Stable cationic coordination polymers of the Cu(II)-vitamin B6 type: Structural analysis, application abilities and physicochemical properties in the solid state and solutions

Abstract

The stability of two cationic coordination polymers, {[Cu(NO3)(pm)2]}nNO3·H2O and {[Cu(Cl)(pn)2]}nNO3 (pm and pn denote pyridoxamine and pyridoxine, respectively), have been investigated in the solid state and solutions. The characterization of the solid precipitates has been acquired by X-ray, FT-IR spectroscopic, elemental analysis and thermogravimetric (27–900 °C) methods. The distorted tetragonal bipyramide geometry of a copper coordination sphere has been found in both compounds. In each case two bidentate vitamin B6 zwitterionic molecules (either pm or pn) are in equatorial positions while the axial ones are occupied by bridging ions (NO3− or Cl−). Interligand hydrogen bonds have been found to stabilize the polymers whereas the packing in crystals results from ionic interactions and charge assisted hydrogen bonding with terminal hydroxyl groups. In Cu-pm crystal lattice water molecules are also involved in the interchain H-bond network. The conductivity measurements and UV–Vis spectroscopy have confirmed the stabilization of the cationic coordination polymers in solutions. The redox properties of the compounds studied has been investigated by using cyclic voltammetry. The acid-base properties in aqueous solutions have been studied and the values of deprotonation constants have been determined by potentiometric and UV–Vis spectroscopic microtitration techniques. Finally, the application of the Cu(II)-vitamin B6 type complexes as sensing materials was proposed.