Borates structure

A variety of organoboron polymer electrolytes were successfully prepared by hydroboration polymerization or dehydrocoupling polymerization. Investigations of the ion conductive properties of these polymers are summarized in Table 7. From this systematic study using defined organoboron polymers, it was clearly demonstrated that incorporation of organoboron anion receptors or lithium borate structures are fruitful approaches to improve the lithium transference number of an ion conductive matrix. 

Sato et al. [195] have studied the surface borate structures and the acidic properties of alumina-boria (3-20 wt.%) catalysts prepared by impregnation method using B(MAS)-NMR measurements and TPD of pyridine, as well as their catalytic properties for 1-butene isomerization. The number of Brpnsted acid sites was found to increase with increasing boria content, and the catalytic activity was explained by the strong Brpnsted acid sites generated by BO4 species on the surface of alumina. 

Borates can be viewed as complex salts in which the Lewis basicity of the structural unit must match the Lewis acidity of the interstitial complex to produce a stable structure. The relationship between basicity of the borate structural unit and its BO4/BO3 ratio was mentioned above, indicating that each specific structural unit has an associated basicity. It was recently shown that the Lewis basicity of borate structural units correlates with the average coordination number of the oxygen atoms they contain, counting H-bonds... 

Many borates are known that contain non-metal cations. Examples include the ammonium borates [39], such as the commercial products ammonium pentaborate, NH4[B506(0H)4] 2 H2O, and ammonium tetraborate, (NH4)2 [6405(011)4] 2 H2O, both of which contain isolated borate anions shown above (Figs. 5a and 6a, respectively) [40]. Isolated borate anions containing more than six boron atoms are rare. However, the mineral ammonioborite [(NH4)3[Bi502o(OH)g] 4 H20 = (NH4)20 5 B2O3 2 2/3 H2O), which may be prepared synthetically by prolonged reflux of a saturated solution of ammonium pentaborate, contains the unusual isolated anion [Bi502o(OH)g] , shown in Fig. 10 [41]. This anion is not known to occur in any metal borate, its formation is apparently directed exclusively by the ammonium cations which can donate H-bonds to interstitial water and the borate structural unit. 

Direction of borate structures by specific cations is also illustrated by the formation of the unusual nonaborate anion in the presence of the imidazo-lium, [C3H7N2], and guanidinium, [C(NH2)3], cations [42]. The reaction of imidazole with three molar equivalents of boric acid in aqueous solution results in the spontaneous formation of the imidazolium salt of the [B90i2(OH)6] anion, shown in Fig. 11, associated with three [C3H7N2] ... 

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... 

Kernite (Na2[B40s(0H)2] 3 H2O = Na20 2 B2O3 4 H2O) is also an important industrial mineral that is mainly used to produce refined borates, boric acid and borax. The polymeric borate structure of the kernite is shown in Fig. 7b above. Upon hydration, kernite converts to the monomeric borate tincal, which dissolves more readily. Thus, kernite may be hydrated to facilitate processing into borax. Although primarily a raw material for the manufacture of refined borates, concentrates of this mineral have been used as industrial products. 

This review gives a brief presentation of the basic concepts and calculation methods of the "anionic group theory" for the NLO effect in borate crystals. On this basis, boron-oxygen groups of various known borate structure types have been classified and systematic calculations were carried out for microscopic second-order susceptibilities of the groups. 

The most common units found in borate structures are shown in Fig. 1. Many of the known borate structures can be rationalized by assigning appropriate charges, protons, or hydroxyl groups (which change the coordination of boron from trigonal to tetrahedral) to these basic units. Thus the B03 unit can become BOj -, B(OH)3, or B(0H)4, respectively. Polymerization by elimination of one water molecule between two hydrated units results in chain formation, and further water elimination gives sheets or networks. These operations are illustrated in Fig. 2 for the triborate ring unit. 

Table I lists many of the known hydrated borate structures, except for those containing silicon. The compounds are arranged according to structural similarity under the classification of Christ and Clark (80)...

Fig. 1. Basic units of borate structures. All trigonally coordinated boron atoms shown can theoretically become tetrahedrally coordinated.

Common Name Methylaminoethanolcatechol borate Adrenalin borate Structural Formula ... 

In recent years, interesting new borate structures have been determined by X-ray diffraction. Therefore, it seems appropriate to survey this new development and to update a previous review ... 

In 1970, Heller suggested a classification of borates based on the number of boron atoms in the fundamental building block . In 1971, J. R. Clark added, in an article on crystal chemistry of borates , a further principle as the fifth rule, namely that "the boric acid group, B(OH)3, may exist in isolated form in the presence of more complex polyanions, or such insular groups may themselves polymerize and attach to side-chains of more complex polyanions , as first observed in the crystal structures of veatchite and paraveatchite. In 1977, Christ and Clark reviewed the various principles and classifications in their article on a crystal-chemical classification of borate structures with emphasis on hydrated borates . In addition to a sixth rule. 

Christ, C. L., and J. R. Clark (1977). A crystal-chemical classification of borate structures with emphasis on hydrated borates. Phys. Chem. Minerals 2, 59-88. 

Many borate structures exist and are fairly interesting. They are stable in air and have been considered for use as important nonlinear optical materials and as hosts for luminescent materials, particularly when the excitation of high energy photons is required, for example, LuMgBsOii Tb, Ce and SrBaO Eu. 

Taking into consideration the above concept, it is intuitively obvious that the simplest way to assess quantitatively acid-base properties of the anhydrous borates is to estimate the dependence of polymerization of anions in the borate structures on the sizes and valences of cations, and also on the ratio (N) of the total number of B03 triangles and BO4 tetrahedra (NB) to the total amount of cations (NM) contained in the borate structural formula N = Nb/Nm. From the crystallochemical point of view it is clear that the increase of the N-ratio increases the anion polymerization and the ratio Nb3+/No2. It leads to a decrease in the oxygen activity coefficient and simultaneously, to more acid properties of these compounds. Also, the value of n = nA/no (nA - number of triangles, - number of tetrahedra) increases (for N < 1), i.e. the ratio of the number of BO3 triangles to BO4 tetrahedra in the structures of compounds increases. 

Numerous anhydrous borate structures can be reduced to various combinations of three types of basic structural units 1) fundamental structural units, 2) combined basic structural units, and 3) full radicals of polyanions. The stability of the FSU, CSU and CRP units in solid and liquid borates is one of the most important issues, and will provide a better understanding of, and control of, phase formation in complex borate systems. 

Other borate structures containing tetrahedrally coordinated boron Coordination groups ranging from BO4 to B(OH)4 are found in some borates, and we shall note here a number of the more interesting structures. 

A wide range of borate structures contain the isolated triangular BOs group (1), while a fewer number contain the isolated tetrahedral B04 group (2). The triangular group tends to be quite symmetrical with O-B-0 angles near 120° and a B-0 distance near 1.3 75 that varies as the sum of the B... 

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