Irradiation Temperature Dependence of the Photomagnetic Mechanisms in a Cyanido-Bridged CuMo Trinuclear Molecule.

We report a new bimetallic cyanido-bridged trinuclear complex [Cu(enpnen)][Mo(CN)]·6.75HO (1) (enpnen = N,N'-bis(2-aminoethyl)-1,3-propanediamine) that shows reversible photomagnetic effect. The photo-induced increase of magnetization is characterized by the irradiation temperature-dependent shapes of the χ T( T) plots and different magnetization values at low temperature in high magnetic field, suggesting multiple photoexcited states. The photomagnetic effect in 1 is explained through two possible processes simultaneously: the light-induced metal-to-metal charge transfer (MMCT) in the Cu-NC-Mo pair and the light-induced excited spin-state trapping (LIESST) effect in Mo center. A numerical model assuming the simultaneous existence of three possible states after irradiation: the MMCT Cu-NC-Mo-CN-Cu state, the LIESST Cu-NC-Mo-CN-Cu state, and the ground-state Cu-NC-Mo-CN-Cu was applied to the data and resulted in Cu-Mo exchange coupling constants J = 11 cm and J = 109 cm for the MMCT and LIESST mechanisms induced states, respectively. Fractions of respective states after irradiations at different temperatures were also calculated, shedding light on the influence of irradiation temperature on the photomagnetic mechanism. The proposed model can provide the interpretative framework for testing and refinement of the mechanism of photomagnetic effect in other coordination networks with cyanido-bridged Cu-[Mo(CN)] linkages.