A square-planar tetracoordinate oxygen-containing Ti₄O ₁₇ cluster stabilized by two 1,1′-ferrocenedicarboxylato ligands

By introducing steric constraints into molecular compounds, it is possible to achieve atypical coordination geometries for the elements. Herein, we demonstrate that a titanium-oxo cluster [{Ti₄(μ₄-O) (μ₂-O)₂}(OPrⁱ)₆(fdc) ₂], which possesses a unique edge-sharing Ti₄O ₁₇ octahedron tetramer core, is stabilized by the constraints produced by two orthogonal 1,1′-ferrocenedicarboxylato (fdc) ligands. As a result, a square-planar tetracoordinate oxygen (ptO) can be generated. The bonding pattern of this unusual anti-van'tHoff/LeBel oxygen, which has been probed by theoretical calculations, can be described by two horizontally σ-bonded 2p_x and 2p_y orbitals along with one perpendicular nonbonded 2p_z orbital. While the two ferrocene units are separated spatially by the ptO with an Fe⋯Fe separation of 10.4Å, electronic communication between them still takes place as revealed by the cluster's two distinct one-electron electrochemical oxidation processes. A square-planar tetracoordinate oxygen (ptO) is realized in an edge-sharing Ti₄O₁₇ octahedron tetramer stabilized by two orthogonal 1,1′-ferrocenedicarboxylato ligands. Whereas the two ferrocene units are separated spatially by the ptO with an Fe⋯Fe separation of 10.4Å, the electronic communication between them still takes place as indicated by the cluster's two distinct one-electron electrochemical oxidation processes.