title: Correspondence of Ru(III) Ru(II) and Ru(IV) Ru(III) mixed valent states in a small dinuclear complex.
abstract: The diruthenium(III) compound [(μ-oxa){Ru(acac)(2)}(2)] [1, oxa(2-) =oxamidato(2-), acac(-) =2,4-pentanedionato] exhibits an S=1 ground state with antiferromagnetic spin-spin coupling (J=-40 cm(-1)). The molecular structure in the crystal of 1⋅2 C(7)H(8) revealed an intramolecular metal-metal distance of 5.433 Å and a notable asymmetry within the bridging ligand. Cyclic voltammetry and spectroelectrochemistry (EPR, UV/Vis/NIR) of the two-step reduction and of the two-step oxidation (irreversible second step) produced monocation and monoanion intermediates (K(c) =10(5.9)) with broad NIR absorption bands (ε ca. 2000 M(-1)cm(-1)) and maxima at 1800 (1(-)) and 1500 nm (1(+)). TD-DFT calculations support a Ru(III)Ru(II) formulation for 1(-) with a doublet ground state. The 1(+) ion (Ru(IV)Ru(III)) was calculated with an S=3/2 ground state and the doublet state higher in energy (ΔE=694.6 cm(-1)). The Mulliken spin density calculations showed little participation of the ligand bridge in the spin accommodation for all paramagnetic species [(μ-oxa){Ru(acac)(2)}(2)](n), n=+1, 0, -1, and, accordingly, the NIR absorptions were identified as metal-to-metal (intervalence) charge transfers. Whereas only one such NIR band was observed for the Ru(III)Ru(II) (4d(5)/4d(6)) system 1(-), the Ru(IV)Ru(III) (4d(4)/4d(5)) form 1(+) exhibited extended absorbance over the UV/Vis/NIR range.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai, India.
authors.forename: Hemlata
authors.initials: H
authors.lastname: Agarwala
authors.forename: Thomas Michael
authors.initials: TM
authors.lastname: Scherer
authors.forename: Somnath
authors.initials: S
authors.lastname: Maji
authors.forename: Tapan Kumar
authors.initials: TK
authors.lastname: Mondal
authors.forename: Shaikh M
authors.initials: SM
authors.lastname: Mobin
authors.forename: Jan
authors.initials: J
authors.lastname: Fiedler
authors.forename: Francisco A
authors.initials: FA
authors.lastname: Urbanos
authors.forename: Reyes
authors.initials: R
authors.lastname: Jiménez-Aparicio
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri