Rietveld refinement of the Tutton salt K2[Fe(H2O)6](SO4)2

Dipotassium hexaaquairon(II) bis( sulfate), K-2[Fe(H2O)(6)]-( SO4)(2), is a member of the isotypic series of Tutton salts with general formula M-2(I)[M-II(H2O)(6)](XO4)(2), where X = S, Se or Cr. The structure contains centrosymmetric Fe(H2O)(6) octahedra, with an average Fe-O distance of 2.14 (4) angstrom. Each octahedron is surrounded by isolated SO4 tetrahedra [average S-O distance = 1.483 (15)angstrom] and distorted KO6(H2O)(2) polyhedra with an average K-O distance of 2.96 (15) angstrom. The polyhedra are linked via common O atoms and a system of medium-strength hydrogen bonds.