Neutron Laue diffraction on the spin crossover crystal [Fe(1-n-propyltetrazole)6](BF4)2 showing continuous photoinduced transformation

The structural aspects of photoinduced phase transitions in spin-crossover compounds were investigated by neutron Laue diffraction. The structures of the ground state and of the metastable LIESST state of the Fe-II spin transition compound [Fe(1-n-propyltetrazole)(6)](BF4)(2), in the quenched state, were determined at 2 K. Sizable differences are observed between the photoinduced and the high-temperature high-spin structures. The structural changes were observed to be continuous, despite the cooperative character of the spin-crossover system, and their kinetics was followed during the photoexcitation at 2 K. The reasons why the nucleation and growth process reported in the literature does not apply here are examined.