This thesis consists of the structures of two compounds as determined by single crystal x-ray diffraction. The first structure is that of a phosphazene - iodine complex: hexamethylcyclotriphosphazene - iodine (1:1 adduct) and the second structure is the redetermination of sodium formate. Crystals of hexamethylcyclotriphosphazene - iodine (1:1 adduct) are triclinic, a = 10.707(13), b = 8.873 (5), c = 8.871(6)Å, α = 96. 65 (6), β = 103.91 (12), ɤ = 97.81(12)°, Z = 2, space-group PI. The structure was determined with Mo-K« diffractometer data by Patterson and Fourier synthesis, and was refined by full-matrix least-squares calculations to R = 0.053 for 1934 observed reflexions. The iodine molecule is weakly bonded to a nitrogen atom on the phosphazene ring, N - I = 2.417(7), I - I = 2. 823 (1) Å, N - I - I = 177.8(2)°. The six-membered phosphazene ring is slightly, but significantly, ncn-planar, the conformation being that of a chair. The molecule has pseudo-m symmetry. Two distinct P-N bonds are present; the longer ones, mean P - N = 1.64 Å, involve the nitrogen that is weakly bonded to the iodine molecule, while the other four P-N bonds are equivalent, mean P - N = 1.598 Å. All the P - C bonds are equivalent, mean P - C = 1.789 Å. The mean endocyclic N - P - N and P - N - P angles are 114.7 and 124.0° respectively, while the mean exocyclic C - P - C angle is 104°. Crystals of sodium formate are mcnoclinic, a = 6.2590 (6), b = 6.7573 (16) , c = 6.716 (5) Å, β = 116.140(6)°, Z = 4, space-grcup C2/c. The structure was determined by direct methods, and was refined by electron density and full-matrix least-squares procedures to E = 0.022 for 250 reflexions. Sodium formate is planar and has C2V symmetry. Partial charges were refined on the formate ion. The partial charges found on each atom are as follows: 0 -0.23(1)e, C +0.16(3)e, H -0.49(10)e, and Sa +0.79(14)e. The sodium ion has six oxygen neighbours at an average distance of 2.45 Å and there are weak Na. ..0 interactions. There is a C - H...Na hydrogen bond which forms continuous rows of sodium formate ions. The C - 0 bond distance is 1.246(1)Å and the 0 - C - 0 angle is 126.3(2)°. / Science, Faculty of / Chemistry, Department of / Graduate

Call number: LD2668 .T4 1966 P298 / Master of Science

The stability of glass is linked to its composition and the atmosphere controls its alteration. The organic pollutants emitted by wooden showcases play a role in the alteration of historic glasses. This study examines the effects of acetic acid, formic acid and formaldehyde on objects from the National Museums of Scotland and on replica glasses aged artificially, all with a soda silicate composition. Composition was determined by electron microprobe and analytical decomposition of the Raman spectra was used to establish correlations between glass structure and composition. This allowed interpretation of the structural variations between bulk and altered glass. The structure of the glasses altered by pollutants is characteristic of an alteration by selective leaching, with transformation of the silicates linked to alkali into silanols, which subsequently underwent condensation reactions to form a more polymerised structure. The SIMS concentration profiles of glass aged in artificial and real atmospheres were used to follow the alteration evolution as a function of time, humidity and pollutant concentration. The water film formed by the humidity at the surface and its acidity control the alteration by leaching of alkali and hydration of the glass. Formaldehyde does not act on the leaching reaction while acids accelerate and amplify it. In mixed polluted atmosphere, formates compounds always predominate in the film even at low formic acid concentration. The humidity and temperature fluctuations in museums maintain the leaching reaction. Knowledge of the harmful effect of organic acid pollutants in the alteration of soda silicate glasses will help improve their conservation.