Compressed Octahedron Research Articles

Crystal Structure of Paramagnetic DyMn2O5 at 298°K

Paramagnetic DyMn2O5 crystallizes in the orthorhombic system with lattice constants a=7.2940±0.0008, b=8.5551±0.0008, and c=5.6875±0.0008 Å, in the space group Pbam(D2h9). There are four DyMn2O5 per unit cell. The crystal structure was solved by a combination of three-dimensional Patterson and Fourier series and refined by the method of least squares. The integrated intensities of 5094 reflections were measured by PEXRAD, with 976 symmetry-independent structure factors significantly above background. The final agreement factor between measured and calculated structure factors is 0.0401. There are two independent Mn atoms. One is pentacoordinated, with a slightly distorted tetragonal pyramidal configuration: two basal Mn–O distances are 1.926±0.006 Å, the other two are 1.911±0.005 Å, and the apical Mn–O bond, nearly normal to the basal plane, is 2.020±0.005 Å. The other Mn occupies a slightly compressed octahedron, with four planar Mn–O bonds of 1.940±0.004 Å and two, normal to this plane, of 1.873±0.004 Å. The octahedral Mn environment closely resembles that in β-MnO2. The Dy is surrounded by a somewhat distorted square-antiprismatic polyhedron of oxygen atoms, the Dy–O distance ranging from 2.341±0.005 to 2.469±0.005 Å, the average being 2.390 Å. The thermal vibrations are significantly anisotropic. The room-temperature paramagnetism could mask an antiferromagnetic ordering of the octahedral Mn atoms.