LAUSR

Herein, we report diruthenium(III) complexes bridged by the deprotonated N,N′-diphenylpyrazine-2,5-dicarboxamide (H2L1) and N,N′-dimesitylpyrazine-2,5-dicarboxamide (H2L2) ligands in meso diastereomeric form, namely, (acac)2RuIII(µ-L1)RuIII(acac)2 (1, acac = acetylacetonato) and (acac)2RuIII(µ-L2)RuIII(acac)2 (2), as well as the monodeprotonated HL1-derived mononuclear counterpart (acac)2RuIII(HL1) (3). Variable-temperature magnetic studies of 1 revealed a weak bridge-mediated intramolecular antiferromagnetic interaction with J = –7.58 cm–1. The dinuclear complexes exhibited anisotropic electron paramagnetic resonance (EPR) signals at g ≈ 2 along with half-field signals at g1/2 ≈ 4, whereas the mononuclear counterpart 3 displayed an EPR signal with rhombic symmetry. Complexes 1 and 2 exhibited two oxidation and reduction steps with comproportionation constants (Kc) of 102 and 106 or 107. Complex 3 displayed one oxidation and two reductions steps. The electrogenerated compounds 1– and 2– exhibited metal-based EPR signals and a very weak and broad near-infrared (NIR) transition at λ ≈ 1200 nm. The C=O bands of the bridge were monitored through IR spectroelectrochemistry, which revealed a shift of these bands to lower energies on reduction. However, the native and reduced states have the same number of bands, which suggests a similar local symmetry for both redox forms and a delocalized electronic situation in the reduced compounds. A combination of electrochemistry and spectroelectrochemistry was used to probe the electronic structures of the various redox states in these complexes.