Alkali metals crystal structure

Table 5.4. Alkali metals crystal structures, lattice parameters of their allotropes, calculated...

Number of Protons/Electrons 11 Number of Neutrons 12 Classification Alkali Metal Crystal Structure Cubic... 

Boiling Point 774.0 °C (1047.15 K, 1425.2 °F) Number of Protons/Electrons 19 Number of Neutrons 20 Classification Alkali Metal Crystal Structure Cubic Density 293 K 0.862 g/cm ... 

Anhydrous double sulfates ( alum anhydrides ) M M (S04)2 are formed by A1 and Ga with NH4 or the alkali metals Crystal structure determination establishes that Al is... 

All the alkali metals crystallize into bcc structures, (a) Find an equation relating the metallic... 

Bidentate /3-diketonates usually have symmetric structure, and many crystal structures show sets of equal M—O, C—C and C—O bonds. Alkali metal enolate structures are symmetric as well as those for the Pd, Rh and A1 enolates. Few structures show unequal M—O distances these enolate complexes (M = Ge, Sn and Sb) are asymmetric as the metal atom is not located at equal distances from the nearest oxygen atoms . 

Titanates and titanoniobates of the general formula A2-vTi vNbv02 +1 (A = alkali metal) crystallize in layered structures possessing [Ti , vNbv02 +i sheets stacked with interlayer A ions [1, 2]. The sheets may be obtained from edge-connected layers of double-ReOr units by shearing every n-octahedron perpendicular to the sheets. Idealized structures of some of these oxides are shown in Figure 1. Several oxides in this family are known to exhibit interlayer chemistry... 

The alkali metals crystallize in the body-centered cubic (bcc) structure at atmospheric pressure (Fig. 21.12). A unit cell of this structure contains two lattice points, one at the center of the cube and the other at any one of the eight corners. A single alkali-metal atom is associated with each lattice point. An alternative way to visualize this is to realize that each of the eight atoms that lie at the corners of a bcc unit cell is shared by the eight unit cells that meet at those corners. The contribution of the atoms to one unit cell is therefore 8 X = 1 atom, to which is added the atom that lies wholly within that cell at its center. 

At present a large variety of solid compounds are called Zintl phases. The name Zintl phase was introduced by Laves According to Laves, Zintl phases are those intermetallic compounds which crystallize in typical non-metal crystal structures. For these compounds one expects an ionic contribution to the chemical bond. This definition has been extended to a large number of solid compounds formed by alkali or alkaline earth metals with metallic or semimetallic elements of the fourth, fifth and partly third group of the Periodic Table for which common structural and bonding properties have been found. The crystal structures and chemical properties of these compounds have been studied extensively . ... 

Now make a similar count for an alkali metal, such as sodium. The alkali metals crystallize in a structure that gives to each atom eight nearest neighbours, and thus the number of bonds per atom is four. Since an alkali metal atom has only one electron in its outermost shell, the number of electrons available per atom is one, whereas eight would be needed to supply each bond with a pair of electrons. The large electron deficiency gives the electrons much freedom. 

Examples of metals that form cubic closest packed solids are aluminum, iron, copper, cobalt, and nickel. Magnesium and zinc are hexagonal closest packed. Calcium and certain other metals can crystallize in either of these structures. Some metals, however, assume structures that are not closest packed. For example, the alkali metals have structures characterized by a body-centered cubic (bcc) unit cell (see Fig. 10.9), where the spheres touch along the body diagonal of the cube. In this structure, each sphere has 8 nearest neighbors (count the number of atoms around the atom at the center of the unit cell), as compared with 12 in the closest packed structures. Why a particular metal adopts the structure it does is not well understood. 

Among the alkali metals, Li, Na, K, Rb, and Cs and their alloys have been used as exohedral dopants for Cgo [25, 26], with one electron typically transferred per alkali metal dopant. Although the metal atom diffusion rates appear to be considerably lower, some success has also been achieved with the intercalation of alkaline earth dopants, such as Ca, Sr, and Ba [27, 28, 29], where two electrons per metal atom M are transferred to the Cgo molecules for low concentrations of metal atoms, and less than two electrons per alkaline earth ion for high metal atom concentrations. Since the alkaline earth ions are smaller than the corresponding alkali metals in the same row of the periodic table, the crystal structures formed with alkaline earth doping are often different from those for the alkali metal dopants. Except for the alkali metal and alkaline earth intercalation compounds, few intercalation compounds have been investigated for their physical properties. 

Fig. 2. Structures for the solid (a) fee Cco, (b) fee MCco, (c) fee M2C60 (d) fee MsCeo, (e) hypothetical bee Ceo, (0 bet M4C60, and two structures for MeCeo (g) bee MeCeo for (M= K, Rb, Cs), and (h) fee MeCeo which is appropriate for M = Na, using the notation of Ref [42]. The notation fee, bee, and bet refer, respectively, to face centered cubic, body centered cubic, and body centered tetragonal structures. The large spheres denote Ceo molecules and the small spheres denote alkali metal ions. For fee M3C60, which has four Ceo molecules per cubic unit cell, the M atoms can either be on octahedral or tetrahedral symmetry sites. Undoped solid Ceo also exhibits the fee crystal structure, but in this case all tetrahedral and octahedral sites are unoccupied. For (g) bcc MeCeo all the M atoms are on distorted tetrahedral sites. For (f) bet M4Ceo, the dopant is also found on distorted tetrahedral sites. For (c) pertaining to small alkali metal ions such as Na, only the tetrahedral sites are occupied. For (h) we see that four Na ions can occupy an octahedral site of this fee lattice.

For the alkali metal doped Cgo compounds, charge transfer of one electron per M atom to the Cgo molecule occurs, resulting in M+ ions at the tetrahedral and/or octahedral symmetry interstices of the cubic Cgo host structure. For the composition MaCgg, the resulting metallic crystal has basically the fee structure (see Fig. 2). Within this structure the alkali metal ions can sit on either tetragonal symmetry (1/4,1/4,1/4) sites, which are twice as numerous as the octahedral (l/2,0,0) sites (referenced to a simple cubic coordinate system). The electron-poor alkali metal ions tend to lie adjacent to a C=C double... 

Fig. 10. Unpolarized Raman spectra (T = 300 K) for solid Ceo, KaCeo, RbsCeo, NaeCeo, KaCco, RbeCeo and CseCeo [92, 93], The tangential and radial modes of Ag symmetry are identified, as are the features associated with the Si substrates. From the insensitivity of these spectra to crystal structure and specific alkali metal dopant, it is concluded that the interactions between the Cao molecules are weak, as are also the interactions between the Cao anions and the alkali metal cations.

Tanuma, S., Synthesis and structure of quasi-one-dimensional carbon crystal carbolite and intercalation with alkali metals and halogens. In Supercarbon, Synthesis, Properties and Applications, ed. S. Yoshimura and R. P. H. Chang, Springer-Verlag, Heidelberg, 1998, pp. 120 127. 

In addition to the above oxides M2O, M2O2, M4O6, MO2 and MO3 in which the alkali metal has the constant oxidation state 4-1, rubidium and caesium also form suboxides in which the formal oxidation state of the metal is considerably lower. Some of these intriguing compounds have been known since the turn of the century but only recently have their structures been elucidated by single crystal X-ray analysis. Partial oxidation of Rb at low temperatures gives RbeO which decomposes above —7.3°C to give copper-coloured metallic crystals of Rb902 ... 

The predominantly ionic alkali metal sulfides M2S (Li, Na, K, Rb, Cs) adopt the antifluorite structure (p. 118) in which each S atom is surrounded by a cube of 8 M and each M by a tetrahedron of S. The alkaline earth sulfides MS (Mg, Ca, Sr, Ba) adopt the NaCl-type 6 6 structure (p. 242) as do many other monosulfides of rather less basic metals (M = Pb, Mn, La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Th, U, Pu). However, many metals in the later transition element groups show substantial trends to increasing covalency leading either to lower coordination numbers or to layer-lattice structures. Thus MS (Be, Zn, Cd, Hg) adopt the 4 4 zinc blende structure (p. 1210) and ZnS, CdS and MnS also crystallize in the 4 4 wurtzite modification (p. 1210). In both of these structures both M and S are tetrahedrally coordinated, whereas PtS, which also has 4 4... 

The variation that exists in the 0 F ratio of MMe6Oi5F-type compounds enables isomorphic replacement of alkali metal cations by other cations with appropriate radii. For instance, a copper-containing compound, Cuo.6Nb6Oi4 6F( 4, which crystallizes in a LiNbeOisF type structure, was obtained [255]. 

Compounds of the same stoichiometry type usually have the same type crystal structure within the row of alkali metals K - Rb - Cs rarely the same type structure with sodium-containing analogues and never ciystallize similarly with lithium-containing compounds. The crystal structure analysis of different fluoride and oxyfluoride compounds clearly indicates that the steric similarity between all cations and tantalum or niobium must be taken into account when calculating the X Me ratio. 

The adsorption of alkali metals on single crystal surfaces can result in the formation of ordered structures (commensurate or incommensurate super-... 

The saline hydrides are white, high-melting-point solids with crystal structures that resemble those of the corresponding halides. The alkali metal hydrides, for instance, have the rock-salt structure (Fig. 5.39). 

In closely related studies, the molecular and crystal structures of lithium, sodium and potassium N,N -di(p-tolyl)formamidinate and N,N -di(2,6-dialkyl-phenyl)formamidinate complexes have been elucidated. These showed the anions to be versatile ligands for alkali metals, exhibiting a wide variety of binding modes. ... 

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