Experimental and DFT studies of sulfadiazine 'piano-stool' Ru(ii) and Rh(iii) complexes.

While sulfadiazine (HL) is extensively used to elaborate complexes of intriguing biological applications ( topical antibiotic silvadene; silver sulfadiazine), the molecular structure modification of sulfadiazine or even other sulfa drugs by coordination to either η-cymene Ru(ii) or η-Cp* Rh(iii) motif has not been investigated. Here, half-sandwich organoruthenium(ii) and organorhodium(iii) compounds of the type [(η--cymene)Ru(L)] (1) and [(η-CMe)Rh(L)] (2) are synthesized, characterized and evaluated for their potential antimicrobial activity. Spectroscopic and single crystal X-ray analysis showed that L is coordinated to Rh(iii) both the sulfonamide and pyrimidine nitrogen atoms forming "piano-stool" geometry. In 2, the NMR equivalence clearly pointed to participation of two L molecules in a fluxional process in which the third bond of the base of the stool is oscillating between two equivalent sulfonamide nitrogen atoms. While 1 was biologically inactive, complex 2 was potent against Gram-positive bacteria, and . Hen white egg lysozyme (HEWL), a model protein, reacted covalently with 2 the loss of one L molecule, while compound 1 decomposed during the interaction with that protein.