Tim Kemmitt

Mesoporous [M]-MSU-x metallo-silicate catalysts by non-ionic polyethylene oxide surfactant templating acid [N0(N+)X-I+] and base (N0M+I-) catalysed pathways

Solutions of low and high pH have been used to form non-ionically templated mesoporous metallo-silicates [M]-MSU-x materials; where [M]=Al, Ti, V and Zr. Two new assembly routes are proposed which exploit the acid and base catalysed hydrolysis and simultaneous condensation of metal oxo-salts and silicon tetraethoxide. Acid catalysed hydrolysis, labeled N0X−I+ or N+X−I+ (N0=nonyl-phenyl polyethylene oxide, X−=Cl− or SO2−4, I+=protonated tetraethyl orthosilicate), produces well-defined materials with uniform pores in the small mesoporous region and moderate pore volumes, but reduced metal incorporation owing to the high solubilities of metal cations in acidic solutions. Base catalysed hydrolysis, labeled N0M+I− (N0=nonyl-phenyl polyethylene oxide, M+=Na+ or NH+4, I−=hydroxylated tetraethyl orthosilicate), also leads to materials with uniform channels in the small mesoporous region. Pore volumes and metal substitution are higher and framework shrinkage during calcination is reduced as a result of thicker pore walls. These new pathways show distinct similarities to those described by Attard et al. [Nature 378 (1995) 366] and Zhao et al. [Science 279 (1998) 548] for the formation of hexagonally symmetric silica from non-ionic surfactants under acidic conditions and also to mesoporous MCM-41 assembly routes via (S+X−I+) anion mediated acid catalysed assembly. The results demonstrate the feasibility of preparing templated mesoporous metallo-silicates from non-ionic polyethylene oxide surfactants and metal oxy-hydroxy cationic precursors, but indicate that further optimisation of the reaction conditions is required to maximise the potential of this synthesis approach.

Redetermination of the borax structure from laboratory X-ray data at 145 K

The title compound, sodium tetraborate decahydrate (mineral name: borax), Na2[B4O5(OH)4]·8H2O, has been studied previously using X-ray [Morimoto (1956). Miner. J. 2, 1–18] and neutron [Levy & Lisensky (1978). Acta Cryst. B34, 3502–3510] diffraction data. The structure contains tetraborate anions [B4O5(OH)4]2− with twofold rotation symmetry, which form hydrogen-bonded chains, and [Na(H2O)6] octahedra that form zigzag chains [Na(H2O)4/2(H2O)2/1]. The O—H bond distances obtained from the present redetermination at 145 K are shorter than those in the neutron study by an average of 0.127 (19) Å.

Formation of epitaxial YBCO thin films by ex-situ processing of a polymerized complex

High T/sub c/ and J/sub c/ YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films have been formed by ex-situ processing of a spin coated organic sol-gel precursor based on a polymerized complex. To form the precursor we have reacted metal cations with a chelating organic acid, then formed polyesterified complexes through reaction with a polyhydroxy alcohol. This method permits a simple, cheap and reliable route to the fabrication of YBCO films. The value of J/sub c/ achieved for the film deposited onto a LaAlO/sub 3/ [100] substrate at 77 K under a zero field is routinely as high as 0.25 MA/cm/sup 2/ with T/sub c,zero/ of 90.6 K.

A rapid, inexpensive surface treatment for enhanced functionality of polydimethylsiloxane microfluidic channels.

A rapid, inexpensive method using alkoxysilanes has been developed to selectively coat the interior of polydimethylsiloxane (PDMS) microfluidic channels with an integral silicaceous layer. This method combines the rapid prototyping capabilities of PDMS with the desirable wetting and electroosmotic properties of glass. The procedure can be carried out on the open faces of PDMS blocks prior to enclosure of the channels, or by flowing the reagents through the preformed channels. Therefore, this methodology allows for high-throughput processing of entire microfluidic devices or selective modification of specific areas of a device. Modification of PDMS with tetraethoxysilane generated a stable surface layer, with enhanced wettability and a more stable electroosmotic flow rate than native PDMS. Modification of PDMS with 3-aminopropyltriethoxysilane generated a surface layer bearing amine functionalities allowing for further chemical derivatization of the PDMS surface.

catena-Poly[sodium(I)-μ-tetra­ethoxy­borato]

The title compound, [Na(C8H20BO4)]n, has twofold crystallographic symmetry, with the Na+ cations bound by four O atoms [Na-O=2.251 (3) A]. The tetraethoxyborate anion acts as a bridging ligand to form one-dimensional polymers running along the twofold crystal axis. The crystal was treated as a racemic twin.

The first example of a mixed alkoxide hydride of boron: sodium boron isopropoxide trihydride.

The title compound, poly[[mu-trihydro(isopropoxy)borato]sodium(I)], [Na(C(3)H(10)BO)](n), forms unique polymeric layers normal to the c axis via Na(+)...O [2.3405 (15) A] and Na(+)...H(borane) [2.22 (3) and 2.28 (3) A] interactions. This arrangement builds on distorted tetrahedral Na(+), oxygen and boron environments, with one of the borane hydride units uncoordinated, and highlights potential H(3)B-O-based chemistry.

Sodium Bis[1,2-ethanediolato(2–)](hydroxyethoxo)silicate(1–) Acetonitrile Solvate, Na[Si(C2H4O2)2(C2H5O2)].0.25C2H3N

The title compound was prepared by the dissolution of silicic acid in alkaline glycol solution, using NaOH. The structure of the five-coordinate Si anion is similar to that found in the potassium salt with one glycolate oxygen not bound to the Si. One hydrogen bond utilizing the H atom of the unbound glycolate hydroxyl and the O atom of an adjacent molecule causes the formation of a tetramer of anions around the fourfold axis. Six glycolate-O...Na-cation interactions complete the intermolecular binding into layers perpendicular to the tetragonal axis. The acetonitrile solvent is bound between these layers in the one cavity of sufficient size, created by the anionic tetramer

Hierarchical anodic alumina template-assisted fabrication of nanowires

Highly ordered, >100μm thick, porous anodic alumina templates have been fabricated and used for growing metal nanowires. With sufficient control over the anodisation parameters such as electrolyte type, anodising potential, and temperature, a hierarchical pore structure (diameter ranging from 30 to 300nm) can be obtained and then used to create similar structural hierarchy in the nanomaterials.

catena-Poly[sodium(I)-μ-tetra­butoxy­borato]

The title compound, [Na(C16H36BO4)]n, has a fourfold axis passing through the Na and B atoms which both are bound by four O atoms. The tetrabutoxyborate anion provides the bridging to form one-dimensional polymers running along [001], just like those found for the tetraethoxyborate structure. The two butoxy ‘tail’ atoms are disordered over two conformations in a 0.887 (9):0.113 (9) ratio.

Poly[tetrasodium(I)-tetra-μ2-bis(butane-1,4-diyldioxy)borato-μ2-1,4-butane­diol]

In the title compound, [Na4(C8H16BO4)4(C4H10O2)]n, there are two coordination types for the four independent Na+ cations: two Na+ cations bond to six diolate O atoms [Na-O = 2.305 (2)-2.609 (2) A], while the other two are five-coordinate via one 1,4-butanediol [2.289 (2) and 2.349 (3) A] and four diolate O atoms [2.295 (2)-2.408 (2) A]. Corresponding to this, there are three- and four-coordinate diolate O atoms, the latter bridging Na atoms. The 1,4-butanediol molecules lie on inversion centres. The boron stereochemistry shows minor local perturbations from its usual tetrahedral state [B-O = 1.457 (4)-1.503 (4) A]. The resulting polymer packs as sheets parallel to the (10-1) plane crosslinked by the butanediol molecules. The structure was solved using data from a multiple crystal.