Alkaline earth metals intermetallic compounds with

Bismuth with a formal oxidation state of —3 Is found In solid-state phases M3BI (M = alkali metal) and M3BI2 (M = alkaline-earth metal). The compound NasBl Is metallic. Less reduced intermetallic phases with the alkali metals and alkaline-earth metals are also known. Examples include MBi (M = Li, Na), MBl2 (M = K, Rb, Cs), and M Bia (M = Mg, Ca, Sr, Ba). The compounds M Bis (M = Ca, Sr, or Ba) superconduct at low temperatures. Some of these intermetallic phases have been extracted with amine solvents to yield anionic bismuth clusters in solution (see Section 2.8.2). 

General characteristics of alloys such as those presented in Fig. 3.3 have been discussed by Fassler and Hoffmann (1999) in a paper dedicated to valence compounds at the border of intermetallics (alkali and alkaline earth metal stannides and plumbides) . Examples showing gradual transition from valence compounds to intermetallic phases and new possibilities for structural mechanisms and bonding for Sn and Pb have been discussed. Structural relationships with Zintl phases (see Chapter 4) containing discrete and linked polyhedra have been considered. See 3.12 for a few remarks on the relationships between liquid and amorphous glassy alloys. 

Bismuthides. Many intermetallic compounds of bismuth with alkali metals and alkaline earth metals have the expected formulas M3Bi and M3Bi2, respectively. These compounds are not salt ike but have high coordination numbers, interatomic distances similar to those found in metals, and metallic electrical conductivities. They dissolve to some extent in molten salts (eg, NaCl—Nal) to form solutions that have been interpreted from cryoscopic data as containing some Bi3 . Both the alkali and alkaline earth metals form another series of alloylike bismuth compounds that become superconducting at low temperatures (Table 1). The MBi compounds are particulady noteworthy as having extremely short bond distances between the alkali metal atoms. 

The term Zintl phase is applied to solids formed between either an alkali- or alkaline-earth metal and a main group p-block element from group 14, 15, or 16 in the periodic table. These phases are characterized by a network of homonuclear or heteronuclear polyatomic clusters (the Zintl ions), which carry a net negative charge, and that are neutralized by cations. Broader definitions of the Zintl phase are sometimes used. Group 13 elements have been included with the Zintl anions and an electropositive rare-earth element or transition element with a filled d shell (e.g. Cu) or empty d shell (e.g. Ti) has replaced the alkali- or alkaline-earth element in some reports. Although the bonding between the Zintl ions and the cations in the Zintl phases is markedly polar, by our earlier definition those compounds formed between the alkali- or alkaline-earth metals with the heavier anions (i.e. Sn, Pb, Bi) can be considered intermetallic phases. 

The hydrides formed in reaction (a) may be classified as (1) saline or ionic hydrides, (2) metallic hydrides and (3) covalent hydrides. The saline hydrides include the hydrides of the alkali and alkaline-earth metals, except BeHj, which is covalent. Transition metals form binary compounds with hydrogen that are classified as metallic hydrides including rare-earth and actinide hydrides. Intermetallic compound hydrides, such as TiFeHj and LaNijH, may be thought of as pseudobinary metallic hydrides. 

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 . ... 

According to thermovolumetric measurements and IR and XRD evidence, the thermal dissociation of aU three alanates follows the same hydrogen evolution pattern [201-204] formation of the pentahydride (Eq. (6.26)), formation of the dihydride (Eq. (6.27)) and decomposition of the dihydride with formation of the corresponding alkaline earth metal-aluminum intermetallic compound (Eq. (6.28)). The pentahydrides can also be obtained by ball-milling M(A1H4)2 with dihydrides (Eq. (6.29)). 

Me Me + -I- ze . When no metal compounds are formed with mercury, the value of Eg is close to or equals zero [1]. Compounds of the alkali metals and the alkaline earths with mercury have the best-defined composition, while copper and zinc do not form any intermetallic compounds with mercury. The compositions of many intermetallic compounds are variable. In diluted amalgams, the compounds are dissociated to various degrees. 

Pu forms intermetallic compounds with intermediate solid solutions with most metallic elements. However, simple eutectic mixtures are usually made with the group Va and Via metals, and very little solubility in either the liquid or solid state is exhibited by alkali and alkaline earth metals. 

The A element is usually a rare earth or an alkaline earth metal and tends to form a stable hydride. The B element is often a transition metal and forms only unstable hydrides. Some weU-defined ratios of B to A in the intermetallic compound x = 0.5, 1, 2, 5 have been found to form hydrides with a hydrogen-to-metal ratio of up to two. 

Compounds of the first of the above-mentioned classes are conveniently called "metal-like refractory compounds, in view of their external and, particularly, internal resemblance to metals and intermetallic compounds The chemical bond in the lattices of these compounds, in addition to the s and p electrons of the metallic and nonmetallic components, respectively, is also formed by the electrons of the deeper, incomplete d and / levels of the transition metals, to which belong almost all metallic components of the metal-like refractory compounds. Isolated atoms of metals of the odd subgroup of group II, the alkaline earth metals, do not have any electrons in the d and / shells, but in compounds with nonmetals, energy states corresponding to these shells may occur. 

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