Structural Characterization. The molecular structures of 1-M were confirmed by single crystal XRD (1-U is shown in Figure and key metrical parameters for all 1-M are compiled in Table ; see Supporting Information Figures for depictions of other 1-M and Table for additional crystallographic data). Complexes 1-M exhibit trigonal bipyramidal geometries, with three hypersilanide ligands in the equatorial plane and two axially-bound THF molecules.