Abstract
The spin-crossover properties of the strongly cooperative compound [Fe(PM-PEA)2(NCS)2] (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline) have been investigated under external in situ pressure, external ex situ pressure and internal pressure. In situ single-crystal X-ray diffraction investigations under pressure indicate a Spin-Crossover (SCO) at about 400 MPa and room temperature. Interestingly, application of ex situ pressure induces the irreversible enlargement of the hysteresis width, almost independently from the pressure value. Elsewhere, the internal pressure effects are examined through the magnetic and photomagnetic investigations on powders of the solid-solutions based on the Mn ion, [FexMn1−x(PM-PEA)2(NCS)2]. Growing the Mn ratio increases the internal pressure, allowing to control the hysteresis width and the paramagnetic residue but also to enhance the efficiency of the photo-induced SCO. The comparison of the quenching and light-induced behaviors reveals a complex phase-diagram governed by internal pressure, temperature and light.
Highlights
The use of pressure to perturb the electronic structure and the physical properties of metal-coordination compounds is an interesting way for the search towards switching materials [1]
We report the effects of internal and external pressure on the strongly cooperative compound [Fe(PM-PEA)2(NCS)2] (with PM-PEA = N-(21-pyridylmethylene)-4-(phenylethynyl) aniline)
The hysteresis width looked enlarged by a few degrees after that a pressure inferior to 300 MPa was applied to the material
Summary
The use of pressure to perturb the electronic structure and the physical properties of metal-coordination compounds is an interesting way for the search towards switching materials [1]. The SCO materials usually contract under the application of an external pressure since the latter favors the diamagnetic low-spin (LS), state which has a lower volume than the paramagnetic high-spin (HS) state This is due to the occupation by electrons of anti-bonding molecular orbitals in HS that increases the iron(II)-ligand bond lengths in contrast to the non-bonding molecular orbitals occupied by electrons in LS. In some cases, the application of pressure on a SCO material can even favor the HS state This non-intuitive behavior was observed in Mössbauer studies in mononuclear phenanthroline [19] or poly(1-pyrazol)borate [20] iron(II) complexes, and was reported for the two-dimensional compound [Fe(btr)2(NCS)2] ̈ H2O (btr = 4,41-bis-(1,2,4-triazole)) [21]. The first part of this work is dedicated to such approach
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