Neutron diffraction study of K-4(HSeO4)(3)(H2PO4). A comparison with X-raystructure

The neutron single crystal diffraction study of K-4(HSeO4)(3)(H2PO4) at roo m temperature confirmed the known X-ray structure regarding the positions o f the heavier atoms with a full occupation of the central position in one X O4 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) as ymmetric, effectively centered; and iii) symmetric centered hydrogen bonds with O ... O distances in the range of 2.512-2.561 Angstrom. Two latter H a toms have very elongated ellipsoids of thermal motion along the correspondi ng 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 o f hydrogen bonds can be described as chains with branches. The structural f eatures are better represented by the formula K-4(HSeO4)(2)[H-1.5(Se,P)O-4] (2).