Synthesis, thermal, spectral and biological properties of zinc(II) 4-hydroxybenzoate complexes

Abstract

New zinc(II) 4-aminobenzoate complex compounds with general formula [Zn(4-NH2benz)2L2]·nH2O, where 4-NH2benz = 4-aminobenzoate; L = nicotinamide (nad), isonicotinamide (inad), N-methylnicotinamide (mnad), thiourea (tu), urea (u), theophylline (tph), and caffeine (caf); n = 0–2; were synthesised and characterised by elemental analysis, thermal analysis, and IR spectroscopy. The thermal behaviour of prepared compounds was studied by TG/DTG and DTA methods in argon atmosphere. During the thermal decomposition, organic ligand, carbon monoxide, carbon dioxide, and aniline were evolved. The final solid product of the thermal decomposition was zinc oxide. The volatile gaseous products were proved by mass spectrometry. Solid intermediate product and the final product of thermal decomposition were identified by IR spectroscopy and X-ray powder diffraction method. It was solved crystal structure of polymeric [Zn(4-NH2benz)2], where the coordination environment around zinc(II) atom is an unsymmetrical distorted trigonal bipyramidal with chromophore ZnO3N2. The antimicrobial activity of zinc(II) carboxylate compounds was tested against various strains of bacteria, yeasts, and filamentous fungi (S. aureus, E. coli, C. albicans, R. oryzae, A. alternata, M. gypseum). The presence of zinc in complexes led to the increase their antimicrobial activity in comparison with free 4-aminobenzoic acid and ligands.