Structure, electrochemistry and spectroscopy of a new diacylhydrazido-bridged diruthenium complex with a strongly near-infrared absorbing RuIIIRuII intermediate

Reaction of Ru(bpy)(2)Cl-2 center dot 2 H2O with 1,2-bis(trifluoroacetyl)hydrazine H-2(adc-CF3) under basic conditions yields the dinuclear [(mu-adc-CF3){Ru(bpy)(2)}(2)](2+) ion which was isolated and crystallized for structure determination in the meso diastereoisomer form as the bis(hexafluorophosphate). The Ru center dot center dot center dot Ru distance was determined at 5.029(1) angstrom, and the N-N bond length at 1.463(5) angstrom reveals a hydrazido(2-) form of the bridge, implying unchanged +II metal oxidation states. Besides bpy-based reduction, the cyclic voltammetric analysis revealed two oxidation waves with a (3+) intermediate. Spectroelectrochemistry demonstrated that this intermediate [(mu-adc-CF3){Ru(bpy)(2)}(2)](3+) with a comproportionation constant of K-c = 10(8.8) and an absorption at 1680 nm (epsilon=9900 M-1 cm(-1)) is a mixed-valent species as evident most convincingly from the EPR parameters at g(1)=2.239, g(2)=2.065, g(3)=1.891 (g(av)=2.101, Delta g=g(1) - g(3)=0.348). (C) 2010 Elsevier B.V. All rights reserved.