Mn(II), Co(II) and Cu(II) Complexes of 1,10-Phenanthroline with co-ligands: synthesis, characterisation, thermal and biological properties

Abstract

Five novel complexes were synthesised in a stoichiometric reaction ratio 1:2:2 of the metal(II) salt, 1,10-phenanthroline and co-ligand (dicyanamide, azide and nitrate) respectively, in a methanol/H2O milieu at 85 °C under reflux in air. The obtained complexes; [Mn(phen)2(NO3)2] (1), [Mn(phen)2(N3)2] (2), [Mn(phen)2(dca)2] (3), [Cu(phen)(BMCA)](NO3) (4); BMCA = bis(methoxycarbimido)aminato ligand and [Co(phen)2(NO3)](􀝀􀜿􀝃 )·(H2O) (5); dcg = dicyanoguanidinate anion have been fully characterised using elemental analysis, infrared and UV-Vis spectroscopy, room temperature magnetic susceptibility measurements and thermal analytical techniques. Crystal structures for the complexes have been obtained and were determined by single crystal X-ray diffraction. Complexes 1 and 2 crystallize in an orthorhombic crystal system with space group Pbcn while complex 3 crystallizes in the monoclinic crystal system with space group P21/c. Complexes 4 and 5 crystallise in the monoclinic crystal system and the structures are stabilised by extended hydrogen bonding networks as well as aromatic π–π stacking interactions. Dicyanamide anion was transformed in 4 and 5 to bis(methoxycarbimido)aminato (BMCA) ligand and dicyanoguanidinate (dcg) anions, respectively. These metal-promoted or mediated transformations proceed through a nucleophilic attack of the nitrile groups of dicyanamide on methanol (case of BMCA), or on another dicyanamide (case of dcg). The magnetic moments of 1-3 are consistent with d5 high spin octahedral geometry. The magnetic moment of 4, is 1.75 B.M corresponding to one unpaired electron which is slightly greater than the spin only value of 1.73 B.M for d1. That of 5, is 3.92 B.M which is in agreement with d7 high spin Co(II) ion octahedral geometry. The thermal properties of the complexes have also been evaluated. The TGA thermograms of all the complexes show that they are stable up to 200 °C. The composition of the residue of 4 after thermal decomposition was characterised by powder X-ray diffraction (PXRD). The PXRD plot clearly shows (111), (200) and (220) peaks for Cu phase. Theoretical calculation were performed on the Cu(II) and Co(II) complexes which experienced dca transformation using DFT-B3LYP/6-31G(d,p) level theory. The complexes were screened for in vitro antibacterial and antifungal activities by the disc diffusion method. Complexes which show high activity against the microorganisms tested, their minimum inhibitory concentration values were determined using microdilution method with two-folded serial dilutions. The MIC values indicate that the complexes showed greater activity against the fungi strains and some bacteria strains tested compared to that of the reference antifungal-fluconazole and antibacterialcloxacillin.