Fig. 3: Solid-state structures of ClickZip chelate isomers.

Comparison of crystal structures of Ph{Lu} and 1,4-cz-[Lu(PhL¹)] highlighting dominating features of the Lu^III ion coordination environment. Hydrogen atoms (except for triazole moiety and water ligand) and labels of non-coordinating atoms were omitted for clarity. Thermal ellipsoids were set at 50% probability. Both compounds crystallized in centrosymmetric groups containing two enantiomeric chelate units with opposite chirality of the coordination cage in TSA conformations Λλλλλ and Δδδδδ, of which only one is shown. A Structure of [Ph{Lu}]⁺ cation (Δδδδδ isomer) found in the crystal structure of [Ph{Lu}]⁺[ClO₄]⁻·7.0H₂O. The 1,5-triazole is part of an 18-membered macrocyclic ring that allows coordination of both pyridines. The hydrogen atom of the triazole points away from the coordination cage. Due to the snug fit around the Lu^III ion, coordination of water is not allowed. B Structure of 1,4-cz-[Lu(PhL¹)(H₂O)]⁺ cation (Λλλλλ isomer) found in the crystal structure of [1,4-cz-[Lu(PhL¹)(H₂O)]⁺[ClO₄]⁻·2H₂O·i-PrOH. The 1,4-triazole is part of an irregularly-shaped 19-membered macrocyclic ring that disfavours simultaneous coordination of both pyridines. Due to a poor fit of the pyridine-triazole-pyridine bridge to the metal, one water molecule is coordinated to the Lu^III ion, forming a hydrogen bond (dashed blue line) to the de-coordinated pyridine. The hydrogen atom of the triazole is turned towards the coordination cage, possibly interfering with the coordination sphere. Note that this solid-state structure may not represent the situation in solution, where equilibrium may exist between coordination of water or pyridine.