The molecular geometry obtained by XRD was optimized using DFT using the ORCA package (see Fig. , and Tables and for the details of DFT-optimized structure of Yb[CH(SiMe 3 ) 2 ] 3 ). Both the starting and optimized geometries were then used to calculate the electronic energy levels using complete active space (CAS) methods using the MOLCAS package. The results, reported in Table , are similar, and in the following we confined our discussion on the results obtained on the DFT-optimized structure. The seven inner-core active 4f orbitals are shown in Figure along with the three energetically higher bonding type orbitals of the Yb -C α bonds. Out of the seven active orbitals, the lowest one is non-bonding, followed by two sets of doubly-degenerate orbitals: