Structural Interconversions of Octahedral, Planar, and Tetrahedral Nickel(II) Complexes

Abstract

A series of bis-(N-R-salicylaldimine(Ni(II) complexes has been prepared in which the R group contains a site capable of coordination. Complexes with R=CH2CHCH2OCH3 but differing in the extent and position of chelate ring substitution have been thoroughly studied. For these complexes it has been shown from measurement of ligand field spectra amd piton contact shifts that in the temperature range —40 to 50° in chloroform solution discrete octahedral, planar and tetrahedral stereoisomers are present in equilibrium. At low temperatures the octahedral form predominates; at higher temperatures the equilibrium is displaced toward the planar and tetrahedral forms. For two complexes the temperature dependence of the distribution of stereoisomers has been estimated from spectral data. The spectra of the octahedral complexes were found to be quite similar to those of associated paramagnetic bis(salicylaldimine)nickel(II)+. suggesting quasi-octahedral coordination in the latter. The spin density distributions in the coordinated ligand systems were shown to be similar in sign in the octahedral and tetrahedral stereoisomers.