Luminescent Di- and Polynuclear Organometallic Gold(I)-Metal (Au2, {Au2Ag}n and {Au2Cu}n) Compounds Containing Bidentate Phosphanes as Active Antimicrobial Agents

The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au2(mes)2(mu-LL)] (LL=dppe: 1,2-bis(diphenylphosphano)ethane 1?a, and water-soluble dppy: 1,2-bis(di-3-pyridylphosphano)ethane 1?b) with Ag+ and Cu+ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au2M(mu-mes)2(mu-LL)][A] (M=Ag, A=ClO4-, LL=dppe 2?a, dppy 2?b; M=Ag, A=SO3CF3-, LL=dppe 3?a, dppy 3?b; M=Cu, A=PF6-, LL=dppe 4?a, dppy 4?b). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au2(mes)2(mu-dppy)] (1?b) and [Au2Ag(mu-mes)2(mu-dppe)][SO3CF3] (3?a) were determined by a single-crystal X-ray diffraction study. 3?a in solid state is not a cyclic trinuclear Au2Ag derivative but it gives an open polymeric structure instead, with the {Au2(mu-dppe)} fragments linked by {Ag(mu-mes)2} units. The very short distances of 2.7559(6) angstrom (Au?Ag) and 2.9229(8) angstrom (Au?Au) are indicative of goldsilver (metallophilic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77 K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self-aggregation of [Au2M(mu-mes)2(mu-LL)]+ units (M=Ag or Cu; LL=dppe or dppy) into an extended chain structure, through Au?Au and/or Au?M metallophilic interactions, as that observed for 3?a. In solid state the heterometallic Au2M complexes with dppe (2?a4?a) show a shift of emission maxima (from ca. 430 to the range of 520-540 nm) as compared to the parent dinuclear organometallic product 1?a while the complexes with dppy (2?b4?b) display a more moderate shift (505 for 1?b to a max of 563 nm for 4?b). More importantly, compound [Au2Ag(mu-mes)2(mu-dppy)]ClO4 (2?b) resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au2Cl2(mu-LL)] (LL dppy 5?b) was also studied for comparative purposes. The antimicrobial activity of 15 and Ag[A] (A=ClO4-, SO3CF3-) against Gram-positive and Gram-negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au2M derivatives with dppe (2?a4?a) were the more active (minimum inhibitory concentration 10 to 1 mu g?mL-1). Compounds containing silver were ten times more active to Gram-negative bacteria than the parent dinuclear compound 1?a or silver salts. Au2Ag compounds with dppy (2?b, 3?b) were also potent against fungi.