The non-Aufbau electronic ground-state was also observed by Bunting et al. for Co(II) complex and Ruiz et al. for ferrocenium complex. The viable reason for this anomalous configuration is the small energy difference of d z 2 with d xz and d yz i.e., 0.097 and 0.174 eV respectively (Table ). Since these d-orbitals are quasi-degenerate, therefore, to avoid inter-electronic repulsion for the Aufbau configuration i.e., d 2