[en] The photoinduced properties of the octacoordinated complex K${}_4$Mo${}^{IV}$(CN)${}_8$⋅2 H${}_2$O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)${}_7$ species originating from the light-induced cleavage of one Mo−CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt-222)]${}_3$[Mo${}^{IV}$(CN)${}_7$]⋅3 CH${}_3$CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)