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The coplanar cluster compound [Et4N]4[(μ4-WSe4)Cu4l6] (1) was prepared from reaction of [Et4N]2[WSe4] with 4 equiv of Cul in N,N-dimethylformamide (DMF) solution in the presence of [Et4N]l. Treatment of 1 with pyridine (py) in dry MeCN gave the neutral cluster [(μ4-WSe4)Cu4(py)6l2] (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 [(μ3-WOSe3)Cu3(py)3(μ-l)]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 [(μ3-WSe4)Cu3(PPh3)3(μ3-l)] (4) which has a cubanelike SeWSe3Cu3l core. Treatment of 1 with 1 equiv of Cul in dimethyl sulfoxide (DMSO) yielded [Et4N]4[μ5-WSe4)(Cul)5(μ-l)2] (5) which has a crownlike core structure. Treatment of 1 in DMF with 2 equiv of Cul in the presence of py resulted in the formation of a two-dimensional polymeric cluster, [(μ6-WSe4)Cu6l4(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. [ABSTRACT FROM AUTHOR]