An investigation of conformation in co-ordination complexes of copper and manganese

Abstract

Those regions of chemistry (biological and structural) which form the context of this thesis are delineated and the conformational patterns which have been observed are described along with a brief discussion of those conformational influences which previously have been deemed significant. The elucidated structures of one manganese(III) and four copper(II) N-N’-alkylene linked bis-salicylaldimine complexes are described. The significant features of these structures, namely: the variations in tetrahedrality of the copper geometry observed in three of the molecular structures, the shortening of the N-N’-ethylene carbon-carbon bond in one of the copper compounds, the solvation of the manganese complex, and the bond axis rotations in the salicylaldimine rings as exhibited by all the complex molecules leads on to a detailed analysis of related bis-chelate salicylaldimine complexes. After some initial geometric considerations the nature of the electronic system associated with a chelate ring and a molecule as a whole, is discussed and attention is paid to the consequences of introducing nitrogen substituents which have a positive inductive effect. Suggestions as to the division of the bis-chelate complexes into square-planar and pseudo-tetrahedral categories and as to the oxidation state of copper in these categories are advanced. Then follow, in order, detailed considerations of the square-planar complexes, wherein a stereo-electronic explanation of the ‘folding’ of the chelate ring is developed and an explanation of the stepped conformation, of its common occurrence and of varying step-size is advanced. The pseudo-tetrahedral bis-chelate complexes are considered in the light of the preceeding concepts and the interactions controlling the magnitude of the dihedral angle and the ring conformations are analysed. An explanation for the relative occurrence of the trans- and cis-isomers is advanced. The N-N’ linked complexes are then considered in this wider context and, inter alia, an explanation of the observed preference for the ‘umbrella’ configuration in ethylene linked compounds is advanced. The conclusions, which are developed for the N2O2 donor set, are shown to be capable of extension to related donor sets, and the cognation of this work and related fields of chemistry is discussed. The inductive effect, hyperconjugation, statistical comparisons and least-squares weight-schemes are discussed in a series of appendices.