Synthesis and biological studies of ruthenium, rhodium and iridium metal complexes with pyrazole-based ligands displaying unpredicted bonding modes

Abstract

A series of new mono, di thienyl pyrazole (L1) and bridged furyl pyrazole (L2) complexes of arene ruthenium, rhodium and iridium {arene=benzene, p-cymene and Cp∗} have been synthesized and characterized by spectroscopic techniques. The formulations of these mono and di thienyl pyrazole complexes are as follows: [(arene)M(L1)Cl2], where M=Ru, arene=benzene (1), p-cymene (2); M=Rh, arene=Cp∗ (3) and M=Ir, arene=Cp∗ (4) [(arene)M(L1)2Cl]Cl, where M=Ru, arene=benzene (5), p-cymene (6); M=Rh, arene=Cp∗ (7) and M=Ir, arene=Cp∗ (8). The bridged furyl pyrazole complexes are formulated as [{(arene)MCl}2L2]PF6, where M=Ru, arene=benzene (9), p-cymene (10); M=Rh, arene=Cp∗ (11) and M=Ir, arene=Cp∗ (12). The structure of the complexes 1–7 and 10 has been established by single crystal X-ray diffraction studies. The orbital occupancy over the metal on complexation and energy gap between HOMO and LUMO of the complexes 1–6 have been analyzed by the density functional theory (DFT). The variation of the heterocyclic moiety in pyrazole ligands significantly alters bonding mode of the ligand. The in vitro antibacterial activity of the complexes 1–6 has been measured by the agar well diffusion assay by using human pathogenic gram-negative and gram-positive bacterial strains. The binding ability of the complexes 1–6 to the CT-DNA has been carried out by using various biophysical techniques viz. UV–Visible, fluorescence spectroscopy and agarose gel electrophoresis.