Manganese-centered ten-vertex germanium clusters: the strong field Ge₁₀ ligand encapsulating a transition metal

The experimental realization of pentagonal prismatic structures for M@ (M = Co, Fe) containing interstitial transition metal atoms makes of interest the chemistry of corresponding manganese derivatives Mn@. The neutral Mn@Ge₁₀ may be regarded as a complex of a polyhedral ligand with an interstitial Mn in the +2 oxidation state. However, the lowest energy Mn@Ge₁₀ structure with the expected sextet spin state for high-spin d⁵ Mn(II) lies ~23 kcal mol⁻¹ in energy above the lowest energy isomer thereby suggesting that such germanium polyhedra function as strong field ligands for encapsulated transition metals. The lowest energy structures for the Mn@ anions (z = −1 to −5) are all centered pentagonal prisms. Higher energy Mn@ structures have outer Ge₁₀ polyhedra based on the tetracapped trigonal prism similar to the lowest energy Co@ structure and on the bicapped square antiprism similar to the B₁₀ deltahedron. Other Mn@ structures have outer Ge₁₀ polyhedra with four or five quadrilateral faces as well as six or eight triangular faces, respectively. Bioctahedral (Ge₅)₂Mn⁵⁻ structures were also found for the pentaanion with a manganese vertex common to two MnGe₅ octahedra. The cationic species Mn@ was found to have a more complicated potential surface than the anions. Tetracapped trigonal prismatic and bicapped square antiprismatic structures as well as a variety of more open structures were found for Mn@.