Low-Symmetry Face-Capped Fe(II) Tetrahedra Through Anisotropic Ligand Extension

Low-symmetry cages are attractive metallo-supramolecular targets, as they may possess different characteristics to their higher symmetry analogs. There are no current generalizable routes for the formation of low-symmetry face-capped tetrahedra. We report here a strategy using tritopic tris-bidentate ligands with arms of different lengths to access novel tetrahedra. The use of "isosceles" ligands (two arms the same, one different) gives tetragonal disphenoid structures, while a "scalene" ligand (all three arms different) gives a rhombic disphenoid structure. In this last case, diastereoselectivity is also achieved. Distortion away from a perfect tetrahedron resulted in alteration of the character of the respective cage. More distorted cages were more prone to loss of structural integrity upon introduction of highly coordinating dimethyl sulfoxide solvent into the cage in acetonitrile solution. As well, increasing distortion was shown to increase the ease of oxidation from Fe(II) to Fe(III) within the cages.