Characterization of a Mixed-Valence Ru(II)/Ru(III) Ion-Pair Complex. Unexpected High-Frequency Electron Paramagnetic Resonance Evidence for Ru(III)–Ru(III) Dimer Coupling

Abstract

In this contribution, we report the synthesis and full characterization of the first mixed-valence Ru(II)/Ru(III) ion-pair complex, [Ru II (bipy) 2 (pic)] + [cis-Ru III Cl 2 (pic) 2 ] − , in the solid state and in aqueous solution, where bipy = 2,2′bipyridine and pic − = picolinate. In addition, unexpected high-frequency electron paramagnetic resonance evidence for interactions between two neighboring Ru(III) ions, resulting in a triplet state, S = 1, was found.

A Personal Account on Inorganic Reaction Mechanisms

“…The Ru−N and Ru−O bonds are much shorter (2.0516(19) and 2.0242(16) Å) than the Ru−Cl bond length (2.3422(6) Å) [71] . The structures of anionic counterparts of the complex ion‐pairs are very similar to that of ( 4 ) with Ru−N and Ru−O bonds shorter than Ru−Cl bonds [62,70] …”

“…Indeed, effective magnetic moments of 2.05, 2.08 and 2.13 B.M. (measured at room temperature) were established for (1) , (2) , and (3) , respectively [62,70] …”

“…Recently, we reported the synthesis of a Ru(II)/Ru(III) mixed‐valence ion‐pair complex [62] . The preparation of the complex was not intentional.…”

“…The serendipitous preparation of the first Ru(II)/Ru(III) mixed‐valence ion‐pair complex became an inspiration to synthesize more such compounds using 2,2’:6’,2”‐terpyridine (terpy), 2,2′‐bipyridine (bipy), and 1,10‐phenanthroline (phen) as neutral chelating polypyridyl nucleophiles. A series of three ion‐pair complexes of different cationic and common anionic counterparts was isolated: [Ru II (bipy) 2 (pic)] + [ cis ‐Ru III Cl 2 (pic) 2 ] − ( 1 ), [Ru II (terpy)(bipy)Cl] + [ cis ‐Ru III Cl 2 (pic) 2 ] − ⋅ (CH 3 ) 2 CO ⋅ H 2 O, (2) , and [Ru II (terpy)(phen)Cl] + [ cis ‐Ru III Cl 2 (pic) 2 ] − ⋅ 2H 2 O, ( 3) [62,70,71] . The compounds were identified, and their structures in the solid state were determined by applying single‐crystal X‐ray diffraction and FT‐IR spectroscopy.…”

“…Bands around 425 and 465 cm −1 were assigned to ν(Ru−N) and ν(Ru−Cl), respectively. The far‐IR spectra of all complexes ( 1‐4 ) exhibit bands at about 282 and 245 cm −1 associated with Ru−Cl symmetric and asymmetric stretching vibrations, respectively [62,70–72] …”