Solid-state structure, dynamical properties in solution and computational studies of a new sodium hemispherand complex

The solid-state structure of 1·NaClO₄ has been determined by X-ray diffraction and shows the Na+ complexed in an approximate hexagonal bipyrimidal fashion. The six ether oxygens form the ground plane, the inner carbonyl group and one of the two outer carbonyl groups occupy the apical positions. The solution structure in methanol, as determined by NMR spectroscopy, has a time-averaged plane of symmetry through the inner phenyl ring. This plane of symmetry is the result of a fast interconversion of conformations in which either one of the outer carbonyl groups is coordinated to the Na⁺. The enthalpy of activation in methanol determined by T_1p measurements is 5 ± 1 kcal mol^–1. This process of fast exchange was supported by TRAVEL/CHARMm simulations which revealed a transition-state structure with the two outer carbonyl groups coordinated to the Na+ with a plane of symmetry through the inner phenyl ring. The calculated activation energy is 6.1 kcal mol^–1, in very good agreement with the experimental value. A significant influence of the solvent on the structure of 1·Na⁺ could be ruled out by an MD simulation in methanol. The structure is very similar to the solid-state structure.