Abstract

Complexes of trivalent lanthanide are being extensively studied because of their wide applications based on their special luminescent and magnetic properties. Dinuclear structures are promising designing platforms because the ion-ion and ligand-ligand, in addition to the ion-ligand, interactions can be tuned to provide unusual and new properties. However, the syntheses of dinuclear lanthanide complexes are very difficult, especially of heteronuclear ones, and molecular modeling tools can aid in their design and predict some of their properties. Thus, two dinuclear complexes [Ln(1)-Ln(2)]asy and [Eu-Tb]sym, depicted in Figure 1, with different chemical environments were investigated by quantum chemical methods. Complexes [Ln(1)-Ln(2)]asy have asymmetric environments for each site, whereas the [Eu-Tb]sym complex has symmetric environments both sites. These structures were successfully modeled with the B3LYP/MWBx method using the Gaussian09 program. We obtained an energy difference in the 60 to 70 kJ mol−1 for discriminating between the [Ln(1)-Ln(2)]asy and [Ln(2)-Ln(1)]asy asymmetric heteronuclear complexes. This discrimination energy has been attributed to the different sizes of cavities formed by the ligands that fit lanthanides with distinct ionic radii. However, we also found that the cavities were able to adjust according to the lanthanide radius and that this observed selectivity may have a strong contribution from the softness/hardness of each cavity. Whereas the entropy difference between the symmetric hetero [Eu-Tb]sym and homonuclear ([Eu-Eu]sym and [Tb-Tb]sym) complexes has a significant contribution in explaining the selectivity toward the heterodimeric [Eu-Tb]sym structure. These results are relevant for formulating designing principles of lanthanide dimeric complexes synthesis.