The AgCl, AgOAc, AuCl, and AuOAc complexes of the new bis(imino)acenaphthene(BIAN)-supported N-heterocyclic carbene ligand and the precursor imidazolium salt have been investigated with respect to their antimicrobial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Psudomonas aeruginosa. The most active antimicrobial is the precursor imidazolium salt, which has a minimum inhibitory concentration (MIC) value of <40 μg/mL. The MIC values for the silver complexes IPr(BIAN)AgCl and IPr(BIAN)AgOAc against Gram-positive S. aureus are comparable to that for AgNO₃, while those against Gram-negative E. coli and P.aeroginosa are significantly larger. Similar behavior was evident for the gold acetate complex IPr(BIAN)AuOAc. However, in the case of the gold chloride analogue, the MIC values are virtually identical for both the Gram-positive and the Gram-negative bacteria.