A. Thompson

P CO2 in low-grade metamorphism; zeolite, carbonate, clay mineral, prehnite relations in the system CaO-Al2O3-SiO2-CO2-H2O

AbstractEquilibria for several reactions in the system CaO-Al2O3-SiO2-CO2-H2O have been calculated from the reactions calcite+quartz=wollastonite+CO2 (5) and calcite+Al2SiO5+quartz=anorthite+CO2 (19) and other published experimental studies of equilibria in the systems Al2O3-SiO2-H2O and CaO-Al2O3-SiO2-H2O.The calculations indicate that the reactions laumontite+CO2=calcite+kaolinite+2 quartz+2H2O (1) and laumontite+calcite=prehnite+quartz+3H2O+CO2 (3) in the system CaO-Al2O3-SiO2-CO2-H2O, are in equilibrium with an H2O-CO2 fluid phase having

THE REACTIONS OF NIOBIUM AND TANTALUM PENTACHLORIDES WITH TRIPHENYLPHOSPHINE AND TRIPHENYLARSINE OXIDES

{\text{X}}_{{\text{CO}}_{\text{2}} }

A thermochemical and spectroscopic investigation of some molecular addition complexes of niobium and tantalum pentachlorides with oxygen- and sulphur-containing ligands

∼-0.0075 for Pfluid=Ptotal=2000 bars.These calculations limit the stability of zeolite assemblages to low p CO2.Using the above reactions as model equilibria, several probelms of p CO2 in low grade metamorphism are discussed. (a) the problem of producing zeolitic minerals from metasedimentary assemblages of carbonate, clay mineral, quartz. (b) the significance of calcite (or aragonite) associated with zeolite (or lawsonite) in low grade metamorphism and hydrothermal alteration. (c) the reaction of zeolites (or lawsonite) with calcite (or aragonite) to produce dense Ca-Al-hydrosilicates (eg. prehnite, zoisite, grossular).

COMPLEXES OF NIOBIUM AND TANTALUM HYDROXIDES WITH DI-OLS

Abstract The reactions of dimethyl sulphoxide and diphenyl sulphoxide with niobium and tantalum pcntachlorides and pentabromides have been investigated. The reactions involve abstraction of the oxygen atom of the sulphoxide group by the metal atom, to form the corresponding oxyhalide and halogen substituted sulphides, together with co-ordination of further molecules of the sulphoxide to the oxyhalide. The oxyhalide-sulphoxide adducts have been isolated and characterised by analysis, m.p. and a study of their infra-red spectra.

Some phosphine oxide and sulphoxide complexes of Nb(V), Mo(V) and W(VI) oxochlorides

Abstract The reactions of niobium and tantalum pentachlorides with excess of triphenylphosphine oxide, triphenylarsine oxide or their hydrogen peroxide adducts, are similar to the reactions of these pentahalides with sulphoxides, in that they involve abstraction of oxygen from the oxides, to form metal oxytrichlorides to which are co-ordinated additional molecules of the undecomposed ligand. The co-products of the reactions are dichlorotriphenylphosphine and dichlorotriphenylarsine respectively. When the triphenylphosphine hydrogen peroxide adduct is used as a reactant however, the dichlorotriphenylphosphine is quantitatively oxidised with liberation of chlorine gas; by contrast, dichlorotriphenylarsine is not oxidised and can be isolated from the reaction with the triphenylarsine hydrogen peroxide adduct. Tantalum pentabromide undergoes a similar reaction with triphenylarsine oxide, the dibromotriphenylarsine being unoxidised by the hydrogen peroxide adduct. No corresponding abstraction of sulphur from triphenylphosphine sulphide by niobium pentachloride appears to occur, preliminary experiments indicating the formation of a 1:1 complex.

The reactions of tetramethylurea and tetramethylthiourea with niobium(V) and tantalum(V) halides

Abstract Dimethylsulphoxide reacts with niobium and tantalum pentafluorides to form the stable 1:2 adducts NbF 5 ,2(CH 3 ) 2 SO and TaF 5 ,2(CH 3 ) 2 SO. The densities, viscosities and electrical conductivities of these complexes in the molten state have been measured over a range of temperatures. The results indicate a high degree of molecular complexity and also of self-dissociation in the liquids.

Halo-alkoxide complexes of niobium(V) and tantalum(V)

Abstract The results of a calorimetric and spectroscopic investigation of the complexes formed between NbCl5, TaCl5 and the ligands Et2O, Et2S, MeCN, POCl3, TBP, HMPA and TPPO are reported and analysed in terms of metal-igand bond strengths and relative acceptor and donor abilities.

Preparation, characterization and reactions of vanadium(IV) β-diketonate complexes

Abstract The dissolution of niobium and tantalum hydroxides in alkaline solutions of catechol and other 1–2,di-ols has been studied and solid crystalline products isolated. These show some variability in composition consequent upon the polynucleation of the metal hydroxide through ageing. Under appropriate conditions such compounds as (NH4)3[Nb(OH)2(C6H4O2)3].H2O may be isolated. This compound absorbs at 340 mμ in ethanol but is immediately hydrolysed in water or aqueous alkali and subsequently, within certain limits of OH- concentration, a species absorbing at 310 mμ — probably a 1: 1 complex and containing polynuclear niobic acid units — is slowly formed. Infra-red absorption measurements give no evidence of the presence of a niobyl radicle, NbO, in the solids. Tantalum hydroxide is much less easily dissolved in catechol than niobium hydroxide and the products contain about 5 moles of catechol to each tantalum atom.