American Chemical Society

Joint Southeast-Southwest Regional Meeting

"New Chemistry for the New Century"

December 6 - 8, 2000

CARBOXYLATE-ALUMOXANES: ENVIRONMENTALLY BENIGN PRECURSORS FOR DEVELOPING ALUMINUM BASED CERAMIC MEMBRANES AND FILTERS. Christopher D. Jones,a Maria Fidalgo,b Mark R. Wiesner,b and Andrew R. Barrona,c* aDepartment of Chemistry, Rice University, Houston, Texas 77005, b Department of Environmental Science and Engineering, Rice University, Houston, TX 77005 and c Center for Nanoscale Science and Engineering, Rice University, Houston, Texas 77005

Carboxylate substituted alumina nano-particles, carboxylate-alumoxanes, synthesized from boehmite in aqueous solution, are an inexpensive and environmentally benign precursor for the fabrication of aluminum based ceramic ultra- and nano-filtration membranes. The size of the carboxylate ligand on the alumoxane controls the pore size and pore size distribution during sintering to alumina, i.e., the pore sizes for carboxylate-alumoxanes with CH3 substituents is different from those with CH2OCH2CH2OCH3 substituents. Physical mixtures of two different carboxylate-alumoxanes allow for membranes of a range of porosity to be fabricated with narrow pore size distributions. Pore size, permeability, and contact angle measurements are reported on membranes prepared from the carboxylate-alumoxanes.

SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF ALUMINUM AND GALLIUM CHLORIDE STABILIZED ARENE-MERCURY COMPLEXES Alexander S. Borovik,a Simon G. Bott,b and Andrew R. Barrona* aDepartment of Chemistry, Rice University, Houston, TX 77005 and bDepartment of Chemistry, University of Houston, Houston, TX 77204

Novel Lewis acid-base mercury (II) complexes featuring strong coordination of arenes toward mercury have been prepared by the reaction of HgCl2 with two equivalents of MCl3 (M = Al, Ga) in a variety of aromatic solvents. These new compounds were found to be extremely efficient activators of CAr-H bonds. The catalytic proton-deuterium exchange and the olefin addition to the aromatic ring will be discussed. Toluene, ethylbenzene, o-xylene, trimethylbenzene complexes were characterized by X-ray crystallography.

ALUMINUM AND GALLIUM COMPOUNDS OF SALICYLIC AND ANTHRANILIC ACIDS: EXAMPLES OF WEAK INTRA-MOLECULAR HYDROGEN BONDING, Catherine S. Branch,a Janusz Lewinski,b* Simon G. Bott,c Janusz Lipkowski,d and Andrew R. Barron,a* aDepartment of Chemistry, Rice University, Houston, Texas, 77005, bDepartment of Chemistry, Warsaw University of Technology, 00-664 Warsaw, Poland, cDepartment of Chemistry, University of Houston, Houston, Texas 77204, dInstitute of Physical Chemistry of the Polish Academy of Science, 01-224 Warsaw, Poland.

Reaction of M(tBu)3 with anthranilic, salicylic, and ortho-toluic acids yields [(tBu)2M(m-O2CC6H4-2-NH2)]2, M = Al (1), Ga (2), [(tBu)2Ga(m-O2CC6H4-2-OH)]2 (3), and [(tBu)2Ga(m-O2CC6H4-2-Me)]2 (4), respectively. Reaction of anthranilic acid with two equivalents of Al(tBu)3 allows for the isolation of yields (tBu)2Al(m-O2CC6H4-2-NH2)Al(tBu)3 (5). Compounds 1 - 5 have been characterized by NMR and IR spectroscopy, mass spectrometry, and X-ray crystallography. The presence of intra-molecular hydrogen bonding, in compounds 1 - 3, is probed by the orientation of the aromatic rings. Variable temperature 1H NMR, however, suggests that the hydrogen bonding is exceptionally weak. Compound 5 is proposed to be a Lewis acid stabilized complex of the intermediate in the synthesis of compound 1.

AN INVESTIGATION OF CARBOXYLATE-ALUMOXANES AS SURFACE REPAIR AGENTS FOR CERAMIC BODIES AND THERMAL BARRIERS FOR CARBON COMPOSITES. Kimberly A. DeFriend-Varela and Andrew R. Barron,* Department of Chemistry and Center for Nanoscale Science and Engineering, Rice University, Houston, TX 77005

We have investigated the use of carboxylate-alumoxanes for use as the pre-ceramic coating on ceramic and carbon composite substrates. Surface damage, such as microcracking, that occurs during machining of a ceramic weakens the bodies strength. In order to overcome these surface flaws, the surface can either be polished down, or coated with a pre-ceramic. The latter application of carboxylate-alumoxanes will be presented. Carbon composites oxidize in oxidizing environments at temperatures below 500 °C. In order for these composites to be used in high temperature applications, they must be protected. Carbon composites were coated with carboxylate-alumoxanes to protect them in high temperature applications by acting as a thermal insulator. Coatings deposited on a-Al2O3 ceramic bodies and carbon composites with aqueous solutions of acetate-alumoxane (A-A) have been investigated. The effects of solution concentration, number of coatings, and increased strength have been determined. ESEM, AFM, elemental mapping, TGA, and micro-hardness testing results will be presented.

CHARACTERIZATION OF OLIGOMERIC ALUMINUM ARYLOXIDE. Laura G. van Poppel,a Simon G. Bott,b Andrew R. Barron.a* aDepartment of Chemistry, Rice University, Houston, TX 77005 and bDepartment of Chemistry, University of Houston, Houston, TX 77204

Tri-tert-butyl aluminum reacts with hydroquinone in a non-coordinating solvent to yield an oligomeric species, [{(tBu)2Al}2(m-OC6H4O)]n. In order to characterize this oligomer, Lewis acid-base complexes have been isolated: [(tBu)2Al(L)]2(m-OC6H4O), where L = with pyridine, THF, and acetonitrile. The THF and pyridine compounds have been characterized by X-ray crystallography and NMR spectroscopy. Along with the isolation of [(tBu)2Al(L)]2(m-OC6H4O) the use of [(tBu)2Al(m-OPh)]2 as a model compound has allowed for a proposal as to the structure of [{(tBu)2Al}2(m-OC6H4O)]n. The tert-butyl gallium analogs have also been prepared and characterized.

CEMENT HYDRATION INHIBITION. Maximilienne Bishop,a Simon G. Bott,b Andrew R. Barron.a* aDepartment of Chemstry, Rice University, Houston, Texas 77005, bDepartment of Chemistry, University of Houston, Houston, Texas 77204.

Tartaric acid, sucrose, and organophosphonates retard cement hydration. The effects of these retarders on the hydration of the main components of Portland Cement and the formation of ettringite were investigated in order to gain insight into the different mechanisms of hydration inhibition. It was found that the organophosphonate initially accelerates the hydration of the aluminate phase and the formation of ettringite, then halts the reactions completely for several hours. In addition, nitrilotris(methylene)triphosphonic acid enhances the dissolution of calcium oxide and subsequently precipitates a layered calcium phosphonate polymer. The structure of this material and the dissolution-precipitation mechanism are discussed with regard to cement hydration inhibition. Tartaric acid was found to be most effective at stopping hydration of the aluminate phases and formation of ettringite, with no initial acceleration period observed. In contrast, sucrose accelerates the formation of crystalline ettringite. The different hydration inhibition mechanisms that may be at work are discussed with possible application to the development of new retarders.


Lysine and p-hydroxybenzonato&endash;alumoxanes (alumina nanoparticles) in the presence of an organic resin (Resin Services Resin HTR 212), hardener systems (Resin Services Hardener 302 and 874) and carbon fiber matting (IM7-GP-6K-5HS) have been used to prepare composite materials of high tensile strengths. SEM and ultrasound have been used to observe the presence and/or absence of voids in the materials. Electron microprobe was used to determine the elemental distribution within the composite.

STRUCTURE AND REACTIVITY OF ALKYL GALLIUM ALKOXIDE TRANSITION METAL COMPLEXES. Stephen J. Obrey,a Simon G. Bott,b and Andrew R. Barron,a* aDepartment of Chemistry, Rice University, Houston, Texas 77005 and bDepartment of Chemistry, University of Houston, Houston, Texas 77204

The reaction of Ga(tBu)3 with neol-H2 (2,2-dimethylpropane-1,3-diol) yields a hydrogen bond stabilized dimeric species [(tBu)2Ga(neol-H)]2 which may act as a bifunctional tetradentate ligand for transition metal compounds. In the reaction of transition metal halides, such as CoCl2, with [(tBu)2Ga(neol-H)]2, formation of the 15 electron square planar alkoxide complexes [Co(tBu)2Ga(neol)]2 is observed. The structural charecteristics and reactivity of the first row transition metal complexes will be discussed.

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