Coordination Intercalation of NbAsO5 with Alkali-Metal Chloride. Synthesis, Structure, and Spectroscopy of Two New Layered Niobium(V) Arsenate Compounds, ANbAsO5Cl (A = Rb, Cs)

Via a direct reaction of NbAsO 5 and ACl (A = Rb, Cs), a new family of layered niobium(V) arsenate compounds, ANbAsO 5 Cl, was synthesized. Single crystals of these new phases were grown by employing either a single flux of the respective chloride or a eutectic flux of ACl/A‘Cl (A‘ = Na, K). The cell constants are a = 6.6605(6) Å, c = 7.680(2) Å for RbNbAsO 5 Cl ( Z = 2, tetragonal, P 4/ n ); a = 6.662(2) Å, b = 7.879(3) Å, c = 6.663(1) Å, β = 90.01(2)° for CsNbAsO 5 Cl ( Z = 2, monoclinic, P 2/ n ). The single-crystal X-ray structures show that the title compounds adopt a layered framework that consists of alternately stacked NbAsO 5 slabs and (100) ACl rock salt sheets. The Nb 5+ cation resides in a distorted [5+1] NbO 5 Cl octahedral coordination environment. The formation of a layered structure can be envisioned if the NbAsO 5 framework is chemically dissected by molten alkali-metal chloride along the planes of long (weak) Nb−O bonds. Topologically, the Cl - anions insert into a three-dimensional framework to replace the long Nb−O bonds (2.23 Å) by coordination intercalation. The [NbAsO 5 Cl] slab adopts the polyhedral arrangement of the single [NbAsO 5 ] slab found in the monoclinic α-NbAsO 5 phase. The chloride capped niobium arsenate anionic slab [NbAsO 5 Cl] - is neutralized by the countercation A + . This paper reports the synthesis, structure, and UV−vis diffuse reflectance spectroscopy of the title compounds.