Initially, CASSCF-SO calculations were performed on each molecule, with the relevant number of electrons in the seven 4f orbitals as the active space. The RAS method was used for further calculations, with RAS2 always being the same as the initial CAS active space. The CASSCF-SO orbitals were used for RASCI-SO calculations with different active spaces. RAS1 was varied, with RAS3 always being the 13 lowest-energy virtual orbitals. The results of these RASCI-SO calculations are summarized in Table , with the implementation of the van den Heuvel equation in the Hyperion software being used to calculated paramagnetic shifts. The phosphorous 1s and 2s orbitals were core-like and easily identified, but the 3s and 3p orbitals were involved in bonding. The molecular orbitals used to represent these were those with the largest contribution from them. In all cases these had a significantly larger contribution from the relevant atomic orbital than from any other atomic orbital. There were also no other molecular orbitals with such a large contribution from that atomic orbital, making the identification unambiguous.