Geometrical and electronic properties of a family of high-spin cobalt(II) dimers bridged by 3,5-bis(pyridin-2-yl)pyrazolate and 3,5-bis(pyridin-2-yl)triazole ligands: insights into their catalysis in two-electron one-step CO2 reduction.

The crystal structure of bis[μ-3,5-bis(pyridin-2-yl)pyrazolato-κ4N2,N3:N1,N5]bis[bis(methanol-κO)cobalt(II)] dinitrate methanol disolvate, [Co2(C13H9N4)2(CH4O)4](NO3)2·2CH4O (I), was solved by X-ray diffractometry in order to gain insights into its electronic and catalytic properties because of its relevance to an analogous cobalt(II) dimer (V) which was shown to be highly active for CO2 reduction. The geometrical and electronic properties are also discussed in relation to other reported CoII dimers having analogous structures (compounds II-IV and VI). Interestingly, I was found to possess quite similar structural features compared with the five other reported analogues (II-VI). The similarly elongated coordinate bond lengths in I-VI further implied a consistency in their spin states at the metal centres. By analogy to a report on V, all these compounds were suggested to possess a high-spin septet state (S = 3), previously evidenced for V by measuring its magnetic susceptibility data. The validity of these considerations was also confirmed by examining the density functional theory (DFT)-based structures, together with the energies of three possible spin states (S = 3, 1 and 0).