Computational and experimental studies on the effect of conformational flexibility on bonding and photophysics of a triaza-macrocycle tripod

The effect of conformational flexibility on coordination and bonding of a chelator, [12N3Me5Ox], on the macrocyclic ring 1,5,9-tris(-5-methylene)-1,5,9-triazadodecane and its lanthanide complexes is depicted by synthesis, characterization, and theoretical techniques. The chelator and its complexes were prepared and characterized by physicochemical methods. Each lanthanide complex was eight coordinated with a pseudo-C₃ symmetric distorted dodecahedron geometry. Density functional theory (DFT) studies suggest that Ln³⁺ ions can be easily incorporated into the chelator cavity without changing the basic geometry. Natural bonding orbitals (NBO) and energy decomposition analysis (EDA) indicate that M–L bonds have ~ 70% ionic character. Exciting and diverse behavior was observed when the results of 12N3Me5Ox were compared with 9N3Me5Ox; with the increase in the size of the macrocyclic ring, the covalency of the metal–ligand bond was increased. The luminescence properties of these complexes were different in the solid and solution state. The f–f transitions of the lanthanide were not observed for the complexes. The theoretical results are in good agreement with the experiments.