A Low-Symmetry Fe^II Tetrahedron From a Flexible Tritopic Ligand

Most high yielding low symmetry cages formed by metal-ligand coordination are assembled through strictly defined ligand and/or metal ion geometries which have been manipulated to form systems with complex architectures. In this work, we report the near-quantitative synthesis of a new S₄-symmetry meso achiral [Fe₄L₄]⁸⁺ homoleptic face-capped tetrahedron from a symmetric and flexible tris-bidentate tritopic ligand. The symmetry of the tetrahedron is solvent mediated, with the meso cage forming near-quantitatively in acetonitrile, while nitromethane causes the partial isomerisation to the racemic homochiral tetrahedron. The formation of this low symmetry tetrahedron is driven by ligand flexibility, which we attribute to the meso isomer effectively minimising its solvent shell and the ligand strongly favouring negative stereochemical coupling between metal centres, compared to the homochiral cage, thus being the dominant cage when in acetonitrile.