Synthesis, Characterization and Thermal Properties of Oligo-N,N′-bis (2,4-dihydroxybenzylidene) ethylenediamine and Its Cobalt (II) and Manganese (II) Complexes

In this study, the new oligomer Schiff base oligo-N,N'-bis (2,4-dihydroxybenzylidene) ethylenediamine (O-DHBEDA), with a double azomethine group, was synthesized by oxidative polycondensation (OP) of N,N'-bis (2,4-dihydroxybenzylidene) ethylenediamine (DHBEDA) with NaOCl as an oxidant in an aqueous alkaline medium at 90 degrees C. About 69.3% DHBEDA was converted to O-DHBEDA. The structures of the products were studied by UV-Vis, FT-IR, H-1-NMR, C-13-NMR and elemental analysis. According to gel-permeation chromatography (GPC) analysis of O-DHBEDA, the number-average molecular weight (M-n), weight-average molecular weight (M-w) and PDI values were found to be 5255 g/mol, 9116 g/mol and 1.73, respectively. During the polycondensation reaction, a part of the azomethine (-CH=N-) groups oxidized to aldehyde (CHO) groups (approx. 4%). Oligomer-metal complexes of oligo-N,N'-bis (2,4-dihydroxybenzylidene) ethylenediamine (O-DHBEDA) with Co (II) and Mn (II) were synthesized and characterized by FT-IR, UV-Vis, TG-DTA and atomic absorption spectroscopy (AAS). TG/DTA analyses were shown to be stable of O-DHBEDA against thermo-oxidative decomposition. The residue values of DHBEDA, O-DHBEDA, O-DHBEDA-Co and O-DHBEDA-Mn were found to be 0%, 7.1%, 14% and 13.4%, respectively, at 1000 degrees C. (C) Koninklijke Brill NV, Leiden, 2008