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.