Barium Azacryptand Sodide, the First Alkalide with an Alkaline Earth Cation, Also Contains a Novel Dimer, (Na₂)²⁻

The first barium sodide, with stoichiometry Ba(2+)(H(5)Azacryptand[2.2.2](-))Na(-).2MeNH(2), was synthesized by the reaction of Ba, Na, and H(6)Azacryptand[2.2.2] in NH(3)-MeNH(2) solution. It was characterized by X-ray crystallography, (23)Na MAS NMR, hydrogen evolution, DSC, optical spectroscopy, and magnetic susceptibility. This is the first sodide in which the sodium anions form (Na(2))(2)(-) dimers. Previous theoretical predictions were verified by a calculation of the potential energy curve for the dimer in the field of the surrounding charges, whose positions were determined from the crystal structure.