CioH 2 8F6N206Ta,monoclinic,P12/al (No. 13), a = 12.553(3) Ä, b = 6.531(3) Ä, c= 12.587(3) Ä, β = 110.25(1)°, V= 968.2 Ä 3 , Ζ = 2, R gt (F) = 0.030, wR(F 2 ) = 0.068, Τ = 293 Κ. Source of material The pure metal was dissolved in concentrated fluoridric acid (40%). Reagent grade betaine (Merck, 99.9% purity) was added to the solution and after a few days of slow evaporation small, transparent crystals were formed, from which a good quality specimen was choosen for X-ray analysis. The

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... tion was performed with the crystal encapsulated in a sealed glass capilary. Betaine is unusualy high sensitive to radiation damage [1] and the intensity of three control reflections measured each 3 h showed a decay which continuously increased attaining a maximum rate of 3.6°h _1 by the end of the data collection. A polynomial interpolation was used to correct for this decay in the data reduction. The structure was solved by direct methods. The hydrogen atoms of the cation were placed at calculated positions and refined as riding using the SHELXL-97 [2] defaults: d(0-H) = 0.82 Ä, d(C-H) = 0.93 Ä. Those of the solvent water molecule could not be located in a difference synthesis and were placed at tentative positions according to the best geometry for hydrogen bonding and refined subject to the restraint rf(O-H) = 0.86(2) Ä. Examination of the crystal structure with