Ruthenium(II)/(III) complexes of bidentate acetyl hydrazide Schiff bases

A series of octahedral Ru^sup II^/Ru^sup III^ complexes of the type [Ru(Y)(CO)(BAX)(PPh^sub 3^)^sub 2^] and [RuCl^sub 2^(BAX)(PPh^sub 3^)^sub 2^] (Y = H or Cl; BAX = benzaldehydeacetylhydrazone anion; X = H, Me, OMe, OH, Cl or NO^sub 2^) have been prepared and characterised by spectral, magnetic and cyclic voltammetric studies. The Ru^sup II^ complexes are low spin diamagnetic (S = 0) whereas the Ru^sup III^ complexes are low spin and paramagnetic (S = 1/2). These Ru^sup II^ and Ru^sup III^ complexes absorb in the visible region respectively at ca. 16,000 and 28,000 cm^sup -1^ which bands are assigned to the MLCT. The correlation of the λ^sub max^ values of the Ru^sup III^ complexes with the σ^sup +^ Hammett parameter, is linear, indicating the profound effect of substituents on the electron density of the central metal. I.r. spectral data reveals that the hydrazone is chelated to ruthenium through the hydrazinic nitrogen and the deprotonated enolic oxygen. The rhombic nature of the e.s.r. spectra of the Ru^sup III^ complexes indicates an asymmetry in the electronic environment around the Ru atom. Ru^sup II^ complexes in CH^sub 2^Cl^sub 2^ show an irreversible Ru^sup II/III^ redox couple at ca. 0.9-0.5 V, while the Ru^sup III^ complexes show two reversible redox couples in the -0.1-0.1 and 0.8-0.6 V range, indicating that the higher oxidation state of ruthenium is stabilised by hydrazones.[PUBLICATION ABSTRACT]