Crystal structures types, metals

S Tantalum and niobium are present in the crystal structure in the form of complex ions. The lowest coordination number, 6, corresponds to the formation of slightly distorted octahedrons. The linking and packaging of the octahedrons depends on the X Me ratio, where X is the total number of oxygen and fluorine atoms, and Me is the total number of tantalum or niobium ions as well as other metals that can replace tantalum or niobium in the octahedral polyhedron. The crystal structure type can be defined based on the X Me ratio, as follows ... 

The fourth and final crystal structure type common in binary semiconductors is the rock salt structure, named after NaCl but occurring in many divalent metal oxides, sulfides, selenides, and tellurides. It consists of two atom types forming separate face-centered cubic lattices. The trend from WZ or ZB structures to the rock salt structure takes place as covalent bonds become increasingly ionic [24]. 

Daams, J.L.C., Villars, P. and van Vucht, J.H.N. (1991) Atlas of Crystal Structure Types for Intermetallic Phases (Materials Park, Oh 44073 American Society for Metals), Vol. 1 1. 

Remarks on the crystal chemistry of the alloys of the 3rd group metals. A large number of intermediate phases have been identified in the binary alloys formed by the rare earth metals and actinides with several elements. A short illustrative list is shown in Tables 5.19 and 5.20. Compounds of a few selected rare earth metals and actinides have been considered in order to show some frequent stoichiometries and crystal structure types. The existence of a number of analogies among the different metals considered and the formation of some isostructural series of compounds may be noticed. 

Crystallographic data (.continued) for transition metal tetrafluorides, 27 98 for transition metal trifluorides, 27 92 Crystallographic disorder, nitrosyl groups, 34 304-305 Crystallography fuscoredoxin, 47 380 prismane protein, 47 232-233 Rieske and Rieske-type proteins, 47 92-109 Crystal radii, of various ions, 2 7 Crystals, 39 402 Crystal structure actinide metals, 31 36 copper-cobalt supetoxide dismutases, 45 ... 

There are two types of objects in supramolecular chemistry supermolecules (i.e., well-defined discrete oligomolecular species that result from the inter-molecular association of a few components), and supramolecular arrays (i.e., polymolecular entities that result from the spontaneous association of a large, undefined number of components) (4, 5). Both are observed in some metal-xanthate structures to be described herein. The most frequent intermolecular forces leading to self-assembly in metal xanthates are so-called secondary bonds . The secondary bond concept has been introduced by Nathaniel W. Alcock to describe interactions between molecules that result in interatomic distances longer than covalent bonds and shorter than the sum of van der Waals radii (6). Secondary bonds [sometimes called soft-soft interactions (7)] are typical for heavier p-block elements and play an important role as bonding motifs in supramolecular organometallic chemistry (8). Other types of intermolecular forces (e.g., Ji- -ji stacking) are also observed in the crystal structures of metal xanthates. 

Two crystal structures of metal complexes of a,a-trehalose 133 are reported. Two Cd (tren) residues are chelated by the Glcp-02,03 and the Glcp-02, 03 diolato moieties, respectively, in the dinuclear complex 135 (O Fig. 29). As in free a,a-trehalose in the crystalline state, direct intramolecular hydrogen bonds are not found due to conformational restraints, but two sequences of the type 02 ---H-0 ---H-06 with a linking water molecule H2O" are observed (the reversed direction is found in free a,a-trehalose) [153]. Only one of the two Glcp-02,03-chelation sites of a, a -trehalose is chosen in a mononuclear complex with Ni-Me3tren, the iVA, iV -trimethyl analog of Ni-tren, in which no support by an intramolecular... 

As noted in section 6.2, when the material of interest is an intermetallic alloy, the solution of its crystal structure may be simplified because intermetallics often form series of isostructural compounds. In contrast to conventional inorganic and molecular compounds, stoichiometries of the majority of intermetallic phases are not restricted by normal valence and oxidation states of atoms and ions therefore, crystal structures of metallic alloy phases are conveniently coded using the classification suggested by W.B. Pearson. According to Pearson, each type of the crystal structure is assigned a specific code (symbol), which is constructed from three components as follows ... 

The crystal structures of metallic oxides include examples of all four main types, molecular, chain, layer, and 3D structures, though numerically the first three classes form a negligible fraction of the total number of oxides. The metals forming oxides with molecular, chain, or layer structures are distributed in an interesting way over the Periodic Table. 

To build up a theory of metallic phase stability the conventional arguments for the discussion of crystal structures have to be completed by the concept of spatial correlation of electrons. The parameters of the spatial correlations may be analyzed from the ample empirical material of determined crystal structures by means of several evident rules. The surprising result is that for many crystal structures two correlations are essential for understanding the special features of the crystal structures. This two-correlations model makes possible an easy survey of metallic structures. Two examples of crystal structure-type families are considered, the Cu-family and the W-family. 

An extended material of valence electron spatial correlations (VEC) had been analyzed (Schubert, 1964), when it became apparent that one correlation of valence electrons alone is not sufficient for the explanation of crystal structures of metallic phases. The outer core electrons had to be taken into consideration. This may best be seen from the crystal structure of indium (Fig. 4) The lattice matrix of In may be given in diagonal form ai = (4.59 4.59 4.95) A. The explicit lattice constants are needed for verification that the proposed VEC is acceptable. The VEC is aj = aAi(l, —1,0 1,1,0 0,0,3/2) and may be decomposed into the equations at = a j + a2 a2 = - aj + a2 a3 = 3 a3/2, which may be verified by means of Fig. 4. If a correlation lattice is inserted into a crystal structure, this does not mean that there are positions of increased electron density in the cell, it only gives the commensurability which is favorable energetically. It is easily verified that the number of valence electron places per cell is = 12 and is equal to the number of valence electrons in the cell given above = 12. The A1 type of the VEC had been inferred from the diamond struc-... 

Tlie aim of this chapter is to provide an overview of materials where fast transport of alkali metal cations and protons is observed. A general discussion of factors affecting conductivity and techniques used to study ion migration paths is followed by a review of the large number of cation conductors. Materials with large alkali ions (Na-Cs) are often isostructural and therefore examined as a group. Tire lithium conductors with unique crystal structure types and proton conductors with unique conduction mechanisms are also discussed. 

Formula weight 204.63. Dark green powder, stable in air at room temperature oxidizes at 400°C in a stream of Og with pronounced incandescence. Decomposes spontaneously in vacuum at about 450°C. Soluble in dilute mineral acids and cone, hydrochloric acid with formation of the corresponding ammonium salt and partial formation of Cu metal. Decomposes violently with cone. H3SO4 and HNO3. d 5.84. Crystal structure type DOg. Heat of formation (25°C) +17.8 kcal./mole. 

ZnsASg Gray. Gives off AsHa with acids. M.p. 1015°C d (x-ray) 5.62. Sublimes at the m.p. to give needles or lamellae. Possesses metal-type conductivity. Hardness 3. Crystal structure type D5g (ZUaPg type). 

TiSg Formula weight 112.02. Brass-yellow flakes with a metallic luster, d 3.22. Crystal structure type C6. 

Atomic weight 50.95. Light-gray metal, ductile when pure. M.p. 1900°C d 6.11. Insoluble in hydrochloric and sulfuric acids, soluble in nitric and hydrofluoric acids. High affinity for O, N, C and H. Surface reactionwith atmospheric Og starts already at 20°C this can lead, particularly in the case of a fine powder, to considerable contamination. Crystal structure type Ag. 

There is a wealth of crystal lattice types of interest in this review. We can differentiate between solid CT complexes and ion-radical salts. The former are the solid-state equivalents of the Mulliken solution CT complexes, and are the "two-chain" crystals. The latter are the so-called "one-chain" compounds, or ion-radical salts, where the organic cation (anion) crystallizes with inorganic anions (cations) as counterions. The crystal structure types have been reviewed by Herbstein [61], Tanaka [62], Soos [63-65] and many others. TaWes 1 and 2 update a classification introduced by Soos [63] and modified later by Wiygul et al. [66]. A few examples are shown diagrammatically in Fig. 4. The IS lattices are the ion-radical salts the IM lattices are the CT crystals, the crystal equivalents of the solution CT complexes. The 2S lattices are the first organic metals found (TTF-TCNQ). 

The above calculations suggest that for simple crystal structures in metals and ionic crystals the surface stresses are positive. This is consistent with a qualitative consideration of how the surface atoms (ions) interact with the underlying atoms in the crystal, i.e. the net attractive interactions should be stronger than the net repulsive interactions. However, for more complex structures a can he zero or even negative for certain orientations. For example, III-IV semiconducting compounds, such as GaAs, can form two types of (111) surfaces. One surface is terminated hy a plane of Ga atoms and the other is terminated hy a plane of As atoms [6]. The calculated value for the former surface is —1,000 mJ/m and for the latter is -1-500 mJ/m. Unfortunately, the lack of experimental measurements of a makes evaluation of the accuracy of the calculations difficult. Finally, it should he re-emphasized that. 

Figure 9.1 Crystal structures of metal oxides, (a) MgO rock salt type. Mg coordination number (CN) 6 O CN 6. (b) Ce02 fluorite-type, Ce CN 8, O CN 4. (c) T1O2 rutile, Ti CN 6, O CN 3. (d) Si02 quartz, Si CN 4,0 CN 2. (e) WO3, Re03 type, acmally distorted, W CN 6, O CN 2. (f) M0O3 layered structure, the coordinations are questionable, (g) Cr03 linear polymer, Cr CN 4, O CN 1 and 2...

Fig. 13 Crystal structure of metal diborides with AIB2 type structure. [Color figure can be viewed in the electronic version.] Reprinted with permission from ref. 52, Copyright 2013, Wiley-VCH Verlag GmbH Co. KGaA. 

Crystal structure. For appreciable solid solubility, the crystal structures for metals of both atom types must be the same. 

A consequence of the spherical symmetry of the electron distribution of an ion and the nondirectional nature of the interaction between ions is that a relatively few crystal structure types are required, and in fact used by simple ionic substances, in contrast to the much greater number adopted by simple covalently bonded substances and metals. 

Another recent database, still in evolution, is the Linus Pauling File (covering both metals and other inorganics) and, like the Cambridge Crystallographic Database, it has a "smart software part which allows derivative information, such as the statistical distribution of structures between symmetry types, to be obtained. Such uses are described in an article about the file (Villars et al. 1998). The Linus Pauling File incorporates other data besides crystal structures, such as melting temperature, and this feature allows numerous correlations to be displayed. 

There is a lively controversy concerning the interpretation of these and other properties, and cogent arguments have been advanced both for the presence of hydride ions H" and for the presence of protons H+ in the d-block and f-block hydride phases.These difficulties emphasize again the problems attending any classification based on presumed bond type, and a phenomenological approach which describes the observed properties is a sounder initial basis for discussion. Thus the predominantly ionic nature of a phase cannot safely be inferred either from crystal structure or from calculated lattice energies since many metallic alloys adopt the NaCl-type or CsCl-type structures (e.g. LaBi, )S-brass) and enthalpy calculations are notoriously insensitive to bond type. 

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