Pressure-induced switching properties of the iron(iii) spin-transition complex [FeIII(3-OMeSalEen)2]PF6

We investigated the effect of an externally applied pressure on the iron(III) Schiff-base compound [Fe(3-OMeSalEen)2]PF6 (H-3-OMeSalEen, condensation product of 3-methoxy-substituted salicylaldehyde and N-ethylethylenediamine), which at ambient pressure displays a thermal spin transition with a 3 K wide hysteresis loop centered at 164 K. Raman spectrometry revealed the occurrence of a complete spin-state switching process for a pressure of P1/2 = 8–9 kbar at room temperature. The evolution of lattice parameters as a function of pressure was followed by X-ray diffraction measurements on single crystals, highlighting the important microscopic aspects at the origin of the pressure-induced transition, i.e. an anisotropic response and a high compressibility of the HS molecular lattice. Variable temperature magnetic susceptibility measurements at different applied pressures revealed the smoothening of the spin transition curves and a linear increase of the transition temperatures by ca. 16.4 (1.0) K kbar?1, in good agreement with the Clausius–Clapeyron law. The non-negligible influence of the pressure transmitting oils on the intrinsic transition properties was also evidenced and attributed to mechanical interactions between the particles and the solidified matrix.