Short-Range and Long-Range Magnetic Ordering, in Third Generation Brannerite Type Inorganic-Organic Vanadates: [{Mn(Bpy)}(VO3)2]≈(H2O)_(1.16) and [{Mn(Bpy)_(0.5)](VO3)2MH2O)_(0.62)

摘要

The three-dimensional [{Mn(Bpy)}(VO3)2]≈(H2O)_(1.16) and [{Mn(Bpy)_(0.5)}(VO3)2]≈(H2O)_(0.62) inorganic-organic compounds, where Bpy is 4,4'-bipyridine, (C_(10)H8N2), have been synthesized using mild hydrothermal conditions under autogenous pressure at 170 °C during three days, obtaining single-crystals suitable for X-ray structure determination. The compounds crystallize in the mono-clinic system, space group C2/m, with a = 16.706(5), b = 3.5265(4), c = 11.558(5) A, and β = 100.77(5)° for 1, and a = 16.305(6),b = 3.5304(11), c = 17.788(6) A, and β = 116.87(4)° for 2. Single crystal X-ray diffraction reveals that both crystal structures are composed of inorganic layers pillared by organic ligands. However, 1 possesses simple layers, while 2 is constructed from double inorganic sheets. This structural organization gives rise to channels along the [010] direction, in which the crystallization water molecules are located. The thermogravimetry and thermodiffractometry experiments show that both crystal structures have a dynamical and reversible response to the removal and uptake of crystallization water molecules. Magnetic, ESR, specific heat, and neutron measurements indicate that both phases possess one-dimensional ferromagnetic coupling of the Mn(II) ions above the Neel temperature. Below 4 K for 1 and 7.5 K for 2, a three-dimensional antiferromagnetic order is established. The sigmoidal shape of the magnetization curves indicates that the three-dimensional antiferromagnetic order can be reverted by the application of higher magnetic fields.