Light induced modulated structure of the spin crossover compound {Fe(abpt)2[N(CN)2]2}

{Fe(abpt)(2)[N(CN)(2)](2)} is an intriguing spin crossover system which crystallizes in two separate phases. Phase A has already been investigated; its crystal structure consists of a single molecule sitting on a center of symmetry. Phase B is the subject of the present structural analysis and presents two independent molecules in the asymmetric unit. We have observed a unique order-disorder phase transition at very low temperature induced either by laser light irradiation or through rapid thermal quenching from room temperature. The corresponding metastable phase exhibits an incommensurate modulation of the crystal structure, disappearing at the HS to LS relaxation temperature (52 K). This modulation is most probably related to a particular ordering of the dicyanamide ligands.