On the Role of the Bridging Dicyanamidobenzene Ligand in a New Binuclear Ruthenium Complex: [{Ru(tpy)(thd)} 2 (μ-dicyd)][PF 6 ] with tpy = 2,2‘:6‘,2‘ ‘-Terpyridine and thd = 2,2,6,6-Tetramethyl-3,5-heptanedione
Résumé
The dicyanamidobenzene-bridge diruthenium complex [{Ru(tpy)(thd)}2(µ-dicyd)][PF6] ([3][PF6]) {dicyd = 1,4-dicyanamidobenzene, tpy = 2,2’:6’,2”-terpyridine, thd = 2,2,6,6-tetramethyl-3,5-heptanedione} and its mononuclear counterpart [Ru(tpy)(thd)(Ipcyd)] (2) {Ipcyd = 4-iodophenylcyanamide anion (Ipcyd-)} were synthesized and fully characterized. Cyclic voltammetry of 3 showed the presence of four reversible one-electron redox couples. UV-Visible-NIR spectroelectrochemistry and EPR spectroscopy of the electrogenerated paramagnetic intermediates were used to ascertain the oxidation-state distribution. The stable starting dinuclear complex 3+ is found to be a ligand-centered anion radical as shown by EPR spectroscopy, magnetic susceptibility measurements, and DFT calculations. Oxidation of 3+ to 32+ led to a EPR silent system due to substantial intramolecular antiferromagnetic interaction of the electron spins carried by the low spin ruthenium(III) atom and the bridging anion radical dicyanamido (dicyd.-), an observation which was supported by UV/Vis/NIR, X-Ray structure and DFT calculations. 33+ presented a EPR spectra consistent with a total effective spin S=1/2 issued from an antiferromagnetic interaction of electron spins carried by two low spin ruthenium(III) atoms and the bridging anion radical dicyd.- in accordance with UV/Vis/NIR. This study shows that the dicyanamidobenzene bridging ligand has indubitably a non-innocent behavior.
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