Gareth L. Nealon

Liquid-crystalline nanoparticles: Hybrid design and mesophase structures

Summary Liquid-crystalline nanoparticles represent an exciting class of new materials for a variety of potential applications. By combining supramolecular ordering with the fluid properties of the liquid-crystalline state, these materials offer the possibility to organise nanoparticles into addressable 2-D and 3-D arrangements exhibiting high processability and self-healing properties. Herein, we review the developments in the field of discrete thermotropic liquid-crystalline nanoparticle hybrids, with special emphasis on the relationship between the nanoparticle morphology and the nature of the organic ligand coating and their resulting phase behaviour. Mechanisms proposed to explain the supramolecular organisation of the mesogens within the liquid-crystalline phases are discussed.

Spacing-dependent dipolar interactions in dendronized magnetic iron oxide nanoparticle 2D arrays and powders

Self-assembly of nanoparticles (NPs) into tailored structures is a promising strategy for the production and design of materials with new functions. In this work, 2D arrays of iron oxide NPs with interparticle distances tuned by grafting fatty acids and dendritic molecules at the NPs surface have been obtained over large areas with high density using the Langmuir-Blodgett technique. The anchoring agent of molecules and the Janus structure of NPs are shown to be key parameters driving the deposition. Finally the influence of interparticle distance on the collective magnetic properties in powders and in monolayers is clearly demonstrated by DC and AC SQUID measurements. The blocking temperature T(B) increases as the interparticle distance decreases, which is consistent with the fact that dipolar interactions are responsible for this increase. Dipolar interactions are found to be stronger for particles assembled in thin films compared to powdered samples and may be described by using the Vogel Fulcher model.

Variations on a Cage Theme: Some Complexes of Bicyclic Polyamines as Supramolecular Synthons

Dedication: One of Alan Sargeson’s great abilities was to seek out knowledge on topics of which he was not the master from those people with the expertise. This led occasionally to publications with a ‘cricket team’ of authors but with a rich brew of information, often international. Alan also insisted that all authors were equal since, without any one, the paper would not be what it was. Hence, he endeavoured to pursue the policy, difficult to maintain over a period where an obsession with absurdities such as the order of authors and point-scoring based on meaningless publication indices became so important in the maintenance of research, of listing authors simply in alphabetical order. In describing work begun while he was still with us, we have attempted to adhere to his principles. Analysis of a body of crystallographic information concerning metal(ii) and metal(iii) complexes of macrobicyclic hexamine ligands and some of their derivatives provides evidence for the action of a variety of intermolecular forces within the lattices. Hydrogen bonding is universal and its forms depend strongly upon the oxidation state and the particular nature of the metal ion bound to the macrobicycle. The introduction of both aliphatic and aromatic substituents leads to lattices in which these substituents associate, although, in the case of aromatic substituents, this is not necessarily a consequence of ‘π-stacking’, despite the fact that the aromatic ring planes form parallel arrays. At least in the case of CoIII, stable enantiomers of the complexes can be obtained, and in {Δ-(+)589-[Co{(NH3)(CH3)sar}]}2Cl2(C6(CO2)6)·26H2O (sar = 3,6,10,13,16,19-hexa-azabicyclo[6.6.6]icosane), the benzene hexacarboxylate anion adopts a chiral conformation in the presence of the optically active cation.

Proton switching of polarity in metalloamphiphile crystals

The metalloamphiphile [Zn(1-decylammonio-8-methylsarcophagine)](ClO4)3·2H2O crystallises in the non-centrosymmetric space group P1 to give a polar crystal, which can be converted to one with a centrosymmetric lattice (space groupI2/a) through deprotonation.

An azobenzene-based photoswitchable crystal growth modifier

An aspartic acid functionalised azobenzene derivative is found to be a light-switchable crystal growth modifier of calcite. UV irradiation of the molecule reversibly switches it to the cis isomer, which is a significantly less effective crystal growth inhibitor than the trans isomer. Visible light, or heat switches the inhibitor back “on”. Extended irradiation degrades the inhibitor such that it is irreversibly switched “off”. It was shown that the trans isomer is preferentially absorbed on to the crystal surface, which is consistent with its greater efficacy as an inhibitor.

Structural Variations in the Complete Series of Lanthanoid Complexes of a Calix[4]arene Trisamide*

Lanthanoid picrate (pic) complexes of 5,11,17,23-tetra-tert-butyl-25-hydroxy-26,27,28-tris(diethylcarbamoylmethoxy)calix[4]arene (LH) have been synthesised and structurally characterised, to complete this series for all lanthanoids (other than promethium). From cerium to lutetium, three structural types are observed: Type I, [Ln(L)(O,O′-pic)](pic), Ln = Ce–Dy; Type II, [Ln(L)(O-pic)](pic), Ln = Tb, Ho; Type III, [Ln(L)(HOEt)](pic)2, Ln = Er–Lu. With lanthanum, three different ten-coordinate complexes were characterised; [Ln(L)(O,O′-pic)(HOEt)](pic), [Ln(L)(O,O′-pic)(OH2)](pic), and [Ln(L)(O,O′-pic)(HOMe)](pic). The crystallisation of Type I and II observed for terbium shows that the stability of the different structures are sensitively poised at the transition points. Nevertheless, the structures show that the vacant space in the coordination sphere left by the trisamide L tends to reduce across the series as expected. It is occupied by a bidentate picrate anion and unidentate solvent molecule with lanthanum, a bidentate picrate anion for cerium to dysprosium (Type I), a unidentate picrate anion for terbium and holmium (Type II), and finally a unidentate solvent molecule from erbium to lutetium (Type III). The coordination number thus reduces from 10 to 8 across the series.

Novel and Disparate Hydrogen-Bonding Associations in 13-Amino-6-hydroxy-13-methyl-1,4,8,11-tetraazacyclotetradecane Tetrahydrochloride Monohydrate

The title compound crystallizes in the monoclinic space group Pn with two independent [LH4]Cl4·H2O formula units (L = 13-amino-6-hydroxy-13-methyl-1,4,8,11-tetraazacyclotetradecane) in the asymmetric unit. Despite pseudo-symmetry, these two units exhibit subtle and interesting differences in their hydrogen-bonded association by the interchange of the water molecule site with one of the chloride anions. Although a pentamine, L crystallizes as a tetrahydrochloride in which the tetracation has a conformation similar to that of tetraprotonated cyclam (1,4,8,11-tetraazacyclotetradecane), despite a different pattern of protonation sites. Difficulties in purification are perpetuated in the crystal, the minor isomeric component co-crystallizing in one of the cation sites.

What Is the Structure of the Antitubercular Natural Product Eucapsitrione

1,5,7-Trihydroxy-6H-indeno[1,2-b]anthracene-6,11,13-trione (1), proposed to be the antitubercular natural product eucapsitrione, has been synthesized in 43% overall yield and six steps, including a key Suzuki-Miyaura biaryl coupling and a directed remote metalation (DReM)-initiated cyclization. The physical and spectroscopic properties of 1 do not match the data reported for the natural product. At this time there is insufficient information available to enable a structure reassignment. During the optimization of the Suzuki-Miyaura coupling, an unprecedented biaryl coupling ortho to the borono group was observed. The scope of this unusual reaction has been investigated.