The coplanar cluster compound [Et4N](4)[(mu(4)-WSe4)Cu4I6] (1) was prepared from reaction of [Et4N](2)[WSe4] with 4 equiv of CuI in N,N-dimethylformamide (DMF) solution in the presence of [Et4N] I. Treatment of 1 with pyridine (py) in dry MeCN gave the neutral cluster [(mu(4)-WSe4)Cu-4(py)(6)I-2] (2) in good yield. Recrystallization of 1 from py/i-PrOH resulted in the reorganization of the coplanar WSe4Cu4 core and the formation of a neutral polymeric cluster [(mu(3)-WOSe3)Cu-3(py)(3)(mu-I)](n) (3) containing a nest-shaped OWSe3Cu3 core and a terminal W=O bond. The interaction of cluster 1 with excess PPh3 in CH2Cl2 gave [(mu(3)-WSe4)Cu-3(PPh3)(3)(mu(3)-I)] (4) which has a cubanelike SeWSe3Cu3I core. Treatment of 1 with 1 equiv of CuI in dimethyl sulfoxide (DMSO) yielded [Et4N](4)[(mu(5)-WSe4)(CuI)(5)(mu- I)(2)] (5) which has a crownlike core structure. Treatment of 1 in DMF with 2 equiv of CuI in the presence of py resulted in the formation of a two-dimensional polymeric cluster, [(mu(6)-WSe4)Cu6I4(py)(4)](n) (6), consisting of an octahedral WSe4Cu6 repeating unit. The solid-state structures of clusters 3, 5, and 6 have been further established by X-ray crystallography. The nonlinear optical properties of 6 have been also investigated. Cluster 6 was found to exhibit good photostability and a large optical limiting effect with the limiting threshold being ca. 0.3 J cm(-2).