Factors influencing the spin crossover

3 PROPERTIES OF SPIN CROSSOVER SYSTEMS 9.3.1 Factors influencing the spin crossover 

The spin crossover is influenced by several factors some of them belong to the sample itself (composition, preparation and handling), some to the physical influences (applied field, pressure, temperature drift). Selected examples of iron(II) spin crossover systems are collected in Table 9.4. 

Representative examples of iron(II) spin crossover systems 

It is a general feature of spin crossover systems that the metal-ligand distances in the HS state are longer than for the corresponding LS state. This finding follows both from volume measurements and from a direct X-ray structure analysis (Table 9.5). Thus, increasing pressure will favour the LS state and consequently the spin transition will occur at a higher Tc than at normal pressure. 

The dilution of the spin crossover system in a similar host lattice with bigger ions (e.g. an iron system in the corresponding zinc compound) will create a negative image pressure. The HS state becomes preferentially stabilised and consequently Tc decreases. Simultaneously the conversion curve xHs versus T becomes more gradual. Analogous behaviour is exhibited by [Fe M1 (2-pic)3]Cl2 EtOH systems (M = Co, Zn) and [Fe Mi (phen)2 (NCS)2] systems (M = Mn, Co, Zn). 

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