Synthesis, biological evaluation and colorimetric sensing studies of platinum group metal complexes comprising pyrazine based thiourea derivatives

A series of complexes ( 1 – 9 ) were synthesized by the reaction of halide bridged metal precursors with the three pyrazine thiourea ligands L1 , L2 and L3 to yield cationic as well as neutral complexes and characterized by various spectroscopic techniques. The cationic complexes are represented by the general formula [(arene)M(L)Cl] + , where L = L1 , L2 and L3 , arene = p -cymene, Cp* and M = Ru, Rh and Ir. All the cationic complexes were isolated with chloride/PF 6 as the counter ion. Reactions of rhodium and iridium dimers with L2 yielded neutral complexes 5 and 6 with the general formula [(arene)M(L)Cl 2 ]. The neutral complexes 5 and 6 were further reacted with NaN 3 to yield azido complexes 10 and 11 . These complexes were, in turn, reacted with acetylene derivatives to yield triazolo complexes 12 – 15 where only a few triazolo complexes of Cp* have been reported. X-ray diffraction studies revealed the complexes having a typical piano stool geometry around the metal center with the thiourea adducts binding to the metal center in a chelating (N, S) manner. Furthermore, the complexes 1 – 9, as well as the ligands were screened for potential anti-bacterial agents out of which complexes 3 and 5 exhibited anti-bacterial activity. Colorimetric sensing studies showed the agglomeration of the silver NPs upon addition of the ligands while the complexes were unresponsive.