The SO effect is not a correction of the SF calculation but can change the molecular point group symmetries at equilibrium geometry. Our results at the MRCI level are listed in Table . The most sophisticated literature values at the SF-CCSD(T) and SO-BLYP levels are listed in Table . The geometries were obtained with several experimental methods , but here we show only one set of experimental values obtained by electron diffraction in the gas phase . The space symmetry of IrF 6 is O h at both the SF and SO levels, but the orbital is splitting at the SO level. The space symmetry of PtF 6 is changed at the SF (D 4h ) and SO (O h ) levels, where the electronic structure becomes closed-shell. From the comparison between the SF-MRCI and SO-MRCI values, the SOC reduces the JT distortions of ReF 6 and OsF 6 . This trend is not reported at the DFT level . From the orbital energy levels shown in Figure , the SO splittings of ReF 6 , OsF 6 , and PtF 6 are larger than the splitting due to JT distortion at the SF level. Our bond lengths at the SF-MRCI level are smaller than those at the SF-CCSD(T) level shown in Table , while is consistent with the conclusion obtained from Table . The JT distortion reduced by the SO effect is also observed in the stabilization energy (cf. Table ).