Brucite structure

Figure 2. The brucite structure of Ni(OH), (a) hexagonal brucite layer, in which the small circles are the Ni atoms and the large circles the O atoms and alternate O atoms are below and above the plane of the Ni atoms (b) stacking of the planes showing the orientation of the O-H bonds.

Table 2. Refined atomic coordinates for the brucite structure.

This compound is isostructural with brucite (Mg(OH)2) and Cdl2. The unit cell is hexagonal with a = 0.3258 nm and c = 0.4605 nm. The structure consists of sheets of corner-sharing, trigonally distorted Fe(OH)6 octahedra stacked along the [001] direction. The Fe" ions occupy only half the available octahedral interstices and this results in a structure in which each filled layer of sites alternates with an empty layer of sites. The OH radical behaves as a single entity. Amakinite is a rare mineral of the composition (Fe,Mg,Mn)(OH)2, also with brucite structure. Fe(OH)2 is readily oxidized by air and even by water, upon which the colour changes from white to brownish. The structure can be maintained up to a replacement of one tenth Fe" by Fe " (Bernal et al., 1959). 

It was easier to prepare clays using cations that formed a brucite structure rather than those forming a gibbsite structure. This is, in part, due to the difficulty of forming octahedrally coordinated Al3+ compounds in the presence of silicon at other than low pH conditions. Henin and co-workers believed that hydroxide sheets are formed on which silica is subsequently fixed. The presence of silica tends to cause the hydroxides to precipitate at lower pH than they normally do. Most of these experiments were carried on at 100°C, although crystalline products were obtained at temperatures of 20°C. The rate of formation varies in the ratio 1 560 between 0°C and 100°C. 

A hydrotalcite is regarded as a very basic support. It consists of platelets in a brucite structure, with Mg2+ ions octahedrally coordinated by O atoms. Part of the Mg2+ ions are isomorphically exchanged for Al3+ ions, creating a positive charge on the framework. Between the platelets, this positive charge is compensated with CO3" or OH ions. The OH ions located at the edge... 

Figure 9.1. Schematic representation of the interlayer structure of a M2+/M3+ LDH, based on the brucite structure. Interlayer anions (A" ) and water are present.

NiOi, NiiOj, NUO4 Oxidizing agents for various organics never isolated as pure oxides Exists in three modifications (a, j3 and /). The form has the brucite structure. The y form has a CdCl2 structure with an elongated cell 3149... 

The Mg(OH)2 brucite structure is a Cdl2 type with OH dipoles instead of single anions. The OH dipoles are oriented parallel to the hexagonal axis with the H atoms on the outer surface of the layers. Thus, each proton is located in the tetrahedral hole formed by the oxygen atom, to which it is covalently bonded, and three O atoms of the neighboring layer. The values for the O—H distance... 

As the nickel antigorite forms, electron micrographs show that the kiesel-guhr/silica gel/nickel hydroxide structure changes. Silica plates develop as layers of hydroxyl groups from the nickel hydroxide brucite structure react with silica tetrahedra. Coenen suggests that the antigorite layer acts as a reactive surface that combines with a further layer of nickel hydroxide. ... 

Neutralization of divalent elements around h = 2 leads to the rapid formation of stable hydroxides M(OH)2 (Table 2.1) which usually exhibit the lamellar brucite structure (Cdl2 structure) with /.T3—OH bridges on both sides of the cationic sheets [12d] (Figure 3.16). 

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