Synthesis and properties of [Ru-2(acac)(4)(bptz)](n+) (n=0, 1) and crystalstructure of [Ru-2(acac)(4)(bptz)]

The neutral complex [Ru-2(acac)(4)(bptz)] (I) has been prepared by the reac tion of Ru(acac)(2)(CH3CN)(2) with bptz (bptz = 3,6-bis(2-pyridyl)- 1,2,4,5 -tetrazine) in acetone. The diruthenium(II,II) complex (I) is green and exh ibits an intense metal-ligand charge-transfer band at 700 nm. Complex I is diamagnetic and has been characterized by NMR, optical spectroscopy, IR, an d single-crystal X-ray diffraction. Crystal structure data for I are as fol lows: triclinic, P1, a = 11.709(2) Angstrom, b = 13.487(3) Angstrom, c = 15 .151(3) Angstrom, alpha = 65.701(14)degrees, beta = 70.610(14)degrees, gamm a = 75.50(2)degrees, V = 2038.8(6) Angstrom (3), Z = 2, R = 0.0610, for 439 7 reflections with F-o > 4 sigmaF(o). Complex I shows reversible Ru-2(II,II )-Ru-2(II,III) and Ru-2(II,III)-Ru-2(III,III) couples at 0.17 and 0.97 V, r espectively; the 800 mV separation indicates considerable stabilization of the mixed-valence species (K-com > 10(13)). The diruthenium-(II,III) comple x, [Ru-2(acac)(4)(bptz)] (PF6) (II) is prepared quantitatively by one-elect ron oxidation of I with cerium(IV) ammonium nitrate in methanol followed by precipitation with NH4PF6. Complex II is blue and shows an intense MLCT ba nd at 575 nm and a weak band at 1220 nm in CHCl3, which is assigned as the intervalence CT band. The mixed valence complex is paramagnetic, and an iso tropic EPR signal at g = 2.17 is observed at 77 and 4 K. The solvent indepe ndence and narrowness of the 1200 nm band show that complex II is a Robin a nd Day class III mixed-valence complex.