Influence of cluster composition on NLO properties of neutral cubane-like heterothiometallic clusters

A series of new candidates as nonlinear optical materials, tetra-nuclear heterobimetallic clusters [MOS3M3′Y(PPh3)3] (M = Mo, M′ = Ag, Y = Br 1; M = W, M′ = Ag, Y = I 2; M = Mo, M′ = Cu, Y = I 3; M = W, M′ = Cu, Y = I 4), have been synthesized by newly developed ligand-redistribution reaction for third-order nonlinear optical (NLO) studies. Single-crystal X-ray diffraction shows that clusters [MoX(μ3-S)3(μ3-Br)(AgPPh3)3] 1 and [WX(μ3-S)3(μ3-I)(CuPPh3)3] 4 (X = O0.5S0.51, O 4) adopt an isomorphous neutral cubane-like skeleton. Their optical nonlinearities were measured by Z-scan technique with an 8 ns pulsed laser at 532 nm. These clusters were found to exhibit effective nonlinear absorption, self-focusing effects and large optical limiting capabilities. The effective NLO susceptibilities χ(3) and the corresponding second-order hyperpolarizabilities γ of these clusters are also reported. The influence of cluster composition on NLO properties has been discussed accordingly.