Physicochemical properties of 3,4,5-trimethoxybenzoates of Mn(II), Co(II), Ni(II) and Zn(II)

The complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with 3,4,5-trimethoxybenzoic acid anion of the formula: M(C10H11O5)2·nH2O, where n = 6 for Ni(II), n = 1 for Mn(II), Co(II), Cu(II), and n = 0 for Zn, have been synthesized and characterized by elemental analysis, IR spectroscopy, X–ray diffraction measurements, thermogravimetry and magnetic studies. They are crystalline compounds characterized by various symmetry. They decompose in various ways when heated in air to 1273 K. At first, they dehydrate in one step and form anhydrous salts. The final products of decomposition are oxides of the respective metals (Mn2O3, Co3O4, NiO, CuO, ZnO). The solubilities of the analysed complexes in water at 293 K are in the orders of 10-2 – 10-4 mol dm-3. The magnetic susceptibilities of the Mn(II), Co(II), Ni(II) and Cu(II) complexes were measured over the range of 76–303 K and the magnetic moments were calculated. The results show that the 3,4,5-trimethoxybenzoates of Mn(II), Co(II) and Ni(II) are high-spin complexes but that of Cu(II) forms a dimer [Cu2(C10H11O5)4(H2O)2]. The carboxylate groups bind as monodentate or bidentate chelating or bridging ligands.