Abstract
Abstract 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(F 2) = 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.
Highlights
Polyanionic transition-metal phosphates have been subjected to growing scientific interest as electrode materials for lithium and sodium-ion batteries [1, 2]
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
Semiquantitative energy-dispersive X-ray spectroscopy (EDX) analyses of different single crystals including the ones investigated on the diffractometer were carried out with a 7610F (JEOL) scanning electron microscope (SEM)
Summary
Polyanionic transition-metal phosphates have been subjected to growing scientific interest as electrode materials for lithium and sodium-ion batteries [1, 2]. The title compound Pbca-Na2Mn3(SO4) was prepared by a solid state reaction route, from a stoichiometric mixture of Na2SO4 (Aldrich, 99.5%) and MnSO4 · H2O (Merck, 99.9%). A stoichiometric mixture of Na2SO4 and MnSO4 · H2O was heated at 800 °C for 12 h quenched to room temperature. This led mainly to colourless crystals of Pbca-Na2Mn3(SO4) besides few crystals of Na2SO4. The two samples were heated at 600 °C for 12 h and at 800 °C for 10 h in Argon This led to the formation of Pbca-Na2Mg2.5Mn0.5(SO4) (4) and Pbca-Na2Mg1.5Mn1.5(SO4) (5) single crystals, respectively. Crystal data Chemical formula Mr Crystal system Space group Temperature (K) a, b, c (Å) V (Å3) Z Radiation type μ (mm−1) Crystal size (mm) Data collection Diffractometer Absorption correction SADABS Tmin, Tmax No of measured reflections No of independent reflections No of observed reflections Rint (sin θ/λ)max (Å−1) Refinement R[F2 > 2σ(F2)], wR(F2), S No of reflections No of parameters No of restraints Δρmax, Δρmin (e Å−3)
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