Laurence McGhee

Oxidation of molecular bromine by uranium hexafluoride in acetonitrile. Preparation and properties of hexafluorouranates(V) containing positive bromine

Abstract Molecular bromine is oxidized by uranium hexafluoride in acetonitrile at ambient temperature. The product is formulated on the basis of its spectra, and its brominating an oxidizing abilities as [Br(C 6 H 9 N 3 )][UF 6 ] in which bromine is bound to an acetonitrile trimer containing C=N bonds.

Iodine and molybdenum K-edge extended X-ray absorption fine structure of some iodine(I) hexafluoromolybdates(V) in the solid state and in acetonitrile solution

Abstract Iodine and molybdenum K-edge extended X-ray absorption fine structure of the compounds [I(NCMe) 2 ][MoF 6 ], [I(py) 2 ][MoF 6 ],[I(py) 2 ][NO 3 ] and [Ag(py) 4 ][MoF 6 ] provide good evidence for the discrete ions [IL 2 ] + , L=MeCN or py, having linear N-I-N skeletons with I-N distances in the range 2.16–2.22 A, and octahedral [MoF 6 ]- with an Mo-F distance of 1.78±0.02 A, both in the solid state and in acetonitrile solution.

Oxidation of tellurium 'by molybdenum and uranium hexafluoride in acetonitrile and reactions between uranium hexafluoride and dichlorine or hydrogen chloride in acetonitrile☆

Abstract Reactions between elemental tellurium and UF6 or MoF6 at room temperature lead to the isolation of solid products formulated as [TeIVF3(NCMe)2][MVF6][MVF5(NCMe)]3 (MMo or U) on the basis of their spectroscopic properties. In contrast, oxidation of Te by SbF5, AsF5 or the [NO]+ cation in MeCN appears to be limited to the formation of the [Te4]2+ cation. Uranium hexafluoride is reduced to [UF5(NCMe)] in the presence of Cl2 or HCl in MeCN, the reduction being followed by Cl-for-F exchange to give [UF5−xClx(NCMe)] mixtures. A rationalization of these reactions is presented.

Chemomechanical polishing of lithium niobate using alkaline silica sol and alkaline silica sol modified with hydrogendifluoride anion

Lithium niobate undergoes a slow reaction with anhydrous HF at room temperature to give LiNbOF4, which is readily hydrolysed to give Nb2O5 as one product. This sequence of reactions is believed to be responsible for the superior performance of aqueous alkaline silica sol modified by the addition of [HF2]– for the Chemomechanical polishing of LiNbO3 wafers, compared with silica sol alone.

Chemomechanical polishing of gallium arsenide and cadmium telluride to subnanometre surface finish. Evaluation of the action and effectiveness of hydrogen peroxide, sodium hypochlorite and dibromine as reagents

Aqueous hydrogen peroxide and sodium hypochlorite in the pH range 7–9 are more effective Chemomechanical polishing reagents for gallium arsenide than is dibromine in methanol. Sodium hypochlorite is an acceptable alternative to hydrogen peroxide for gallium arsenide: it also produces good-quality surface finishes on cadmium telluride over the same pH range. The results of dip–etch and polishing reactions, studied using [82Br]-labelled dibromine, atomic absorption spectroscopy (AAS) and pH or concentration variation, are used to propose a model for Chemomechanical polishing of these materials.

Direct evidence for the formation of a passivating layer during chemomechanical polishing of silica by a hydrogen difluoride-based reagent

The sparingly soluble material (the passivating layer) formed during chemomechanical polishing of silica wafers by [HF2]––cerium(IV) oxide–sucrose mixtures at low pH has been identified as K2SiF6 coated with a thin silica layer.

IR laser degradation of some fluoro-polymers

Abstract The degradation of three fluoro-polymers, poly(chlorotrifluoroethene) Kel-F, poly(vinylidene difluoride) (PVDF) and poly(perfluoro-ethene-propene) (FEP) by CW CO 2 laser irradiation in vacuo results in the formation of small fluorocarbons and solid materials. The latter have been characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Exploratory investigations of the ability of selected materials to adsorb/absorb Br 2 and anhydrous HF and the reaction between a PVDF film and aluminium are reported.

Oxidation of tellurium by high oxidation state fluorides in acetonitrile

Abstract Elemental I 2 is oxidised by either MoF 6 or UF 6 in MeCN at ambient temperature to give solid [I(NCMe) 2 ][MF 6 ], M = Mo or U [1]. Bromine under similar conditions is oxidised by UF 6 to give [Me CN-(Me)CN Br] - [UF 6 ] in which ‘positive’ Br is bound to a CN trimer [2]. A third type of cation is formed by oxidation of Te using either MoF 6 or UF 6 . The products are crystalline solids which are formulated on the basis of their analyses, 125 Te n.m.r., vibrational and electronic spectra as [TeF 3 (NCMe 6 ], 3MF 5 NCMe, M = Mo or U. Similar reactions occur between Mo or W metals and MoF 6 or WF 6 to give MF 5 . NCMe and this aided the characterisation of the Te-containing salts. Although SbF 5 and AsF 5 are strong oxidising agents in acidi media [3], the complexes SbF 5 NCMe and AsF 5 .NCMe are weak oxidising agents in MeCN. Oxidation of Te by these species is limited to the formation of Te 4 2+ . The NO + cation shows intermediate behaviour hence the order of oxidising ability experimentally established in MeCN is UF 6 > MoF 6 > NO + > SbF 5 .NCMe, AsF 5 .NCMe.

Halogen etching of group 13-15 (3-5) semiconductors and its relevance to chemical-mechanical polishing. The reactions of dibromine, dichlorine and sodium hypochlorite with gallium arsenide and related materials

Room-temperature etching of gallium arsenide, gallium antimonide, indium phosphide, indium arsenide and indium antimonide by dibromine or dichlorine has been studied under anhydrous conditions using Raman spectroscopy to identify the primary products and radiotracers, [82Br] or [36Cl], to probe interactions among the species formed. Comparisons are drawn with etching behaviour in solution particularly with sodium hypochlorite towards GaAs for which the reactive species at pH<8.0 is shown to be Cl2 . Under anhydrous conditions the GaAs surface is passivated rapidly owing to the formation of an involatile liquid layer, believed to be a solution of Ga2Cl6 in AsCl3 . Above pH=8.0, where the dominant etchant is believed to be [OCl]– , an active surface, in which considerable reconstruction has occurred, is formed. The etching behaviour has enabled the chemomechanical polishing of 13–15 semiconductors by Br2 and NaOCl based reagents to be rationalised. In particular, it is shown that the alumina component of a NaOCl-based polishing reagent has a minimal chemical role.

Co-ordination chemistry of iodine(I) with tetraazamacrocycles or monodentate ligands. Comparisons with bromine(I) and with some d-block metals

Co-ordination compounds of iodine(I), including those with tetraazamacrocyclic ligands, have been prepared either by direct reaction with the [I(NCMe)2]+ cation or by the previously reported ligand-induced disproportionation reaction of I2. The syntheses and the properties of the iodine complexes so prepared are compared with analogous work involving bromine, iron(II) or copper(II).