Pressure effects on a spin-crossover monomeric compound [Fe(pmea)(SCN)(2)] (pmea = bis[(2-pyridyl)methyl]-2-(2-pyridyl)ethylamine)

Inorg Chem. 2010 Jan 18;49(2):745-51. doi: 10.1021/ic902161v.


Spin-crossover (SCO) compounds are a sort of bistable material whose electronic and magnetic properties can be tuned by external physical stimuli, such as heat, light, and pressure. The title SCO compound [Fe(pmea)(NCS)(2)] (1; pmea = bis[(2-pyridyl)methyl]-2-(2-pyridyl)ethylamine) undergoes spin transition in such a way that it is an ideal candidate to investigate pressure effects on the SCO behavior. First, the spin transition is complete and abrupt so that the pressure-dependent spin transition should be remarkable. Second, the T(1/2) value under ambient pressure is 184 K, which guarantees that the SCO temperature under various pressures does not exceed that restrained by high-pressure devices. The magnetic data of compound 1 under different external pressures were analyzed through a known method, as reported by Gutlich, which gave an interaction parameter Gamma of 264(5) cm(-1) and a volume change DeltaV degrees (HL) of 32(3) A(3) molecule(-1) [HL represents a high-spin (HS) <--> low-spin (LS) transition], respectively. Meanwhile, the calculated entropy change DeltaS degrees (HL)(T) at 1 bar is 59.79 J mol(-1) K(-1), which is a typical value that drives the spin transition from a LS to HS state. The pressure effects on the SCO behavior of compound 1 reported here may provide information for a deep understanding of the correlation between pressure and spin transition.