Zinc borates structures

High Dehydration Temperature - In contrast to other forms of zinc borates, the water of hydration of the zinc borate is retained up to 290°C, thus allowing it to be used in polymers requiring high processing temperatures. The proposed molecular structure for the zinc borate is depicted in Fig. 

Zinc antimonide, 3 44, 53—54 Zinc atomizing process, 26 598 Zinc baths, 9 828-829, 830t Zincblende semiconductors, 22 141 band structure of, 22 142-144 transport properties of, 22 148, 149t Zinc borates, 4 282-283 Zinc brass... 

Another example of cation control over borate structure is found in the recently elucidated structure of the industrially important synthetic zinc borate Zn[B304(0H)3] [2 ZnO 3 B3O3 3 H2O], shown in Fig. 12 [45]. This compound has a polytriborate structure reminiscent of that found in colemanite (Fig. 7a) [29]. Yet, due to the different coordination requirements of the Ca and Zn cations, the anionic polyborate chains in these two compounds have different spatial arrangements. In the case of colemanite, parallel triborate chains are linked together into extended sheets by coordination with interstitial (and H2O). These sheets are bound... 

Fig. 12. The structure of the synthetic industrial zinc borate Zn[B304(0H)3] (2 ZnO 3 B2O3 3 H2O)...

Raman spectroscopy has seldom been used for elucidating structures of crystalline solids. However, with IR, it has proved valuable for observing isostructural rare-earth borates (110) and for measurement of phonon coupling in the zinc borate Zn40(B02)8 (304). 

This zinc borate can normally be prepared either by reacting boric acid with zinc oxide or by reacting borax pentahydrate with zinc sulfate. A recent single crystal x-ray crystallography study showed that it has a structure of Zn[B304(0H)3] (Figure 9.3).47,48 It has been used extensively in PVC,49 polyamide,50 polyolefin,51 52 epoxy,53 phenolics,54 and various elastomers.55... 

Schubert, D.M, Alam, F, Visi, M.Z, and Knobler, C. 2003. Structural characterization and chemistry of the industrially important zinc borate, Zn[B304(0H)3]. Chem. Mater., 15(4), 866-871. 

Shen, K.K. and Sprague, R.W. 1981. On the use of a unique form of zinc borate as a flame retardant in fiberglass reinforced unsaturated polyesters and vinyl esters—A structure-activity relationship study. Reinforced Plastics/Composites Institute, The Society of Plastics Industry, Inc., Boltan, U.K., February 16-20 Section 13B, pp. 1-5. 

Zinc borate is a boron-based fire retardant available as a fine powder with a chemical composition of (Zn0) < B203)y(H20)z. The most commonly used grades have the structure 2Zn0-3B203-zH20. 

In a fire, zinc borate on its own forms a vitreous mass on the polymer surface providing a barrier between the flame and the source of support. In antimony- or halogen-based systems it helps formation of Sb-O-Cl groups, extinguishing the flame and suppressing fumes while promoting formation of polyaromatic structures. The Borax material has until now been used mainly for total (or more recently, partial (40-75%)) replacement of the more expensive antimony oxide in PVC, polyolefins, nylons, and elastomers. 

Zinc borate can also change the oxidative decomposition pathway of halogen-free polymers. It is not completely clear if this is happening because of an inhibition effect of boron oxides toward the oxidation of hydrocarbons or the oxidation of graphite structures in the char, or is due purely to the formation of a protective sintered layer. In combination with ATH, zinc borate creates a porous ceramiclike residue, which has much better insulative properties than those of pure anhydrous alumina. It was shown that zinc borate accelerates dehydration of magnesium hydroxide and creates a ceramiclike structure with dehydrated MgO. 

The monocation tris(diethylether) ethylzinc is formed from diethyl zinc as a tetrakis(penta-fluorophenyl)borate salt.85 Longer-chain linear and cyclic ether complexes (2) of zinc alkyls have also been observed. The reaction between zinc dialkyls and primary amines gives a number of structurally diverse products dependent on the reaction conditions and the amine.86 The... 

The zinc acetate complex of tris(3-/-butyl-5-methylpyrazol-l-yl)borate was prepared as a structural model for carbonic anhydrase and comparison with the enzyme active site structures confirmed that the complexes are excellent structural models.239 A mononuclear zinc hydroxide complex can also be formed with the tris(pyrazolyl) borate ligand system as a structural model for carbonic anhydrase.240... 

A structurally characterized example of a dinuclear zinc complex with a bridging phosphate monoester was provided by Kitajima and co-workers using the tris(pyrazolyl)borate ligand system. The P—O bond in a tris- or bis-phosphate ester is cleaved by a hydroxo zinc complex resulting in the monoester compound.443... 

Synthesis of functional models of carbonic anhydrase has been attempted with the isolation of an initial mononuclear zinc hydroxide complex with the ligand hydrotris(3-t-butyl-5-methyl-pyrazolyl)borate. Vahrenkamp and co-workers demonstrate the functional as well as the structural analogy to the enzyme carbonic anhydrase. A reversible uptake of carbon dioxide was observed, although the unstable bicarbonate complex rapidly forms a dinuclear bridged complex. In addition, coordinated carbonate esters have been formed and hydrolyzed, and inhibition by small ions noted.462 A number of related complexes are discussed in the earlier Section 6.8.4. 

Recently, Lipton et al. [25] have used zinc-67 NMR to investigate [Zn(HB(3,5-(CH3)2pz)3)2] complexes which have been doped with traces of paramagnetic [Fe(HB(3,4,5-(CH3)3pz)3)2]. The low-temperature Boltzmann enhanced cross polarization between XH and 67Zn has shown that the paramagnetic iron(II) dopant reduces the proton spin-lattice relaxation time, Tj, of the zinc complexes without changing the proton spin-lattice relaxation time in the Tip rotating time frame. This approach and the resulting structural information has proven very useful in the study of various four-coordinate and six-coordinate zinc(II) poly(pyrazolyl)borate complexes that are useful as enzymatic models. 

Another zinc fluoride has been prepared incorporating a pyrazolyl borate ligand. Reaction of [KHB(3-R-5-methylpyrazol-l-yl)] (R=/ -tol) with [Zn(OAc)2.2H2OJ leads to the production of [TpR MeZnOAc], which is transformed to the fluoride derivative upon addition of KF [99], This compound has been structurally characterised. Use of [Zn(C104)2] as the starting material in combination with [KHB(3- Bu-5-methylpyrazol-l-yl)], followed by addition of KF leads to [TptBu,MeZnF], Further reaction of this compound at the fluoride anion leads to a variety of species. Abstraction of F by BF3.solv. (solv. = py, Et20) leads to [TpZn(solv.)][BF4], whilst use of [HSiEt3] leads to formation of the hydride species,... 

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