Luminescent tetranuclear copper(I) clusters containing tetradentate N,S Schiff base ligands. X-ray crystal structure of Cu(4)L(2) (L=N,N'-(2,2'-diphenyl)-bis(1,3-diphenyl-4-iminomethyl-5-thiopyrazole))

Six new tetranuclear copper(I) cluster compounds based on tetradentate N2S2 and bidentate N,S Schiff base ligands have been prepared and were characterized through chemical analysis, mass spectra and UV-Vis spectra. For Cu-4(L(4))(2), L(4) = N,N'-(2,2'-diphenyl)-bis(1,3-diphenyl-4-iminomethyl-5-thiopyrazole) , the molecular structure was solved by X-ray crystallography. The crystal of Cu-4(L(4))(2) was monoclinic, space group P2(1)/c with a = 24.122(5), b = 15.467(4), c = 26.608(9) Angstrom, with Z = 4 and R = 0.084 for 4536 reflections. The structure of Cu-4(L(4))(2) includes a tetrahedral core of Cu(I) centers each with NS2 coordination and the sulfurs each mu(2)-bridged between two copper atoms. The six copper-copper distances of the tetrahedron vary from 2.77 to 2.96 A. The photophysical properties of the Cu(4)L(2) and Cu(4)L(4) complexes were examined both in solution and in the solid state. Each displayed a broad, unstructured emission band in the red with luminescence lifetimes > 1 mu s in the solid state or in frozen solution. The dynamics of the emission from Cu-4(L(4))(2) in the presence of several aromatic organic and several tris(beta-dionato) chromium(III) compounds were probed. The second-order quenching constants displayed a Marcus type relationship with respect to the calculated potentials for electron transfer from the cluster centered excited states to the quencher consistent with this process occurring via simple electron transfer.