Crystal structure and vibratrional spectra of tetrasodium dimagnesium dihydrogen diphosphate octahydrate Na4Mg2(H2P2O7)-8H2O

A tetrasodium dimagnesium dihydrogen diphosphate octahydrate Na4Mg2(H2P2O7)4 _ 8H2O was synthesized. It crystallizes in the monoclinic system, space group P21/m (no. 11), Z =4; and its unit-cell parameters are: a = 8.0445(3)A° , b = 11.5244(5)A°, c = 9.0825(4)A° , beta = 113:1401(2)°, V = 774:28(6)A°3. The structure was determined by single-crystal X-ray diffractometry and refined to a R index of 0.0294 (wR = 0.0727) for 1878 independent reflections with I>2sigma(I): The framework is made by the alternance of layers of MgO6/NaO6 octahedra and double tetrahedra PO4 along b-axis. Such layers are characterized by the presence of strong hydrogen bonds. (H2P2O7)2- anions exhibit bent eclipsed conformation. Besides, the crystal was analyzed by FT–IR and micro-Raman vibrational spectroscopy. No coincidences of the majority of the Raman and infrared spectra bands of Na4Mg2(H2P2O7)4 _ 8H2O confirms a centrosymmetric structure of this material. The vibrational spectra confirm the bent POP configuration in this compound