Crystal Structure of the Transition-Metal Molybdates. I. Paramagnetic Alpha-MnMoO4

Paramagnetic alpha-MnMoO4, the stable phase at STP, is monoclinic with lattice constants a=10.469±0.005, b=9.516±0.005, c=7.143±0.005 Å, and β=106°17′±6′, and space group C2/m. The crystal structure has been solved and refined by a combination of three-dimensional Patterson and Fourier series and by the method of least squares. 1873 independent integrated intensities were measured by PEXRAD; the final agreement factor between measured and calculated structure factors is 0.0574. Two crystallographically independent Mn atoms are surrounded by highly distorted oxygen octahedra; the Mn–O distance varies between 2.091±0.006 and 2.252±0.003 Å, with average length 2.164 Å. Two crystallographically independent Mo atoms are surrounded by slightly distorted oxygen tetrahedra, with Mo–O distances ranging from 1.724±0.005 to 1.851±0.004 Å, the average being 1.761 Å. The thermal vibrations are significantly anisotropic. An analysis is given of various current methods for estimating the standard deviation in the measured structure factor.