Polynuclear Cu(i) and Ag(i) phosphine complexes containing multi-dentate polytopic ligands: syntheses, crystal structures and photoluminescence properties

A series of polynuclear metal complexes, [Cu-2(L-1)(PPh3)(4)](ClO4)(2) (1), [Cu-3(L-2)(PPh3)(6)](ClO4) (2), [Cu-3(L-3)(PPh3)(6)] (3), [Ag-2(L-1)(PPh3)(4)](BF4)(2) (4), [Ag-4(L-2)(2)(PPh3)(6)] (5) and [Ag-3(L-3)(PPh3)(5)] (6), have been obtained from the reactions of the highly conjugated bridging ligands 2,3-bis(2-pyridyl)pyrazine (L-1), 2,3-bis(2-tetrazoyl)pyrazine (H2L2) and 2,3-bis(2-tetrazoyl)imidazole (H3L3) with [Cu(MeCN)(4)]ClO4 and AgBF4, respectively. Their crystal structures have been determined by X-ray crystallography and their photophysical properties have been investigated in detail. Complexes 1 and 3 show photoluminescence in CH2Cl2 solution, while all the complexes exhibit obvious luminescence in the solid state; detailed photophysical studies and density functional theory calculations of these complexes have revealed that their lowest energy absorptions and emissions are predominantly derived from either metal-to-ligand charge-transfer (MLCT) or intraligand (IL) excited states.