Sandra E. Dann

Structure and oxygen stoichiometry in Sr3Fe2O7−y, 0 ≤ y ≤ 1.0

Abstract Powder neutron diffraction has been used to determine the structure of four compounds from the series Sr 3 Fe 2 O 7− y , y = 0, 0.25, 0.42, and 1.0. All these compounds crystallize with structures based on that of Sr 3 Ti 2 O 7 with oxygen systematically removed from a site linking the FeO 6 octahedra together. Complete removal of oxygen from this site produces an unusual, square-pyramidal coordination around each iron(III) ion and a stoichiometry of Sr 3 Fe 2 O 6 ; this compound is isostructural with La 2 SrCu 2 O 6 . A bond valence parameter, R 0 , for Fe 4+ has been derived as 1.788(2) A.

Experimental Evidence for the Involvement of Dinuclear Alkynylcopper(I) Complexes in Alkyne–Azide Chemistry

Dinuclear alkynylcopper(I) ladderane complexes are prepared by a robust and simple protocol involving the reduction of Cu(2)(OH)(3)OAc or Cu(OAc)(2) by easily oxidised alcohols in the presence of terminal alkynes; they function as efficient catalysts in copper-catalysed alkyne-azide cycloaddition reactions as predicted by the Ahlquist-Fokin calculations. The same copper(I) catalysts are formed during reactions by using the Sharpless-Fokin protocol. The experimental results also provide evidence that sodium ascorbate functions as a base to deprotonate terminal alkynes and additionally give a convincing alternative explanation for the fact that the Cu(I)-catalysed reactions of certain 1,3-diazides with phenylacetylene give bis(triazoles) as the major products. The same dinuclear alkynylcopper(I) complexes also function as catalysts in cycloaddition reactions of azides with 1-iodoalkynes.

Alkynylcopper(I) polymers and their use in a mechanistic study of alkyne–azide click reactions

Polymeric dinuclear alkynylcopper(I) complexes, for example phenylethynylcopper(I), can be prepared by a robust method involving the interaction of terminal alkynes with copper(II) salts in acetonitrile. The use of the ladder polymers provides heterogeneous catalysts for copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions and provides important mechanistic information.

Structure and magnetic properties of Sr2FeO4 and Sr3Fe2O7 studied by powder neutron diffraction and Mössbauer spectroscopy

Sr2FeO4 and Sr3Fe2O7 have been studied using low-temperature powder neutron diffraction, magnetometry and 57Fe Mossbauer spectroscopy. Sr2FeO4 orders antiferromagnetically at 60 K whilst the Neel temperature of Sr3Fe2O7 is 110 K. At room temperature the Mossbauer spectrum of Sr3Fe2O7 is interpreted in terms of a disproportionation, Fe4+↔ Fe3++ Fe5+, though neutron diffraction measurements show a single, crystallographic iron site. Neutron diffraction data collected below the Neel temperatures from Sr2FeO4(4 K) and Sr3Fe2O7(6 and 90 K) only show broad weak magnetic reflections indicative of antiferromagnetic ordering in two dimensions. Mossbauer data collected below TN from Sr2FeO4 indicate the presence of at least four magnetically different Fe4+ sites.

Hydrothermal synthesis of zeolites

Recent developments have included the synthesis of new, large pore zeolite structures, zeotypes and metal substituted zeolites, along with the in situ investigation of zeolite synthesis and control of morphologies. In terms of new zeolite structures there is increasing realisation of the aim to specifically design templates to control zeolite structures, and the use of the fluoride ion as a mediating agent has been influential. In terms of zeotypes considerable effort has been directed at transition metal containing systems, particularly those of cobalt, with the potential to generate redox active catalytic centres. Growth of zeolite films on substrates has also been developed and progress is being made in studying directly, using diffraction and NMR techniques, the crystallisation of zeolites.

Investigation of zeolite scales formed in the Bayer process

Synthetic sodium aluminosilicate Bayer refinery scale has been prepared in 8 and 4.2 M sodium hydroxide solutions at four temperatures in the temperature range 80–240°C. The effect of different anions (CO32−, OH− SO42−, Cl− and C2O42−) and varying anion concentrations (10−2–10−1 M) on the type of aluminosilicate phase formed has also been investigated. These synthetic phases have been compared with industrial scale formed in different parts of low and high temperature Bayer processing plants. Synthetic and plant scales were both characterised using powder X-ray diffraction, IR spectroscopy and SEM. The plant scale crystallises as two different zeolitic aluminosilicate phases, depending on the temperature in the area of the plant. This behaviour has been shown to closely mirror the formation of synthetic scale in sodium hydroxide solutions containing the carbonate anion. The large concentration of organic ions present in Bayer liquor appear to have little effect on the type of scale formed and are relatively insignificant in promoting scale formation.

The synthesis and structure of Sr2FeO4

Abstract Strontium ferrate(IV), Sr2FeO4, crystallizes with a tetragonal unit cell, I4 mmm , a = 3.8642(1), c = 12.3968(2) A, and V = 185.1 A3. The structure of this compound is of the K2NiF4 type as refined by Rietveld analysis of powder X-ray diffraction data. This material contains iron(IV) in a very slightly distorted octahedral environment (4 × 1.93) + (2 × 1.95).

The structure and oxide/fluoride ordering of the ferroelectrics Bi2TiO4F2 and Bi2NbO5F

The structures of two complex layered oxide-fluorides have been determined from the analysis of room temperature X-ray and constant wavelength neutron powder diffraction data. Bi2TiO4F2 and Bi2NbO5F adopt a single layer Aurivillius-type structure with an ordered array of fluoride/oxide anions. The structure of Bi2TiO4F2 has also been studied at 24 K using time-of-flight neutron powder diffraction, which is well below the previously reported ferroelectric transition temperature. The structures of both materials can be described in the tetragonal space group I4/mmm, but show significant atomic displacements from the positions described in the original structural models proposed for these compounds as a result of disordered tilts and/or distortions of the M(O,F)6 octahedra. No three-dimensional long-range ordered structural distortion was observed upon cooling of Bi2TiO4F2 to 24 K. 19F MAS NMR data have been collected and support the presence of only one fluoride site. Bond valence calculations allow the assignment of the oxide and fluoride ions within the structure, and the proposed model has the fluoride ions located in the equatorial sites of the titanium or niobium octahedra.

The effect of the cation composition on the synthesis and properties of ultramarine blue

Abstract The effect of potassium cations on the shade of the ultramarine blue pigment system has been investigated through analysis of commercial materials, ion exchange reactions of sodium-form ultramarine blue and a detailed study of the effect of adding potassium sources to ultramarine precursor mixtures. Incorporation of potassium cations has the result of producing redder shade material and the replacement of around 20% of the sodium in the standard reaction mixture produces the optimised red-shade pigment. The origin of this hue control may be a direct effect, involving interaction of potassium ions with the ultramarine blue structure and the S3− chromophore or, more likely, potassium ions aids the stabilisation of S3− within the sodalite framework during the ultramarine blue formation process. In the commercial process, the role of the potassium source in red shade formation may be performed by the incorporation of potassium-rich feldspar additives.

Antisolvent crystallization of pharmaceutical excipients from aqueous solutions and the use of preferred orientation in phase identification by powder X-ray diffraction

Crystallization of lactose from 10% (w/v) aqueous solutions was investigated with the use of polar antisolvents. Crystal growth was observed at 50-65% antisolvent content and showed a morphological transition from a polyhedral to needle-like habit with increasing antisolvent content, which coincided with a polymorphic transition from alpha lactose monohydrate (Lα·H(2)O) to beta lactose (Lβ). Where dehydrating antisolvents were employed such as methanol and ethanol, evidence of Lα·H(2)O dehydration to form Lα(S) was also observed at 95% antisolvent content. Powder X-ray diffraction (PXRD) analysis of the crystals highlighted the preferred orientation effects exhibited by large crystals of this kind, indicating the difficulties experienced by the non-specialist when performing phase identification of lactose polymorphs. The same studies were applied to raffinose pentahydrate, trehalose dihydrate and mannitol to assess the effects of crystallization conditions on other pharmaceutical excipients.