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 A₂S (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 A₂S in the 2:1 stoichiometry at 800°C/72 h/in vacuo yields α-Zr₂N₂S with the expected layered structure of La₂O₂S. Above 850 °C, α-Zr₂N₂S (P₃m1; a = 3.605(1) Å, c = 6.421(3) Å) neatly transforms to β-Zr₂N₂S (P6₃/mmc: a = 3.602(1) Å, c = 12.817(1) Å). The structures of the α- and β-forms are related by an a/2 shift of successive Zr₂N₂ layers. (2) The same reaction at low temperatures (300-400 °C) yields ACl intercalated phases of the formula AxZr₂N₂SCl_x (0 < x < 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 (R₃m, a ~3.6 Å, c ~28.4 (Na), 28.9 (K), and 30.5 Å (Rb). AxZr₂N₂SCl_x phases are hygroscopic and reversibly absorb water to give monohydrates. (3) Reaction of ZrNCl with excess A₂S at 400-1000°C gives A₂S intercalated phases of the formula A_2xZr₂N₂S_1+x (0 < x < 0.5), where the alkali ions reside between the S···S van der Waals gap of a ZrNCl type structure (R₃m, a ~3.64 Å, c 29.48 Å). Structural characterization of the new phases and implications of the results are described.