Structure and Dynamic Behavior of the Na-Crown Ether Complex in the Graphite Layers Studied by DFT and ¹H NMR

Diffusion of alkali metals in graphite layers is significant for the chemical and electrochemical properties of graphite intercalation compounds (GICs). Crown ethers co-intercalate into graphite with alkali metal (Na and K) cations and form ternary GICs. The structures and molecular dynamics of 15-crown-5 and 18-crown-6 ether coordinating to Na⁺ or K⁺ in GICs were investigated by DFT calculations and ¹H solid state NMR analyses. DFT calculations suggest a stacked structure of crown ether-metal complex with some offset. ¹H NMR shows two kinds of molecular motions at room temperature: isotropic rotation with molecular diffusion and axial rotation with fluctuation of the axis. The structure and dynamics of crown ether molecules in GIC galleries are strongly affected by the geometry of the crown ether molecules and the strength of the interaction between alkali metal and ligand molecules.