Structure and dynamics of a chiral cubanoid complex composed of lithium and salphen

Abstract

Lithium ions have gained increasing attention due to their wide range of applications, e.g., in lightweight energy devices and functional crystals. In order to understand the scientific role of the lithium ion in materials science as well as fundamental chemistry, it is important to elucidate the coordination structures and dynamic properties of lithium complexes. However, in the numerous libraries of coordination structures, the coordination complexes containing lithium and salphen (N,N’-o-phenylenebis(salicylideneimine), Salp) have been scarcely studied. Herein, we describe a molecular structure of a cubanoid complex composed of lithium ions and Salp ligands, and the detailed investigation of the equilibrium between the enantiomeric complexes. X-ray crystallographic analysis revealed that the complex has a cubane structure surrounded by two Salp ligands in a chiral orientation. The rigid Salp ligand favors a square-pyramidal structure of the five-coordinate lithium center. The equilibrium between the two enantiomers in organic solvents is characterized in detail by variable-temperature (VT)-NMR, diffusion-ordered (1H-DOSY) NMR, and electrospray ionization time-of-flight mass spectroscopy (ESI-TOF MS) analyses. The results indicated that the exchange rate for the structural conversion between the enantiomeric cubane structures is solvent-dependent and low at low temperature.