Pressure Effects on a Spin-Crossover Monomeric Compound [Fe(pmea)(SCN)₂] (pmea = bis[(2-pyridyl)methyl]-2-(2-pyridyl)ethylamine)

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 T1/2 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 Gütlich, which gave an interaction parameter Γ of 264(5) cm−1 and a volume change ΔV°HL of 32(3) Å3 molecule−1 [HL represents a high-spin (HS) ↔ low-spin (LS) transition], respectively. Meanwhile, the calculated entropy change ΔS°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.