Boronic porous solids

K. B. Babb, D.A. Lindquist, S.S. Rooke, W.E. Young, and M.G. Kleeve, Porous Solids of Boron Phosphate, Aluminum Phosphate, and Silicon Phosphate, eds. S. Komarneni, D.M. Smith, and J.S. Beck, Advances in Porous Materials, vol. 371. (Materials Research Society, 1995), pp. 279-290. 

We are interested in vanadoborate cluster materials both as precursors to porous solids and as a new class of molecular magnets. We have synthesized a variety of vanadoborate cluster compounds 1-7, primarily by use of two different synthetic routes. The first involves hydrothermal synthesis, using sodium tetraborate ( borax ) as the boron source and the second uses molten boric acid as the reaction medium. In general anionic clusters are found. Herein we report that these have novel electronic and bonding arangements which affect their magnetic behaviour and also that they may be cross-linked together by metal centers such as Cd to form stable microporous phases. 

Chemical vapor infiltration (CVI) is widely used in advanced composites manufacturing to deposit carbon, silicon carbide, boron nitride and other refractory materials within porous fiber preforms. " Because vapor phase reactants are deposited on solid fiber surfaces, CVI is clearly a special case of chemical vapor deposition (CVD). The distinguishing feature of CVI is that reactant gases are intended to infiltrate a permeable medium, in part at least, prior to... 

Aluminum is an effective sintering aid for B4C and SiC ceramics if combined with elemental boron and carbon. Phase relations in the B-C-Al-Si system may hence indicate suitable procedures to initiate transient liquid phase or enhanced solid-state sintering. Furthermore, liquid A1 may be used to infiltrate porous B4C bodies acting as a reinforcing phase. 

Acidity has been characterized much more in detail as it concerns non-porous boria-silica systems. Travert et al. [139] studied the adsorption of CO, pyridine and acetonitrile. CO does not adsorb at all. Pyridine and acetonitrile do adsorb, and spectral features show the proton transfer between the solid and the adsorbate. Spectral features would indicate a quite remarkable strength of interaction. Adsorbed species show instead a labile nature this apparent conflict is interpreted by assuming that, in the absence of adsorbate, boron atoms prefer trigonal coordination, whereas in the presence of the adsorbate, tetrahedral coordination is necessarily adopted. The conversion from trigonal to tetrahedral coordination is an endothermic step, destabihzing the surface adducts. 

In Chapter 6, B. M. Rombo et al. delve into the formation of boronate-linked supramolecular architectures based on boronate ester formation—for example, small molecule diesters form supramolecular self-assemblies in the solid state based on a phenyl-boron-phenyl sandwich motif in which these small oligomers link together to generate macrocycles and other polymers. The polymeric macrocyclics and linear structures demonstrate self-repair capabilities and constitute a new class of wide band-gap semiconducting materials. Through the incorporation of polyvalent boronates, covalent organic frameworks are described, which create highly crystalline, porous network materials. 

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