  [Cu$^{\mathrm{II}}$(enpnen)]$_{2}$[Mo$^{\mathrm{IV}}$(CN)$_{8}$]$\cdot$7H$_{2}$O
(enpnen = N,N$^\prime$-bis(2-aminoethyl)-1,3-propane-diamine) molecular cluster
compound was subject to a series of irradiations with the light of 405 nm. On
irradiation isothermal magnetization at 1.8 and 5 K in the field range 0-70 kOe
as well as magnetic susceptibility in the temperature range of 2-300 K were
subsequently detected. Both types of magnetic signals were next analyzed
assuming that the irradiation triggers two independent processes: the metal to
metal charge transfer (MMCT) leading to a state with the Arrhenius-type
relaxation and the spin crossover (SC) transition ending in a state whose
relaxation displays a threshold behavior. The first mechanism leads to an
electron from the spinless Mo(IV) configuration being transferred to one of the
Cu(II) ions transforming the trimer into the state Cu(II)-N-C-Mo(V)-C-N-Cu(I),
with spin 1/2 on the Mo(V) ion and the spinless Cu(I) ion. The other mechanism
gives rise to an excited paramagnetic Mo(IV)$^{*}$ 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.
