Endiol ligand formation from 2-pyridinecarboxaldehyde on a Mo(IV) centre. The X-ray crystal structure and properties of the Mo(IV) binuclear complex

The reaction of 2-pyridinecarboxaldehyde with K3Na[Mo(CN)4O2]·6H2O in water–ethanol solution at pH ca. 9 result in formation of an [{Mo(CN)3O}2(μ-pyr)]4− ion salt isolated as (PPh4)4[{Mo(CN)3O}2(μ-pyr-1κ2N,O;2κ2N,O)]·7H2O, where H2pyr = 1,2-bis(2-pyridyl)ethene-1,2-diol. The X-ray crystal structure shows, that the pyr is in the form of endiol with CC bond and formal 2- charge. Cyclic voltammetry measurements indicate that binuclear complex can be reversibly oxidised to Mo(IV,V) with E1/2 = + 37 mV and to Mo(V,V) at +262 mV and reduced to Mo(III,III) at −468 mV (scan speed 100 mV/s). The formation of a Mo(IV,V) mixed valence complex is confirmed by the UV–Vis spectra in the presence of oxygen,