Thermal properties of the hybrid compound [Cu(en)2(VO3)2]•3H2O — phase analysis upon heating and cooling. Crystal structure characterization of its two polymorphic modifications

Abstract The inorganic-organic hybrid compound [Cu(en)2(VO3)2]•3H2O (1) was prepared by crystallization at room temperature from the CuSO4•5H2O – KVO3 – ethylenediamine – H2O system. Upon cooling 1, phase transition occurred at 176 K. Single-crystal diffraction analysis of the high- temperature and low-temperature phases has shown both phases to be polymeric, incorporating metavanadate chains (VO3)nn– coordinated via oxygen atoms to copper(II) atoms. The four remaining positions of the copper atoms with octahedral environment are taken by nitrogen atoms of two ethylenediamine ligands. The low-temperature phase exhibits displacive modulation in its structure. The band gap of the high-temperature phase is 2.95 eV. The compound is paramagnetic (1.79 µB) and exhibits no distinct magnetic interactions. A detailed phase analysis upon heating of 1 to 600 °C revealed the final products of the thermal decomposition to be monoclinic Cu(VO3)2, Cu2V2O7 as ziessite and V2O5. After cooling to room temperature, monoclinic Cu(VO3)2 transformed to its triclinic polymorph, while ziessite became transformed to blossite.