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

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.