Isomerism in Phenyl 2‐Pyridyl Ketoxime Metal Complexes

Abstract The octahedral complex [RhCl 2 (ppkoH)(ppko)] ( 1 ) was obtained from the reaction between RhCl 3 and phenyl 2‐pyridyl ketoxime (ppkoH). Attempts to prepare the corresponding octahedral platinum compound from K 2 PtCl 6 gave instead the square planar [Pt 2+ (ppko) 2 ] ( 2 ), but when the halogen was changed to bromine, the octahedral [Pt 4+ Br 2 (ppko) 2 ] ( 3 ) was formed. The crystal structures were determined by X‐Ray crystallography. All the compounds have two N,N‐chelating oxime ligands. In 1 , one of them is deprotonated, while in 2 and 3 both ligands are deprotonated. Compounds 1 and 3 have two halogen ligands in trans position. In 1 the oxime groups are situated mutually in cis position with an intramolecular hydrogen bond between the two N−O(H) groups. The formation of 2 involves reduction of the platinum metal and the complex has oximes in trans position to each other. Compound 3 has an all‐ trans geometry. Since octahedral and square planar compounds have a possibility to isomerism, we studied the relative stability of different geometries by DFT calculations. A mixture of isomers is likely to be formed in the reactions, but the most stable form was found to crystallize. The properties of the electron density in the preferred isomers were also investigated via QTAIM methods.