Helicate versus Mesocate in Quadruple-Stranded Lanthanide Cages: A Computational Insight

Abstract

To drive the synthesis of metallo-supramolecular assemblies (MSAs) and to fully exploit their functional properties, robust computational tools are crucial. The capability to model and to rationalize different parameters that can influence the outcome is mandatory. Here, we report a computational insight on the factors that can determine the relative stability of the supramolecular isomers helicate and mesocate in lanthanide-based quadruple-stranded assemblies. The considered MSAs have the general formula [Ln2L4]2− and possess a cavity suitable to allocate guests. The analysis was focused on three different factors: the ligand rigidity and the steric hindrance, the presence of a guest inside the cavity, and the guest dimension. Three different quantum mechanical calculation set-ups (in vacuum, with the solvent, and with the solvent and the dispersion correction) were considered. Comparison between theoretical and experimental outcomes suggests that all calculations correctly estimated the most stable isomer, while the inclusion of the dispersion correction is mandatory to reproduce the geometrical parameters. General guidelines can be drawn: less rigid and less bulky is the ligand and less stable is the helicate, and the presence of a guest can strongly affect the isomerism leading to an inversion of the stability by increasing the guest size when the ligand is flexible.

Maximized axial helicity in a Pd2L4cage: inverse guest size-dependent compression and mesocate isomerism

“…74 This means that nearly all so far postulated M 2 L 4 mesocates are transient species, rather than isolable ones. 75,76…”

“…74 This means that nearly all so far postulated M 2 L 4 mesocates are transient species, rather than isolable ones. 75,76 In our attempts to grow single crystals of the helical cage 1$NO 3 , we were surprised to obtain crystals of a markedly different [Pd 2 L 4 ] 4+ cage complex (here denoted as 1 ′ ). X-ray analysis revealed that 1 ′ crystallizes in the orthorhombic space group Pccn with half of the Pd 2 L 4 cage in the asymmetric unit.…”

Transparent and colour-neutral luminescent solar concentrators using bright Eu3+ supramolecular cages towards photovoltaic windows

“…In such quadruple-stranded Ln 3+ cages, ligands scaffold and guest molecule can influence the formation of helicates or mesocates. 26 The cage [Eu 2 L F 4 ] 2− is a helicate with both the right-handed (P, ΔΔ) and left-handed (M, ΛΛ) isomers in a 1:1 ratio in the unit cell. Finally, the crystal structure evidences that the two Eu centres have a different coordination number (Figure 2d).…”