Ahstnet X-ray diffraction panems of equimolecular concentrated aqueous solutions of yttrium chloride and bromide have been investigated from s = 0.4 A-' up to s = 15 .&-I, An assumed coordination of eight water molecules around each ymium cation, at a distauce of 2.36 A. reproduces the intensity at high s values in agreement with the values obtained by some of the present authors from WAFS experiments. Narrow interference maxima at s = (4n sin0)jX E 0.9 A-' may be interpreted as the existence of a local order of the hydrated yttrium cations surrounded by anions and free water molecules. Structural models with and without close packing of lhe hydrated cations were built to simulate fhat local order.

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Betaine potassium iodide dihydrate,(C5H1 ιΝ02)2ΚΙ · 2Η2θ presents unique features amongst the rich variety of properties exhibited by the betaine family of compounds investigated in recent years [2][3][4][5][6]. The study of dielectric and pyroelectric properties provided evidence for a structural phase transition, probably of first order, occurring close to 100 Κ [7], Both iodine and potassium ions occupy special positions. Examination of the crystal structure shows that potassium ion is octahedrally coordinated by four oxygen atoms from betaine molecules in a plane close to (010) and by two water molecules. The iodine ion is bonded to the carboxylic group of the aminoacid by electrostatic interactions. Zigzag chains of water and betaine molecules linked via hydrogen bonds run throughout the structure. The carboxylic 02 atom is involved in a relatively strong hydrogen bond being an acceptor of the water molecule (0(3)-H31 0(2)', i = 2-x,-y,ì-Ζ, 2.654(3) Â) while the atom Ol is only involved in much weaker C-H-O interactions. This correlates well with the observed difference in the carboxylic C-0 bonds. Neighbouring water molecules are linked together via a weaker hydrogen bond (

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