Spectroscopic characterization of complexes of tetracycline with cobalt(II), nickel(II), cadmium(II) and inorganic Sn(II)

Complexes of Co(II), Ni(II), Cd(II) and inorganic Sn(II) with tetracycline (TC) have been synthesized and characterized by elemental analyses, vibrational spectra, electronic spectra, 1 H NMR spectra, magnetic susceptibility measurement, thermal studies and X-ray powder diffraction studies. TC forms a 1:1 complex with the metal ions through the oxygen of the hydroxyl group at the A ring and the carbonyl oxygen atom of the amide group in coordination. The results of spectral techniques and magnetic susceptibility measurement correlate well. Kinetic and thermodynamic parameters were computed from the thermal data using the Coats and Redfern method, which confirm first order kinetics. X-ray powder diffraction data determined the cell parameters of the complexes. The molecular structures of the complexes have been optimized by MM2 calculations and supported square planar/tetrahedral geometry around Metal (II) ions.