Transition Metal-Substituted Lithium Pnictogenide phases. Synthesis and Crystal Structure Determinations of Novel Phases in the Li–M–X Systems (M=V, Nb, Ta; X=P, As)

An organically templated manganese phosphate, Mn6(H2O)2(HPO4)4(PO4)2·C4N2H12·H2O, has been synthesized hydrothermally and characterized by synchrotron powder X-ray diffraction, thermogravimetric analysis, and magnetic measurements. The compound is structurally closely related to both a magnesium phosphate and an iron phosphate, and crystallizes in the triclinic space group P-1 (No. 2) with a=12.81926(12) ?, b=15.87361(20) ?, c=6.47912(7) ?, =99.8660 (11)°, = 90.3913(10)°, =103.4265(9)°, V=1261.928(25) ?3, and Z=2. The structure consists of anionic sheets of manganese phosphate separated by piperazinium cations and water molecules. The basic building unit of the inorganic layers is a hexamer of edge-sharing Mn polyhedra. Magnetic susceptibility measurements and bond valence calculations confirm the assignment of high-spin Mn2+ (d5) in the title compound.