Сrystal structure and spin-trimer magnetism of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2]статья
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Дата последнего поиска статьи во внешних источниках: 11 апреля 2017 г.
Аннотация:The novel borophosphate Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] was prepared in hydrothermal conditions at 553K. Its crystal structure was determined using single-crystal X-ray diffraction data obtained from a non-merohedral twin and refined against F2 to R = 0.057. The compound crystallizes in the orthorhombic space group Pbcn, with unit-cell parameters a = 20.076(2) Å, b = 9.151(1) Å, c = 12.257(1) Å, V = 2251.8(2) Å3, and Z = 4. The structure is formed by borophosphate slabs and chains of Mn2+-centered octahedra and tetrahedra sharing edges and vertices. These 2D and 1D fragments interconnect into a framework with open channels that accommodate Rb+ cations and water molecules. The title compound is characterized by a new structure type. It also shows topological relationships with borophosphates built from symmetrically independent sections, which present three-membered rings of two borate and one phosphate tetrahedra sharing oxygen vertices, amended by additional PO4 and HPO4 tetrahedra. The temperature dependence of magnetic susceptibility of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] reveals a paramagnetic behavior at elevated temperatures with the predominance of antiferromagnetic exchange interactions and an effective magnetic moment corresponding to the high-spin S=5/2 state of Mn2+ ions. At 12.5 K, a magnetic transition is evidenced by ac-susceptibility and specific heat measurements. Spin-trimer model with the leading exchange interaction J ~ 3.2 K is derived from density-functional band-structure calculations and accounts for all experimental observations.