Figure 3 . DFT adsorption structures. Top and side views of La-MPBCP system (a) and [La-MPBCP]+3 system (b). NBO donor and acceptor orbitals responsible for intermolecular interactions, lone pair (LP) (c) and (d). Bond length La-N and the adsorption energy (Eads ) are expressed in (Å) and kcal/mol, calculated with the PBE0-D3/def2-TZVP method. Color code for spheres: dark gray (C); blue (N); yellow (H); red (O); orange (La).