Crystal structure, vibrational spectra, and thermal decomposition and nitrogen adsorption behaviour of a new tetramanganese(II) dipyrophosphate decahydrate, Mn4(P2O7)2•10H2O

A new manganese(II) pyrophosphate, Mn-4(P2O7)(2)center dot 10H(2)O, has been synthesized and characterized by single-crystal X-ray diffraction [orthorhombic space group Pnma, with unit cell parameters of a=9.3288(3) angstrom, b=25.9532(9) angstrom, c=8.4783(3) angstrom; Z=4]. All the pyrophosphate anions show non-linear P-O-P bonds with an average angle of 128.60 angstrom. The framework of this new pyrophosphate is made up of packed layers of MnO6 octahedra connected by double-tetrahedra P2O7 groups and a layer of Mn(H2O)(6) units. The [P2O7](4) anions adopt a bent, near-staggered conformation. The absence of coincidences for the majority of the IR and Raman bands is in accord with the centrosymmetric structure of the material. The vibrational spectra have been interpreted in part on the basis of factor group effects. The structural changes occurring during heating have been investigated by TG-ATD. When Mn-4(P2O7)(2) (.)10H(2)O is gradually heated, it decomposes into an intermediate hydrated salt at 96 degrees C and then to anhydrous Mn2P2O7 at 325 degrees C. This thermal behaviour is different from that of Zn-4(P2O7)(2)center dot 10H(2)O. The crystal structure of the new managenese(II) pyrophosphate is compared with the known structures of Zn-4(P2O7)(2)center dot 10H(2)O, Mn2P2O7 center dot 2H(2)O and anhydrous Mn2P2O7. The adsorption and desorption isotherms of Mn-4(P2O7)(2)center dot 10H(2)O, Zn-4(P2O7)(2)center dot 10H(2)O and MnKHP2O7 center dot 2H(2)O have been investigated by BET measurements and the results show that the capacity for N-2 sorption of the Mn(II) salt is two times lower than is that of the Zn(II) isotype and two or three times higher than is that of MnKHP2O7 center dot 2H(2)O.