Date of Award
Doctor of Philosophy (PhD)
Professor T. Birchall
Reactions of stannane or methylstannanes (CH₃)₄_nSnHn (n = 1-4) in fluorosulphuric acid at low temperatures (-85°C) produce [(CH₃)₃_nSnHn]⁺ (where n = 0→3) and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy have been used in their characterization. Hydrogen evolution, ¹¹⁹Sn NMR and Mössbauer spectroscopic evidence is presented to show that at higher temperatures these species decompose to Sn²⁺, Sn²⁺ plus (CH₃)₂Sn²⁺ and (CH₃)₂Sn²⁺ depending on the starting hydride. Tin-119 NMR spectra of dialkyltin cationic species in strong acid solutions are field dependent. Relaxation time measurements at three different magnetic fields have established that the dominant spin-lattice relaxation mechanism for these species at higher magnetic field is shielding anisotropy. A comparison of spin-lattice and spin-spin relaxation rates indicates that at ambient temperature a rapid chemical exchange process is occuring. In the case of the (CH₃)₂Sn(SO₃F)₂-HSO₃F system, variable temperature ¹¹⁹Sn NMR spectra reveals the presence of three tin species which are involved in this exchange process.
Tin-119 NMR data for a series of tin(lI) and tin(IV) acid derivatives have been determined. Tin(II) compounds exhibit a wide range of chemical shifts varying from -617 ppm to -1628 ppm, whereas tin(IV) derivatives cover a narrow range around -800 ppm. Stoichiometric mixtures of tin(II) and tin(lV) derivatives of the same acid have been analysed by ¹¹⁹Sn NMR and Mössbauer spectroscopy. Reaction occurs only between Sn(OCOCF₃)₂ and Sn(OCOCF₃)₄ to form a mixed valence tin(II), tin(lV) compound. Partial oxidation of Sn(OCOCF₃)₂ results in the formation of a mixed valence tin compound whose structure has been determined by X-ray crystallography to be [Sn(II)₄Sn(IV)O₂(O₂CCF₃)₈]. This structure consist of discrete noncentrosymmetric units with point group S₄, the central feature of which is a Sn(11)₄Sn(lV)O₂ unit containing two μ₃ oxygen atoms which each form a bridge between a Sn(lV) atom and two symmetry related Sn(lI) atoms. Among the two pairs of Sn(ll) atoms, each pair is bridged by two trifluoroacetates.
A systematic route has been established in the preparation of mixed valence tin compounds by the reaction of SnF₂ with tin(lV) carboxylates. These reactions have been followed by ¹⁹F and ¹¹⁹Sn NMR spectroscopy. In one case an X-ray crystal structure determination showed the compound to be [Sn(lI)₂Sn(lV)₂F₄(O₂CCF₃)₈2CF₃CO₂H]. This consists of eight membered rings with alternating Sn(II) and Sn(IV) atoms bridged by fluorine and trifluoroacetate groups.
Manivannan, Veeragathy, "Structural Studies of Tin Compounds in Acid Media" (1986). Open Access Dissertations and Theses. Paper 1061.