Boronic characterization

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

Tetrahydroborates. The tetrahydroboranes constitute the most commercially important group of boron hydride compounds. Tetrahydroborates of most of the metals have been characterized and their preparations have been reviewed (46). The important commercial tetrahydroborates are those of the alkah metals. Some properties are given ia Table 4. 

CH2CN)4Yb[( J.-H)2BH]2, and (CgH N)4Yb[( J.-H)2BH4]2 have been stmcturally characterized by x-ray crystallography and shown to contain ytterbium to boron hydride Yb—H—B linkages. Thermal decomposition of lanthanaboranes can be used to generate lanthanide metal borides. 

Amine—borane adducts have the general formula R3N BX where R = H, alkyl, etc, and X = alkyl, H, halogen, etc. These compounds, characterized by a coordinate covalent bond between boron and nitrogen, form a class of reducing agents having a broad spectmm of reduction potentials (5). 

The reaction between a trinuclear metal carbonyl cluster and trimetbyl amine borane has been investigated (41) and here the cluster anion functions as a Lewis base toward the boron atom, forming a B—O covalent bond (see Carbonyls). Molecular orbital calculations, supported by stmctural characterization, show that coordination of the amine borane causes small changes in the trinuclear framework. 

W.R. Blumenthal and G.T. Gray III, Structure-Property Characterization of a Shock-Loaded Boron Carbide Aluminum Cermet, in 4th Oxford Conf. on Mech. Prop, of Mat. at High Rates of Strain, Int. Phys. Conf. Ser. 102, Oxford, 1989, 363 pp. 

The hydrides of the later main-group elements present few problems of classification and are best discussed during the detailed treatment of the individual elements. Many of these hydrides are covalent, molecular species, though association via H bonding sometimes occurs, as already noted (p. 53). Catenation flourishes in Group 14 and the complexities of the boron hydrides merit special attention (p. 151). The hydrides of aluminium, gallium, zinc (and beryllium) tend to be more extensively associated via M-H-M bonds, but their characterization and detailed structural elucidation has proved extremely difficult. 

Boron (like silicon) invariably occurs in nature as 0X0 compounds and is never found as the element or even directly bonded to any other element than oxygen. The structural chemistry of B-O compounds is characterized by an extraordinary complexity and diversity which rivals those of the borides (p. 145) and boranes (p. 151). In addition, vast numbers of predominantly organic compounds containing B-O are known. 

Reaction of methyl a-L-rhamnopyranoside with triphenylboroxole gave a syrupy boronate ester which was characterized as a crystalline phenyl-carbamate. Removal of the phenylboronic acid residue gave a product identified as methyl a-L-rhamnopyranoside 4-N-phenylcarbamate, since it was identical with that resulting from removal of the ketal group from methyl 2,3-O-isopr opylidene-a-L-rhamnopyranoside 4-N-phenylcarbamate (12). This establishes the structure of the original ester as methyl a-L-rhamnopyranoside 2,3-phenylboronate (24). 

The conversion of arylboronic acids to the corresponding neopentyl glycol arylboronic esters has several advantages The esters are readily soluble in organic solvents, shelf stable, non-hygroscopic and easily characterized as a single entity.9 Furthermore, boronic esters can be utilized in many of the transformations where arylboronic acids usually are employed, making them an attractive alternative from a practical point of view. 

Cubic boron nitride (c-BN) is a different material altogether from h-BN, with a structure similar to that of diamond, which is characterized by extremely high hardness (second to diamond) and high thermal conductivity.As such, it is a material of great interest and a potential competitor to diamond, particularly for cutting and grinding applications. Its characteristics and properties are shown in Table 10.3... 

A structurally related tetrameric macroheterocycle is compound 13 that is prepared in a one-pot synthesis (yield 64%) from salicylaldehyde and (3-aminophenyl)boronic acid in methanol (Fig. 4). Due to its insolubility it has been characterized only by mass spectrometry. If a substitutent is introduced at the imine function (R = Me, Ph), trimeric structures (14 and 15) are... 

The phenyl ether oxygen atoms allow the two borazaphenanthrene rings to pivot with respect to each other, therefore this dimeric boronic acid anhydride can potentially exist in two isomeric forms, either face-to-face or helical (Fig. 18). In the face-to-face form the boron atoms of the bis(borazaphe-nanthrene) moieties have syn-orientation, while they have approximate anti-orientation in the helical form. Compound 68 has been characterized by X-ray crystallography in the helical form [109]. The dimensions of the cavity can be described by the transannular C C contacts between the carbon atoms in 2-position of the phenyl ether units, which have values of 5.12 and 6.21 A. 

Borasiloxanes are derivatives of the well-studied class of siloxanes (R2SiO) , in which part of the four-coordinate silicon atoms have been substituted by three-coordinate boron atoms. They are therefore characterized by the presence of Si-O-B units and can have one-dimensional oligomeric [120] or polymeric [121], two-dimensional cyclic [122-126], or three-dimensional cagelike [127-131] structures 83-92 as outlined in Figs. 23 and 24. 

Wells et al. characterized group 13-stibine adducts by single crystal X-ray structure analyses first in 1997 [35]. The solid state structures of three borane-stibine adducts of the type X3B—Sb(Tms)3 (X = Cl 6, Br 7, I 8), obtained by reaction of boron trihalides BX3 and Sb(Tms)3 in n-pentane, were determined. 

Hexaborides of a CaBg type are formed by K, the alkaline earths, Y and the larger lanthanides, as well as Th and some actinides ". The crystal structure of these compounds with cubic symmetry (Pm3m, O, ) (see Fig. 1) is characterized by a three-dimensional skeleton of Bg boron octahedra, the interstices of which are filled by metal atoms. The connection between two octahedra is by a B—B bond of length 1.66 X 10 pm, whereas the B—B bond lengths in one octahedron are 1.76 X 10 pm. ... 

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