A new borophosphate compound with helix structure: (NH₄) _0.5(H₃O)_0.5Mg(H₂O) ₂BP₂O₈

A new borophosphate compound, (NH₄)_0.5(H ₃O)_0.5Mg(H₂O)₂BP₂O ₈, was prepared by hydrothermal synthesis and characterized by X-ray single crystal diffraction. The title compound belongs to hexagonal system, space group P6₅22, a = 0.94507(19) nm, c = 1.5803(5) nm, γ = 120°, V = 1.2224(5) nm³, M_r = 279.06, Z = 6, D _c = 2.258 g/cm³, F(000) = 834, R₁ = 0.0360, wR₂ = 0.1070, μ = 0.663 mm^-1. The crystal structure of the compound contains infinite one-dimensional borophosphate ribbons _∞¹{[·BP₂O₈] ^3-}, built of corner sharing BO₄ and PO₄ tetrahedra arranged around 6₅ screw axes. The borophosphate helices are interconnected by MgO₄(H₂O)₂ coordination octahedra to form a three-dimensional framework. The elemental analysis, IR, DTA/TGA and the calculation of the electric charge balance show the presence of ammonium ions and protons. Both ammonium ions and hydroniums are located within the free loop of helical ribbons, and close to the inner wall of the helical channels _∞¹{[BP₂O₈] ^3-}, respectively, balancing charge and stabilizing helical ribbons.