Synthesis and Crystal Structures of K2SnAs2 and a New Modification of NaAs

Solid state reactions of potassium or sodium with tin and arsenic resulted in the formation of a new ternary Zintl phase, K2SnAs2 (1) and a new modification of the binary Zintl phase NaAs (2), the syntheses and structures we report herein. Compound 1 is described in the orthorhombic space group Cccm with the unit cell dimensions a = 14.653(5), b = 25.415(6), c = 6.953(4) Å, V = 2589(2) Å3 at 203 K, R(int) = 0.1686 and final R values R1 = 0.0780 [I > 2σ(I)); wR2 = 0.1810 (all data)). Compound 2 crystallizes in the monoclinic space group P21/c and accords to the LiAs structure type with the unit cell dimensions a = 6.242(9), b = 5.849(7), c = 11.55(2) Å, β = 117.1(2)°, V = 375(1) Å3 at 173 K, R(int) = 0.0812 and final R values R1 = 0.0677 [I > 2σ(I)); wR2 = 0.1541 (all data).