cu(Ag) coordination polymers, and a rare example in the broader field of metalorganic frameworks.16 The packing diagram of 1 down the a- or b-axis exhibits irregular-shaped channels with an interesting ABAB stacking manner (Figure 1b). When viewed along the c axis, the packing diagram reveals hexagonal channels that are occupied by [NMe4]þ cations and NO3- anions (Figure 1a), very rare examples of channels that simultaneously include both cations and anions; only one example possessing this feature has previously been reported for M/S/Cu(Ag) clusters.5c Perhaps more interestingly, the [NMe4]þ cations in each hexagonal channel can be divided into two groups, each of which can form a trigonal prism (Figure 2c). The two trigonal prisms interlace each other to generate a smaller

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Figure 5. (a) Partial view of the 3-D anionic ball-and-stick plot for 3, showing the 4-connected node of the nest-shaped building cluster [MoOS3Cu3]þ; H atoms are omitted for clarity; (b) packing diagram of 3 (ball-and-stick representation) viewed along the c-axis, showing the honeycomb framework; terminal bpee ligands and H atoms have been omitted (S yellow, C gray, N blue, Cu red, Mo green, O pink).

hexagonal channel in which NO3- anions are situated (Figure 2c, Supporting Information Figure S1). Consequently, the NO3- anions are included by the [NMe4]þ cations, and the framework of 1 can be regarded as a dualinclusive structure (Figure 1a, Supporting Information Figure S1). To the best of our knowledge, such a novel dual-inclusive structure has not been reported thus far. The non-interpenetrating 3-D framework of 1 is supported solely by single cyanide bridges, so should possess a huge free volume. PLATON analysis shows that the effective free volume in the 3-D anionic framework of 1 is 64.1% of its crystal volume (890.3 A˚3 out of the 1389.7 A˚3 unit cell volume of 1), which is greater than the free volume of most open zeolites and comparable to that of the previously reported highly porous Pt3O4 net (67%).17 As a result, the 3-D anionic framework can host six [NMe4]þ cations and two NO3- anions in each unit cell. Crystal Structure of 3¥{[(NH4) 3 2DMF]⊂[Mo2O2S6Cu6(CN)3(bipy)4]} 2. 2 crystallizes in the monoclinic space group

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Figure 6. Absorption spectra of (a) cluster 1, (b) cluster 2, and (c) cluster 3 obtained from experimental observation (blue line) and TD-DFT/PCM calculations at the B3LYP/LanL2DZ level (red dash). For the latter, a Lorentzian function has been employed with the spectral line width set to 70 nm. The theoretical spectra have been scaled assuming a linear relationship between experimental spectra and TD-DFT/PCM excitation energies (see Supporting Information, Figure S5).

C2/c. The structural analysis demonstrates that 2 exhibits an unusual 3-D pillar-layer-alternating honeycomb framework based on the nest-shaped [MoOS3Cu3]þ cluster (Figure 3). In comparison with that in 1, the [MoOS3Cu3]þ nest in 2 possesses the same composition but exhibits a distinctly different mode of connection (Figure 4a). The six available coordination sites of each building cluster [MoOS3Cu3]þ are occupied by three bridging CN-, two bridging bipy, and one terminal bipy ligands. Each [MoOS3Cu3]þ nest links another four crystallographically equivalent [MoOS3Cu3]þ units through a double bipy bridge and three single cyanide bridges; each building cluster [MoOS3Cu3]þ in 2 therefore serves as a 4-connected node, unlike that in 1 which functions as a 6-connected node; this results in a diamondoid topology (Figure 4b) for 2. The distances between adjoining tetrahedral nodes are 8.810, 9.384, and 12.605 A˚.

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Figure 7. Absorption spectra lowest-energy-band assignments (peak 1 in Figure 6) for clusters 1, 2, and 3. The molecular orbitals are obtained through DFT/PCM calculations at the B3LYP/LanL2DZ level.

Interestingly, 2 has an unusual pillar-layer-alternating framework. Each [MoOS3Cu3]þ nest connects three other units through single CN- bridges to form a 2-D (6,3) corrugated honeycomb-like sheet (Supporting Information, Figure S2), in which the neighboring nests are arranged in a mouth-to-mouth style. Pairs of bridging bipy ligands serve as parallel double bridges to link pairs of [MoOS3Cu3]þ nests, each from the adjacent corrugated layers, which results in the aforesaid unusual pillar-layer-alternating framework (Figure 3b,c). These pillared bipy bridges are perpendicular to the ab plane with π-π stacking interactions in the range of 3.437-3.780 A˚; the neighboring corrugated layers pillared by bipy ligands have an interlayer Cu 3 3 3 Cu distance of ca. 11.341 A˚. The packing diagram of 2 viewed down the a-axis shows the corrugated layers and bipy pillars stacked in an interesting ABAB manner (Figure 3c), while viewed along the b-axis, these layers and pillars are stacked in an identical manner (Figure 3b). PLATON analysis reveals that the effective free volume of 2 is 29.6% of its crystal volume (1918.6 A˚3 out of the 6489.2 A˚3 unit cell volume in 2), which is significantly smaller than that of 1. Crystal Structure of 3¥{[(NH4) 3 2DMF]⊂[Mo2O2S6Cu6(CN)3(bpee)4]} 3. 3 crystallizes in the monoclinic crystal system and C2/c space group. The structural analysis demonstrates that 3 also exhibits an unusual 3-D pillar-layer-alternating honeycomb framework (Figure 5, Supporting Information Figure S3). The six available coordination sites of each [MoOS3Cu3]þ cluster in 3 are occupied by one terminal bpee, two bridging bpee, and three bridging CN- ligands. Each building cluster [MoOS3Cu3]þ in 3 is a 4-connected node coupling an additional four crystallographically equivalent units through a double bpee bridge and three single cyanide bridges (Figure 5a). The topology of 3 exhibits a diamondoid network, the distances between neighboring tetrahedral nodes being 8.688, 9.435, and 14.859 A˚ (Supporting Information, Figure S3c). In the pillar-layer-alternating structure of 3, 2-D (6,3) corrugated honeycomb layers similar to those in 2 (Supporting Information, Figure S4) are pillared by parallel double bpee bridges (Supporting Information, Figure S3a). These pillared bpee bridges are perpendicular to the ab plane with π-π stacking interactions in the range of 3.447-3.768 A˚; the neighboring corrugated layers pillared by bpee ligands have an interlayer Cu 3 3 3 Cu distance of ca. 13.539 A˚. As with 2, the

Zhang et al.

Figure 8. Assignment of the strongest absorption peak (peak 2 in Figure 6) of clusters 1, 2, and 3. The molecular orbitals are obtained through DFT/PCM calculations at the B3LYP/LanL2DZ level.

Figure 9. Z-Scan measurements of 2 in 1.0  10-4 mol dm-3 DMF solution at 532 nm, with 5 ns laser pulses, and with a linear transmittance of 89%. The open circles represent the Z-scan experimental data, and the solid lines are the theoretical fitting curves: (a) data collected under the open-aperture configuration; (b) data obtained by dividing the normalized Z-scan data obtained under the closed-aperture configuration by the normalized Z-scan data in a).

packing diagram of 3 viewed along the a-axis shows the corrugated layers and bpee pillars stacked in an interesting ABAB manner (Supporting Information, Figure S3b), while viewed along the b-axis, these layers and pillars are all stacked in an identical manner (Supporting Information, Figure S3a). PLATON analysis reveals that the effective free volume of 3 is

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30.4% of its crystal volume (2246.5 A˚3 out of the 7392 A˚3 unit cell volume in 3), again notably smaller than that of 1. Density Functional Theory Studies. Density functional theory (DFT) and TD-DFT calculations were performed using the Gaussian 03 program18 to rationalize the experimental absorption spectra. Model compounds of clusters 1, 2, and 3 were created using experimental X-ray single-crystal structures. The restricted singlet wave functions for clusters 1, 2, and 3 in DMF solution (dielectric constant, ε = 36.71) were tested to be stable using the polarized continuum model (PCM) at the B3LYP/

Figure 10. Z-Scan measurements of 3 in 1.74  10-4 mol dm-3 DMF solution at 532 nm, with 5 ns laser pulses, and with a linear transmittance of 87%. The open circles represent the Z-scan experimental data, and the solid lines are the theoretical fitting curves: (a) data collected under the open-aperture configuration; (b) data obtained by dividing the normalized Z-scan data obtained under the closedaperture configuration by the normalized Z-scan data in a).

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LanL2DZ level. The electronic excitation energies of 1, 2, and 3 in DMF solution were then obtained through TD-DFT calculations within the PCM framework at the same level of theory. The dipole-allowed excitation energies obtained from TDDFT/PCM calculations at the B3LYP/LanL2DZ level are displayed in the Supporting Information. Theoretical absorption spectra generated using Lorentzian functions19 contain bands that are systematically shifted from the experimental absorption bands (cf. Supporting Information, Figure S5). Figure 6 compares the scaled absorption spectra with the experimental results, displaying a qualitative agreement in the spectral shape. The lowest-energy (Peak 1) and the strongest (Peak 2) absorption bands are approximately assigned to be n f π* or π f π* in nature. As schematically illustrated in Figures 7 and 8, the lone pair orbitals, n, are largely centered on the S or N atoms, while the π and π* orbitals are dominated by contributions from the d orbitals of the metal atoms (the 4d orbital of the Mo atom or the 3d orbital of the Cu atom) and the p orbitals of the S atoms. Nonlinear Optical Properties. The third-order NLO properties of 1-3 were investigated with linearly polarized 5 ns pulses at 532 nm generated from a Q-switched frequencydoubled Nd:YAG laser in 1.0  10-4 (1), 1.0  10-4 (2), and 1.74  10-4 (3) mol dm-3 DMF solutions, respectively. Typical results from the Z-scan experiments14 for 1-3 are displayed in Figures S6, 9-10. The nonlinear absorption components were evaluated from open-aperture Z-scan studies (Figures S6a, 9a and 10a).14,20 The NLO absorptive coefficients (R2) of 1-3 were calculated to be 2.6  10-12, 9.3  10-12, and 6.0  10-12 m W-1, respectively. The nonlinear refractive properties of 1-3 were assessed by dividing the normalized Z-scan data obtained under the closed-aperture configuration by the normalized Z-scan data obtained under the open-aperture configuration (Figures S6b, 9b, and 10b).21 With the measured values of the difference in the normalized transmittance values at the valley and peak positions, effective third-order nonlinear refractive indices (n2) were calculated to be 1.5  10-18, 8.6  10-18, and 7.1  10-18 m2 W-1 for 1-3, respectively. The valley/peak patterns of the corrected transmittance curves show self-focusing behavior of the propagating light in the cluster samples. The theoretical curves accurately reproduce the general appearance of the experimentally determined data. On the basis of the above NLO absorptive and refractive values of 1-3, the concentration-independent hyperpolarizability γ, which reflects the integrated third-order NLO property, was deduced to be 7.33  10-30, 3.54  10-29, and 2.75  10-29 esu for clusters 1-3, respectively. As shown in Table 5, the hyperpolarizability values γ of 1-3 are certainly larger than

Table 5. The Hyperpolarizability Values (γ) of Some Representative Heterothiometallic Clusters Measured at 532 nm with Nanosecond-Duration Laser Pulses compound

structure type

γ (esu)

ref

1 2 3 {[Et4N]2[MoS4Cu4(CN)4]}n {[Bu4N][WS4Cu3(CN)2]}n [Et4N]2[MoS4Cu4(SCN)4(2-pic)4] [Et4N]4[Mo4O4S12Cu8{(Ph2PS)2N}4] [MoOS3Cu3(4-pic)6] 3 BF4 [W2S8Pd4(dppm)2] 3 4DMF [Et4N]3[MoOS3(μ3-I)(AgI)3] [WS4Cu2(dppf)2] 3 4DMF

3-D polymer 3-D polymer 3-D polymer 3-D polymer 3-D polymer planar open shape dodecanuclear square nest-shape windmill-shape cubane-like linear-shape

7.33  10-30 3.54  10-29 2.75  10-29 1.15  10-29 3.4  10-30 1.29  10-31 1.81  10-30 2.89  10-31 6.20  10-31 9.07  10-31 6.20  10-31

this work this work this work 7a 7b 22a 22b 22c 22d 22e 22f

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those of many other heterothiometallic clusters with different cluster skeletons, such as anionic planar open shape, cubanelike, dodecanuclear square, nest-shape, windmill-shape, and linear-shape.8,22 In addition, clusters 1-3 are constructed with the same nest-shaped building blocks and possess similar 3-D honeycomb-like frameworks, but the observed NLO behaviors of 1-3 are quite distinct. Specifically, as the length of the pillar ligands increases from CN- in 1 to bipy in 2 or bpee in 3, the hyperpolarizability γ increases by five or four times. Therefore, the varying backbone connecting ligands are responsible for this modification in their NLO response.

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Conclusions An interdiffusion synthetic method has been successfully developed that facilitates the construction of a novel noninterpenetrating 3-D M/S/Cu coordination polymer with an unprecedented dual-inclusive structure, rare “ACS” topology and a huge free volume, as well as two unusual noninterpenetrating 3-D pillar-layer-alternating honeycomb-like Mo/S/Cu clusters. This method is particularly efficient at minimizing the formation of precipitate while eliminating the use of terminal halogen atoms or large counterions in reaction systems. The cyanide bridge has proven to play a key role in constructing non-interpenetrating 3-D M/S/Cu networks. Z-scan experiments have shown that 1-3 possess strong third-order NLO properties. TD-DFT studies provide insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials. Further studies on the synthesis of new M/S/Cu clusters by this novel interdiffusion method are currently in progress. Acknowledgment. Financial support from the National Natural Science Foundation of China for the Distinguished Young Scholar Fund to C.Z. (50925207), the Ministry of Science and Technology of China for the International Science Linkages Program (2009DFA50620), the Special Fund for International Collaboration & Exchange of Jiangsu Province (BZ2008049) and UJS, and the Commonwealth of Australia under the International Science Linkages program (“Joint Research Centre for Functional Molecular Materials”) is gratefully acknowledged. M.G.H. is an Australian Research Council Australian Professorial Fellow. Supporting Information Available: Additional figures (Figures S1-S6) demonstrating the inclusive relationship of [NO3]-, [NMe4]þ, and the 3-D framework of 1 (Figure S1), the 2-D (6,3) corrugated honeycomb-like sheet in 2 (Figure S2), the overall view and topological view of 3 (Figure S3), the 2-D (6,3) corrugated honeycomb-like sheet in 3 (Figure S4), the correlation between experimental and calculated absorption spectra of clusters 1, 2, and 3 (Figure S5), Z-scan measurement of 1 in 1.0  10-4 mol dm-3 DMF solution at 532 nm employing 5 ns laser pulses (Figure S6), and X-ray crystallographic information files (CIFs) for 1-3 are available. This information is available free of charge via the Internet at http://pubs.acs.org.

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