Mixed-ligand schiff base cobalt(III) complexes with phenolaldehydes or phenolketones as ligands

Abstract

Mixed-ligand cobalt(III) complexes of the type [Co(L)(SB)] were prepared and characterized, where L is an aldehyde- or ketone-phenolate anion such as salicylaldehydate (sal), 5-chlorosalicylaldehydate (5-Cl-sal), 3,5-dichlorosalicylaldehydate (3,5-Cl-sal), or o-hydroxyacetophenonate (oap), whereas SB is a deprotonated Schiff base anion such as N, N′ disalicylideneethylenediaminate (sal 2en), N, N′-disalicylidene-1,3-propanediaminate (sal 2tn), N, N′-bis(7-methylsalicylidene)ethylenediaminate (7,7′-Me-sal 2en), or N, N′-bis(7-ethylsalicylidene)-1,3-propanediaminate (7,7′-Me-sal 2tn). For SB = sal 2en and sal 2tn, two isomers each were obtained as green and brown crystals; both exhibited, however, the same 1H NMR and absorption spectra in methanol, chloroform or dichloromethane. On the other hand, only the green form has thus far been obtained for SB = 7,7′-Me-sal 2en and 7,7′-Me-sal 2tn. X-ray analysis of a single crystal of [Co(sal)(7,7′-Me-sal 2tn)] has shown that two phenolato-oxygens of the Schiff base in the complex are in the cis position, and the three phenolate-oxygen atoms including that of the salicylaldehydato are situated in meridional position. The CoO (aldehyde) distance was found to be longer than the CoO (phenolato) distance in the above complex and also the CoO distances in amino acid complexes. The stability of the possible geometric structures of the complexes has been examined on the basis of conformational analysis.