Short-bite PNP ligand-supported rare tetranuclear [Cu4I4] clusters: structural and photoluminescence studies.

The group 11 metal complexes of two short-bite PNP ligands, C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2 (1) and C6H5N{P(OC6H4C3H5-o)2}2 (2), are described. Ligands 1 and 2 on treatment with copper(I) halides (CuX, X = Cl, Br, or I) yielded dimeric, tetranuclear complexes of the type [(CuX)4{C6H5N(PR2)2}] (R = OC6H3(OMe-o)(C3H5-p), X = Cl (3), Br (5), I (7); R = OC6H3(C3H5-o), X = Cl (4), Br (6), I (8)). The chloro-derivative 3 adopts the common "stair-step" geometry, whereas the bromo- and iodo-derivatives form Cu4 square planes with two tetracoordinating μ4-halides capping the axial positions to give octahedral geometry with two other μ2-halides being in the plane. The iodo-derivative 8 with a very short Cu-Cu distance of 2.568 Å shows photoluminescence in the solid state.