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

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 2:1 stoichiometry at 800 degreesC/72 h/in vacuo yields alpha-Zr2N2S with the expected layered structure of La2O2S. Above 850 degreesC, alpha-Zr2N2S (P (3) over bar m1; a = 3.605(1) Angstrom, c = 6.421(3) Angstrom) neatly transforms to beta-Zr2N2S (P6(3)/mmc: a = 3.602(l) Angstrom, c = 12.817(l) Angstrom). The structures of the alpha- and beta-forms are related by an a/2 shift of successive Zr2N2 layers. (2) The same reaction at low temperatures (300-400 degreesC) yields ACl intercalated phases of the formula A(x)Zr(2)N(2)SCl(x) (0 < x < similar to0.15), 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 (R (3) over barm, a similar to 3.6 Angstrom, c similar to 28.4 (Na), 28.9 (K), and 30.5 Angstrom (Rb). A(x)Zr(2)N(2)SCl, phases are hygroscopic and reversibly absorb water to give monohydrates. (3) Reaction of ZrNCl with excess A(2)S at 400-1000 degreesC gives A(2)S intercalated phases of the formula A(2alpha)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 (R (3) over barm, a similar to 3.64 Angstrom, c similar to 29.48 Angstrom). Structural characterization of the new phases and implications of the results are described.