The room temperature electron density distribution in potassium tetrathionate, K 2 S 4 0 6 , was investigated using accurate single-crystal-Xray diffraction data up to sin 9/A = 0.90 Â"The conventional all-data refinement yielded RIR W values of 0.018/0.017, respectively, for 3316 observed reflections. In order to reduce parameter bias introduced by bonding effects, various refinements with high-order data were also performed. The resulting (X -X H0 ) dynamic deformation density maps of the two crystallographically independent anion complexes [S 4 0 6 ] 2 " agree qualitatively. No significant σ-type single bond peaks are found at the midpoints of the S -S bonds. Instead, extended "lone pair" deformation density maxima are observed close to the S -S bonds, as well as above and below the S -S -S planes, providing evidence for a directional character of the sulfur lone-pair orbitals. The density distributions associated with the terminal S0 3 groups are as expected.

The re-evaluation of the optimal X-ray diffraction data of a synthetic coesite crystal earlier proposed by us to possess Plyja space group symmetry yielded improved agreement factors assuming a small amount of (100)-twinning of the known C2/c phase.

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Li + (C 4 H 5 0 5 rC 4 H 6 0 5 , P2 U a = 5.269(3) Â, 6= 16.915(5) A, c = 6.403(3)Â, β = 94.05(2)°, Ζ = 2, D cxp = 1.588(6) g/cm 3 , D x = 1.598 g/ cm 3 . The Li + ion is found in a fivefold coordination surrounded by oxygen atoms in the form of a distorted pyramid with an almost rectangular base. The conformation of the malic acid moieties is anti. The crystal structure is characterized by endless chains of molecules connected threedimensionally by strong hydrogen bonds.