The crystal and molecular structures of six compounds have been determined using X-ray diffraction techniques, one has been redetermined using neutron diffraction techniques and one has been attempted using direct method techniques for structure solution.(1) The crystal structure of 3,4,5-triamino-1,2,4-triazole hydrobromide, c 2N6H7Br, was determined from three-dimensional four circle diffractometer data. 1240 unique reflections were collected from a crystal mounted about the b axis on a Hilger and Watts four circle Automatic Diffractometer. The monoclinic unit cell, space group C2/c, has dimensions a= 686.9 (1) pm, b = 1069.3 (2) pm, iii c = 1855.0 (2) pm, S = 95.66 (3) 0 , with z = 8. The bromine atom was located from a Patterson synthesis. The remaining atoms (including hydrogens) were located from Fourier and difference Fourier syntheses. The structure was refined by least squares to a conventional R of 0.036. The molecule is found to be planar, a feature common to all reported 1,2,4-triazole structures. A feature of the crystal packing is the strong intermolecular hydrogen bond involving the hydrogen atom bound to N(l) and the bromine atom.(2) The crystal structure of 3-(S Benzoylhydrazino)-4-amino-5 mercapto-1,2,4-triazole, c 9N6 oH10 s, was determined from three dimen sional four-circle diffractometer data. 1750 unique reflections were collected on a Picker four-circle Automatic Diffractometer from a crystal mounted about the b axis. The monoclinic unit cell, space group C2/c, has dimensions a= 1812.5 (9)pm, b = 606.9 (2) pm, c = 2063.8 (9) pm, B = 104.875 (8) 0 , with Z 8. All non hydrogen atoms were determined by direct methods using the symbolic addition procedure of Dewar and Stone. The hydrogen atoms were located from a difference Fourier synthesis. The structure was refined by least squares to a conventional R of 0.049. Again as in the other triazoles, the triazole ring is found to be planar. The observed bond distances and angles are comparable with those reported for similar structures.(3) The crystal structure of the sodium salt of 4-amino-5 mercapto-1,2,4-triazole trihydrate, Na+c 2N4 o 3H9 s-, was determined from three dimensional equi-inclination Weissenberg X-ray diffraction data. 1381 unique reflections were collected from two crystals mounted about the b and c axes on a Supper Automated Diffractometer. The monoclinic unit cell, space group P2 1 /c, has dimensions a = 1167.86 (12) pm, b = 1026.42 (11) pm, C = 669.65 (8) pm, s = 100.84 (8)0, with z = 4. All non hydrogen atoms were located by direct methods using the symbolic addition procedure of Dewar and Stone. The hydrogen atoms were located from a difference Fourier synthesis. The structure was refined by least squares to a conventional R of 0.058. As in the other triazole structures, the triazole ring is found to be planar. A feature of the crystal packing is that two of the water molecules are strongly bound to the sodium atom while the third water molecule is weakly bound to the nitrogen atom N(l) of the triazole ring.(4) The crystal structure of 4-amino-benzylidine-5-mercapto 1,2,4-triazole, c9N4H8S, was determined from three dimensional diffractometer data. 1812 unique reflections were collected from a crystal not orientated along a principal axis on a Siemens Automatic Diffractometer. The monoclinic unit cell, space group P2 1 /c, has dimensions a= 1084.35 (4) pm, b = 447.32 (2) pm, c = 2044.14 (7) pm, B 106.25 (8) 0 , with z 4. All non hydrogen atoms were located by direct methods using the syrrbolic addition procedure of Germain and Woolfson. ·The hydrogen atoms were located from a difference Fourier synthesis. The structure was refined by least squares to a conventional R of 0.029. The triazole ring is found to be planar but in this case the benzylidine group is bent 0 upwards by 4 to the plane of the triazole ring. In this structure there are no close intermolecular interactions.(5) The crystal structure of a 1:1 adduct of 6-mercapto-3 iv phenyl-s-triazolo(4,3-b)-s-tetrazine and pyridine, c14N7H11 s, was determined from three dimensional diffractometer data. 5397 unique reflections were obtained from a crystal not orientated about a principal axis on a Siemens Automatic Diffractometer. The orthorhombic unit cell, space group Pbcn, has dimensions a= 1204.56 (7) pm, b = 1494.23 (9) pm, c = 3153.25 (13)pm, with Z = 16. In this structure, there are two molecules per asymmetric unit. All the non hydrogen atoms of the two tetrazine molecules were located by direct methods using the symbolic addition procedure of Germain and Woolfson. The atoms of the two pyridine molecules together with the hydrogen atoms were located from difference Fourier syntheses. The least squares refinement was halted at a conventional R of 0.044. The triazole V and tetrazine rings are approximately planar wit.h the phenyl group rotated by 7° in one molecule and 12.5° in the other to the triazolo tetrazine plane. The crystal packing of the molecules is such that they are stacked in two sets of parallel sheets approximately 0 perpendicular to the be plane and arranged at 130 to each other. The pyridine molecules are stacked parallel to the tetrazine molecules and in such a position that the hydrogen atom attached to the nitrogen atom N(7) in the other triazoles, is now closest to the nitrogen atom of the pyridine molecule.(6) The crystal and molecular structure of 2-iodo-2-phenyl hydrazonoacetonitrile, c 8N3H6 I, has been determined from three dimensional equi-inclination Weissenberg X-ray diffraction data with 740 visually estimated reflections. The orthorhombic unit cell, space group Pn2 1 a, has dimensions a= 1284 (1) pm, b = 1487.5 (9) pm, c = 478 (2) pm, with Z 4. The structure was determined using the heavy atom technique and refined by least squares to a conventional R of 0.13. The conformation of the molecule is found to be the Z isomer i.e. the iodine atom is cis to the phenyl group across the C=N bond.(7) The crystal and molecular structure of mercury II cyanide, c 2N2Hg, has been redetermined using three dimensional neutron diffraction data. 216 unique reflections were collected on a four circle neutron diffractometer at the Australian Atomic Energy Commission's reactor HIFAR. The tetragonal unit cell, space group I 42d, had dimensions a= 964.3 (6) pm, c = 888 (1) pm, with Z 8. The structure was refined by least squares to a conventional R of 0.036. In most organo-mercury (II) compounds, the c-_Hg-C skeleton is found to be 0 linear but in this case the C-Hg-C angle was found to be 175.0 (2) . The crystal packing of the molecules is such that a capillary is formed perpendicular to the c axis.(8) The crystal structure of the natural product, Acrovestone, c32H42 o8 , has been attempted using three dimensional equi-inclination Weissenberg X-ray diffraction data. 4526 unique reflections were collected from two crystals mounted about the band c axes on a Supper Automated Pbca, has c =1819.0 direct Diffractometer. dimensions (10) The orthorhombic a= 1679.0 (9) unit pm, b = 1961.1 pm, with Z = 8. The structure cell, (12) space pm, was attempted methods using both symbolic addition and tangent group by formula techniques without success.