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 Sn-8 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)(infinity)[Sn-8(4-)]. NaSn2 dissolves readily in ethylenediamine, under the formation of a reddish brown solution indicative of the presence of [Sn-9](4-) anions.