Craig E. Barnes

Imprint Coating: A Novel Synthesis of Selective Functionalized Ordered Mesoporous Sorbents

Molecular imprinting of surfaces of mesoporous sorbents is a novel method for introducing template-selective recognition sites. This method makes use of the unique surface environment of hexagonally packed mesopore surfaces of selected pore sizes (see the schematic representation) and coats such surfaces with functional ligands by binding to a metal ion template.

Preparation of silica aerogel using ionic liquids as solvents

Ionic liquids have been used as effective solvents to synthesize aerogels; a long aging time can be used to produce stable aerogel structures without the need for supercritical drying processes.

Synthesis and studies of cis-Mo(CO)2(L–L′)2 and Mo(L–L′)3 complexes of 2-(phenylazo)pyridines (L–L′) and the crystal structures of Mo(CO)2(4-methyl-2-(phenylazo)pyridine)2 and Mo(4-methyl-2-(phenylazo)pyridine)3

Abstract The complexes cis -Mo(CO) 2 (X-2-(phenylazo)pyridine) 2 ( III ) and Mo(X-2-(phenylazo)pyridine) 3 ( IV ) (X=4-CH 3 O ( a ), 4-CH 3 ( b ), H ( c ), 4-Cl ( d ), 5-Br ( e ), 5-CF 3 ( f ), 6-CH 3 ( g )), cis -Mo(CO) 2 (2-(2-CH 3 -phenylazo)pyridine) 2 ( IIIh ), and Mo(2-(2-CH 3 -phenylazo)pyridine) 3 ( IVh ) have been synthesized and characterized by cyclic voltammetry, by visible and infrared spectroscopy, and by 1 H, 13 C, and 95 Mo NMR spectroscopy. Correlations among these data and correlations of the data with the Hammett σ parameter within each series of complexes were investigated. Initially, correlations were found only for the Hammett σ parameter with the first oxidation potential and with the first reduction potential for both the type III and type IV complexes and with the sum of the carbonyl stretching frequencies for the type III complexes. However, combining 95 Mo NMR linewidth and chemical shift data for this quadrupolar metal allowed separation of the nephelauxetic and spectrochemical effects and revealed a number of additional correlations. The X-ray crystal structures of cis -Mo(CO) 2 (4-CH 3 -2-(phenylazo)pyridine) 2 ( IIIb ) and Mo(4-CH 3 -2-(phenylazo)pyridine) 3 ( IVb ) also have been determined. In IIIb each CO is trans to a pyridyl nitrogen of a 2-(phenylazo)pyridine ligand. In IVb each pyridyl nitrogen is trans to an azo nitrogen, yielding the facial isomer of the complex.

ENHANCED IONIC RECOGNITION BY A FUNCTIONALIZED MESOPOROUS SOL-GEL: SYNTHESIS AND METAL ION SELECTIVITY OF DIAMINOETHANE DERIVATIVE

A newly developed double-imprinting methodology was extended to synthesize mesoporous sol-gels that contain a diaminoethane functional group. Formation of a bis[(3-trimethoxysilyl)propyl] ethylenediamine metal complex, followed by hydrolysis and condensation with tetraethylorthosilicate in the presence of dodecylamine surfactant resulted in the formation of the solid xerogel. Acid washing protonated the amino groups that release the metal ions. This resulted in the formation of binding sites that are uniquely designed with the coordination environment the metal ion prefers. Mesopores were formed by the extraction of the surfactant micelles to give this material relatively large surface areas and good mass-transfer characteristics. A copper (II) imprinted gel showed significantly more enhancement of copper (II) uptake capacities at various concentrations than did a nonimprinted gel made without the metal ion template. The imprinted material also exhibited improved selectivity for removal of copper (II) from Cu2+-Zn2+ aqueous solutions. A sample of the copper imprinted sorbent, which absorbed a total of 99.3% of the copper from a 10− mol/L aqueous solution, removed 95% within 15 minutes. This material has copper distribution coefficients (K d) as high as 12 000 at 10−4 mol/L. A separation factor, K > 85, with respect to copper (II) was achieved with an aqueous Cu2+-Zn2+ system at pH 5.0.

Building block syntheses of site-isolated vanadyl groups in silicate oxides

Cross-linking of the cubic silicate building block, Si8O20 with vanadyl chloride leads to porous solids in which a homogeneous dispersion of isolated vanadyl groups is maintained throughout the matrix even at high loadings of vanadium.

Non-aqueous template-assisted synthesis of mesoporous nanocrystalline silicon orthophosphate

The first synthesis of mesoporous nanocrystalline silicon orthophosphate Si5P6O25 is presented. The synthetic procedure is based on the non-hydrolytic sol–gel reaction in the presence of Pluronic P123 template and subsequent calcination in air. The condensation of silicon acetate, Si(OAc)4, and tris(trimethylsilyl)phosphate, OP(OSiMe3)3 (TTP), in non-aqueous solvents driven by elimination of trimethylsilyl acetate provides a homogeneous network with a high content of Si–O–P bonds and SiO6 moieties. After burning out the template, mesoporous silicon orthophosphate was obtained with surface areas up to 128 m2 g−1 and pore sizes around 20 nm. The nanocrystalline Si5P6O25 phase forms relatively easily (500 °C, 4 h) in comparison with other synthetic routes. All samples were characterized by SEM, TEM, elemental analysis, TGA, nitrogen adsorption, SAXS, 1H, 13C, 29Si, and 31P solid-state NMR spectroscopy, and powder XRD. These xerogels showed superior catalytic activity and selectivity in methylstyrene dimerization.

Novel non-hydrolytic templated sol–gel synthesis of mesoporous aluminosilicates and their use as aminolysis catalysts

A novel non-hydrolytic sol–gel (NHSG) synthesis of mesoporous aluminosilicate xerogels is presented. The polycondensation between silicon acetate, Si(OAc)4, and tris(dimethylamido)alane, Al(NMe2)3, leads to homogeneous aluminosilicate xerogels containing Si–O–Al linkages through dimethylacetamide elimination. The addition of Pluronic P123 and F127 templates provides stiff gels that are, after calcination at 500 °C, converted to stable mesoporous xerogels with a high surface area (>600 m2 g−1) and wormhole-type pores (d = 5.9 nm). The xerogels exhibit high catalytic activity in aminolysis of styrene oxide (82% conversion) with the turnover frequency up to 100.

Control of micro/mesoporosity in non-hydrolytic hybrid silicophosphate xerogels

Non-hydrolytic sol–gel reactions of acetoxysilanes with trimethylsilyl esters of phosphoric and phosphonic acids produce cross-linked matrices containing homogeneous dispersions of silicon and phosphoryl groups connected together by networks of Si–O–P(O) linkages. These polycondensation reactions proceed cleanly and under mild conditions for a wide variety of precursor silanes RnSi(OAc)4−n (R = alkyl, aryl; n = 1, 2) and phosphoryl compounds RP(O)(OSiMe3)2 (R = alkyl, aryl) to provide hybrid xerogels, the final properties of which are a sensitive function of the organic substituents and the Si : P ratio of the precursors. The reactions of bridged acetoxysilanes (AcO)3Si–X–Si(OAc)3 and phosphoryl reagents (Me3SiO)2P(O)–X–P(O)(OSiMe3)2 have also been investigated and found to produce gels that exhibit large surface areas (up to 700 m2 g−1). The presence of SiO6 structural units in bridged-phosphoryl xerogels is related to their microporosity while the absence of such moieties in bridged-acetoxysilane networks is congruent with significant mesoporosity. Several important parameters are identified which can be used to tailor the properties of these hybrid matrices such that gels with specific polarity, porosity and surface area can be targeted at the time of synthesis.

Reactions of thioether carboxylic acids with mercury(II). Formation and X-ray crystal structure of mercury(II) mercaptoacetate

Abstract Reactions of Hg(II) salts with thioether carboxylic acids o -C 6 H 4 [CH(SCH 2 COOH) 2 ] 2 ( 1a ) and PhCH(SCH 2 COOH) 2 ( 3 ) in water were found to lead to the decomposition of these ligands with the formation of mercury(II) mercaptoacetate Hg(SCH 2 COOH) 2 ( 2 ) and aldehydes o -C 6 H 4 (CHO) 2 and PhCHO, respectively. A similar reaction was observed between Hg(NO 3 ) 2 and CH 3 (CH 2 ) 2 CH(SCH 2 COOH) 2 ( 4 ). The X-ray structure of Hg(SCH 2 COOH) 2 ( 2 ) shows a linear –S–Hg–S– moiety. The mechanism of the formation of 2 in the reactions between Hg 2+ and thioether carboxylic acids in water is discussed.

Alkylidene dynamics in the cluster complex Cp∗Rh(CpCo)2(CO)2(μ-CH2): Observation of an intermediate containing a μ3-methylidene ligand ☆

Abstract The dynamic behaviour of the methylidene ligand in the triangular cluster complex, Cp∗Rh(CpCo)2(CO)2(μ-CH2) 3, has been investigated using multidimensional NMR techniques. Two distinct processes have been identified whereby the methylidene ligand moves between bridging different metal-metal bonds in the complex: (1) methylidene jumps from a RhCo bond to the CoCo bond and (2) degenerate methylidene jumps between the two RhCo bonds of the metal triangle. An intermediate has been observed for the latter process. Based on 1H and 13C NMR data, we propose that the methylidene ligand in this intermediate occupies a triply-bridging coordination position above the metal triangle, simultaneously interacting with all three metal atoms in the complex. To our knowledge, this is the first observation of an intermediate involved in the dynamic behaviour of an alkylidene ligand. Furthermore, it is only the second example of a μ3-methylidene ligand to be reported. The implications of these results in the areas of alkylidene mobility on metal surfaces and catalysis are discussed.