REDOX PROPERTIES AND ELECTROCATALYTIC ACTIVITY OF THE OXO AQUA SYSTEM [RU(TERPY)(BPZ)(O)](2+)/[RU(TERPY)(BPZ)(H2O)](2+) - X-RAY CRYSTAL-STRUCTURE OF [RU(TERPY)(BPZ)CL]PF6-CENTER-DOT-MECN (TERPY=2,2',2''-TERPYRIDINE BPZ=2,2'-BIPYRAZINE)

Complexes of the type [Ru(terpy)(bpz)X](n+), where terpy = 2,2',2''-terpyridine, bpz = 2,2'-bipyrazine, and X = Cl- (1), H2O (2), have been prepared and characterized by UV-visible and H-1 NMR spectroscopies, and for the chloride derivative also by X-ray diffraction. [Ru(terpy)(bpz)Cl]PF6 . MeCN crystallizes in the triclinic space group P (1) over bar with the following crystallographic parameters: a = 8.9173(4) Angstrom, b = 12.6018(8) Angstrom, c = 13.1743(8) Angstrom, alpha = 70.392(5)degrees, beta = 81.005(4)degrees, gamma = 76.954(5)degrees, V = 1353.4(2) Angstrom(3), Z = 2, R(1) = 0.024 [for 5531 reflections F-0 > 4 sigma(F-0)], and omega R(2) = 0.061 for 6187 unique reflections. The redox properties of 2 have been investigated by electrochemical techniques over the pH range 0-12 in water. Only one reversible voltammetric wave (E(1/2) = +0.66 V vs SCE at pH = 7) is observed for 2 in the pH range 0-11, which has been assigned to the Ru(II) Ru(IV) couple. The two-electron nature of the redox process has been confirmed by a spectrophotometric titration of 2 with Ce(IV). The second-order rate constant, k(cat), for the oxidation of benzyl alcohol by the electrogenerated [Ru(IV)(terpy)(bpz)(O)](2+) was evaluated by cyclic voltammetry. At pH = 11 in phosphate buffer, k(cat) was estimated to be 23.0(7) M(-1) s(-1). An electrocatalytic rate constant, k(cat) = 36.1(15) M(-1) s(-1), was measured in 0.1 M NaOH for the oxidation of benzyl alcohol by a related compound, [Ru(IV)(terpy)(bpy)(O)](2+), where bpy = 2,2'-bipyridine.