Crystal structure and Charge Distribution of ErFeMnO4

The structure of synthetic ErFeMnO4 has been refined by single-crystal X-ra y diffraction. Space group is R (3) over barm, a=3.4831(1) Angstrom, c=25.6 09(4) Angstrom, V=269.07(5) Angstrom (3), Z=3. Er is in octahedral coordina tion, whereas Fe and Mn occupy a single crystallographic type of distorted trigonal bipyramid, with one of the two apical bonds shorter and the other longer than the three basal bonds. Assuming Er in the centre of symmetry R- 1 = 0.031, but the Charge Distribution analysis suggests that the position of Er was not completely determined, and the Fourier difference indicates s plitting of the Er cation around the centre of symmetry. Refinement in the split-atom model for Er lowers R-1 to 0.016, reduces the displacement param eter of Er and removes the anomalies in the Fourier difference. A deviation from the mean structure in this kind of compounds seems regularly associat ed with the presence of distorted trigonal bipyramids. (C) 2000 Elsevier Sc ience B.V. All rights reserved.