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In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging
Published on: September 2, 2016
Pressure-Induced Spin Crossover at Room Temperature in a Nanoporous Host-Guest Framework Structure
Banele Vatsha1, Rowan Goliath2, Giovanni Hearne2
1Department of Chemical Sciences, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, Johannesburg, Gauteng, South Africa.
Abstract:
The two-dimensional (2D) metal-organic framework compound Fe2 (azpy)4 (NCS)4 (azpy=trans-4,4'-azopyridine, NCS=thiocyanate) has been pressurized in isopropanol and ethanol that act as guest molecules and pressure-transmitting media. Room temperature conversion of metal-ion sites from high-spin to low-spin states under high-pressure-driven uptake of guest molecules was investigated. Upon isopropanol guest inclusion, spin conversion of ∼66 % low-spin abundance is attained by ∼3 GPa. Spin-crossover progression stimulated by ethanol guest inclusion is more sluggish and ∼56 % low-spin abundance is attained by ∼5.5 GPa. This pressure-facilitated guest-specific triggering of spin crossover is suggestive of guest-molecule interactions with the local coordination network of the Fe(II) core, which increases the ligand field. Appreciable low-spin abundances attained at room temperature upon pressurization, are comparable to maximal ∼50 % spin conversions only attainable below ∼150 K at ambient pressure.
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