Metaborate chain

Fig. 8-1.—A portion of the infinite metaborate chain (BO ) in CaBt04 (left), and the metaborate ring [B 0 ] in K BtO . Small circles represent boron atoms, large circles oxygen atoms.

Metaboric acid, HB02, is reported69 to contain chains of linked tetrahedra and triangles. 

Extended anions in which individual BCty gioups are linked into lings or chains, such as B3 0 3 or B2 042 (metaborate). 

Chain Bj04(0H) and sheet B Of /3-Metaboric acid-II 448) CsBjOs... 

Information is also directly available about the electron distribution in the B-0 bond from x-ray diffraction studies (Gajhede et al., 1986 Kirfel et al., 1983) and, indirectly, from studies of the gradient of the electric field at B and O (Snyder et al., 1976 Gajhede, 1985 Tossell and Lazzer-etti, 1988a Tossell, 1990b). For solid lithium metaborate, LiBO, with chains of BO, triangles, x-ray studies yield deformation densities that do... 

The oxygen to boron ratio of the metaborates (2 1) requires that at least one of the oxygen atoms must be shared between two boron atoms to obtain the customary boron coordination number. Metaborates with the triangular BO3 group crystallize in (a) a trimeric ring structure, or (h) a chain structure. Sodium and potassium metaborates and orthorhombic... 

Ur any 1, Sodium and Calcium Metaborate. The spectra of uranyl, sodium, and calcium metaborates are illustrated in Figure 1, and Table II lists the absorption maxima for three compounds. The bands in the 92% B compounds are also located. Data on the sodium and calcium salts, as representative of the ring and chain metaborate structures, are in agreement with results reported by Goubeau and Hummel (6). The spectra given by Wier and Schroeder (20) are more complex and may not represent pure phases. 

The three metaborate spectra each have two strong bands in the asymmetric B—O stretching region. — 1450 and — 1220 cm." ). The higher frequency band is identified with the side-chain or branch oxygen atom, while the lower frequency band is identified with a ring or chain... 

Of the borates much the most common are the metaborates these have chain and ring forms. Sodium metaborate, correctly formulated NagBgOg, contains the six-membered ring ions ... 

Calcium metaborate, typical of the bipositive metal borates, has negatively charged chains ... 

Orthorhombic metaboric acid is built of molecules 8303(011)3 which are linked into layers by O—H—O bonds (Fig. 24.13). Monoclinic metaboric acid is apparently built of chains of composition [8304011(0112)], recognition of the OH group and the H2O molecule resting on the location of the H atoms. The direct bonding of a water molecule to B is most unexpected. Cubic HBO2 has a framework structure built from tetrahedral BO4 groups with hydrogen bonds between certain pairs of O atoms. 

Other discrete and chain-polymer anions can be formed by linking of two or more rings by shared tetrahedral boron atoms, in some cases with dehydration (cf. metaborate below). 

The cyclie groups occur at metaborates, as the rings of (B O ), for example, K B O, or as groups in infinite chains of B-0 bonding, with the infinite repetition of the (B02) formula, for example, CaB20. Note that the stratified structures are less spread to borates than to silicates. 

Metaboric acid is known to exist in three modifications. The stable room-temperature modification crystallizes in a cubic three-dimensional structure. Of the two modifications one has a monoclinic chain structure, while the other is orthorhombic of the layer type [43]. In this latter modification B303(0H)3 molecules are fixed in a perfectly planar network by hydrogen bonds, O—H 0, of 2.68 to 2.83 A length (Figure 31). Centre-related layers are separated by... 

Metaboric acid HBO2 forms various crystal structures by dehydration of the trimer (7 >100°C). The orthorhombic form, obtained by quenching, is made of trimer l ings linked by hydrogen bonds in a layered structure (Figure 4.10c). The monoclinic form is made of chains [B304(0H)(0H2)L iu which 3- and 4-coordinated boron coexist. In the cubic form, BO4 tetrahedra are linked by hydrogen bonds (6). 

---