Crystal structure of a new polymorphic modification of Na2Mn3(SO4)4.

The new polymorph of Na2Mn3(SO4)4 was prepared via solid state reaction route in a powder form and its crystals were grown by self-flux method. The crystal structure was determined from single crystal X-ray diffraction data. This polymorph crystallizes with an orthorhombic symmetry, space group Pbca, with a = 9.8313(4), b = 8.7467(3), c = 29.6004(11) Å, V = 2545.38(17) Å3, Z = 8. Its structure refinement yielded the residual factors R(F) = 0.025 and wR(F2) = 0.065 for 227 parameters and 2605 independent reflections at 2σ(I) level. The use of group-subgroup schemes in the Bärnighausen formalism enabled an accurate comparison of the Pbca- and Cmc 21-polymorphs of Na2Mn3(SO4)4. Both polymorphs contain similar [Mn3(SO4)4]2− building blocks formed of Mn2O11 dimer units and MnO5 trigonal pyramids that are interconnected by sharing corners with the SO4 tetrahedra. However, the stacking of these building blocks along the longest axes of the Pbca- and Cmc 21-structures is different. This induces differences in the coordination of the sodium atoms and in the orientation of the SO4 tetrahedra. [ABSTRACT FROM AUTHOR]