Browsing by Author "Symons, Martyn C. R."

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Infrared Studies of Halide Ion Solvation in Methanol1
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (08), 1978) Strauss, Imants M.; Symons, Martyn C. R.
Concentrated solutions of alkali halides in methanol at low temperature have infrared spectra in the O—H stretching region that are dominated by features assigned to solvent shared ion-pairs [graphic omitted]. Such units cannot form in concentrated solutions of tetra-alkylammonium halides, but their low-temperature infrared spectra nevertheless show up to six resolved O—H features. These are assigned to a range of anion solvates in which both primary and secondary solvation has been reduced relative to dilute solutions. On warming, these features rapidly broaden and merge into a single very broad feature. (Dilute solutions of CH3OH in CH3OD were used to avoid intermolecular coupling effects). Solutions of tetra-alkylammonium halides in methylene chloride, on the addition of methanol gave mainly the mono-solvate at ambient temperatures, but on cooling, marked aggregation was observed, and several of the features obtained from methanolic solutions were again detected. Addition of water in low concentrations resulted in rapid loss of features assigned to terminal methanol molecules and also of features assigned to primary solvent molecules. The rôle of these water molecules may be to form linked units of anions, or possibly, cyclic units containing fewer terminal solvent molecules and fewer primary methanol molecules.
Low temperature infrared spectroscopic study of the solvation of ions in water
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Strauss, Imants M.; Symons, Martyn C. R.
In general, when aqueous electrolyte solutions are frozen, the infrared spectrum in the O–H stretching region reveals narrow bands assignable to ice and to salt hydrates. Using as solvent dilute solutions of HOD in D2O, we have detected several novel hydrate bands using this procedure. However, in some cases, glassification occurred, and in others it could be achieved using certain dilute additives, such as t-butyl alcohol. These glasses gave bands which were appreciably narrower than those for the solutions at 0°C, and consequently, two or more features could sometimes be resolved. This has enabled us to assign bands to HOD molecules hydrogen bonded to the halide ions and to various oxyions. These bands were all on the high frequency side of the main water band and were generally narrower than this band. The shift is discussed in terms of the number of primary and secondary solvent molecules associated with the anions, and the narrowing in terms of the precision of anion hydrogen bonding. In contrast, most cations simply induce a small shift in the broad water band, which may be to high or low frequencies. This shows that the spectral properties of water molecules bound to the cations are dominated by the other water molecules to which each is hydrogen bonded. At high concentrations of salt, new bands were obtained, shifted from the position of the anion solvate band by the cations. These are assigned to solvent shared ion-pairs.
Reaction between ethylene and O– ions on the surface of magnesium oxide
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (07), 1977) Taarit, Younes Ben; Symons, Martyn C. R.; Tench, Anthony J.
Interaction between ethylene and O– centres on magnesium oxide surfaces gives a radical having a nearly isotropic hyperfine coupling to two equivalent hydrogen atoms (58 G), a very weak coupling to a single proton, and strong coupling to 13C which indicates nearly unit spin-density in a 2p orbital on a single carbon atom. These results agree with expectation for H2C[double bond, length as m-dash]Ċ– anions, isoelectronic with the relatively stable H2C[double bond, length as m-dash]N radical in every respect. We suggest that after initial abstraction to give H2C[double bond, length as m-dash]ĊH radicals (not detected), ionization of the acidic acetylenic type proton occurs but this remains hydrogen-bonded to the radical anion: H2C[double bond, length as m-dash]Ċ–—HO–. In contrast, reaction of ethylene oxide with F+s centres on the surface gave H2Ċ—CH2O– radicals.
Solvation Spectra: Part 53—Infrared and Nuclear Magnetic Resonance Studies of the Tetrahydroborate Anion in various Pure Solvents and Binary Aqueous Mixtures
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (09), 1977) Strauss, Imants M.; Symons, Martyn C. R.; Thompson, Vicky K.
Borohydride salts have been studied in various solvents by infrared and n.m.r. spectroscopy. Solutions in water containing HOD in low concentration exhibit an O—D stretching frequency profile indicative of relatively strong hydrogen bonding to the anion, comparable with that for chloride ions. The asymmetric B—H stretching band for BH–4(v3) is a broad singlet in water (∼2270 cm–1) but shifts strongly to lower frequencies as basic aprotic solvents, such as hexamethylphosphoramide, are added. This is again indicative of “hydrogen-bonding” to the anions by water. The proton resonance for water shifts linearly on adding borohydride salts and from this shift and previously estimated cation shifts, a molal shift for BH–4 in water of + 0.08 p.p.m. has been derived. This falls between the shifts induced by chloride and bromide ions. The 1H resonance for the anion in water (a multiplet from coupling to the two types of magnetic boron nuclei, 10B and 11B) moves up-field as basic aprotic solvents are added after a small initial down-field shift or plateau. Heating also causes an up-field shift. We conclude that hydrogen-bonding induces a down-field shift which parallels the low-frequency shift in v3. Possible structures for the hydrogen-bonded complex are considered. In contrast, addition of t-butyl alcohol or triethylenediamine to aqueous borohydride solutions induces a rapid down-field shift. This is interpreted in terms of clathrate cage formation.