Interactions in molecular crystals .118. The sodium(benzo-15-crown-5) salt of 2,6-di(tert-butyl)-4-methylphenol, a sodium phenolate with an extremely short Na+center dot center dot center dot O- distance: Structure and density functional calculations

The structure of crystals, isolated in low yield, from the attempted metallation of diphenylmethane in tetrahydrofuran solution containing benzo-15-crown-5 at a sodium metal mirror is determined, surprisingly, to be the sodium (benzo-15-crown) salt of 2,6-di(tert-butyl)-4-methylphenol, an antioxidative stabilizer to prevent ether peroxide formation. The structure of the solvent-shared contact ion pair (monoclinic P2(1)/n, Z = 4, R-1 = 0.06) proves a strong Na+... O- interaction at the extremely short distance of only 216 pm, a sixfold O-coordination of the Na+ cation in a pentagonal pyramid, and a hemispherical distortion of the crown ether. Density functional calculations at the B3LYP/6-31G* level, based on the structural data, reproduce, within a one-dimensional hypersurface approach, the rather short Na+... O- distance, and predict Mulliken charges of +0.32 for Na+ and -0.71 for O-, as well as a considerable polarization of the trialkyl phenolate anion.