Abstract: The invention relates to a spin-transition parent compound in powdered form, comprising a network having molecules which are each formed from a complex in which a metallic ion M having an electronic configuration in d5 or in d6 or in d7, is bonded to at least one aminotriazole ligand of the formula ?L.sub.2 N-trz!, wherein L is an alkyl radical (C.sub.n H.sub.2n+1) and n is an integer which is equal to or greater than zero, each molecule also including a sulforganic anion comprising a sulfito radical (SO.sub.3.sup.-), and the network also including at least one water molecule (H.sub.2 O) per molecule of the metallic complex M, said water molecule(s) in the network only being bonded to the aminotriazole ligand by a hydrogen bond.In this compound, the anion may be, for example, a sulfito-aryl having a benzene radical or a sulfito-aryl derived from a benzene radical, or a sulfito-aryl having a saturated or unsaturated organic chain, an alkyl sulfito-halide or an aryl sulfito-halide.