Boron nitrogen anions

In covalent azides, the pseudohalogen azide RN3 has an angular structure as in HN3. Triazidoborazine [H3N3B3(N3)3] and other boron azides, for example, salts of the tetraazidoborate ion B(N3 (4 have been considered as boron nitride precursors (see Boron-Nitrogen Compounds). The M(Ns)3 azido complexes of the other group 13 elements (Al, Ga, In, Tl) and their M(N3)4 tetraazido anions are all known. They and their derivatives are also used as precursors for the nitrides. 

The 6-membered B3O3 ring also occurs in many more complex borate anions. Cyclic boron-nitrogen molecules are considered later in this chapter. The cyclic molecule (c), X = SH, is the predominant species in the vapour of HBS2 at temperatures below 100°C. In the crystalline tribromo compound of type (c), (BrBS)3, the molecular structure (d) was found. 

The interactions of PABA with RNA were investigated with UV-Vis and PM-IRRAS spectroscopy. Figure 3.33 shows the absorption spectra of a PABA layer (both salt and base form) and a PABA/RNA bilayer. The layer of PABA in the salt form (Figure 3.33, a) exhibits the characteristic absorption bands around 400 and 800 nm attributed to tt-tt and bipolaron band transitions, respectively [53, 54]. The blue shift in the bipolaron band of the base form of the PABA layer (Figure 3.33, b) from 800 to 740 nm was observed upon exposure to PBS at pH 7.4 because of the removal of D-fructose and fluoride [37]. Subsequent complexation of the PABA layer in its base form with RNA resulted in a red shift in the bipolaron band from 740 to 800 nm, together with a small increase in the absorbance. These results reportedly confirmed the complexation of RNA with PABA under neutral conditions by the formation of the bilayer through anionic boronate esters, and subsequent conversion of the base form of PABA back to a self-doped salt form. The creation of the anionic tetrahedral boron forms the basis of multilayer formation. Further, the formation of boronate esters and a boron-nitrogen dative bond, as well as electrostatic interactions of anionic phosphates with cationic amines is supported by PM-IRRAS spectroscopy. After complexation... 

The boron-nitrogen bond features in the remaining structures. The first crystal-structure analysis of a stable optically active compound with boron as the asymmetric centre has been reported. This is (-h)-4-methylpyridine-trimethylamlne-bromo-hydroboron hexafluorophosphate. The structure contains two independent anions and cations, and in each case the geometry and absolute stereochemistry are the same. There is very little difference between the B-N bonds to the pyridine (1.57 A) and trimethylamine (1.59 A) ligands. The Br-B-N and N-B-N angles are all very close to the tetrahedral value. 

The Fermentation Process The process by which this antifungal substance is produced is an aerobic fermentation of an aquaous nutrient medium inoculated with a pimaricin-producing strain of Streptomycesgihrosporeus. The nutrient medium contains an assimilable source of carbon such as starch, molasses, or glycerol, an assimilable source of nitrogen such as corn steep liquor and Inorganic cations such as potassium, sodium or calcium, and anions such as sulfate, phosphate or chloride. Trace elements such as boron, molybdenum or copper are supplied as needed in the form of impurities by the other constituents of the medium. 

A remarkable variety of compounds in the Ca-(B,C,N) system has opened a window for research in related fields. With the elements boron, carbon and nitrogen, substance classes such as borocarbides, boronitrides, and carbonitrides can be considered to contain anionic derivatives of binary compounds B4C, BN, and C3N4. Until now, most compounds in these substance classes have been considered to contain alkali, alkaline-earth, or lanthanide elements. Lanthanide borocarbides are known from the work of Bauer [1]. Lanthanide boronitrides represent a younger family of compounds, also assigned as nitridoborates [2] following the nomenclature of oxoborates. 

Structures of the lanthanide nitridoborates appear as layered structures with approximate hexagonal arrangements of metal atoms, and typical coordination preferences of anions. As in many metal nitrides, the nitride ion prefers an octahedral environment such as in lanthanum nitride (LaN). As a terminal constituent of a BNx anion, the nitrogen atom prefers a six-fold environment, such as B-N Lns, where Ln atoms form a square pyramid around N. Boron is typically surrounded by a trigonal prismatic arrangement of lanthanide atoms, as in many metal borides (Fig. 8.10). All known structures of lanthanide nitridoborates compromise these coordination patterns. 

Lipophilic ion exchangers traditionally used for polymeric membrane preparation are the anionic tetraphenylborate derivatives and the cationic tetraalkylammonium salts. The charges on both lipophilic ions are localized on a single (boron or nitrogen) atom, but the steric inaccessibility of the charged center, due to bulky substituents, may inhibit ion-pair formation in the membrane and provide, when necessary, non-specific interactions between ionic sites and sample ions. 

Application of the equivalent cores method to solid compounds is slightly more complicated, requires additional assumptions, and is therefore less accurate than the application to gaseous compounds. However, fairly good correlations have been obtained for solid compounds of boron, carbon, nitrogen, and iodine20. The correlations were restricted, because of the nature of the assumptions involved, to molecular compounds or to compounds in which the core-ionized atoms are in anions. 

To develop an additive that selectively coordinates with salt anions and frees lithium ion for conduction, McBreen and co-workers pursued a molecular design and tailor-synthesis approach that yielded several families of novel compounds based on nitrogen or boron centers with strongly electron-withdrawing substituents. 

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