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 d iffraction and shows the Na+ complexed in an approximate hexagonal bip yrimidal fashion. The six ether oxygens form the ground plane, the inn er 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 i nner phenyl ring, This plane of symmetry is the result of a fast inter conversion of conformations in which either one of the outer carbonyl groups is coordinated to the Na+, The enthalpy of activation in methan ol determined by T-1p measurements is 5+/-1 kcal mol(-1). This process of fast exchange was supported by TRAVEL/CHARMm simulations which rev ealed a transition-state structure with the two outer carbonyl groups coordinated to the Na+ with a plane of symmetry through the inner phen yl ring, The calculated activation energy is 6.1 kcal mol(-1), in very good agreement with the experimental value, A significant influence o f 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-sta te structure.