A High-Resolution Solid-State 23Na NMR Study of Sodium Complexes with Solvents, Small Ligand Molecules, and Ionophores. 23Na Chemical Shifts as Means for Identification and Characterization of Ion–Ion, Ion–Solvent, and Ion–Ligand Interactions

We have recorded static and magic angle spinning (MAS) 23Na NMR spectra of a variety of inorganic salts, solvent complexes, and complexes with small ligand molecules and ionophores in the solid state, in order to obtain the 23Na chemical shifts of the ion–ion, ion–solvent, and ion–ligand interactions, respectively. In all cases, MAS resulted in considerable reduction of the linewidths. The observed 23Na chemical shifts were corrected by subtracting the displacements by the quadrupole interaction when the quadrupole coupling constants cannot be ignored. We found that the range of the 23Na chemical shifts found in the solid state is about 60 ppm and the 23Na chemical shift of NaBPh4 appears at the highermost region (−52 ppm). The 23Na NMR chemical shifts of these complexes exhibited their characteristic peak positions, depending on variety of ligand molecules (H2O, ether, or carbonyl) and Na–O interatomic distances but independent of the type of counterion. Finally, an attempt was made to relate the 23Na chemical shifts to the magnitude of electron transfer from the ligand molecules to 3p orbital of Na+ ion, by means of an ab initio molecular orbital method.