Magnetic interactions controlled by light in the family of Fe(II)-M(IV) (M = Mo, W, Nb) hybrid organic-inorganic frameworks.

Three new hybrid organic-inorganic frameworks employing octacyanidometallates and 4,4'-bypiridine dioxide (4,4'-bpdo) as bridging molecules were prepared and characterized. The three-dimensional coordination frameworks {[Fe II (μ-4,4'-bpdo)(H 2 O) 2 ] 2 [M IV (CN) 8 ]·9H 2 O} n (Fe2Mo, Fe2W and Fe2Nb; M = Mo, W and Nb) are composed of cyanido-bridged chains, which are interconnected by the organic linkers. Magnetic measurements for Fe2Nb show a two-step transition to the antiferromagnetic state, which results from the cooperation of antiferromagnetic intra- and inter-chain interactions. Fe2Mo and Fe2W, on the other hand, behave as paramagnets at 2 K because of the diamagnetic character of the corresponding octacyanidometallate(IV) building units. However, after 450 nm light irradiation they show transition to the metastable high spin Mo IV or W IV states, respectively, with distinct ferromagnetic intrachain spin interactions, as opposed to the antiferromagnetic ones observed in the Fe2Nb framework.