In some of the calculations herein, we used Partial Harmonic Vibrational Analysis (PHVA) as described first by Head and coworkers and later by Li and Jensen 30 to reduce the computational cost. In PHVA, a subblock of the Hessian matrix is diagonalized to obtained vibrational frequencies within that portion of the molecule. This scheme is particularly useful in this study because the Cr-Cr stretching mode is localized, allowing us to skip some of the displacements, especially those associated with bulky ligands, that do not couple directly or indirectly with the Cr-Cr stretching mode. The selection scheme of the atoms to be displaced is detailed below.