Theoretical description of phenomena observed in a systematic study of the spin crossover in Fe(II) complexes with halogenated ethyltetrazoles - Part II. The quasi-chemical model (specific molecular interactions)

Spin crossover in halogenated ethyltetrazole complexes of Fe(II) was earlier explained(1) within the model of ordering arising from non-specific molecular interactions and is now analysed by using a quasi-chemical approximation taking into account specific interactions in HS-LS associates. Non-specific molecular interactions are also included employing the formalism of excess energies. The equations obtained predict both incomplete and two-step spin crossover and provide a rational explanation of these phenomena. A comparison is given of these two approaches to the description of critical phenomena in spin crossover.