Spectroelectrochemistry and DFT Analysis of a New RuNOn Redox System with Multifrequency EPR Suggesting Conformational Isomerism in the RuNO7 State
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Inorganic Chemistry 46 (22): 9254--9261 (2007)

Ru(NO)(bpym)(terpy)(PF6)3, bpym = 2,2'-bipyrimidine and terpy = 2,2':6',2''-terpyridine, with a RuNO6 configuration (angle Ru-N-O 175.2(4)°) was obtained from the structurally characterized precursor Ru(NO2)(bpym)(terpy)(PF6), which shows bpym-centered redn. and metal-centered oxidn., as evident from EPR spectroscopy. The relatively labile Ru(NO)(bpym)(terpy)3+, which forms a structurally characterized MeCN substitution product Ru(MeCN)(bpym)(terpy)(PF6)2 upon treatment with MeOH/MeCN, is electrochem. reduced in 3 1-electron steps of which the 3rd, leading to neutral Ru(NO)(bpym)(terpy), involves electrode adsorption. The 1st-two redn. processes cause shifts of n(NO) from 1957 via 1665 to 1388 cm-1, implying a predominantly NO-centered electron addn. UV-visible-NIR Spectroscopy shows long-wavelength ligand-to-ligand charge transfer absorptions for RuII(NO-1)(bpym)(terpy)+ in the visible region, whereas the paramagnetic intermediate Ru(NO)(bpym)(terpy)2+ exhibits no distinct absorption max. \textgreater309 nm. EPR spectroscopy of the latter at 9.5, 95, and 190 GHz shows the typical invariant pattern of the RuNO7 configuration; however, the high-frequency measurements at 4 and 10 K reveal a splitting of the g1 and g2 components, which is tentatively attributed to conformers resulting from the bending of RuNO. DFT calcns. support the assignments of oxidn. states and the general interpretation of the electronic structure. on SciFinder(R)
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