Synthesis, spectroscopic, thermal, antimicrobial and electrochemical characterization of some novel Ru(iii), Pt(iv) and Ir(iii) complexes of pipemidic acid

Abstract

Three new solid complexes of pipemidic acid (Pip-H) with Ru3+, Pt4+ and Ir3+ were synthesized and characterized. Pipemidic acid acts as a uni-dentate chelator through the nitrogen atom of the -NH piperazyl ring. The spectroscopic data revealed that the general formulas of Pip-H complexes are [M(L)n(Cl)x]·yH2O ((1) M = Ru3+, L: Pip-H, n = 3, x = 3, y = 6; (2) M = Pt4+, L: Pip-NH4, n = 2, x = 4, y = 0 and (3) M = Ir3+, L: Pip-H, n = 3, x = 3, y = 6). The number of water molecules with their locations inside or outside the coordination sphere were assigned via thermal analyses (TG, DTG). The DTG curves refer to 2-3 thermal decomposition steps where the first decomposition step at a lower temperature corresponds to the loss of uncoordinated water molecules followed by the decomposition of Pip-H molecules at higher temperatures. Thermodynamic parameters (E∗, ΔS∗, ΔH∗ and ΔG∗) were calculated from the TG curves using Coats-Redfern and Horowitz-Metzeger non-isothermal models. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were carefully used to assign properly the particle sizes of the prepared Pip-H complexes. The biological enhancement of Pip-H complexes rather than free chelate were assessed in vitro against four kinds of bacteria G(+) (Staphylococcus epidermidis and Staphylococcus aureus) and G(-) (Klebsiella and Escherichia coli) as well as against the human breast cancer (MCF-7) tumor cell line.