Crystals of uridine, C9HI2N206, are monoclinic, space group P21 with a=4.981 (4), b= 14.649 (8), c= 13"964 (8)A, fl= 95"45 (8) ° and Z= 4, The structure was solved by the direct method and refined by least-squares calculations, using Ni-filtered Cu Ke diffractometer data. The final R index was 0.033 for 2232 reflections, and the standard deviations in the atomic positions are about 0.003 A. The two independent molecules have very similar conformations; the conformation about the glycosidic bond is anti, the sugar ring is puckered with C(Y) endo, and the conformation about C(4")-C(5') is gauchegauche.

The crystal structures of,8-D-mannitol and e'-D-mannitol have been solved in three and two dimensions respectively by superposition procedures on the Patterson synthesis. The space group of the ,8 form is P212~21, with four molecules in the unit cell of dimensions a= 8.672, b= 16.875 and c=5.560/~; the space group of the e' form is C222~, with four molecules in special positions in a unit cell with dimensions a= 8"94, b=4.92 and c= 18.24 A. The molecules have the same conformation in both structures, with 2 symmetry and a planar carbon chain. The dimorphism is due to different systems of intermolecular hydrogen bonding.

A cadmium rhenium oxide has been prepared with the formula Cd2Re20~. Its structure is of the pyrochlore type. For the face-centered cubic unit cell, a = 10.219 A. The room temperature resistivity is about 2 X 10~3 ohm cm.

No abstract

CsH6N2, monoclinic, P2x/c, a=11.709 (4), b=5-673 (6), c=7.594 (6) A, fl=95.55 (4) °, M.W. 94.12, Z=4, Dm= 1"24, Dx= 1"248 g cm -3. The molecules form hydrogen-bonded dimers in centrosymmetrically related pairs via N(7)-H(7A). • • N'(1) hydrogen bonding [3.071 (7) A]; the dimers stack along b. Charge densities on each atom site and dipole moments are derived from an INDO calculation.