Cobalt(II)–lanthanoid(III)(Ln = La, Nd, or Gd) complexes of N,N′-ethylenebis(3-carboxysalicylideneimine). Interaction of ligating groups on the Co–Ln centre

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Abstract
Cobalt(II)–lanthanoid(III) complexes of N,N′-ethylenebis(3-carboxysalicylideneimine)(H4csalen), [CoLa(csalen)(CH3OH)(NO3)], [CoNd(csalen)(H2O)2(NO3)], and [CoGd(csalen)(H2O)(NO3)], have been prepared and characterized, where the cobalt ion is bound at the N2O2 site and the lanthanoid ion at the O4 site of the binucleating ligand. Based on electronic and e.s.r. spectra the configuration around the cobalt ion was shown to be planar at room temperature in dimethylformamide (dmf) or dimethyl sulphoxide (dmso) while square pyramidal at liquid-nitrogen temperature with a solvent molecule at the axial site. When a nitrogen-containing base such as pyridine or n-propylamine was added to dmf solutions of the Co–Ln complexes the base was co-ordinated to the cobalt ion to afford five-co-ordination around the metal at room temperature. At liquid-nitrogen temperature the configuration around the cobalt was dependent upon the nature of the added base: six-co-ordination for pyridine or its derivatives and five-co-ordination for aliphatic amines. It is suggested that substrates possessing N- and O-donor groups such as 2-aminoethanol are specifically bound at the Co–Ln centre, via N to the cobalt and O to the lanthanoid ion.