Redox and Addition Reactions of Binary Fluorides

Berry, John Albert (1976) Redox and Addition Reactions of Binary Fluorides. PhD thesis, University of Glasgow.

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Abstract

This thesis describes the study of complexation and redox reactions of iodine pentafluoride, and redox and addition reactions of uranium hexafluoride and rhenium hexafluoride. Solutions of IF5 in acetonitrile and pyridine were studied using Raman, 1H and 19F nmr spectroscopy. In CH3CN solution, the I-F...I contacts which occur in liquid IF5, are replaced by C=N...I contacts as the concentration of CH3CN increases, A large decrease in the frequency of the v1 band of IF5 and small increases in the C-C and C=N stretching frequencies of CH3CN are observed in the Raman spectra. The results obtained suggest a maximum number of four CH3CN molecules can co-ordinate to each IF5 A 1:1 complex is formed between IF5 and C5H5N and spectra of mixtures of the two liquids can best be explained in terms of an equilibrium between this complex and the two components. The solid 1:1 adduct, IF5. 1,4-Dioxane was prepared and characterised by elemental analysis and vibrational spectroscopy. Vibrational, and 1H and 19F n. m. r, spectra were recorded of its solutions in CH3CN. A polymeric structure for the adduct, based on a chain-structure is suggested. Reactions of IF5 with metals and metal fluorides were investigated, using IF5 or CH3CN as solvent. Thallium metal reacts with IF5 to form insoluble T1+ IF6-, which readily hydrolyses to give TIIOF4. Silver metal reacts with IF5 in CH3CN to give a viscous oil, whose spectra indicate that IF6- is not formed. The reaction between copper and IF5 in CH3CN gives a blue-white soluble solid whose composition is variable. The product from the reaction between mercury and IF5 is also of variable composition. Thallium (I) fluoride reacts with IF5 in CH3CN to give (T12)3+ IF6 3- as one product. These redox reactions all involve a 2-electron reduction of I(V) to I(III), but the reaction products depend on the stability of the I(III) species towards disproportionation. The products were identified by elemental analysis and vibrational spectroscopy. The addition reactions of IF5 with metal fluorides indicate that, in at least some instances, adduct formation is preferred to fluoride ion addition, T1F reacts with IF5 to produce either the soluble solid T1F. IF5 or the viscous liquid T1F. 3IF5. The latter is formed if IF5 is present in a very large excess. CuF2 reacts with IF5 in CH3CN forming the adduct CuF2. 4CH3CN. 4IF5. This is a blue-green oil and was characterised by elemental analysis, 1H and 19F nmr, e.p.r., electronic and vibrational spectroscopy. A structure based on these data is presented. Tungsten hexafluoride and molybdenum hexafluoride do not react with iodine in IF5 but rhenium hexafluoride forms a stable solution containing the I2+ ion. This was confirmed by electronic and resonance Raman spectroscopy. No isolable product is formed. Uranium hexafluoride also forms a species containing I2+, but a further reaction occurs and uranium pentafluoride is obtained as a pale green precipitate, UF5 is very soluble in CH3CN, with which it forms an isolable 1:1 adduct, and was characterised in the solid state by vibrational spectroscopy and in solution by Raman and electronic spectroscopy. Thallium, cadmium and copper metals are all readily oxidised by UF6 in CH3CN, forming soluble hexa- fluorouranates(V). These are isolable as the solvates T1(UF6)3. 5CH3CN, Cd(UF6)2.5CH3CN and Cu(UF6)2.5CH3CN. Electronic spectra obtained agree with the latest literature spectra. Values of vibrational frequencies obtained from vibronic couplings in electronic spectra agree well with the values from i. r. spectra. No silver compound could be isolated because of rapid solvent polymerisation caused by UF6 in the presence of Ag. UF6 is reduced by CH3CN to give UF5, while the solvent is slowly polymerised. The increase in concentration of UF5 with time is seen from Raman and electronic spectra, run at 30 minute intervals. ReF6 attacks CH3CN too rapidly to allow reactions involving excess ReF6 to be carried out. However Cu(ReF6)2.4CH3CN.O.5IF5 was prepared using a mixture of IF5 and CH3CN as solvent. The reduction of UF6 by CH3CN to give UF5, interferes with relatively slow reactions such as F- ion addition. HgF2 and UF6 in CH3CN give Hg(UF6)2,6CH3CN, and no U(Vl) species is isolated. CUF2 and UF6 give a mixture of U(V) and U(VI) compounds and the equilibrium UF8 2- + UF5↔ UF7- +UF6- is believed to exist in the reaction mixture, CuF2. 4CH3CN. 4IF5 behaves as a fluoride ion donor towards PF5 and WF6 in CH3CN. The PF6- ion was detected in solution by 19F, and 31P I. N. D. O. R. nmr spectroscopy, while WF7- was observed in both 19F nmr and Raman spectra. However, the reactions between CuF2, 4CH3CN, 4IF5 and ReF6 and UF6 in IF5 are much less straightforward. The products were not completely characterised, but fluorido ion addition is at most only a side reaction. This may indicate that UF6 and ReF6 are poorer F-acceptors than PF5 and WF6. Another explanation is that despite the F- ion donor properties of CuF2. 4CH3CN,4IF5 in CH3CN, it does not behave as such in IF5 The co-ordinated CH3CN in CuF2. 4CH3CN. 4IF5 remains unattacked, despite high concentrations of ReF6 or UF6 and a long period of reaction.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Inorganic chemistry
Date of Award: 1976
Depositing User: Enlighten Team
Unique ID: glathesis:1976-78737
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:57
Last Modified: 30 Jan 2020 14:57
URI: http://theses.gla.ac.uk/id/eprint/78737

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