New isomorphous complexes of Co(II) and Zn(II) with the 5-nitroorotate ligand: Crystal and molecular structures, spectroscopic and DFT studies, magnetic properties and antimicrobial activities

Abstract

Two novel isomorphous Co(II) and Zn(II) complexes of 5-nitroorotate have been synthesized and characterized by a single crystal X-ray diffraction, FT-IR, Raman and UV-Vis-NIR spectroscopy as well as thermal analysis. Both tetraaqua(5-nitroorotato)cobalt(II), [Co(5-NO2HOr)(H2O)4] (1) and tetraaqua(5-nitroorotato)zinc(II), [Zn(5-NO2HOr)(H2O)4] (2) crystallize in the orthorhombic system (space group Pca21). Each metal ion is chelated by the carboxylate oxygen (O1) and the deprotonated nitrogen (N1) atoms of the 5-nitroorotate ligand. Four water molecules complete the distorted octahedral coordination sphere around the metal center with an elongated axial M‒O bonds. The pattern of hydrogen bonding in the crystals of (1) and (2) is somewhat different than that reported for similar metal-orotate complexes. Weak C‒O···π and N‒O···π intermolecular interactions promote the crystal cohesion. Theoretical studies were performed using the DFT/B3LYP method and a detailed interpretation of the vibrational spectra has been made on the basis of the calculated potential energy distribution (PED). The electronic spectra and photoluminescent properties of (1), (2) and K(5-NO2H2Or) (3) were investigated. Temperature and field-dependent magnetic studies of (1) revealed the existence of a weak antiferromagnetic exchange coupling transmitted by medium-strong O‒H···O intermolecular hydrogen bonds. In addition, (1), (2) and (3) were studied in vitro for their activity against selected Gram-positive (S. aureus) and two Gram-negative (E. coli, P. aeruginosa) bacteria and one yeast (C. albicans).