Pressure-Induced Unexpected Stabilization of the High-Spin State of Iron(II) in a Metal–Organic Framework

Le résumé fourni par la source

The effect of hydrostatic pressure on the spin state of the metal organic framework {Fe(R-pbpy + ) 2 [μ 2 -M(CN) 4 ] 2 ·2H 2 O} (pbpy = phenylbipyridinium, R = CH 3, M = Pd) was investigated by Raman spectroscopy and single crystal X-ray diffraction (SC-XRD). As expected, the application of a hydrostatic pressure of 1.2 GPa fully transforms the high-spin ( S = 2) ferrous ions into the low-spin ( S = 0) form. Surprisingly, further increase of the pressure to 2.0 GPa induces a pressure-driven return to the S = 2 state, which can be switched again to the S = 0 state at 2.5 GPa. This unusual sequence of pressure-driven spin-state transitions is completely reversible and is also observable in two analogous compounds with M = Pt and R = Br. High-pressure X-ray crystal structure analysis reveals concurrent pressure-driven structural changes, assigned to an electron transfer (ET) process between the redox-active ligands. These processes cause a simultaneous elongation of the metal–ligand bond lengths and a contraction of the lattice volume, stabilizing, thus, the high-spin state in the pressure range of ca. 1.5–2.3 GPa, opposite to classical thermodynamics of spin crossover.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.