The topotactic reduction of the oxychloride Sr(3)Fe(2)O(5)Cl(2) with LiH results in the formation of Sr(3)Fe(2)O(4)Cl(2). Neutron powder diffraction data show that Sr(3)Fe(2)O(4)Cl(2) adopts a body-centered tetragonal crystal structure (I4/mmm, a = 4.008(1) Å, c = 22.653(1) Å at 388 K) with anion vacancies located within the SrO layer of the phase. This leads to a structure consisting of infinite sheets of corner-sharing Fe(II)O(4) square planes. Variable-temperature neutron diffraction data show that Sr(3)Fe(2)O(4)Cl(2) adopts G-type antiferromagnetic order below T(N) ∼ 378(10) K with an ordered moment of 2.81(9) μ(B) per iron center at 5 K consistent with the presence of high-spin Fe(II). The observed structural and chemical selectivity of the reduction reaction is discussed. The contrast between the structure of Sr(3)Fe(2)O(4)Cl(2) and the isoelectronic all-oxide analogue (Sr(3)Fe(2)O(5)) suggests that by careful selection of substrate phases, the topotactic reduction of complex transition metal oxychlorides can lead to the preparation of novel anion-deficient phases with unique transition metal-oxygen sublattices which cannot be prepared via the reduction of all-oxide substrates.

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Reduction of La(1-x)Ca(x)MnO(3) (0.6 ≤ x ≤ 1) perovskite phases with sodium hydride yields materials of composition La(1-x)Ca(x)MnO(2+δ). The calcium-rich phases (x = 0.9, 1) adopt (La(0.9)Ca(0.1))(0.5)Mn(0.5)O disordered rocksalt structures. However local structure analysis using reverse Monte Carlo refinement of models against pair distribution functions obtained from neutron total scattering data reveals lanthanum-rich La(1-x)Ca(x)MnO(2+δ) (x = 0.6, 0.67, 0.7) phases adopt disordered structures consisting of an intergrowth of sheets of MnO(6) octahedra and sheets of MnO(4) tetrahedra. X-ray absorption data confirm the presence of Mn(I) centers in La(1-x)Ca(x)MnO(2+δ) phases with x < 1. Low-temperature neutron diffraction data reveal La(1-x)Ca(x)MnO(2+δ) (x = 0.6, 0.67, 0.7) phases become antiferromagnetically ordered at low temperature.

The kinetics of the hydrolysis of the oleate ester of polyoxyethylene (20) sorbitan (Tween 80) in aqueous buffers were studied at an initial concentration of0.020% (w/v) and over the pH range of 1.10 to 10.28. The hydrolysis appears to be specific acid-catalysed at pH va!ues below 3 and specific base-catalysed at pH values greater than 7.6. The pseudo first-order rate constants for hydrogen and hydroxyl ion catalysis were determined, and the temperature and ionic strength dependence of the acid-catalysed reaction was studied. Both the initial, acid-and base-catalysed hydrolysis of Tween 80 exhibited an unusual initial, micellar surfactant concentration-rate dependence, opposite to that previously reported for the hydrolysis of anionic surfactants of the n-alkyl sulphate-type. Specifically, as the initial concentration of Tween 80 was increased above its reported critical micellar concentration, there was a progressive, marked decrease in the rate of the reaction, with the rate eventually reaching a plateau value between 0.100 and 1.00% (w/v); It is suggested that this behaviour is due to alterations in the micellar state of the surfactant as its concentration is increased. The influence of the chemical structure of the Tween surfactant on the acid-catalysed hydrolysis reaction at 80" was also examined using the oleate (Tween 80), stearate (Tween 60), and palmitate (Tween 40) esters of polyoxyethylene (20) sorbitan.Tweens are non-ionic surface-active mono-fatty acid esters of polyoxyethylene sorbitan, usually containing approximately 20 moles of ethylene oxide. Because of their high surface activity and relatively low toxicity, they have been used as solubilizers, wetting agents, and emulsifiers in pharmaceuticals. However, their ability to function effectively in these products depends on the chemical stability of the ester linkage of the monomer.There is a paucity of quantitative information on the degradation kinetics of nonionic surfactants of the Tween-type (Aoki, Hiroshi & Ise, 1968). We have examined the kinetics of hydrolysis of some esters of polyoxyethylene sorbitan. MATERIALS A N D METHODS MaterialsPolyoxyethylene (20) sorbitan mono-oleate (Tween 80), mono-stearate (Tween 60), and mono-palmitate (Tween 40) were supplied by the Atlas Powder Company (Wilmington, Del., U.S.A.) and were used as received. All other chemicals were of reagent grade quality.

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The low-temperature topotactic reduction of Sr(3)Fe(2-x)Co(x)O(5)Cl(2) oxychloride phases with LiH allows the preparation of phases of composition Sr(3)Fe(2-x)Co(x)O(4)Cl(2) (0 ≤ x ≤ 1). The reduced phases adopt body-centered tetragonal structures which are isostructural with Sr(3)Fe(2)O(4)Cl(2) and contain square-planar (Fe/Co)O(4) centers connected into apex-linked sheets, analogous to the CuO(2) sheets present in superconducting cuprate phases. As the cobalt concentration in Sr(3)Fe(2-x)Co(x)O(4)Cl(2) is increased the antiferromagnetic order of the Sr(3)Fe(2)O(4)Cl(2) host phase is suppressed, ultimately leading to spin-glass behavior, at low temperature, in Sr(3)Fe(2-x)Co(x)O(4)Cl(2) phases with x ≥ 0.8. The limited influence of cobalt substitution on the reactions which form the Sr(3)Fe(2-x)Co(x)O(4)Cl(2) phases is discussed and contrasted to that of the related SrFeO(3-δ)-SrFeO(2) system.

When samples of certain teas were analysed for lead, repeat determinations made on the same samples showed a wide variation in the results. This was found to be due to dust particles, with a high lead content, which were dispersed throughout the tea leaves. Further work showed that there was also more iron, zinc and copper in the dust than in the leaves. Analyses of tea prepared as for drinking showed that only a small amount of the lead, cadmium, nickel, iron, zinc and copper present in the leaves passed into the brew. The proportion of each metal extracted into the brew appeared to be independent both of the strength of brew and of the type of water used. Work with tannic acid solution indicated that soluble polyphenols could be responsible for complexing metals.

A simple rapid method for the spectrophotometric determination of 0 to 2-5-pg amounts of fluoride with an accuracy of better than 0.1 pg is described. The stability and purity of the reagents have been studied and the optimum conditions for the sensitivity of the reaction established. The method can be applied to the analysis of aqueous solutions either directly or, if there are interferences, after a simple micro distillation.