2016. 57, 4 – UDC 548.73:541.49:546.48 CHARACTERIZATION AND CRYSTAL STRUCTURE OF A NEW LAYERED CADMIUM DIPHOSPHATE: KCdHP2O72H2O S. Kouass1, A. Selmi2,3, H. Chebbi4,5, A. Guesmi5,6 1Laboratoire des Matйriaux Utiles, Institut National de Recherche et dAnalyse Physico-chimique Sidi-Thabet, 2020 Tunis, Tunisia 2Universitй de Gafsa, Facultй des Sciences, Unitй de Recherche Matйriaux, Energie et Energies Renouvelables MEER, Sidi Ahmed Zarroug, 2112 Gafsa, Tunisia 4Universitй de Tunis, Institut Prйparatoire aux Etudes dIngйnieurs de Tunis, Rue Jawaher Lel Nehru, 1089 Montfleury, Tunis, Tunisia E-mail: chebhamouda@yahoo.fr 3Universitй de Carthage, Facultй des Sciences de Bizerte, Laboratoire de Chimie des Matйriaux, 7021 Zarzouna, Bizerte, Tunisia 5Universitй de Tunis El Manar, Facultй des Sciences, Laboratoire de Matйriaux, Cristallochimie et Thermodinamique Appliquйe, El Manar II, 2092 Tunis, Tunisia Received March, 7, 2015 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. <...> 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. <...> Many members of the chemical system K—Cd—P—O have particular structures, e.g. K4Cd3(HPO4)4(H2PO4)2 is an open-framework cadmium phosphate [ 1 ]; KCdPO4 6H2O belongs to the series of struvite analogs [ 2 ]; Cd0.5Ce2(PO4)3 with monazite structure type is known as a promising class used to immobilize wastes from nuclear power plants [ 3 <...>