Towards rationalizing photoswitchable behavior of Cu2IIMoIV cyanido-bridged molecule

Abstract [Cu II (enpnen)]2[Mo IV (CN)8] ⋅ 7H2O (enpnen = N,N ′ - bis(2- aminoethyl)- 1,3 - propane- diamine) molecular cluster compound (1) was subject to a series of irradiations with the light of 405 nm. On irradiation isothermal magnetization at 1.8 and 5 K in the field range 0–70 kOe as well as magnetic susceptibility in the temperature range of 2–300 K were subsequently detected. Both types of magnetic signals were next analyzed assuming that the irradiation triggers two independent processes: the metal to metal charge transfer (MMCT) leading to a state with the Arrhenius-type relaxation and the spin crossover (SC) transition ending in a state whose relaxation displays a threshold behavior. The first mechanism leads to an electron from the spinless Mo(IV) configuration being transferred to one of the Cu(II) ions transforming the trimer into the state Cu(II)-N-C-Mo(V)-C-N-Cu(I), with spin 1/2 on the Mo(V) ion and the spinless Cu(I) ion. The other mechanism gives rise to an excited paramagnetic Mo(IV) ∗ linked to two paramagnetic Cu(II) centers with a possible superexchange interaction. The spin of the excited Mo(IV) ∗ species is equal to 1 and associated to a disruption of the 5s-electronic pair. A reasonable result of simultaneous fitting the full series of susceptibility and magnetization data to the model taking into account both mechanisms corroborates their presence.