First Iron(II) Clathrochelate with a Temperature-Induced Spin Crossover to an Elusive High-Spin State

Here, we report the first (pseudo)clathrochelate of iron(II) to undergo a temperature-induced spin crossover (SCO) to an elusive high-spin state “trapped” in one of its solvatomorphs. An SCO-inducing ability of the resulting extended-tripodal (cage) ligand in an otherwise SCO-inactive type of iron(II) complexes arises from its molecular design that adapts to the metal ion in the two spin states by experiencing a massive trigonal twist distortion. Combined with the amenability of this ligand to further functionalization to produce a series of iron(II) (pseudo)clathrochelates with tunable SCO behaviors, it opens up a possibility for this unique class of trigonal-prismatic complexes to soon emerge as effective switchable components for molecular electronics and spintronics.