Beryllium , crystal structure

Table 21-IV shows some properties of the metals and their crystal forms. Since different crystal forms are involved in the series, trends in the properties are obscured. Figure 21-2 shows scale representations of the crystal structures of metallic beryllium, calcium, and barium.

THE STRUCTURE OF THE CARBOXYL GROUP. II. THE CRYSTAL STRUCTURE OF BASIC BERYLLIUM ACETATE... 

A colorless mineral known as corundum (composed of aluminum oxide) is colorless. A red variety of corundum known as ruby, a precious stone, owes its color to impurities of chromium within the crystal structure of corundum. Blue and violet varieties of corundum are classified as sapphires, the blue being the result of iron and titanium impurities, and the violet of vanadium impurities within the corundum crystal structure. Another colorless mineral is beryl (composed of beryllium aluminum silicate) but blue aquamarine, green emerald, and pink morganite, are precious varieties of beryl including different impurities aquamarine includes iron, emerald chromium and vanadium, and morganite manganese. 

Nucleophilic carbene 4 (R = Me, R = H) has been shown to disrupt the polymeric structure of beryllium dichloride to form an ionic carbene complex, 10 (15). The crystal structure of 10 revealed that the cation possesses a distorted tetrahedral coordination geometry at the beryllium center. The average Be-Cl bond distance (2.083(7) A) is... 

Investigations of the equilibria obtaining in solution have provided information concerning the stoichiometry and stability of the species formed when the beryllium ion is hydrolyzed. Although the identification of the minor species can never be regarded as definitive, there is little doubt that the principal species are Be2(OH)3+ and Be3(OH)3+ in acid solutions and Be(OH)3 and Be(OH)r in strongly basic solutions. Further support for these conclusions is provided by some crystal structures. The structure of [Be3(0H)3(H20)6]... 

The interaction of beryllium with nitrilotripropionic acid (H3ntp) has been investigated in some detail (244). This acid forms a strong complex (log Kt = 9.24) that can be isolated as a solid. The crystal structure of the anion [Be(ntp)] is shown in Fig. 23. The structure confirms the coordination of the nitrogen atom along with an oxygen atom from each carboxyl group. 

A summary of physical and chemical constants for beryllium is compiled in Table 1 (3—7). One of the more important characteristics of beryllium is its pronounced anisotropy resulting from the close-packed hexagonal crystal structure. This factor must be considered for any property that is known or suspected to be structure sensitive. As an example, the thermal expansion coefficient at 273 K of single-crystal beryllium was measured (8) as 10.6 x 10-6 parallel to the -axis and 7.7 x 10-6 parallel to the t-axis. The actual expansion of polycrystalline metal then becomes a function of the degree of preferred orientation present and the direction of measurement in wrought beryllium. 

The crystal structure of beryllium carbide is cubic, density = 2.44 g/mL. The melting point is 2250—2400°C and the compound dissociates under vacuum at 2100°C (1). This compound is not used industrially, but Be2C is a potential first-wall material for fusion reactors, one on the very limited list of possible candidates (see Fusion energy). 

The density of beryllium is 1.847 g/cm3 based upon average values of lattice parameters at 255C (a — 22.856 nm and c — 35.832 nm). Beryllium products generally have a density around 1.850 g/cm3 or higher because of impurities, such as aluminum and other metals, and beryllium oxide. The crystal structure is close-packed hexagonal. The alpha-form of beryllium transforms to a body-centered cubic structure at a temperature very close to the melung point. 

Fig. 4. Computer-generated crystal structure models nop row. left to right) Cuprite, zinc-blende, rutile, perovskite. iridymite (second row) Cristobalite. potassium dihydrogen phosphate, diamond, pyrites, arsenic (third rowt Cesium chloride, sodium chloride, wurtzite. copper, niccolite (fourth row) Spinel, graphite, beryllium, carbon dioxide, alpha i uanz. [AT T Bel Laboratories ...

To our knowledge there is no experimental evidence for n bonding between a BeR2 unit and a simple alkene or alkyne ligand. However a n interaction has been found in the X-ray crystal structure of the dimeric dipropynylberyllium trimethylamine adduct (48). The unit cell of this molecule contains two independent centrosymmetric dimers in which the alkynyl groups exhibit different types of interaction with the beryllium atoms, one of them forming an effectively electron-precise dimer unit by n interaction as portrayed in XX. 

The crystal structure of cyclopentadienylberyllium chloride has been determined by X-ray diffraction (280). As portrayed in CIII, the molecule has the same structure in the solid state as in the gas phase. These results rule out the possibility suggested by the mass spectrum (281) that H5C5BeCl is associated. Although not precisely located, the hydrogen atoms of the cyclopentadienyl ring show a slight tendency to bend toward the beryllium atom, in agreement with theoretical predictions (63). 

If we consider the fluorides, for example, which form pure coordination lattices (p. 33), then those from the alkaline earth metals with the exception of magnesium and beryllium crystallize in the fluorite structure, in which the cation is surrounded by eight fluorine ions for CaF2 and CdF2, which have the same structure, r+/r is 0.71 and 0.69 respectively just at the limit V 3— 1 — 0.73. The fluorides of other divalent ions, such as Mn, Fe, Co and Ni and also Mg, crystallize in a structure with coordination number six (rutile type). It is only for BeF2 that the ratio r+/r = 0.23 lies below the limit of this coordination number and it has a structure similar to that of cristobalite (Si02) with four neighbours (see also p. 66). 

With the exception of manganese and urauium, all true metals have one of the following crystal structures body-centered cubic (sodium, potassium, molybdenum), iron face-centered cubic (copper, silver, gold), iron close-packed hexagonal (beryllium, magnesium, zirconium). 

FIGURE 15.5. Beryllium chloride (a) in the gaseous state, and (b) in a crystal. In the gaseous state the coordination number of the beryllium is 2, in the crystal it is 4, giving a continuous series of BeCl tetrahedra that share edges, (c) A stereoview of the coordination in the crystal structure [diagrammed in (b)] (Refs. 44 and 45). 

The physicochemical properties of beryllium compounds and alloys have been reviewed subjects include phase diagrams, crystal structure, and density data on alloys and compounds, with a special section devoted entirely to halides and chalcogenides. ... 

As for the beryllium-bearing analcime, there is little difference between the diffraction patterns of the original specimens and those heated to 500°C, except for the lattice constant change from 13.35 to 13.02A. Therefore, one may assume little change in the crystal structure of the analcime during gradual dehydration. 

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