Properties and one-step synthesis of (2-acetylpyridine)tetraammineruthenium(II), [Ru-II(2-acpy)(NH3)(4)](2+) and tetraammine(2-benzoylpyridine)ruthenium(II), [Ru-II(NH3)(4)(2-bzpy)](2+) Redox potentials, UV-Vis and NMR spectra

A more direct and efficient route to the syntheses of [Ru(NH3)(4)(X-Y)](BF4 )(2), where X-Y can be 2-acetylpyridine (2-acpy) or 2-benzoylpyridine (2-bz py), based on the reactions of [RuCl(NH3)(5)]Cl-2 with these ortho-substitu ted azines is described. The [Ru(2-acpy)(NH3)(4)](BF4)(2) and [Ru(NH3)(5)(2 -bzpy)](BF4)(2) complexes have a molar conductance of 328 and 292 Ohm(-1) c m(2) mol(-1), respectively, corresponding to a 1:2 species in solution. The se complexes showed two intense absorption bands around 620-650 and 380 nm, the energies of which are solvent dependent, decreasing with the increase of the Gutman's donor number of the solvent, and were assigned as metal-to- ligand charge transfer (MLCT). The complexes have oxidation potentials (Ru- II/III) of +0.380 V vs. Ag/AgCl (2-acpy) and +0.400 V vs. Ag/AgCl (2-bzpy), and reduction potentials (X-Y0/-) of -1.10 V vs. Ag/AgCl (2-acpy) and -0.9 50 V vs. Ag/AgCl (2-bzpy) on CF3COOH/NaCF3COO at pH=3.0, scan rate 100 mV s (-1), [Ru]=1.0x10(-3) mol l(-1). Both processes show a coupled chemical rea ction. Upon oxidation of the metal center, the MLCT absorption bands are bl eached and restored upon subsequent reduction. In order to confirm the stru cture of the complexes a detailed LH NMR investigation was performed in d(6 )-acetone. Further confirmation of the structure was obtained by recording the N-15 NMR spectrum of [Ru(NH3)(4)(2-bzpy)](2+) in d(6)-DMSO using the IN EPT pulse sequence improving the sensitivity of N-15 by polarization transf er from the protons to the N-15. The Nuclear Overhauser Effect (NOE) experi ments were made qualitatively for [Ru(NH3)(4)(2-acpy)](2+), and showed that H-6 of the pyridine is close to a NH3 proton, which should then be in a ci s position, and, hence, confirming that acpy is acting as a bidentate ligan d. (C) 1999 Elsevier Science Ltd. All rights reserved.