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

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-NO(2)HOr)(H2O)(4)] (1) and tetraaqua(5-nitroorotato)zinc(II), [Zn(5-NO(2)HOr)(H2O)(4)] (2) crystallize in the orthorhombic system (space group Pca2(1)). 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...pi and N-O...pi 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-NO(2)H(2)Or) (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).