Non-Conventional Standpoint on Spin Crossovers in the Organometallic Compounds of Iron Group

We have considered the spin crossover (SC) complex compounds containing spin-active metal ions of iron group, which can induce the spin transitions (ST) of high spin (HS) – low spin (LS) type under influence of temperature (TIST), pressure (PIST) or light (LIESST) from non-conventional point of view. We have analyzed the physical peculiarities of the studied ST systems observed in numerous papers for X ray, spectral, calorimetric and magnetic measurements. On this basis, we suppose that ST (for example, in bulk of SC compounds with TIST) can be considered as phase transitions (PT) of post-critical type (PCT)