A new crystal phase of barium nitroprusside trihydrate studied by neutron diffraction at 20 K

The crystal of barium penta­cyano­nitro­syl­ferrate trihydrate {barium nitro­prusside trihydrate, BaFe(CN)₅(NO)]·3H₂O} has been studied by neutron diffraction at 20 K. The study was performed to characterize the structural phase generated by the phase transition undergone by the crystals at 80 K, at which temperature the unit‐cell volume doubles. This crystal phase still exists at 20 K. The crystal structure, in space group P1, is completely ordered. The positional changes of the water mol­ecules in the present structure with respect to those of the compound at 105 K are presented.