Characterization and crystal structure of a new layered cadmium diphosphate: KCdHP2O7∙2H2O

Abstract

A new potassium cadmium hydrogen diphosphate dihydrate, KCdHP₂O₇∙2H₂O (1), has been synthesized by slow evaporation at room temperature and characterized by FT-IR, Raman, TG-DTA, and single crystal X-ray diffraction. Compound (1) crystallizes in the orthorhombic Pcmn space group with the unit cell parameters a = 6.5814(8) Å, b = 7.9428(9) Å, c = 15.961(6) Å, V = 834.4(3) Å3 and Z = 4. Its structure consists of polyhedral layers parallel to the ab plane where each CdO₆ octahedron (m position) shares four edges with three different diphosphate groups. In the Cd octahedron, two oxygen atoms residing in (m) special positions belong to coordinated water molecules. These layers are joint by K⁺ cations (4c Wyckoff position) and hydrogen bonds, leading thus to a two-dimensional framework. The structural model is supported by the bond-valence-sum validation tool as calculated valences are close to the formal oxidation numbers.