Crystal structure and charge distribution of YbFeMnO4

The structure of synthetic YbFeMnO4 has been refined by single-crystal X-ra y diffraction. Space group R (3) over bar m, a = 3.4580 (1), c = 25.647 (3) Angstrom, V = 265.59 (3) Angstrom(3), Z = 3. Yb is in octahedral coordinat ion, whereas Fe and Mn are disordered on a single crystallographic type of trigonal bipyramid, in which the cation is off-centred from the basal plane . Assuming perfect stoichiometry, R-1 = 0.0195, but the charge distribution (CD) analysis suggests incomplete occupation of the Yb site. Refinement of the occupancy lowers R-1 to 0.0175, resulting in s.o.f.(Yb) = 0.963 (3), w ith a significant improvement of the Fourier difference. The electroneutral ity is likely preserved through incomplete occupancy of one of the two oxyg en sites: the compound is thus non-stoichiometric, with the formula Yb0.963 FeMnO3.945. Another mechanism for preserving the electroneutrality is the o xidation of a small amount of Mn2+ to Mn3+, which is, however, less probabl e because of the reduction conditions in which the sample was synthesized. Both models give a satisfactorily CD result, but they cannot be definitivel y distinguished by X-ray data.