Andrew M. Fogg

A novel family of layered double hydroxides—[MAl4(OH)12](NO3)2·xH2O (M = Co, Ni, Cu, Zn)

A class of layered double hydroxides with the layer composition [MAl4(OH)12](NO3)2·xH2O, where M = Zn, Cu, Ni and Co, has been synthesised for the first time and its anion exchange chemistry explored. These materials are related to the minerals chalcoalumite, mbobomkulite and nickelalumite (see M. Fleischer, R. G. Burns, L. J. Cabri, C. A. Francis and A. Pabst, Am. Miner., 1982, 67, 413).

High pressure bulk synthesis and characterization of the predicted multiferroic Bi(Fe1∕2Cr1∕2)O3

Bi(Fe1∕2Cr1∕2)O3, a recently proposed candidate multiferroic perovskite, is prepared in a bulk form by high pressure solid-state synthesis. The material is isostructural with polar BiFeO3 but is paramagnetic at room temperature due to disorder of the Fe3+ and Cr3+ cations on the B site. Mossbauer and magnetization measurements show a transition to a cooperative magnetic state below 130K.

Intercalation chemistry of the novel layered double hydroxides [MAl4(OH)12](NO3)2·yH2O (M = Zn, Cu, Ni and Co). 1: New organic intercalates and reaction mechanisms

The intercalation chemistry of a recently synthesized family of layered double hydroxides, [MAl4(OH)12](NO3)2·yH2O (M = Zn, Cu, Ni, Co), has been explored. A range of dicarboxylates, mono- and disulfonates have been intercalated successfully, and the resulting materials fully characterised. The interlayer spacing of the dicarboxylates is found not to vary linearly with the length of the carboxylate chain, but instead the acid species are arranged so that the ends of the dicarboxylate chains point directly at the localized metal atoms in the layers. In situ diffraction experiments have been performed to investigate the kinetics and mechanisms of the intercalation processes. The dicarboxylates are found to intercalate very quickly, with the reactions being complete within a few minutes at room temperature. In contrast, the sulfonates intercalate more slowly, and quantitative kinetic parameters may be measured for these reactions. All the reactions were found to be direct one-step transformations. The sulfonate intercalation processes are proposed to be nucleation controlled in the vast majority of cases for the M = Zn, Cu and Co materials, with the rate limiting step being the expansion of the interlayer space to accommodate the relatively large organic guest anions. In contrast, the reactions of the M = Ni LDH are found to be purely diffusion controlled: as soon as the guest reaches the host particles, it intercalates.

Yb3O(OH)6Cl·2H2O: An Anion-Exchangeable Hydroxide with a Cationic Inorganic Framework Structure

The first anion-exchangeable framework hydroxide, Yb(3)O(OH)(6)Cl·2H(2)O, has been synthesized hydrothermally. This material has a three-dimensional cationic ytterbium oxyhydroxide framework with one-dimensional channels running through the structure in which the chloride anions and water molecules are located. The framework is thermally stable below 200 °C and can be reversibly dehydrated and rehydrated with no loss of crystallinity. Additionally, it is able to undergo anion-exchange reactions with small ions such as carbonate, oxalate, and succinate with retention of the framework structure.

Intercalation chemistry of the novel layered double hydroxides [MAl4(OH)12](NO3)2·yH2O (M = Zn, Cu, Ni and Co). 2: Selective intercalation chemistry

The successful intercalation of a variety of organic dicarboxylates and sulfonates into the novel LDHs [MAl4(OH)12](NO3)2·yH2O (M = Zn, Cu, Ni and Co) has recently been reported [G. R. Williams, T. G. Dunbar, A. J. Beer, A. M. Fogg and D. O’Hare, J. Mater. Chem., DOI: 10.1039/b514874j, ref. , the preceeding paper in this issue]. A number of the guests intercalated are isomeric, and the separation of mixtures of these isomers could be useful industrially. Benzenedicarboxylates and napthalenesulfonates were chosen to be the focus of these studies owing to their industrial importance. Preferential intercalation is seen for 1,4-benzenedicarboxylate over 1,2-benzenedicarboxylate, and for 2-naphthelenesulfonate over 1-naphthalanesulfonate. Optimum choice of the reaction conditions can allow almost 100% selectivity for one isomer over another in each case. The intercalation of 1,5-naphthalenedisulfonte over 2,6-naphthalenedisulfonate is found to be less selective (between 45% and 90% of the guest intercalated is 1,5-NDS dependent on the intercalation conditions). The isomer intercalated preferentially can be controlled by the reaction conditions, and by appropriate choice of conditions an almost complete separation of a mixture of these isomers is possible.

A kinetic investigation of gibbsite precipitation using in situ time resolved energy dispersive X-ray diffraction

The precipitation of gibbsite Al(OH)3 from a supersaturated caustic aluminate solution is the rate determining step in the production of alumina (Al2O3) by the Bayer process. Seeded secondary nucleation and ordered growth experiments of gibbsite from sodium, potassium and deuterated sodium aluminate solutions, at 60 and 80°C, have been investigated for the first time using the in situ energy dispersive X-ray diffraction (EDXRD) technique. Gibbsite was the only phase precipitated from sodium and potassium aluminate solutions under all experimental conditions investigated. A mixture of gibbsite and bayerite was precipitated from deuterated sodium aluminate solution at 60°C while gibbsite was the only phase observed at 80°C. Bayerite persisted over the duration of the experiment, suggesting that bayerite and gibbsite precipitated independently and that bayerite did not undergo polymorphic transformation to gibbsite. Kinetic calculations using the Cardew model indicate that seeded precipitation at 60°C is a nucleation controlled reaction with nucleation occurring more readily in potassium aluminate solutions than in corresponding sodium aluminate solutions. Calculations of the growth rate for experiments at 80°C suggest that growth occurred preferentially over nucleation. These calculations confirm that suitable experimental conditions were chosen for the promotion of either nucleation or ordered growth over the other growth processes from caustic aluminate solutions.

Superconducting intercalation compounds of metal nitride halides

The crystal structures of the layered host lattices, β-ZrNBr and β-HfNCl have been determined. They have been found to be isostructural with rhombohedral SmSI. New lithium intercalation compounds (Li x MNX; M=Zr, Hf; X=Cl, Br, I) have been prepared by treatment of either β-ZrNBr, β-HfNCl, α-ZrNBr or α-ZrNI with an excess of BuLi in hexane. These intercalates are all superconducting and show transition temperatures (T c ) of 12, 20, 11 and 11 K respectively. The lithium intercalates of the host lattices β-ZrNBr, α-ZrNBr and α-ZrNI are the first examples of intercalation into these materials.

The selective intercalation of organic carboxylates and sulfonates into hydroxy double salts

This paper reports the first systematic investigation of the selectivity of organic guest intercalation into hydroxy double salts. The organic guests 1,2- and 1,4-benzenedicarboxylate (1,2- and 1,4-BDC) have been incorporated into a range of hydroxy double salts by anion exchange. Intercalates of [Zn5(OH)8](NO3)2·yH2O, [Zn5(OH)8]Cl2·yH2O, [Zn5(OH)8](CH3COO)2·yH2O, [Zn3Ni2(OH)8](NO3)2·yH2O, and [Zn3.8Co1.2(OH)8](NO3)2·yH2O were prepared, and the resultant materials fully characterized. 1,5- and 2,6-Napthalanedisulfonate (1,5- and 2,6-NDS) were also successfully intercalated into the [Zn5(OH)8](NO3)2·yH2O material. It was found that the initial anions are almost completely replaced by the new organic guests in the majority of cases. Selected reactions were investigated by in situ X-ray diffraction, and the reactions observed to proceed directly from the host to the product largely under nucleation control. No intermediate phases were detected. The competitive intercalation of isomeric pairs of guest anions was explored, and very high degrees of preferential intercalation found for 1,4- over 1,2-BDC into all hydroxy double salts (HDSs) studied, and for 2,6- over 1,5-NDS into [Zn5(OH)8](NO3)2·yH2O. The selectivity was found to be largely invariant with reaction time, reaction temperature, solvent system, and guest concentration. It was also observed to be very similar across all the HDSs explored. In situ diffraction and NMR demonstrate that the selective intercalation is a thermodynamically controlled phenomenon. It is therefore suggested that preferential intercalation is governed in the main by the strength of the interactions between the HDS layers and the guest ions.

Synthesis and structure of pillared molybdates and tungstates with framework layers.

Six new layered lanthanide molybdate and tungstate phases pillared by either naphthalenedisulfonate (NDS) or fumarate anions have been synthesized hydrothermally and structurally characterized. Five of these materials, [Nd(H(2)O)MoO(4)](2)[2,6-NDS] (1), [Nd(H(2)O)MoO(4)](2)[1,5-NDS] (2), [La(H(2)O)WO(4)](2)[1,5-NDS] (3), [La(H(2)O)WO(4)](2)[2,6-NDS] (4), and [Ce(H(2)O)MoO(4)](2)[fumarate] (6), have a closely related cationic inorganic layer structure which comprises a bilayer of polyhedra leading to the formation of a framework layer containing small, inaccessible pores. These layers are pillared by the organic anions which also bridge between the lanthanide cations within the layers. In the La/WO(4)/2,6-NDS system, a second polymorph, [La(2)(H(2)O)(2)W(2)O(8)][2,6-NDS] (5), is observed. In this compound, the tungstate anions have dimerized, forming W(2)O(8)(4-). This dimer is unique and comprises two square-based pyramidal tungsten centers which are opposed to each other.

Structure and magnetism of the A site scandium perovskite (Sc0.94Mn0.06)Mn0.65Ni0.35O3 synthesized at high pressure

Scandium perovskite (Sc0.94Mn0.06)Mn0.65Ni0.35O3, synthesized at high pressure and high temperature, has a triclinic structure (space group ) at room temperature and ambient pressure with a √2ap×√2ap×2ap structure with α≈90°,β≈89°,γ≈90°. Magnetic measurements show that the material displays Curie–Weiss behaviour above 50 K with C=2.11 emu K mol−1 (μeff=4.11 μB per formula unit) and θ=−95.27 K. Bond valence sum analysis of the crystal structure shows that manganese is present in three different oxidation states (+2, +3, +4), with the +2 oxidation state on the A site resulting in a highly tilted perovskite structure (average tilt 21.2° compared with 15.7° calculated for LaCaMnNbO6), giving the formula .