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.