Crystals of K4[Ru2CII00] are tetragonal, space group I4/mmm with a = 7.097 (2), c = 17.015 (3) A and Z = 2. The structure was first determined by Mathieson, MeUor & Stephenson [Acta Cryst. (1952). 5, 185-186] from a zero-level Weissenberg photograph for the formula K4[Ru2CII00].H20. New intensities were collected on an automatic four-circle diffractometer with Mo Kff radiation, and anisotropic full-matrix leastsquares refinement was performed. The final R was 0.034 for the 245 measured reflexions. This refinement shows that there is no water molecule in the structure.

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M. M. PETIT-RAMEL, G. THOMAS-DAVID, G. PERICHET et P. POUYET. Can. J. Chem. 62, 22 (1984). Les constantes d'association relatives aux complexes des ions Hg2' avec les formes monomkre (TM) et dimkre (TD) de la thymine sont calculCes a partir de mesures protomCtriques effectuCes dans un large domaine de pH: 2 < pH < 11. Le traitement des donnCes de chacun des systkmes est conduit par une mtthode de pit-mapping et l'on peut donner la ripartition des diverses espkces complexes en fonction du pH.En ce qui conceme le monomkre, les ions Hg2' ayant une coordinence de degrC deux, traduite par la configuration linCaire d'espkces non chClatCes, on peut mettre en evidence les complexes [H~ (

(Refu le 16 juillet 1973(Refu le 16 juillet , accept6 le 12 oetobre 1973 The crystal structure of a picolinic acid polynuclear chelate with beryllium has been determined. Tri-/zhydroxo-tri(pyridine-2-carboxylato)triberyllium monohydrate, [Bea(OH)a(C~H4NCOO)a].H20, crystallizes in the monoclinic system, space group P2Jc with a= 15.914, b=9.262, c= 15.480 ~, fl= 105"43 ° and Z= 4. The Cu Kg intensities were collected on a four-circle Siemens AED diffractometer and the structure was determined by means of the symbolic addition procedure. Before refinement, the atomic parameters were divided into different groups and the anisotropic full-matrix least-squares method was successively applied to each (R = 0.045).

The protonation constants of 1 -canavanine (Can) and its structural analogue 1-arginine (Arg) have been calculated at 25 °C and at ionic strength μ = 0.1 (NaNO3). Under the same conditions, the stability constants of the binary and ternary complexes with Cu(II) have been determined by potentiometry, spectrophotometry, and by circular dichroïsm in the visible region. A comparative study of these two amino acids allows us to differentiate the order of protonation of the three functional groups (carboxylic, amino, and guanidyl), mainly by the different modes of complexation with copper(II), which is found in an octahedral coordination: arginine behaves like a bidentate ligand (glycine type) whereas canavanine behaves like a tridentate ligand. Keywords: 1-arginine, 1-canavanine, circular dichroïsm, copper ternary coordination, potentiometry.