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

A series of octahedral RuII/RuIII complexes of the type [Ru(Y)(CO)(BAX)(PPh3)2] and [RuCl2(BAX)(PPh3)2] (Y = H or Cl; BAX = benzaldehydeacetylhydrazone anion; X = H, Me, OMe, OH, Cl or NO2) have been prepared and characterised by spectral, magnetic and cyclic voltammetric studies. The RuII complexes are low spin diamagnetic (S = 0) whereas the RuIII complexes are low spin and paramagnetic (S = 1/2). These RuII and RuIII complexes absorb in the visible region respectively at ca. 16,000 and 28,000 cm−1 which bands are assigned to the MLCT. The correlation of the λmax values of the RuIII complexes with the σ+ 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 RuIII complexes indicates an asymmetry in the electronic environment around the Ru atom. RuII complexes in CH2Cl2 show an irreversible RuII/III redox couple at ca. 0.9–0.5 V, while the RuIII 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.