Local structure of Rb2Li4(SeO4)3·2H2O by the modeling of X-ray diffuse scattering — from average-structure to microdomain model

Local structure of dirubidium tetralithium tris(selenate(VI)) dihydrate — Rb2Li4(SeO4)3· 2H2O has been determined basing on the modeling of X-ray diffuse scattering. The origin of observed structured diffuse streaks is SeO4 tetrahedra switching between two alternative positions in two quasi-planar layers existing in each unit cell and formation of domains with specific SeO4 tetrahedra configuration locally fulfilling condition for C-centering in the 2a×2b×c superstructure cell. The local structure solution is characterized by a uniform distribution of rather large domains (ca. thousand of unit cells) in two layers, but also monodomains can be taken into account. Inside a single domain SeO4 tetrahedra are ordered along ab-diagonal forming two-string ribbons. Inside the ribbons SeO4 and LiO4 tetrahedra share the oxygen corners, whereas ribbons are bound to each other by a net of hydrogen bonds and fastened by corner sharing SeO4 tetrahedra of the neighboring layers.

Experimental sections of the reciprocal space showing diffraction effects observed for RLSO. Bragg spots are visible on sections with integer indices (1 kl section — on the left), streaks — on sections with fractional ones (1.5 kl section — on the right). At the center: resulting local structure of the A package modeled as a microdomain: two-string ribbons of ordered oxygen-corners-sharing SeO4 and LiO4 terahedra extended along ab-diagonal are seen; ribbons are bound by hydrogen bonds (shown in pink); the multiplied 2a×2b unit cell is shown.Figure optionsDownload as PowerPoint slideHighlights
► X-ray diffuse scattering in RLSO was registered and modeled.
► The origin of diffuse streaks is SeO4 tetrahedra switching in two structure layers.
► The local structure is characterized by a uniform distribution of microdomains.
► Inside a single domain SeO4 tetrahedra are ordered along ab-diagonal forming ribbons.
► The ribbons are bound to each other by a net of hydrogen bonds.