Synthesis and Crystal Structure of a New Mixed Alkali Oxalate A1−x (NH4) x (H2C2O4)(HC2O4)(H2O)2 with A = K, Rb

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In the present study we report the synthesis, crystal structure, spectroscopic and thermal analysis of mixed alkali A1−x (NH4) x (H2C2O4)(HC2O4)(H2O)2 with A = K, Rb. Single crystal refinements showed that the two compounds Rb0.86(NH4)0.14(H2C2O4)(HC2O4)(H2O)2 and K0.53(NH4)0.47(H2C2O4)(HC2O4)(H2O)2 adopt P − 1 space group. The nine fold coordination cationic sites are randomly occupied by Rb+/NH4 + and K+/NH4 + respectively for rubidium and potassium compounds. The structure consists of a three-dimensional network formed by the succession along (c) axis of corrugated sheets formed by alkali polyhedra layers in the packing of four-membered rings [A4(HC2O4)2(H2C2O4)2] linked and bridged by oxalate groups that behave as bi and tetradentate ligand under three different coordination modes. The stability of the crystal lattice is ensured by interesting hydrogen bonding contacts: N–H···O and O–H···O. The thermal behavior under air reveals two anomalies at 368 and 402 K attributed respectively to a structural phase transition probably due to the reorientation of ammonium tetrahedral and to the release of crystalline water. IR spectroscopy further confirms that this material loses crystallization water gradually in the temperature range 400–460 K. Crystal structures of Rb0.86(NH4)0.14(H2C2O4)(HC2O4)(H2O)2 and K0.53(NH4)0.47(H2C2O4)(HC2O4)(H2O)2 adopt isotypic three dimensional frameworks formed by the succession along (c) axis of corrugated sheets. Structure of A1−x (NH4) x (H2C2O4)(HC2O4)(H2O)2.