title: Bis(acetylacetonato)ruthenium complexes of noninnocent 1,2-dioxolene ligands: qualitatively different bonding in relation to monoimino and diimino analogues.
abstract: Coordination compounds [Ru(acac)(2)(Q)] (acac=acetylacetonate; Q=o-benzoquinone) were prepared as complexes 1 (Q=o-benzoquinone), 2 (Q=3-methoxy-o-benzoquinone), 3 (Q=4-methyl-o-benzoquinone), and 4 (Q=3,5-di-tert-butyl-o-benzoquinone). The structures of 1 and 2 were determined to reveal a Ru(III)/o-benzosemiquinone formulation, supported by analysis of experimental data (spectroscopy, magnetism of 1) and by DFT calculations. The S=1 ground state calculated for 1 stands in contrast to the spin-paired analogues with arylimino-o-benzosemiquinonato and diimino-o-benzoquinone ligands. The close contacts of about 5.3 Å possible between semiquinone O atoms of different molecules in the crystal allow for intermolecular spin-spin interactions and an overall complex magnetic behavior. One quasireversible oxidation and two reversible one-electron reductions yielded the corresponding molecular ions, which were characterized by UV-visible-NIR and EPR spectroelectrochemistry in terms of [Ru(III)(acac)(2)(Q(0))](+) , [Ru(III)(acac)(2)(Q(2-))](-), and [Ru(II)(acac)(2)(Q(2-))](2-) descriptions in agreement with DFT results. The use of acceptor-substituted 1,2-dioxolenes resulted in the isolation of ionic species Na[Ru(acac)(2)(Q)] (Na(5); Q=4-chloro-o-benzoquinone) and Na(6) (Q=4-nitro-o-benzoquinone), which were similarly investigated as compounds 1-4. Magnetic susceptibility and EPR results confirm an S=1/2 ground state based on ruthenium(III). The combined studies reveal a remarkable substituent sensitivity, and in comparison to recently analyzed Ru(acac)(2) complexes with o-benzoquinone monoimine and diimine ligands, the all-O-donor-containing new systems are distinguished by a qualitatively different metal-ligand interaction based on closer intermolecular radical-radical contacts and on weaker intramolecular dπ-π* interactions.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai-400076, India.
authors.forename: Dipanwita
authors.initials: D
authors.lastname: Das
authors.forename: Biprajit
authors.initials: B
authors.lastname: Sarkar
authors.forename: Doyel
authors.initials: D
authors.lastname: Kumbhakar
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