Synthesis and characterization of the largest isolated clusters of tin, [Sn12](12-), in (AE)Na10Sn12 (AE = Ca or Sr).

Reported are two isostructural Zintl compounds, CaNa(10)Sn(12) and SrNa(10)Sn(12), with mixed alkali and alkaline-earth cations and isolated clusters of Sn(12)(12-) with the shape of giant truncated tetrahedra. The compounds were synthesized by heating the corresponding mixtures of elements at 950 degrees C. The structures were solved and refined from single-crystal X-ray diffraction data in the cubic space group I43m (No. 217), where Z = 2 with a = 11.1847(6) and 11.2176(4) A for CaNa(10)Sn(12) and SrNa(10)Sn(12), respectively. Both compounds are diamagnetic and therefore electronically balanced.