NBO calculation. The natural bond orbital (NBO) analysis quantifies the donor-acceptor interactions between orbitals. The results of the NBO analysis using Gaussian16 program packages of 1 and 2 show the interactions between Ln and Pt ions (Table ). There are strong Pt→La charge transfers in the range of ~36 kcal/mol. Moreover, there are several donor-acceptor Pt/Pt-S→La interactions in the range of 8-122 kcal/mol (threshold > 8 kcal/mol). On the other hand, 2 had weaker interactions than 1 did. (Table , 8-55 kcal/mol).