Modification of Spin Crossover Behavior through Solvent Assisted Formation and Solvent Inclusion in a Triply Interpenetrating Three-Dimensional Network

The 3D coordination polymer [Fe(4ditz)3](PF6)2·solv consists of three interpenetrating infinite networks. There are
cavities between iron atoms of different networks, which are partly filled with solvent molecules. With a change of
the solvent used during synthesis from methanol to ethanol, the magnetic behavior of the materials changes. Both
show an abrupt two-step spin crossover from low spin (S = 0) to high spin (S = 2) with the methanolate curve
lying 7 K higher and showing a small hysteresis. Single crystal and powder diffraction studies show that they both
have the same structure, but in powder form, the methanolate slowly loses methanol to finally leave about 0.075
MeOH/Fe. In comparison, the bigger ethanol remains at 0.25 EtOH/Fe. These results, in conjunction with
thermodynamic data, strongly suggest that the differences in magnetic behavior are largely entropic in nature.
Possible reasons for this are discussed.