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Three-Way Switchable Single-Crystal-to-Single-Crystal Solvatomorphic Spin Crossover in a Molecular Cocrystal

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journal contribution
posted on 20.11.2020, 23:30 by Andrés Reyes Zuluaga, Aidan J. Brock, Michael C. Pfrunder, Wasinee Phonsri, Keith S. Murray, Phimphaka Harding, Aaron S. Micallef, Kathleen M. Mullen, Jack K. Clegg, David J. Harding, John C. McMurtrie
The Fe­(III) spin-switching complexes [Fe­(qsal-5-Y)2]­X (where Y = F, Cl, Br, I or OMe; X = NCS, Cl, OTf, NO3, BF4, PF6, or BPh4) display a variety of thermal spin transition profiles, including abrupt, stepped, and hysteretic, with potential applications as temperature- or gas-dependent switches or memory/storage devices. Here, the complex [Fe­(qsal-OMe)2]­NCS is encased within discrete anionic supramolecular motifs in cocrystalline [Fe­(qsal-OMe)2]­[(1,3,5-triiodotrifluorobenzene)­(NCS)]·MeOH/H2O (1·IFB·solvent). The MeOH and H2O solvate within these robust crystals can be reversibly exchanged, giving an artificial triple hysteresis, with six different stable magnetic states and a ΔT1/2 of 95 K (MeOH versus H2O solvatomorphs), which represent the workings of a stimulated logic gate that can be reset with heat or vacuum. Variable-temperature single-crystal X-ray diffraction (VT-SCXRD) elucidated the entire spin transition profile of the parent complex [Fe­(qsal-OMe)2]­(NCS)·MeCN (1·MeCN) and the anionic supramolecular framework-like adducts [Fe­(qsal-OMe)2]­[(1,3,5-triiodotrifluorobenzene)­(NCS)] (1·IFB), [Fe­(qsal-OMe)2]­[(1,3,5-triiodotrifluorobenzene)­(NCS)]·MeOH (1·IFB·MeOH) and [Fe­(qsal-OMe)2]­[(1,3,5-triiodotrifluorobenzene)­(NCS)]·H2O (1·IFB·H2O), with full structures collected every 5 or 10 K (total of 202 individual structures) over a temperature range of 100–450 K. The reversible solvent exchange and magnetic changes suggest that crystalline 1·IFB may be used as a specialized molecular magnetic sensor for MeOH and H2O.