Ab initio calculations were performed using the ORCA 4.2.1 program. The active space consists of 7 electrons in 7 orbitals (CASSCF (7,7)). For the state-averaged CASSCF procedure, 1 octet, 48 sextets, 392 quartets, and 784 doublets were considered for the configuration state functions (CSFs) and used for the spin-orbit coupling calculations. The low-lying energy states from spin-orbit coupling are summarized in Table . Ab initio ligand field theory (AILFT) 11b was applied to check the ligand field splitting of 4f-orbitals of 2'-Me (Figure ). The results showed a ligand field splitting energy of ~450 cm -1 . In terms of orbital stability, the axial (Pt-Gd-Pt direction) fz 3 , fxz 2 and fyz 2 orbitals are most stabilized, the equatorial fx(x 2 -3y 2 ) and fy(3x 2 -y 2 ) orbitals are intermediate while the diagonal fxyz, fz(x 2 -y 2 ) orbitals are the least stabilized. This order (axial, equatorial, diagonal) is similar to the results of the single-crystal XAFS -less ionic orientation order (parallel, perpendicular, 45 degrees). In addition, fz 3 orbital is less stable than fxz 2 , fyz 2 orbital, because fz 3 orbital also undergoes electrostatic repulsion from the lone pair of the Pt ion.