Two new acidic diphosphates Rb2M(H2P2O7)2·2H2O (M = Zn and Mg): Crystal structures and vibrational study

Two new complex diphosphates Rb2M(H2P2O7)2·2H2O [M = Zn (I), Mg (II)], have been synthesized using wet chemistry. Their crystals have been isolated and characterized by X-ray diffraction, FTIR and micro-Raman techniques. Both compounds crystallize in the triclinic system, S.G. P-1, Z = 1 and following parameters (Å,°), [6.9573(1), 7.3615(1), 7.7938(1), 81.851(1), 70.622(1), 86.263(1), R1/wR2=0.0315/0.1083R1/wR2=0.0315/0.1083 for (I) and 6.9546(1), 7.3752(1), 7.8117(1), 81.986(1), 70.275(1), 85.988(1), R1/wR2=0.0275/0.0865R1/wR2=0.0275/0.0865 for (II)]. The crystal packing in (I) and (II) consists in a three-dimensional network made by layers, parallel to ac-plane. H2P2O72− shows bent eclipsed conformation and the M2+ ion lies on inversion centre. IR and Raman spectra confirm the bent geometry of the POP bridge angle.