Synthesis, characterization and electrochemical properties of β-diketone complexes of ruthenium(III)

The reactions of ruthenium(III) chloride (1 mol) with acetylacetonylidene-4-aminoantipyrine (HL¹), monobenzoylacetylacetonylidene-4-aminoantipyrine (HL²), dibenzoylmethanylidene-4-aminoantipyrine (HL³) and antipyrine-4-azo-β-ethylacetoacetate (HL⁴) (1 mol) produce complexes of the general formula RuHLCl₃. The ligand antipyrine-4-azo-β-acetylacetone (HL⁵) (1 mol) reacts with RuCl₃·3H₂O to produce RuL⁵ Cl₂(H₂O)·H₂O. The ligands HL¹-HL³ react as neutral bidentates in the ketoenamine form, whereas HL⁴ reacts as a neutral bidentate in the hydrazo form. HL⁵ reacts as a monobasic tridentate in the azo form. The complexes were characterized using a variety of analytical, spectral, magnetic and thermal measurements. The electrochemical redox properties of complexes I-V have been studied by cyclic voltammetry in acetonitrile. The chloro-bridged dimer complexes I-IV showed two reversible diffusion-controlled oxidation peaks. The first was attributed to the oxidation of the ruthenium(III) to the corresponding mixed-valence complex and the second to the ruthenium(IV) complex. The redox properties of complexes I-IV are dependent on the nature of ligand. The monomeric complex V has quite different properties.