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. 

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Published in: Zeitschrift für Kristallographie - Crystalline Materials
License: http://creativecommons.org/licenses/by/4.0
See article on publisher's website: http://dx.doi.org/10.1515/zkri-2019-0038