A new lithium manganese phosphate with an original tunnel structure in the A2MP2O7 family

A new member of the A₂MP₂O₇ diphosphate family, Li₂MnP₂O₇, has been synthesized by solid-state reaction and characterized using single-crystal X-ray diffraction. Li₂MnP₂O₇ crystallizes in the monoclinic space group P2₁/a (#14) with the cell parameters a=9.9158(6) Å, b=9.8289(6) Å, c=11.1800(7) Å, β=102.466(5)°, Z=8 and V=1063.9(1) Å³. Its mixed framework exhibits an original Mn₂O₉ unit, built up of one MnO₅ trigonal bipyramid sharing one edge with one MnO₆ octahedron. These Mn₂O₉ units are sharing corners with P₂O₇ diphosphate groups, forming the undulating Mn₄P₈O₃₂]_∞ layers. The MnP₂O₇]_∞ 3D framework, resulting from the interconnection of the undulating Mn₄P₈O₃₂]_∞ layers, exhibits different kinds of intersecting tunnels containing the Li cations.