Synthesis and characterization of Schiff base, Co(II) and Cu(II) metal complexes and poly(phenoxy-imine)s containing pyridine unit

Abstract

In the first stage, two different Schiff base ligands were prepared by the condensation of 2-amino-5-bromopyridine and 2-amino-5-chloropyridine with salicylaldehyde in methanol at the molar ratio of 1:1. Ligands: C12H9ON2Br (L1), C12H9ON2Cl (L2). In the second stage, four different metal complexes were obtained from Schiff bases with Co(OAc)2·4H2O and Cu(OAc)2·2H2O Molecular formulas of the metal complexes obtained were [Co2(L1)2(H2O)(OCH3)]H2O, [Cu2(L1)2(H2O)(OCH3)]H2O, [Co2(L2)2(H2O)(OCH3)]H2O and [Cu2(L2)2(H2O)(OCH3)] H2O. In the third stage, ortho-vanillin (VAN) was polymerized via oxidative polycondensation in aqueous alkaline medium with air as oxidant. Then, poly(phenoxy-imine)s were synthesized from condensation reactions of poly (ortho-vanillin) (PVAN) with 2-amino-5-bromopyridine and 2-amino-5-chloropyridine in THF medium at 60 °C. All synthesized compounds were characterized by spectral and electrochemical techniques. Thermal properties of the compounds were determined by TGA-DTA and DSC analyses. The molecular weights of the polymers were calculated from SEC analyses. Poly[2-((5-bromopyridin-2-yl-imino)methyl)-6-methoxyphenol] (PVANBr) and poly[2-((5-chloropyridin-2-yl-imino)methyl)-6-methoxyphenol] (PVANCl) were determined to have electrical conductivity of 10−3 S cm−1. Electrochemical band gaps (Eg’) of PVANBr and PVANCl were calculated as 2.10 and 1.95 eV, respectively. Initial decomposition temperatures of [Co2(L1)2(H2O)(OCH3)]H2O, [Cu2(L1)2(H2O)(OCH3)]H2O, [Co2(L2)2(H2O)(OCH3)]H2O and [Cu2(L2)2(H2O)(OCH3)]H2O were found to be 309, 271, 305 and 259 °C, respectively.