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, [Cu₂(L¹)(PPh₃)₄](ClO₄)₂ (1), [Cu₃(L²)(PPh₃)₆](ClO₄) (2), [Cu₃(L³)(PPh₃)₆] (3), [Ag₂(L¹)(PPh₃)₄](BF₄)₂ (4), [Ag₄(L²)₂(PPh₃)₆] (5) and [Ag₃(L³)(PPh₃)₅] (6), have been obtained from the reactions of the highly conjugated bridging ligands 2,3-bis(2-pyridyl)pyrazine (L¹), 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.