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Boron and Aluminum

Of the elements in Group Illb, only boron and aluminum will be discussed here. Descriptions of the rarer metals of the group, gallium, indium and thallium, as wrell as those for the entire Ilia group and the rare-earth metals, appear in more specialized works. [Pg.126]

The ionic radius of aluminum (0.50 A) is 2.5 times that of boron (0.20 A), and the ionic volumes are in a ratio of about sixteen to one these ratios make it easy to understand why boron in its oxidized form exhibits behavior so much more acidic than that of trivalent aluminum and thus why boron is regarded as a typical metalloid although its congeners are metals. [Pg.126]


Group 13 (IIIA) Perchlorates. Perchlorate compounds of boron and aluminum are known. Boron perchlorates occur as double salts with alkah metal perchlorates, eg, cesium boron tetraperchlorate [33152-95-3] Cs(B(C104)4) (51). Aluminum perchlorate [14452-95-3] A1(C104)2, forms a series of hydrates having 3, 6, 9, or 15 moles of water per mole of compound. The anhydrous salt is prepared from the trihydrate by drying under reduced pressure at 145—155°C over P2O5 (32). [Pg.66]

Hydrides. Unlike boron and aluminum, which form many stable and useful hydrides, there is very Htde evidence for the existence of TIH and TIH (13). Lithium tetrahydridothallate(III) [82374 7-8], LiTlH, has been obtained from TlCl and LiH in ether at — 15 C (14). It decomposes rapidly... [Pg.469]

Beryllium, calcium, boron, and aluminum act in a similar manner. Malonic acid is made from monochloroacetic acid by reaction with potassium cyanide followed by hydrolysis. The acid and the intermediate cyanoacetic acid are used for the synthesis of polymethine dyes, synthetic caffeine, and for the manufacture of diethyl malonate, which is used in the synthesis of barbiturates. Most metals dissolve in aqueous potassium cyanide solutions in the presence of oxygen to form complex cyanides (see Coordination compounds). [Pg.385]

The temperature-independent parachor [P] may be calculated by the additive scheme proposed by Quale.The atomic group contributions for this method, with contributions for silicon, boron, and aluminum from Myers,are shown in Table 2-402. At low pressures, where Pi. pc, the vapor density term may be neglected. Errors using Eq. (2-168) are normally less than 5 to 10 percent. [Pg.416]

Stereoelectronic factors are also important in determining the stmcture and reactivity of complexes. Complexes of catbonyl groups with trivalent boron and aluminum compounds tend to adopt a geometry consistent with directional interaction with one of the oxygen lone pairs. Thus the C—O—M bond angle tends to be in the trigonal (120-140°) range, and the boron or aluminum is usually close to die carbonyl plane. ... [Pg.237]

The enantioselective inverse electron-demand 1,3-dipolar cycloaddition reactions of nitrones with alkenes described so far were catalyzed by metal complexes that favor a monodentate coordination of the nitrone, such as boron and aluminum complexes. However, the glyoxylate-derived nitrone 36 favors a bidentate coordination to the catalyst. This nitrone is a very interesting substrate, since the products that are obtained from the reaction with alkenes are masked a-amino acids. One of the characteristics of nitrones such as 36, having an ester moiety in the a position, is the swift E/Z equilibrium at room temperature (Scheme 6.28). In the crystalline form nitrone 36 exists as the pure Z isomer, however, in solution nitrone 36 have been shown to exists as a mixture of the E and Z isomers. This equilibrium could however be shifted to the Z isomer in the presence of a Lewis acid [74]. [Pg.233]

Thermolysis rates are enhanced substantially by the presence of certain Lewis acids (e.g. boron and aluminum halides), and transition metal salts (e.g. Cu ", Ag1).46 There is also evidence that complexes formed between azo-compounds and Lewis acids (e.g. ethyl aluminum scsquichloridc) undergo thermolysis or photolysis to give complexed radicals which have different specificity to uncomplexed radicals.81 83... [Pg.73]

Compounds of boron and aluminum may have unusual Lewis structures in which... [Pg.201]

Boron and aluminum halides have incomplete octets and act as Lewis acids. [Pg.722]

Brown, H. C., The Reactions of Alkali Metal Hydrides and Boro-hydrides with Lewis Acids of Boron and Aluminum, Congr. Lect., 17th Int. Congr. Pure Appl. Chem. p. 167. Butterworths, London, 1960. [Pg.19]

Each of these elements (boron and aluminum) has three valence electrons. Therefore, each of these elements can comfortably form three bonds ... [Pg.314]

In the compounds shown above, boron and aluminum are using their valence electrons to form bonds, but notice that neither one has an octet. Each element is capable of forming a fourth bond in order to obtain an octet, but then each element will bear a formal charge of -1. [Pg.314]

The mechanism by which the Group III hydrides effect reduction involves activation of the carbonyl group by coordination with a metal cation and nucleophilic transfer of hydride to the carbonyl group. Hydroxylic solvents also participate in the reaction,59 and as reduction proceeds and hydride is transferred, the Lewis acid character of boron and aluminum becomes a factor. [Pg.396]

Several factors affect the reactivity of the boron and aluminum hydrides, including the metal cation present and the ligands, in addition to hydride, in the complex hydride. Some of these effects can be illustrated by considering the reactivity of ketones and aldehydes toward various hydride transfer reagents. Comparison of LiAlH4 and NaAlH4 has shown the former to be more reactive,63 which is attributed to the greater... [Pg.398]

Closely related to, but distinct from, the anionic boron and aluminum hydrides are the neutral boron (borane, BH3) and aluminum (alane, A1H3) hydrides. These molecules also contain hydrogen that can be transferred as hydride. Borane and alane differ from the anionic hydrides in being electrophilic species by virtue of the vacant p orbital and are Lewis acids. Reduction by these molecules occurs by an intramolecular hydride transfer in a Lewis acid-base complex of the reactant and reductant. [Pg.400]

We have unified experimental and theoretical DFT data to illustrate the significance of this difference between boron and aluminum, and to show the consistency of data from different laboratories and different methods. The results are shown in Fig. 6. For B-ZSM-5, proton transfer takes place at proton affinities of the probe molecule of at least 854 kJ/mol, which is somewhat higher than that reported for A1 zeolites (821 kJ/mol) [235]. [Pg.213]

The analogy between the trivalent boron compounds and car-bonium ions extends to the geometry. Although our arguments for a preferred planar structure in carbonium ions are indirect, there is electron diffraction evidence for the planar structure of boron trimethyl and the boron trihalides.298 Like carbonium ions, the boron and aluminum analogs readily form a fourth covalent bond to atoms having the requisite non-bonding electrons. Examples are the compounds with ammonia, ether, and fluoride ion.297... [Pg.157]

Fig. 6. Variation of enthalpies of boron and aluminum fluorides with chlorine substitution. Fig. 6. Variation of enthalpies of boron and aluminum fluorides with chlorine substitution.
Oi and coworkers88 employed a cationic palladium(II) complex to catalyze Diels-Alder reactions. The benefits of such a catalyst compared to traditional catalysts such as boron and aluminum halides were reported to possess better stability to air and moisture,... [Pg.353]

Comparison with experimental values are meaningful only for boron and aluminum. The MRCI values for AI (0.45 eV) and the MCDF results for B (0.26 eV) and A1 (0.43 eV) are in good agreement with the Hotop and Lineberger values (0.28 and 0.44 eV, respectively). The MRCI and MCDF EAs for the other atoms agree with each other (0.29 and 0.30 eV for Ga, 0.38 and 0.39 eV for In, 0.27 and 0.29 eV for Tl). The RCC EA of TI is much higher at 0.40(5) eV. A major difference between the RCC and the other two methods lies in the number of electrons correlated. While [52] and [53] correlate valence electrons only, three for the neutral atom and four for the anion, we correlated 35 electrons in Tl and 36 in TE. A RCC study of all five elements was undertaken [54], with the aim of determining all five EAs and, in particular, the effect of inner-shell correlation and virtual space used on the calculated values. [Pg.167]

Several factors affect the reactivity of the boron and aluminum hydrides. These include the metal cation present and the ligands, in addition to hydride, in the metallo... [Pg.265]

Figure 4.1 Degree of dopant ionization as a function of concentration for boron and aluminum estimated at room temperature. The calculation is based on ionization data from Table 4.1 and an effective hole mass of 1.24 m.. Figure 4.1 Degree of dopant ionization as a function of concentration for boron and aluminum estimated at room temperature. The calculation is based on ionization data from Table 4.1 and an effective hole mass of 1.24 m..
For implanted acceptor activation there have been several reviews during the last few years since Troffer et al. s often-cited paper on boron and aluminum from 1997 [88]. Aluminum is now the most-favored choice of acceptor ion despite the larger mass, which results in substantially more damage compared with implanted boron. Mainly it is the high ionization energy for boron that results in this choice, as well as its low solubility. In addition, boron has other drawbacks, such as an ability to form deep centers like the D-center [117] rather than shallow acceptor states and, as shown in Section 4.3.2, boron ions also diffuse easily at the annealing temperatures needed for activation. The diffusion properties may be used in a beneficial way, although it is normally more convenient if the implanted ion distribution is determined by the implant conditions alone. [Pg.146]


See other pages where Boron and Aluminum is mentioned: [Pg.123]    [Pg.250]    [Pg.224]    [Pg.201]    [Pg.718]    [Pg.64]    [Pg.314]    [Pg.1510]    [Pg.205]    [Pg.367]    [Pg.132]    [Pg.249]    [Pg.157]    [Pg.79]    [Pg.54]    [Pg.218]    [Pg.63]    [Pg.154]    [Pg.116]    [Pg.125]    [Pg.249]    [Pg.169]    [Pg.319]    [Pg.224]   


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Boron-aluminum

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