Mark I. Ogden

Proline-functionalised calix[4]arene: an anion-triggered hydrogelator

A water-soluble, chiral calix[4]arene has been found to form hydrogels when triggered by the presence of specific anions, with efficacy linked to the Hofmeister series; the gel properties are modified by the associated cations, and gelation can be reversibly switched off by increasing pH.

A brief review of Cn-symmetric calixarenes and resorcinarenes

Calixarene and resorcinarene macrocycles are renowned for their ability to form inclusion complexes or act as molecular scaffolds. The addition of chirality to these non-planar molecules is an exciting enhancement of their already robust potential, offering much promise as ligands for chiral catalysis and enantioselective separations. Chiral calixarenes can be produced by the attachment of a chiral moiety or by the placement of an achiral functionality on the macrocyclic structure so as to render it asymmetric. The latter method is particularly intriguing, often resulting in molecules which have C n dissymmetry. This review describes examples of the C n -dissymmetric calixarenes and resorcinarenes prepared to date and discusses aspects of their chirality, including their pictorial and written descriptors.

Controlling crystal growth with modifiers

Modifying crystal growth processes using additives is a well established approach to solving problems in many processes. Nature also makes extensive use of crystalline inorganic structures modified by soluble and insoluble organic materials. This Highlight discusses some of the recent and interesting developments in this area, with an emphasis on the control of crystal growth rates, covering both inhibitors and the lesser known promoters of crystal growth. Hybrid materials resulting from the incorporation of modifiers into crystalline structures are also discussed, with an emphasis on non-classical crystallisation mechanisms, involving the oriented attachment of nanoparticles.

Investigation into the effect of phosphonate inhibitors on barium sulfate precipitation

The effect of a series of phosphonate molecules on barium sulfate precipitation was tested. While an increase in the number of phosphonate groups generally resulted in increased inhibition of barium sulfate precipitation, two notable exceptions showed that a relatively high number of phosphonate groups does not guarantee inhibition while a relatively low number of phosphonate groups does not imply no inhibition. Increasing the pH showed an increased effect of additives on barium sulfate precipitation up to pH 8. However, on increasing from pH 8 to 12, a loss of inhibition in the additives was observed which appears to be due to the barium sulfate surface changing with pH. r 2002 Elsevier Science B.V. All rights reserved.

Voltammetric and NMR studies of a bis(ferrocenecarboxamide)-substituted diaza 18-crown-6 receptor that simultaneously complexes and electrochemically recognises both cations and anions

Voltammetric and NMR investigations of a bis(ferrocenecarboxamide)-substituted diaza 18-crown-6 receptor in an aprotic environment have been carried out. This receptor molecule can complex metal cations or anions individually and can accommodate both a cation and anion. The binding of anions is significantly enhanced by the presence of a bound metal cation, with selectivity for HSO4– over Cl–. The receptor is capable of electrochemically recognising the complexed anions, cations and anion/cation pairs.

Versatile cation complexation by a calix[4]arene tetraamide (L). Synthesis and crystal structure of [ML][ClO4]2·nMeCN (M = FeII, NiII, CuII, ZnII or PbII)

Transition-metal complexes of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(diethylcarbamoylmethoxy)calix[4]arene (L) in the cone conformation have been synthesised for the first time. Single-crystal structure determinations have been carried out on the complexes of Fe2+, Ni2+, Cu2+ and Zn2+, as well as of Pb2+, the stoichiometry in each case being assigned as [ML][ClO4]2·nMeCN (n= 4–6). The structures of the complexes of Fe2+, Zn2+ and Pb2+ are broadly similar with the metal atoms co-ordinated to all eight oxygen atoms of L. The copper complex is somewhat different with the four Cu–O (amide) distances being very much shorter than the four Cu–O (ether) distances. A completely different structure is observed in the nickel complex, where L has undergone significant rearrangement to accommodate the metal cation in a distorted-octahedral environment. Molecularmechanics calculations have been carried out to investigate the remarkable versatility of L as a metal cation receptor.

Delamination and re-assembly of surfactant-containing Li/Al layered double hydroxides

Exchange of the chloride anion intercalated in [LiAl2(OH)6]Cl.nH2O with a range of surfactants is reported. Attempts to delaminate (or exfoliate) the surfactant-exchanged intercalates, where the surfactant was an alkyl sulfate, were unsuccessful. In contrast, delamination of the layered double hydroxides [LiAl2(OH)6][C12H25C6H4SO3.nH2O] and [LiAl2(OH)6][C8H17C6H4SO3.nH2O] was successful. The necessity of the alkyl chain of the surfactants was demonstrated by the failure of [LiAl2(OH)6][CH3C6H4SO3.nH2O] to delaminate. The delamination of the unique Li/Al LDH is thus found to be dependent on the guest surfactant structure in terms of both chain length and head group moiety.

A novel bis(N,N′-dimethyl-1,4,7-triazacyclononane)calyx[4]arene ligand that forms a ferromagnetic dinuclear nickel(II) complex with three end-on azide bridging ligands

A new bis(N, N′-dimethyl-1,4,7-triazacyclononane)calix[4]arene ligand L has been prepared and a single-crystal structure determination of a novel ferromagnetic dinuclear nickel(II)-L complex containing three 1,1 end-on azide bridging ligands is described.

The role of phosphonate speciation on the inhibition of barium sulfate precipitation

Abstract The inhibition of barium sulfate precipitation in the presence of phosphonate containing molecules was investigated experimentally and speciation curves were used to elucidate the interactions involved. Inhibition of precipitation was found to be pH dependent and loss of inhibition was observed at both very high and low pHs. Maximum inhibition for all the inhibitor molecules occurred at pH 8. While speciation curves showed that inhibition could be improved by the presence of 2 or more fully de-protonated phosphonate groups (for pure aminophosphonates) on the molecule at pH⩽8, at pH 12 inhibition was insensitive to the number of de-protonated phosphonate groups. It is, therefore, suggested that surface charge repulsion affects inhibition at very high pH. For molecules which are not pure aminophosphonates, stereochemistry, functional groups and the ionisation state appear to play a significant role in inhibition at 3

Crystallographic Determination of Three Ni-α-Hydroxyoxime-Carboxylic Acid Synergist Complexes

X-ray crystal structures of three dicarboxylato-bis-α-hydroxyoximenickel(II) complexes have been obtained. These contain a short chained (C8) analogue of LIX®63 hydroxyoxime, along with either benzoate, isobutyrate or propionate. All have pseudo-octahedral structures with monodentate carboxylate anions located cis to one another and neutral, chelating α-hydroxyoxime ligands. Intra-molecular hydrogen bonding between each anionic acids carboxylate group and an adjacent oxime hydroxyl group is evident. Inter-molecular hydrogen bonding is also observed. These provide the first definitive structural elucidation of the types of nickel complexes that could be formed during synergistic extraction by LIX®63 and carboxylic acids.