Topochemical anion metathesis routes to the Zr2N2S phases and the Na2S and ACl derivatives (A = Na, K, Rb).

ABSTRACT

Anion metathesis reactions between ZrNCl and A(2)S (A = Na, K, Rb) in the solid state follow three different pathways depending on reaction temperature and reactant stoichiometry (1) the reaction of ZrNCl with A(2)S in the 21 stoichiometry at 800 degrees C/72 h/in vacuo yields alpha-Zr(2)N(2)S with the expected layered structure of La(2)O(2)S. Above 850 degrees C, alpha-Zr(2)N(2)S (P3 macro m1; a = 3.605(1) A, c = 6.421(3) A) neatly transforms to beta-Zr(2)N(2)S (P6(3)/mmc a = 3.602(1) A, c = 12.817(1) A). The structures of the alpha- and beta-forms are related by an a/2 shift of successive Zr(2)N(2) layers. (2) The same reaction at low temperatures (300-400 degrees C) yields ACl intercalated phases of the formula A(x)Zr(2)N(2)SCl(x) (0 < x < approximately 0.15), where alkali ions are inserted between the S/Cl.S/Cl van der Waals gap of a ZrNCl-type structure. The S and Cl ions are disordered and the c lattice parameters are alkali dependent (R3 macro m, a approximately 3.6 A, c approximately 28.4 (Na), 28.9 (K), and 30.5 A (Rb). A(x)Zr(2)N(2)SCl(x) phases are hygroscopic and reversibly absorb water to give monohydrates. (3) Reaction of ZrNCl with excess A(2)S at 400-1000 degrees C gives A(2)S intercalated phases of the formula A(2)(x)Zr(2)N(2)S(1+)(x) (0 < x < 0.5), where the alkali ions reside between the S.S van der Waals gap of a ZrNCl type structure (R3 macro m, a approximately 3.64 A, c approximately 29.48 A). Structural characterization of the new phases and implications of the results are described.