A Diruthenium‐Based Mixed Spin Complex Ru 2 5+ ( S =1/2)‐CN‐Ru 2 5+ ( S =3/2)

An unusual tetra‐nuclear linear cyanido‐bridged complex [Ru 2 (μ‐ap) 4 ‐CN‐Ru 2 (μ‐ap) 4 ](BPh 4 ) ( 1 ) (ap=2‐anilinopyridinate) has been synthesized and well characterized. The crystallographic data, magnetic measurement, IR, EPR and theoretical calculation results demonstrate that complex 1 is the first example of mixed spin Ru 2 5+ ‐based complex with uncommon electronic configurations of S =1/2 for the cyanido‐C bound Ru 2 5+ and S =3/2 for the cyanido‐N bound Ru 2 5+ . This phenomenon can be understood by the theoretical calculation results that from the precursor Ru 2 (μ‐ap) 4 (CN) ( S =3/2) to complex 1 the energy gap between π* and δ* orbitals of the cyanido‐C bound Ru 2 5+ core increases from 0.57 to 1.61 eV due to the enhancement of asymmetrical π back‐bonding effect, but that of the cyanido‐N bound Ru 2 5+ core is essential identical (0.56 eV). Besides, the analysis of UV/Vis‐NIR spectra suggests that there exists metal to metal charge transfer (MMCT) from the cyanido‐N bound Ru 2 5+ ( S =3/2) to the cyanido‐C bound Ru 2 5+ ( S =1/2), supported by the TDDFT calculations.