Novel Fluorescent Cationic Silver Thiosemicarbazone Clusters Containing Different Eight-Membered Ag4S4 Metallacycles

The reaction of silver acetate and silver nitrate with the new phosphinethiosemicarbazone ligand 2-(2-(diphenylphosphino)benzylidene)-N-ethylthiosemicarbazone (HLPEt) gave rise to the complexes [Ag(LPEt)](4).2MeOH (1) and [Ag(2)(LPEt)(HLPEt)](2).(NO(3))(2) (3). Slow crystallization of the mother liquors obtained from the synthesis of 1 and 3 afforded suitable crystals of [Ag(2)(LPEt)(HLPEt)](2)(CH(3)COO)(2).6MeOH (2) and [Ag(2)(LPEt)(HLPEt)](2)(NO(3))(2).2MeOH.2H(2)O (4), respectively. Complexes 2 and 4 are tetranuclear silver clusters displaying a similar Ag(4)S(4)P(4) core, but containing different sizes, conformations for the Ag(4)S(4) metallacycles, and crystal packings. The four complexes are strongly luminescent in methanol solutions. A comparison between the emission bands of compounds 1-4 lead us to conclude that the luminescence is notably affected by the charge and the counterion of the cluster.