Insights on the photomagnetism in copper octacyanomolybdates

High level ab initio calculations on the photoinduced high-spin molecule [Mo(CN)(2)(CN-Cu(tris(2-aminoethyl)amine)(6)](8+) are reported. The calculations indicate that the mechanism of the photoinduced transformation from a paramagnetic to a ferromagnetic state involves a local Mo d-d transition followed by the deformation of the coordination sphere from dodecahedron to square antiprism. Subsequently, Mo loses a ligand and becomes seven coordinated in a pentagonal bipyramid coordination. The resulting Mo-IV(S = 1) ion interacts ferromagnetically with the five remaining Cu-II ions through the cyanide bridges. The estimated coupling is about +50 K and the resulting magnetic susceptibility curve resembles the experimental one taking into account that part of the sample is magnetically deactivated during the measurement. The calculated potential energy profile along the linear interpolated reaction coordinate shows a small barrier for the reverse reaction in agreement with the thermal reversibility of the photoinduced state. Moreover, we find that the reverse reaction can be induced by light.