Structural and Physical Studies of Co(III) Salen Derivatives.

Abstract

A number of ligands that belong to the salen-type family were synthesized in this thesis. These ligands were synthesized from salicylaldehyde and 1,2-phenylenediamine, 1,3- diamino-2-hydroxypropane, 1,2-diamino-ethane, N-(3-aminopropyl)-1,3-propanediamine, diethylenetriamine, diaminomaleonitrile, 2,2-dimethyl-1,3-propanediamine and 1,3- diaminopropane. From this range of ligands, H2salophen was chosen as the ligand for further studies. This work is aimed primarily at elucidating the structures and spectroscopic properties of [Co(salophen)(amine)2](OAc) derivatives, where salophen is N,N’-disalicylidene-1,2- phenylenediamine and the amines used were butylamine, benzylamine, a- methylbenzylamine, dibutylamine, N-methylpiperazine and piperidine. Three novel crystal structures of [CoIII(salophen)L2]Cl derivatives, where L = butylamine, benzylamine, and piperidine, with Co-N distances that range from 1.901 Å to 2.024 Å, have been reported in this thesis. The novel crystal structure of [Co(salophen)(N-MePipz)(OAc)] is also reported in this thesis. These cobalt complexes have been analysed by 1H, 13C and 59Co NMR as well as electronic and IR spectroscopy. A 59Co NMR spectrum was obtained for the [Co(salophen)(BuNH2)2]CH2Cl2×Cl complex. The spectrum exhibits a single line at 8504 ppm. The binding constants of all [Co(salophen)(amine)2](OAc) complexes, where amine = butylamine, benzylamine, a-methylbenzylamine, dibutylamine, N-methylpiperazine and piperidine, were determined by spectroscopic titrations. The titrations were carried out at various concentrations of the amine and at temperatures ranging from 25°C to 45°C. It was found that the primary amines had much larger values of K1 and K2 compared to the secondary amines. Typical values of K1 and K2 were 8000 M-1 and 63.6 M-1 respectively at 25°C, for a-methylbenzylamine. Of the primary amines, it was found that a- methylbenzylamine had the largest value of K1 and K2 compared to the other two amines. For the secondary amines, it was found that N-methylpiperazine had the bigger value of K1 compared to that of dibutylamine.