Syntheses, Structures, and Antimicrobial Activities of Gold(I)– and Copper(I)–N‑Heterocyclic Carbene (NHC) Complexes Derived from Basket-Shaped Dinuclear Ag(I)–NHC Complex

Novel dinuclear gold­(I)- and copper­(I)-N-heterocyclic carbene (NHC, L-1a) complexes [M2(L-1a)]­(PF6)2 (M = AuI (Au-1·PF 6 ) and M = CuI (Cu-1·PF 6 )) were synthesized by transmetalation of the dinuclear silver­(I)–NHC complex [Ag2(L-1a)]­(PF6)2 (Ag-1·PF 6 ) with [AuCl­(Me2S)] or CuI in over 70% yield. These NHC complexes were characterized by CHN elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, and solution (1H and 13C) NMR spectroscopy. X-ray crystallography revealed that Au-1·PF 6 and Cu-1·PF 6 are dinuclear molecules consisting of two linear intramolecular C–M–C bonds (M = AuI and CuI), one M···M interaction, and two metal atoms arranged in a T-shaped geometry; their molecular structures are very similar to the basket-shaped cage structure of the parent complex Ag-1·PF 6 . Because of the smaller ionic radius of copper­(I), Cu-1·PF 6 has the smallest upper space of the basket among the three complexes. Au-1·PF 6 and Cu-1·PF 6 were very stable in the solid state and in solution. They did not undergo nucleophilic reaction with thiols 2-mercaptoethanol and 2-benzimidazolethiol (Hbmt) at least for several hours, whereas Ag-1·PF 6 did react, forming precipitates of silver­(I) thiolate and the free ligand L-1a·PF 6 . The minimum inhibitory concentration values toward a panel of bacteria, yeasts, and molds were examined in a water-suspension system and a solution system containing dimethyl sulfoxide. The antimicrobial spectra of the three compounds were metal-dependent, and Au-1·PF 6 showed the greatest activity toward Gram-positive bacteria.