The effect of Co-Co distance and bonding is inferred from relaxed scan calculations of compounds 2 and 3 with varying Co-Co distances (Figure ). We apply symmetry arguments to understand how 3d orbitals overlap in these bimetallic complexes with tetrahedral ligand configuration. As shown in Figure , the Co 3d orbitals with e symmetry have the appropriate orientation for σ-overlap, whereas the t2 orbitals allow for π-and δ-bonding. In the case of high-spin Co 2+ (d 7 ) species, the e symmetry orbitals on each Co center are fully occupied, and thus do not participate in Co-Co σ-bonding. This symmetry constraint explains the lack of Co-Co σ-bonding in 2. As discussed above, σ-bonding for octahedrally coordinated metal centers results from overlap of the 3d orbitals with eg symmetry, such as in the low-spin Co 2+ (d 7 ) species 3 and 4 (Figure ).