Binuclear Cluster-to-Cluster-Based Supramolecular Compounds

Binuclear Cluster-to-Cluster-Based Supramolecular Compounds: Design, Assembly, and Enhanced Third-Order Nonlinear Optical Performances of {[Et4N]2[MoO...
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Binuclear Cluster-to-Cluster-Based Supramolecular Compounds: Design, Assembly, and Enhanced Third-Order Nonlinear Optical Performances of {[Et4N]2[MoOS3Cu2(µ-CN)]2 · 2aniline}n and {[Et4N]4[MoOS3Cu3CN(µ′-CN)]2(µ-CN)2}n

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 1 253–258

Wen-Hua Zhang,†,‡ Ying-Lin Song,§ Yong Zhang,† and Jian-Ping Lang*,†,‡ Key Laboratory of Organic Synthesis of Jiangsu ProVince, School of Chemistry and Chemical Engineering, Suzhou UniVersity, Suzhou 215123, P. R. China, State Key Laboratory of Coordination Chemistry, Nanjing UniVersity, Nanjing, 210093, P. R. China, and School of Physical Science and Technology, Suzhou UniVersity, Suzhou 215006, Jiangsu, People’s Republic of China ReceiVed March 11, 2007; ReVised Manuscript ReceiVed September 13, 2007

ABSTRACT: Reaction of a cluster precursor [Et4N]2[MoOS3(CuCN)] (1) with equimolar [Cu(MeCN)4](PF6) in MeCN/aniline gave rise to an interesting polymeric cluster {[Et4N]2[MoOS3Cu2(µ-CN)]2 · 2aniline}n (2), while treatment of 1 in MeCN with 2 equiv of CuCN and KCN in H2O afforded the other polymeric cluster {[Et4N]4[MoOS3Cu3CN(µ′-CN)]2(µ-CN)2}n (3). Generated by addition of one or two Cu+ onto the [MoOS3Cu] cluster core in 1, the butterfly shaped [MoOS3Cu2] fragment in 2 or the incomplete cubanelike [MoOS3Cu3] fragment in 3 was dimerized into a prismatic [MoOS3Cu2]2 cage core or a double incomplete cubanelike [MoOS3Cu3]2 core. These two expanded cores serve as a unique planar 4-connecting node (2) or a rare chairlike 4-connecting node (3) to link equivalent nodes via cyanide bridges, forming two kinds of different 2D (4,4) networks. The third-order nonlinear optical (NLO) properties of 1-3 in DMF were also investigated. Introduction The design and synthesis of new materials with large thirdorder nonlinear optical (NLO) capability for the potential applications in advanced optical materials is the focus of intense research.1 A promising approach to develop such materials with improved NLO effects is to incorporate metal centers into organic materials. Various metal complexes such as metallocenes, phthalocyanines, and dithiolenes exhibited good NLO properties.2 Among them, a number of Mo(W)/Cu/S clusters derived from tetrathiometallate [MS4]2- (M ) Mo, W) anions also showed good third-order NLO effects.3 However, enhancement of the NLO performances of clusters of this type via tuning their frameworks remains a great challenge. This is because the clusters generated from direct reactions of [MS4]2- with Cu(I) salts could not be rationally constructed, and no other efficient ways were developed to increment the NLO responses of Mo(W)/Cu/S clusters with low NLO activity. In the past decade, we were interested in the synthesis and third-order NLO optical properties of Mo(W)/Cu/S clusters derived from [MS4]2- or [(η5-C5Me5)MS3]- (M ) Mo, W).4 Considering that a number of Mo(W)/Cu/S clusters have been reported in the literatures and some of them may possess relatively low third-order NLO activity,4,5 we attempted to assemble some small clusters with low NLO activity into larger clusters. However, the resulting larger clusters did not show better NLO effects compared with those of their parent clusters.4f,h On the other hand, we recently communicated the construction of a cluster-based supramolecular cube [((η5C5Me5)WS3Cu3)8Cl8(CN)12Li4] from reactions of a preformed incomplete cubanelike cluster [PPh4][(η5-C5Me5)WS3(CuCN)3] with LiCl and 1,4-pyrazine.6 The luminescent properties of the * To whom correspondence should be addressed: Fax/Tel.: +86 512 65880089. E-mail: [email protected]. † Key Laboratory of Organic Synthesis of Jiangsu Province, Suzhou University. ‡ Nanjing University. § School of Physical Science and Technology, Suzhou University.

cube were significantly changed relative to those of the precursor. This result inspired us that it may be a good way to assemble the small clusters with low NLO activity into the cluster-based supramolecular compounds to get better NLO performances. After screening the numerous known Mo(W)/ Cu/S clusters in the literature, a binuclear cluster [Et4N]2[MoOS3(CuCN)]7 (1) drew our attention. As described later in this paper, 1 showed relatively low NLO responses in DMF and its cluster dianion has a simple [MoOS3Cu] core. When one or two Cu+ were introduced into the core framework of 1, a butterfly shaped [MoOS3Cu2] fragment or an incomplete cubanelike [MoOS3Cu3] fragment may be generated. The two fragments are found in some third-order NLO cluster materials1,3 and may be considered as NLO active fragments. If they are further self-aggregated or linked by cyanides to finite or infinite cluster-based arrays, the NLO performances of the resulting cluster-based supramolecular compounds may be improved to some extent. With this idea in mind, we carried out reactions of 1 with 1 or 2 equiv of Cu(I) salts, and two unique 2D clusterbased supramolecular compounds {[Et4N]2[MoOS3Cu2(µCN)]2 · 2aniline}n (2) and {[Et4N]4[MoOS3Cu3CN(µ′-CN)]2(µCN)2}n (3) were isolated therefrom. The NLO effects of 2 and 3 in DMF were confirmed to be much better than those of 1. We report here their syntheses, structures, and third-order NLO properties. Materials and Methods 8a

(NH4)2[MoOS3] and [Cu(MeCN4)](PF6)8b were prepared according to the literature methods. Other chemicals were obatined from commercial sources and used as received. All solvents were predried over activated molecular sieves and refluxed over the appropriate dry agents under argon. Aniline and DMF were freshly distilled under reduced pressure. The IR spectra were recorded on a Nicolet MagNa-IR 550 as KBr disks (4000-400 cm-1). The elemental analyses for C, H, and N were performed on an EA1110 CHNS elemental analyzer. UV–vis spectra were measured on HITACHI U-2810 spectrophotometer. [Et4N]2[MoOS3(CuCN)] (1). This compound was prepared by a modified procedure according to the method reported by Gheller and co-workers.7 To a suspension of CuCN (0.90 g, 10 mmol) and KCN

10.1021/cg070235n CCC: $40.75  2008 American Chemical Society Published on Web 11/27/2007

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Table 1. Summary of Crystallographic Data for 1-3 compounds

1

2

3

formula FW crystal system space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z Fcalc (g cm-3) F(000) µ (mm-1) total no. of reflns. no. of unique reflns. no. of obsd. reflns. no. of variables R1a wR2b GOFc ∆Fmax/∆Fmin (e Å-3)

C17H40CuMoN3OS3 558.16 monoclinic P21/n 11.7530(12) 16.8295(16) 13.3393(12) 104.118(3) 2558.8(4) 4 1.449 1160 1.557 28555 5859 (Rint ) 0.0501) 4781 [I > 2.00σ(I)] 236 0.0618 0.1344 1.124 0.925/-0.798

C15H27Cu2MoN3OS3 584.60 monoclinic P21/c 12.908(3) 16.105(3) 11.332(2) 115.88(3) 2119.5(9) 4 1.832 1176 2.876 23654 4854 (Rint ) 0.0496) 3795 [I > 2.00σ(I)] 238 0.0515 0.0797 1.165 0.859/-0.672

C19H40Cu3MoN5OS3 737.30 monoclinic P21/c 16.014(3) 11.566(2) 16.186(3) 103.61(3) 2913.9(10) 4 1.681 1496 2.815 27703 5306 (Rint ) 0.0769) 4443 [I > 2.00σ(I)] 335 0.0811 0.1568 1.249 0.934/-0.912

a R1 ) ∑||Fo| - | Fc||/∑|Fo|. b wR2 ) {w∑(|Fo| - |Fc|)2/∑w|Fo|2}}1/2. c GOF ) {∑w(|Fo| - |Fc|)2/(n - p)}1/2, where n is the number of reflections and p is total number of parameters refined.

(2.60 g, 40 mmol) in 10 mL of water was added (NH4)2[MoOS3] (2.45 g, 10 mmol). The dark-red mixture was stirred for 20 min and filtered. To the filtrate was added a solution containing Et4NBr (4.20 g, 20 mmol) in 5 mL of water to give a orange-red precipitate, which was filtered, washed with cooled EtOH and Et2O, and dried in vacuo. Yield: 2.50 g (45%). Anal. calcd for 1, C17H40CuMoN3OS3: C, 36.58; H, 7.22; N, 7.53. Found: C, 36.82; H, 7.01; N, 7.44. IR (KBr): 2987m, 2941w, 2123s, 1621w, 1459s, 1389s, 1312w, 1189m, 1119w, 1081w, 1027m, 895s, 795m, 494s, 455s. UV–vis (DMF, λmax (nm (ε M-1 cm-1))): 296 (17800), 391 (7500), 429 (6500). {[Et4N]2[MoOS3Cu2(µ-CN)]2 · 2aniline}n (2). To a solution of 1 (0.116 g, 0.2 mmol) in 30 mL of MeCN/aniline (v/v ) 2:1) was slowly added a solution of [Cu(MeCN4)](PF6) (0.074 g, 0.2 mmol) in 20 mL MeCN. The mixture was briefly stirred and was allowed to stand for 2 h to give some red precipitate, which was filtered off. The same procedures were repeated two times, and Et2O (10 mL) was layered onto the final clear filtrate to give dark-red crystals of 2 1 week later, which were collected by filtration, washed with Et2O, and dried in vacuo. Yield: 0.059 g (50%). Anal. calcd for 2, C15H27Cu2MoN3OS3: C, 30.82; H, 4.66; N, 7.19. Found: C, 30.62; H, 4.53; N, 7.42. IR (KBr): 2987w, 2940w, 2090s, 1929w, 1598s, 1482w, 1443s, 1382s, 1273w, 1219w, 1150w, 1065w, 911s, 756m, 695s, 511m, 448s. UV–vis (DMF, λmax (nm (ε M-1 cm-1))): 295 (11800), 337 (8300), 449 (4100). {[Et4N]4[MoOS3Cu3CN(µ′-CN)]2(µ-CN)2}n (3). To a solution of 1 (0.116 g, 0.2 mmol) in 20 mL of MeCN was slowly added a suspension containing CuCN (0.036 g, 0.4 mmol) and KCN (0.026 g, 0.4 mmol) in 2 mL H2O. The mixture was briefly stirred, was allowed to stand for 2 h, and was then filtered. A similar workup to that used in the isolation of 2 afforded dark-red crystals of 3 2 days later. Yield: 0.080 g (54%). Anal. calcd for 3, C19H40Cu3MoN5OS3: C, 30.95; H, 5.47; N, 9.50. Found: C, 31.18; H, 5.24; N, 9.55. IR (KBr): 2987m, 2941w, 2133s, 2083s, 1636m, 1459s, 1389s, 1304w, 1181w, 1073w, 1034w, 1003w, 903s, 795w, 695w, 648w, 448m. UV–vis (DMF, λmax (nm (ε M-1 cm-1))): 290 (14300), 386 (10300). X-ray Crystallographic Study. X-ray quality crystals of compounds 1-3 were obtained directly from the above preparations. All measurements were made on a Rigaku Mercury charge-coupled device (CCD) X-ray diffractometer (3 kW, sealed tube) using graphite monochromated Mo KR radiation (λ ) 0.71070 Å). Each single crystal was mounted at the top of a glass fiber and cooled at 193 K in a stream of gaseous nitrogen. Cell parameters were refined on all observed reflections by the program CrystalClear (Rigaku and MSc, version 1.3, 2001). Diffraction data were collected in ω mode with a detector distance of 35 mm to the crystal. Indexing was performed from six images, each of which was exposed for 15 s. The collected data were reduced by the program CrystalClear (Rigaku/MSc, 2001, version 1.3), and an absorption correction (multiscan) was applied. The reflection data were also corrected for Lorentz and polarization effects.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 Mo(1) · · · Cu(1) Mo(1)-S(3) Mo(1)-S(1) Cu(1)-S(1) O(1)-Mo(1)-S(3) S(3)-Mo(1)-S(2) S(3)-Mo(1)-S(1) C(1)-Cu(1)-S(1) S(1)-Cu(1)-S(2)

2.6418(7) 2.1779(13) 2.2472(13) 2.2082(14) 110.40(13) 110.93(6) 110.94(5) 128.40(17) 108.40(5)

Mo(1)-O(1) Mo(1)-S(2) Cu(1)-C(1) Cu(1)-S(2) O(1)-Mo(1)-S(2) O(1)-Mo(1)-S(1) S(2)-Mo(1)-S(1) C(1)-Cu(1)-S(2)

1.719(4) 2.2400(14) 1.875(6) 2.2123(14) 108.55(16) 109.84(14) 106.07(5) 123.18(17)

Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2a Mo(1) · · · Cu(1) Mo(1)-O(1) Mo(1)-S(3) Cu(1)-N(1) Cu(1)-S(1) Cu(2)-C(1B) Cu(2)-S(3) S(1)-Cu(2A) O(1)-Mo(1)-S(1) S(1)-Mo(1)-S(3) S(1)-Mo(1)-S(2) N(1)-Cu(1)-S(2) S(2)-Cu(1)-S(1) S(2)-Cu(1)-S(3A) C(1B)-Cu(2)-S(2) S(2)-Cu(2)-S(3) S(2)-Cu(2)-S(1A) C(1)-N(1)-Cu(1)

2.7020(8) 1.718(3) 2.2373(12) 1.945(4) 2.3036(13) 1.936(4) 2.3119(13) 2.4911(17) 109.26(13) 111.97(5) 108.77(4) 116.04(12) 104.72(5) 108.75(5) 117.46(13) 104.89(4) 108.71(5) 176.3(4)

Mo(1) · · · Cu(2) Mo(1)-S(1) Mo(1)-S(2) Cu(1)-S(2) Cu(1)-S(3A) Cu(2)-S(2) Cu(2)-S(1A) S(3)-Cu(1A) O(1)-Mo(1)-S(3) O(1)-Mo(1)-S(2) S(3)-Mo(1)-S(2) N(1)-Cu(1)-S(1) N(1)-Cu(1)-S(3A) S(1)-Cu(1)-S(3A) C(1B)-Cu(2)-S(3) C(1B)-Cu(2)-S(1A) S(3)-Cu(2)-S(1A) N(1B)-C(1B)-Cu(2)

2.7165(8) 2.2133(12) 2.2580(12) 2.2867(13) 2.5241(18) 2.2860(13) 2.4911(17) 2.5241(17) 109.01(12) 109.44(12) 108.36(4) 122.61(12) 100.72(13) 102.43(5) 120.32(13) 100.81(14) 103.20(5) 177.6(4)

a Symmetry codes. A: -x, -y + 1, -z + 1. B: -x, y - 1/2, -z + 3/2. C: x, -y + 3/2, z - 1/2.

The structures of 1-3 were solved by direct methods9 and refined against F2 for all independent reflections. All non-hydrogen atoms were refined anisotropically. The two hydrogen atoms of the amide group of the solvated aniline in 2 were located from Fourier map, and their N-H distances were fixed at 0.87Å. All other hydrogen atoms were located in their calculated positions. The two Et4N+ cations in 3 were disordered and treated with a disorder model. All calculations were performed on a Dell PC using the SHELXTL-97 software package. A summary of the key crystallographic information for 1-3 was given in Table 1. Selected bond lengths (Å) and angles (deg) for 1-3 were listed in Tables 2–4. Third-Order Nonlinear Optical (NLO) Measurements for 1-3. The DMF solutions of 1-3 were placed in a 2-mm quartz cuvette for NLO measurements. The clusters were stable toward air and laser light under the experimental conditions. The nonlinear absorption and

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Crystal Growth & Design, Vol. 8, No. 1, 2008 255

Table 4. Selected Bond Lengths (Å) and Angles (deg) for 3a Mo(1) · · · Cu(1) Mo(1) · · · Cu(3) Mo(1)-S(2) Mo(1)-S(3) Cu(1)-N(2B) Cu(1)-S(1) Cu(2)-N(1A) Cu(2)-S(3) Cu(3)-S(1) N(1)-Cu(2A) O(1)-Mo(1)-S(2) S(2)-Mo(1)-S(1) S(2)-Mo(1)-S(3) C(1)-Cu(1)-N(2B) N(2B)-Cu(1)-S(2) N(2B)-Cu(1)-S(1) C(2)-Cu(2)-N(1A) N(1A)-Cu(2)-S(2) N(1A)-Cu(2)-S(3) C(3)-Cu(3)-S(1) S(1)-Cu(3)-S(3) C(2)-N(2)-Cu(1C) N(1)-C(1)-Cu(1)

2.7415(16) 2.6395(15) 2.230(2) 2.266(2) 2.041(7) 2.348(2) 2.028(8) 2.349(2) 2.227(2) 2.028(8) 111.5(2) 109.00(8) 107.66(9) 114.9(3) 105.2(2) 102.0(2) 110.0(3) 104.2(2) 112.2(2) 126.7(3) 109.14(9) 177.1(7) 176.7(7)

Mo(1) · · · Cu(2) Mo(1)-O(1) Mo(1)-S(1) Cu(1)-C(1) Cu(1)-S(2) Cu(2)-C(2) Cu(2)-S(2) Cu(3)-C(3) Cu(3)-S(3) N(2)-Cu(1C) O(1)-Mo(1)-S(1) O(1)-Mo(1)-S(3) S(1)-Mo(1)-S(3) C(1)-Cu(1)-S(2) C(1)-Cu(1)-S(1) S(2)-Cu(1)-S(1) C(2)-Cu(2)-S(2) C(2)-Cu(2)-S(3) S(2)-Cu(2)-S(3) C(3)-Cu(3)-S(3) C(1)-N(1)-Cu(2A) C(3)-N(3)-Cu(3) N(2)-C(2)-Cu(2)

2.7907(14) 1.710(6) 2.263(2) 1.944(9) 2.324(2) 1.935(9) 2.334(2) 1.968(12) 2.228(3) 2.041(7) 111.5(2) 110.5(2) 106.55(9) 116.2(2) 113.8(2) 103.08(9) 117.9(3) 110.6(3) 101.66(9) 123.2(3) 169.4(7) 172.0(12) 178.2(7)

Figure 1. Electronic spectra of 1 (5.0 × 10-5 M), 2 (2.8 × 10-5 M), and 3 (2.2 × 10-5 M) in DMF in a 1-cm thick glass cell.

a Symmetry codes. A: -x, -y + 2, -z. B: x, -y + 3/2, z - 1/2. C: -x, y + 1/2, -z + 1/2.

refraction were investigated with a linearly polarized laser light (λ ) 532 nm; pulse widths ) 4.5 ns; repetition rate ) 2 Hz) provided by a frequency-doubled, mode-locked, Q-switched Nd-YAG laser. The spatial profiles of the optical pulses were nearly Gaussian after passing through a spatial filter. The laser beam was focused with a 30-cm focal length focusing mirror. The radius of the beam waist was measured to be 32 µm (half-width at 1/e2 maximum). The incident and transmitted pulse energies were measured simultaneously by two energy detectors (Laser Precision Rjp-735), which were linked to a computer by an IEEE interface.10 The NLO properties of the samples were manifested by moving the samples along the axis of the incident laser irradiance beam (z-direction) with respect to the focal point and with incident laser irradiance kept constant (Z-scan methods). The closed-aperture curves are normalized to the open-aperture curves. An aperture of 0.2 mm radius was placed in front of the detector to measure the transmitted energy when the assessment of laser beam distortion was needed. To eliminate scattering effects, a lens was mounted after the samples to collect the scattered light.

Results and Discussion Synthesis and Characterization. Compound 1 was first reported by Gheller7 and reprepared by us with a modified method in 45% yield. The synthetic strategy using 1 as a precursor is that as described below; the coordination is unsaturated for the three S atoms (one terminal S and two µ2-S atoms) in the [MoOS3(CuCN)]2- dianion of 1. Since the terminal O atom of the [MoOS3(CuCN)]2- dianion of 1 does not react with Cu+, the incorporation of one or two Cu+ ions into the core framework of 1 via the S atoms may result in the formation of a so-called butterfly shaped [MoOS3Cu2] core or incomplete cubanelike [MoOS3Cu3] core.3c The resulting cluster cores may be further self-aggregated into larger clusters or polymeric clusters through the bridging S atoms or cyanides. In fact, reactions of 1 in aniline with equimolar [Cu(MeCN)4](PF6) in MeCN followed by filtration and slow diffusion of Et2O into the filtrate gave rise to [MoOS3Cu2]based polymeric cluster 2 in 50% yield. On the other hand, reaction of 1 in MeCN with 2 equiv of CuCN in the presence of KCN in H2O followed by a workup similar to that used in the isolation of 2 afforded a [MoOS3Cu3]-supported polymeric cluster 3 in 54% yield. Compounds 1-3 were relatively stable toward air and moisture. 1 was highly soluble in common solvents such as DMF, DMSO, and MeCN while 2 and 3 were

Figure 2. Perspective view of the [MoOS3(CuCN)]2- dianion of 1 with labeling scheme and 50% thermal ellipsoids.

slightly soluble in DMF and DMSO and insoluble in MeCN, acetone, CH2Cl2, benzene, and Et2O. The elemental analysis was consistent with the chemical formula of 1-3. In the IR spectra of 1 and 2, a strong band at 2123 cm-1 (1) and 2090 cm-1 (2) can be assigned as the terminal and bridging cyanide stretching vibrations, respectively. The IR spectrum of 3 exhibited the terminal and bridging cyanide stretching vibrations at 2133 and 2083 cm-1. 11a Besides a terminal ModS stretching vibration at 492 cm-1 in the IR spectrum of 1, bands at 892 and 456 cm-1 (1), 908 and 447 cm-1 (2), and 904 and 430 cm-1 (3) may be assigned as the terminal ModO and the bridging MosS stretching vibrations, respectively.11b The UV–vis spectra of 1 and 2 in DMF were characterized by three bands, while that of 3 had two absorptions (Figure 1). Relative to the band at 391 nm (1), those at 337 nm (2) and 386 nm (3) are slightly blue-shifted, and they are probably dominated by the S f Mo(VI) charge-transfer transitions of the [MoOS3] moiety.11c The identities of 1-3 were further confirmed by single crystal X-ray analysis. Crystal Structures of 1-3. As shown in Figure 2, the cluster dianion of 1 contains a central MoOS3 moiety coordinated to one CuCN group to form a [MoOS3Cu] core, which is similar to those found in a series of binuclear Mo/Cu/S clusters such as [PPh4]2[S2MoS2(CuCl)],12a [Et4N]2[O2MoS2(CuL)] (L ) SPh, S(o-Tol), S(p-Tol), and [Et4N][O2MoS2(CuL′)]; L′ ) PPh3, 1,2bis(diphenylphosphino)ethane, 1,1,1-tris[(diphenylphosphino) methyl]ethane).12b Cu(1) adopts a trigonal planar coordination geometry. The Mo(1) · · · Cu(1) contact (2.6418(7) Å) is in between that of [PPh4]2[S2MoS2(CuCl)] (2.6206(18) Å) and that of [Et4N]2[O2MoS2(CuSPh)] (2.6598(8) Å). Compound 2 crystallizes in the monoclinic space group P21/c and its asymmetric unit consists of half of a [MoOS3Cu2(µCN)]22- dianion, one Et4N+ cation, and one aniline solvated molecule. The cluster dianion has a hexagonal prismatic

256 Crystal Growth & Design, Vol. 8, No. 1, 2008

Figure 3. (a) Perspective view of the repeating unit of 2 with labeling scheme and 50% thermal ellipsoids. (b) View along the a axis of 2 showing the extended 2D (4,4) network.

[MoOS3Cu2]2 cage structure with a crystallographic inversion center lying on the midpoint of the Mo(1) and Mo(1A) contact (Figure 3a). The cage has two butterfly shaped [MoOS3Cu2] fragments interconnected via four Cu-S bonds, and resembles those in [M2E2S6Cu4(PR3)4] (M ) Mo, W; E ) O, S).13 Each [MoOS3Cu2] fragment in 2 can be viewed as being built of the addition of one Cu+ onto the [MoOS3Cu] core of 1. In each [MoOS3Cu2] fragment, Cu(1) or Cu(2) is coordinated by one bridging cyanide and three sulfur atoms resulting in a tetrahedral coordination geometry. The oxidation states of the Mo and Cu atoms in 1, +6 and +1, respectively, are retained in 2. The Mo(1) · · · Cu(1) (2.7020(8) Å) and Mo(1) · · · Cu(2) (2.7165(8) Å) contacts are longer than that found in 1 (2.6418(7) Å). This is consistent with the higher coordination of copper(I) center leading to longer bond distances. As the four coordination sites (C(1), C(1A), N(1B), N(1C)) of the four cyanides surrounding the prismatic [MoOS3Cu2]2 cage core nearly lie on the plane composed of the four Cu atoms (their mean deviation from this plane being 0.16 Å), this core topologically serves as an uncommon planar 4-connecting node to link four equivalent nodes, forming a 2D (4,4) layer network (extending along the bc plane) with parallelogrammatic meshes (Figure 3b). The networks are ca. 12 Å apart with Et4N+ cations and aniline solvent molecules lying between the sheets. The terminal O atoms interact with amine groups of aniline to afford

Zhang et al.

Figure 4. (a) Perspective view of the repeating unit of 3 with labeling scheme and 50% thermal ellipsoids. (b) View along the a axis of 3 showing the extended 2D (4,4) network.

N-H · · · O intra- or intermolecular hydrogen bonds, thereby forming a three-dimensional network. Compound 3 also crystallizes in the monoclinic space group P21/c and its asymmetric unit contains half of a {[MoOS3Cu3CN(µ′-CN)]2(µ-CN)2}4- cluster tetra-anion and two disordered Et4N+ cations. The cluster tetra-anion comprises two incomplete cubanelike [MoOS3Cu3] fragments that are strongly linked by a pair of µ′-CN groups, forming a centrosymmetric double incomplete cubanelike [MoOS3Cu3(µ′-CN)]2 core structure (Figure 4a). The core structure is related to that in [PPh4]2[(η5C5Me5)WS3Cu2(CN)2(µ-CN)2] · 0.5(4,4′-bipy).14 In the structure of the latter compound, the two anions are weakly bridged via pairs of Cu-µ-CN-Cu bridges (Cu-C/N ) 2.44(3) Å), and the two Cu centers are trigonal planar while the third one is pseudo-tetrahedral. In 3, the two cluster anions are tightly connected by the two Cu-µ-CN-Cu bridges as the Cu(1)-N(2A) or Cu(1A)-N(2) bond lengths are much shorter, amounting to 2.041(8) and 2.028(8) Å. Thus Cu(1) and Cu(2) adopt a distorted tetrahedral geometry with bond angles of 102.0(2)-116.2(2)° around Cu(1) and 104.2(2)-117.9(3)° around Cu(2). Cu(3) has a trigonal planar environment. The Mo(1) · · · Cu contacts of 3 changeaccordingly:Mo(1) · · · Cu(1))2.7415(16)Å,Mo(1) · · · Cu(2) ) 2.7907(14) Å, and Mo(1) · · · Cu(3) ) 2.6384(19) Å. The mean Mo(1) · · · Cu contact for the tetrahedrally coordinated Cu atoms

Cluster-to-Cluster-Based Supramolecular Compounds

Figure 5. Z-scan data of the DMF solutions of 1 (5.49 × 10-4 M), 2 (5.00 × 10-4 M), and 3 (4.25 × 10-4 M) at 532 nm. The data were evaluated under the open-aperture configuration. The green open circles (1), pink dots (2), and blue squares (3) are the experimental data, and the solid curves are the theoretical fit.

is somewhat longer than that of 2 while the short Mo(1) · · · Cu(3) one is similar to that of 1. The Mo-µ3-S and Cu-µ3-S bond lengths are normal compared to those of the corresponding ones in 2. Topologically, each [MoOS3Cu3] fragment in 3 can be viewed as being built of the addition of two Cu+ ions onto the [MoOS3Cu] core of 1. There are four other bridging cyanides around the [MoOS3Cu3(µ′-CN)]2 core. Because two coordination sites (N(2), C(2A)) of two cyanides are above the Cu4 plane (Cu(1), Cu(2), Cu(1A), Cu(2A)) while the other two (N(2B), C(2C)) are below the Cu4 plane, this core has a unique chairlike 4-connecting node to interconnect four equivalent nodes to form another 2D (4,4) network extended along the bc plane (Figure 4b). The average layer-to-layer separation is ca. 9.7 Å with the [{MoOS3Cu3CN(µ′-CN)2]n4n- anionic layers separated by [Et4N]+ cations. Nonlinear Optical (NLO) Properties of 1-3. As shown in Figure 1, the electronic spectra of 1-3 showed relatively low linear absorption in 532 nm, which promises low intensity loss and little temperature change by photon absorption during the NLO measurements. The nonlinear absorption performance of 1-3 in DMF was evaluated by the Z-scan technique under an open-aperture configuration (Figure 5). The open-aperture Z-scan experiments revealed that the NLO transmittances for 2 and 3 (84% and 46%, respectively) are much better than that of 1 (94%). Although the detailed mechanism is still unknown, the NLO absorption data obtained under the conditions used in this study can be evaluated from the reported methods.10 The nonlinear absorptive indexes R2 for 1-3 were calculated to be 1.28 × 10-11 (1), 5.10 × 10-11 (2), and 1.58 × 10-10 m W-1 (3), indicating that 2 and 3 exhibit better nonlinear absorption properties than 1. Intriguingly, compounds 1-3 were not detected to have nonlinear refractive effects, implying that their nonlinear refractive effects are weak in our experimental conditions. In accordance with the observed R2 values, the effective thirdorder susceptibilities15 χ(3) for 1-3 were calculated to be 1.66 × 10-11 (1), 6.63 × 10-11 (2), and 2.06 × 10-10 esu (3) while the corresponding hyperpolarizability γ values16 were 1.55 × 10-29 (1), 6.78 × 10-29 (2), and 2.47 × 10-28 esu (3), respectively. These results showed that 2 and 3 possess better third-order optical nonlinearities than 1. The hyperpolarizability γ value can be used to represent NLO properties of neat materials.15,16 Although the γ value of 1 is normal, those of the assembled products 2 and 3 are better than

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those of the metal sulfide clusters derived from [MoS4]2- or [MoOS3]2- or [(η5-C5Me5)2Mo2S2(µ-S)2],4b,4g,16,17 such as [MoS4Cu4(R-MePy)5Br2] · 2(R-MePy)0.5 (1.06 × 10-31 esu), [(nBu)4N]2[MoOS3(Cu(NCS)3)] (4.8 × 10-29 esu), [MoOS3Cu3(4pic)6] · 0.5[Mo2O7] (1.32 × 10-30 esu), and [(η5-C5Me5)2Mo2(µ3S)4(CuI)2] (1.18 × 10-29 esu), and are much better than those observed in C60 (7.5 × 10-34 esu) and C70 (1.3 × 10-33 esu),18a organometallic compounds such as trans-[Mo(CO)4(PPh3)2] (8.49 × 10-32 esu) and cis-[Mo(CO)4(PPh3)2] (4.38 × 10-31 esu),18b and their films like TiOPc (1.04 × 10-33 esu).19 It is noted that when 1 was converted into 2 and 3, an obvious increase of the γ value was found, i.e., the γ values of 2 and 3 are 4.4 and 15.9 times larger than that of 1, respectively. Structurally, when one or two Cu+ ions were incorporated into the [MoOS3Cu] core of 1, a [MoOS3Cu2]2 core for 2 or a [MoOS3Cu3] core for 3 is formed. According to the previous results,3 clusters containing [MoOS3Cu3] cores always showed high NLO activity while those containing [MoOS3Cu] cores have low NLO activity. Thus, such an increased order of γ values among 1–3 may be reasonable, and their NLO performances are likely to be cluster core-dependent. Besides this, the enhanced NLO performances of 2 and 3 may be also ascribed to the skeletal expansion of these fragments and the formation of the cluster-based supramolecular arrays.3a,20 It should be noted that the γ values for 1-3 were obtained from a dilute solution and much larger γ values can be expected if these clusters could be engineered into a thin film. Conclusion In the work reported here, we have demonstrated that rational incorporation of one or two Cu+ions into the core framework of 1 produced two unique Mo/Cu/S cluster-based supramolecular assemblies 2 and 3. From this synthetic strategy, the third-order NLO performances of 2 and 3, relative to those of the less NLOactive cluster 1, were greatly enhanced due to the formation of highly NLO active [MoOS3Cu2] and [MoOS3Cu3] fragments, the skeletal expansion of these fragments, and the formation of the cluster-based supramolecular frameworks. It is anticipated that this methodology may be applied to produce other Mo(W)/ Cu/S clusters and transition metal complexes with better NLO effects. Acknowledgment. This work was financially supported by the NNSF of China (Grant No. 20525101), the NSF of Jiangsu Province (Grant No. BK2004205), the Specialized Research Fund for the Doctoral Program of Higher Education (Grant No. 20050285004), the Qin-Lan Project of Jiangsu Province, and the State Key Laboratory of Coordination Chemistry, Nanjing University in China. Supporting Information Available: Crystal structural data for 1-3 in CIF format. This material is available free of charge via the internet at http://pubs.acs.org.

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