Neutron diffraction study of K4(HSeO4)3(H2PO4). A comparison with X-ray structure

The neutron single crystal diffraction study of K4(HSeO4)3(H2PO4) at room temperature confirmed the known X-ray structure regarding the positions of the heavier atoms with a full occupation of the central position in one XO4 tetrahedron by a Se atom and a half occupation by Se and P in the other. There are three independent protons participating in i) asymmetric; ii) asymmetric, effectively centered; and iii) symmetric centered hydrogen bonds with O···O distances in the range of 2.512 - 2.561 Å. Two latter H atoms have very elongated ellipsoids of thermal motion along the corresponding hydrogen bonds as distinct from the X-ray structure in which these two H atoms were found to be disordered between two positions each. The system of hydrogen bonds can be described as chains with branches. The structural features are better represented by the formula K4(HSeO4)2[H1.5(Se,P)O4]2.