Arie van der Lee

Giant negative linear compressibility in zinc dicyanoaurate

The counterintuitive phenomenon of negative linear compressibility (NLC) is a highly desirable but rare property exploitable in the development of artificial muscles, actuators and next-generation pressure sensors. In all cases, material performance is directly related to the magnitude of intrinsic NLC response. Here we show the molecular framework material zinc(II) dicyanoaurate(I), Zn[Au(CN)(2)](2), exhibits the most extreme and persistent NLC behaviour yet reported: under increasing hydrostatic pressure its crystal structure expands in one direction at a rate that is an order of magnitude greater than both the typical contraction observed for common engineering materials and also the anomalous expansion in established NLC candidates. This extreme behaviour arises from the honeycomb-like structure of Zn[Au(CN)(2)](2) coupling volume reduction to uniaxial expansion, and helical Au…Au aurophilic interactions accommodating abnormally large linear strains by functioning as supramolecular springs.

Synthesis and structural characterisation of the first N-heterocyclic carbene ligand fused to a porphyrin.

The functionalisation of two neighboring beta-pyrrolic positions of a porphyrin by a fused N-heterocyclic carbene ligand, the subsequent metallation of this external coordination site by palladium(II) and the structural characterisation of the resulting compounds are presented.

High-pressure synthesis of a polyethylene/zeolite nano-composite material

Meso/micro-porous solids, such as zeolites, are complex materials used in an impressive range of applications. Here we photo-polymerized ethylene using non-catalytic high-pressure techniques at 0.5-1.5u2009GPa under ultraviolet (351-364u2009nm) irradiation on a sub-nanometre scale in the channels of a pure SiO2 zeolite, silicalite, to obtain a unique nano-composite material with drastically modified mechanical properties. The structure obtained contains single polyethylene chains, which adapt very well to the confining channels as shown by optical spectroscopy and X-ray diffraction. The formation of this nano-composite results in significant increases in bulk modulus and density, and the thermal expansion coefficient changes sign from negative to positive with respect to silicalite. Mechanical properties may thus be tuned by varying the amount of polymerized ethylene. Our findings could allow the high-pressure, catalyst-free synthesis of a unique generation of technological, functional materials based on simple hydrocarbons polymerized in confining meso/micro-porous solids.

Selective Lanthanides Sequestration Based on a Self‐Assembled Organosilica

In this paper, we investigate the cation-exchange properties of a self-assembled hybrid material towards trivalent ions, lanthanides (La(3+), Eu(3+), Gd(3+), Yb(3+)) and Fe(3+). The bis-zwitterionic lamellar material was prepared by sol-gel process from only 3-aminopropyltriethoxysilane (APTES), succinic anhydride, and ethylenediamine. In ethanol heated under reflux, the exchange ethylenediammonium versus Ln(3+) proved to be complete by complexometry measurements and elemental analyses, one Cl(-) ion per one Ln(III) remaining as expected for charge balance. In aqueous solution at 20 degrees C, the material was found to be selective towards lanthanide in spite of the similarity of their ionic radii. The cation uptake depends on the nature of the salt, the difference between two lanthanides reaching up to 20 % in some cases. Finally, ion-exchange reaction with FeCl(3) was chosen as a probe to get more information on the material after incorporation of trivalent ions. Based on Mössbauer spectroscopic investigations on the resulting material in conjunction with the XRD analysis of materials containing trivalent ions, a structural model was proposed to describe the incorporation of trivalent ions by exchange reaction within the original zwitterionic material.

X-Ray crystal structures of copper(II) and cobalt(II) complexes with Schiff base ligands. Reactivity towards dioxygen

Copper(II) and cobalt(II) Schiff base complexes with derivatives of the pentadentate ligand bis(salicylideneimino-3-propyl)amine [H2salDPT] have been prepared. The X-ray crystal structures of the copper(II) complexes Cu[salDPT] and Cu[sal(n-propyltrimethylsilyl)DPT] were determined and revealed five-coordination at the metal centre in both cases. The 1 ∶ 1 dioxygen adduct of Co[sal(n-propyltrimethylsilyl)DPT] was also isolated and its X-ray molecular structure determined.

Experimental and Theoretical Study of the Reactivity of Gold Nanoparticles towards Benzimidazole-2-ylidene Ligands

The reactivity of benzimidazol-2-ylidenes with respect to gold nanoparticles (AuNPs) has been investigated using a combined experimental and computational approach. First, the grafting of benzimidazol-2-ylidenes bearing benzyl groups on the nitrogen atoms is described, and comparisons are made with structurally similar N-heterocyclic carbenes (NHCs) bearing other N-groups. Similar reactivity was observed for all NHCs, with 1)u2005the erosion of the AuNPs under the effect of the NHC and 2)u2005the formation of bis(NHC) gold complexes. DFT calculations were performed to investigate the modes of grafting of such ligands, to determine adsorption energies, and to rationalize the spectroscopic data. Two types of computational models were developed to describe the grafting onto large or small AuNPs, with either periodic or cluster-type DFT calculations. Calculations of NMR parameters were performed on some of these models, and discussed in light of the experimental data.

Highly Convergent Synthesis of Chiral Bicyclophosphinates by Domino Hydrophosphinylation/Michael/Michael Reaction

Diastereoselective domino reactions of iminoalcohols and allenyl H-phosphinates produce chiral phosphorus bicycles in a regio- and stereoselective fashion. A predictive model for diastereoselection is used for these new chiral phosphinic esters.

Hydrogen bond-directed assembly of silsesquioxanes cubes: synthesis of carboxylic acid POSS derivatives and the solid state structure of octa[2-(p-carboxyphenyl)ethyl] silsesquioxane

The octa[2-(p-carboxyphenyl)ethyl] and octa[2-(4-carboxy-1,1′-biphenyl)ethyl] silsesquioxane were synthesised under mild reaction conditions upon hydrogenolysis of the corresponding benzyl-ester derivatives. The octa[2-(p-carboxyphenyl)ethyl] silsesquioxane was shown to self-assemble upon formation of carboxylic acid dimers. The presence of eight carboxylic acid functional groups allowed to obtain an ordered silsesquioxane hybrid network. The X-ray crystal structures of the octa-ester and of the octa-acid were determined. The three-dimensional conformation of the ester provided an interpenetrated compact packing of the molecular building blocks without any specific supramolecular interaction. The two-dimensional character of the acid and the directionality of the hydrogen bond pattern of a dimer of acid led to the formation of hydrogen-bonded ribbons. It showed that functionalized silsesquioxane precursors capable of hydrogen bonding are of interest to generate nanostructured materials through self-organization processes. Moreover, the use of carboxylic acid groups is interesting not only because of their ability to form carboxyl dimer structures by hydrogen bonding but also because of their ability to form metal carboxylate derivatives that may lead to new organised hybrid metal organic silica frameworks.

Diacetylenes with Ionic‐Liquid‐Like Substituents: Associating a Polymerizing Cation with a Polymerizing Anion in a Single Precursor for the Synthesis of N‐Doped Carbon Materials

Imidazolium- and benzimidazolium-substituted diacetylenes with bromide or nitrogen-rich dicyanamide and tricyanomethanide anions were synthesized and used as precursors for the preparation of N-doped carbon materials. On pyrolysis under argon at 800 °C both halide precursors afforded graphite-like structures with nitrogen contents of about 8.5%. When the dicyanamide and tricyanomethanide precursors were thermolyzed at the same temperature, graphite-like structures were obtained that exhibit nitrogen contents in the range 17-20 wt%; thereby, the benefit of associating a polymerizing cation with a polymerizing anion in a single precursor was demonstrated. On pyrolysis at 1100 °C the nitrogen contents of the latter pyrolysates remain high (ca. 6 wt%). Adsorption measurements with krypton at 77 K indicated that the materials are nonporous. The highest electrical conductivity was observed for a pyrolysate with one of the lowest nitrogen contents, which also has the highest degree of graphitization. Thus, the quest for N-rich carbons with high electrical conductivities should include both maximization of the nitrogen content and optimization of the degree of graphitization. Crystallographic investigation of the precursors and spectroscopic characterization of the pyrolysates prepared by heating at 220 °C indicate that construction of the final carbon framework does not involve the intermediate formation of a polydiacetylene.

Stability and solid-state polymerization reactivity of imidazolyl- and benzimidazolyl-substituted diacetylenes: pivotal role of lattice water

1,6-Bis(1-imidazolyl)-2,4-hexadiyne (1) and 1,6-bis(1-benzimidazolyl)-2,4-hexadiyne (5) have been prepared by a novel method that consists in refluxing excess imidazole and benzimidazole with 2,4-hexadiyne-1,6-diol bis(p-toluenesulfonate), pTS (3). This procedure is a viable alternative to the widely used Hay coupling protocol in case the target diyne possesses substituents capable of deactivating the copper catalyst by complexation. Diyne 1 crystallizes as a hydrate, 1·H2O (2). For this compound, water is essential to achieve a crystalline material, and attempts to obtain crystals without included solvent were unsuccessful. In the structure of 2, the organic fragments organize around the water molecule and interact with it through a dense network of hydrogen bonds. The CC–CC moieties are not oriented suitably for topochemical polymerization, and when trying to alter the organization of the crystal by heating so as to induce polymerization, water is lost in an abrupt fashion that leads to instantaneous decomposition into polyaromatic-like species. Similar results were observed when water was removed in vacuo at room temperature. The benzimidazole-containing compound can be crystallized with water molecules (4) or without (5). X-ray crystallography shows that the structure of 5 is organized by numerous C–H⋯N, C–H⋯π, and imidazolyl⋯imidazolyl π–π interactions. The diacetylene molecules almost have the right arrangement for topochemical polymerization, with possibly reacting CC–CC fragments not being parallel, a rare situation in diacetylene chemistry. Yet, experiments show that topochemical polymerization does not occur. Incorporation of water in the lattice of 5 leads to a solvate that is topochemically reactive. Unlike 2, however, water molecules in 4 are not isolated but are organized as ribbons. Spectroscopic characterization of the polymer of 4 indicates that it is a blue phase polymer, with water coordinated to it. This study shows that it is possible to use water, and more generally solvent molecules, to transform a nonreactive diacetylene into a reactive one, even though this approach is less predictable than the cocrystal approach developed by Fowler, Lauher, and Goroff. The solvate approach is simple to implement, quite versatile because of the large range of solvents available, and one does not face the problem of having to remove the host in case one needs to recover the polymer. Previous studies describing a similar approach are scarce.