Ketoximato-complexes. Part 3. Structure and properties of tris chelates of cobalt(III), iron(II), and ruthenium(II)

Abstract

A number of tris chelates derived from dihydrogenviolurate (H₂va^–) and 1,3-dimethylviolurate (dmva^–) have been synthesized. Complexes of general formula [ML₃]^n–(M = Co^III, n= 0; M = Fe^II or Ru^II, n= 1; L = H₂va or dmva) are described and characterized by i.r., u.v.–visible, and ¹H n.m.r. spectra. Infrared data support the assumption of the same fac co-ordination structure for all the complexes in the solid state. The ¹H n.m.r. spectra are in accordance with an octahedral arrangement in the fac configuration in solution. The ¹H n.m.r. shifts are a probe of electron-density changes at the N(1) and N(3) sites of the co-ordinated heterocycle. Measurements of pK_a for the [M(H₂va)₃]^n– complexes are presented and are consistent with the n.m.r. data. The energies of the π→π* and d→π* electronic transitions of the protonated and deprotonated species provide information about the energies of the molecular orbitals of the violurate ligand. The results are interpreted in terms of Lewis-acid charge withdrawal and π-back bonding.