NaSn₂: A novel binary Zintl phase with 2D polyanions of Realgar-type units [Sn₈]^4-

NaSn₂, obtained from the reaction of stoichiometric amounts of the elements, crystallizes in a new structure type, in which two-dimensional polyanions are separated by Na⁺ cations. The tin framework is made up of Realgar-type Sn₈ units. The density of states obtained from the TB-LMTO-ASA calculations with the implementation of the electron localization function (ELF) reveals that NaSn₂ has all characteristics of a Zintl phase. Thus, the title compound can be written as (Na⁺) _4∞²[Sn₈^4-]. NaSn₂ dissolves readily in ethylenediamine, under the formation of a reddish brown solution indicative of the presence of [Sn₉] ^4- anions.