Halides crystal structure

The induction energy is inlierently non-additive. In fact, the non-additivity is displayed elegantly in a distributed polarizability approach [28]. Non-additive induction energies have been found to stabilize what appear to be highly improbable crystal structures of the alkalme earth halides [57]. 

The melting and boiling points of the aluminium halides, in contrast to the boron compounds, are irregular. It might reasonably be expected that aluminium, being a more metallic element than boron, would form an ionic fluoride and indeed the fact that it remains solid until 1564 K. when it sublimes, would tend to confirm this, although it should not be concluded that the fluoride is, therefore, wholly ionic. The crystal structure is such that each aluminium has a coordination number of six, being surrounded by six fluoride ions. 

The formation of acyl halide-Lewis acid complexes have been observed by several methods. For example, both 1 1 and 1 2 complexes of acetyl chloride, with AICI3 can be observed by NMR spectroscopy. The existence of acylium ions has been demonstrated by X-ray diffraction studies on crystalline salts. For example, crystal structure determinations have been reported for /i-methylphenylacylium and acetylium ions as SbFg salts. There is also a good deal of evidence from NMR measurements which demonstrates that acylium ions can exist in nonnucleophilic solvents. " The positive charge on acylium ions is delocalized onto the oxygen atom. This delocalization is demonstrated in particular by the short O—C bond lengths in acylium ions, which imply a major contribution from the structure having a triple bond ... 

The crystal structures of the halides of the heavier Group 2 elements also show some interesting trends (Table 5.3). Por the fluorides, increasing sizx of the metal enables its... 

Table 5.3 Crystal structures of alkaline earth halides ...

Turning next to an ionic crystal, where the ions may be regarded as spheres, the total volume of the crystal is equal to the volumes of these spheres, together with the appropriate amount of void space between the spheres. To take the simplest case, it is convenient to discuss a set of substances, all of which have the same crystalline structure—for example, the 17 alkali halide crystals that have the NaCl structure. 

Figure 19-4 contrasts the effective sizes of the halide ions. Each of these dimensions is obtained from the examination of crystal structures of many salts involving the particular halide ion. The effective size found for a given halide ion is called its ionic radius. These radii are larger than the covalent radii but close to the van der Waals radii of neutral atoms. 

The formation of the combination of defects may be described as a chemical reaction and thermodynamic equilibrium conditions may be applied. The chemical notations of Kroger-Vink, Schottky, and defect structure elements (DSEs) are used [3, 11]. The chemical reactions have to balance the chemical species, lattice sites, and charges. An unoccupied lattice site is considered to be a chemical species (V) it is quite common that specific crystal structures are only found in the presence of a certain number of vacancies [12]. The Kroger-Vink notation makes use of the chemical element followed by the lattice site of this element as subscript and the charge relative to the ideal undisturbed lattice as superscript. An example is the formation of interstitial metal M ions and metal M ion vacancies, e.g., in silver halides ... 

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

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). 

The elucidation of the factors determining the relative stability of alternative crystalline structures of a substance would be of the greatest significance in the development of the theory of the solid state. Why, for example, do some of the alkali halides crystallize with the sodium chloride structure and some with the cesium chloride structure Why does titanium dioxide under different conditions assume the different structures of rutile, brookite and anatase Why does aluminum fluosilicate, AljSiCV F2, crystallize with the structure of topaz and not with some other structure These questions are answered formally by the statement that in each case the structure with the minimum free energy is stable. This answer, however, is not satisfying what is desired in our atomistic and quantum theoretical era is the explanation of this minimum free energy in terms of atoms or ions and their properties. 

Fig. 2.—The arrangement of ions in cube-face layers of alkali halide crystals with the sodium chloride structure.

Dithiocarbamate complexes of copper have been sythesized at a high rate. Reports of new complexes include the morpholine-4- (44), thio-morpholine, AT-methylpiperazine-4-, and piperidine- (291) dithiocarba-mates. Novel, polymeric complexes of the type Cu(pipdtc)2 (CuBr) in = 4, or 6) and Cu(pipdtc)2 (CuCl)4 have been prepared by reactions of[Cu(pipdtc)2] with the respective copper halide in CHCla-EtOH (418). The crystal structures of the polymers are known to consist of sheets of individual [Cu(pipdtc)2] molecules linked to polymeric CuBr chains via Cu-S bonds. A series of copper(I) dtc complexes have been the subject of a Cu and Cu NQR-spectral study (440). 

The telluride halides crystallize in monoclinic lattices, but only In-TeBr and InTel are isotypic 162). InTeCl forms a layer type of structure, as do InSCl and its analogs, but, owing to the size of the Te atom and the enhanced covalency of the In-Te bond, only a coordination number of 4 for indium is realized. The structure is built up of strongly distorted, InTesraCli/j tetrahedra that share the corners and edges occupied by Te atoms. The Cl atoms are coordinated to one tetrahedron each, and do not take part in the layer formation 324, 325). 

With boron and an appropriate amount of some sort of alkaline metal halide present in the starting materials for the solid-state reactions, then we obtain zirconium cluster materials belonging to the 6-14 family. Single-crystal X-ray data of products from iodine-rich reactions were used to determine the crystal structures of Na[(Zr6B)Cl3.87(5)lio.i3], and Cs[(Zr6B)Cl2.i6(5)lii.84] [21]. Both phases... 

Fig. 10 Fragment of crystal structures of tetracyanopyrazine complexes with halides showing coordination of anions to four, three or two acceptor moieties in Bu4N+[C1, (TCP)4] (a), Et4N+[(Br )2, (TCP)3] (b) and Bu4N+[r, (TCP)] (c) salts, respectively [23]...

The (EDT-TTF-I)2Br salt described above [36] and the 1 1 (TTFI4)I salt reported by Gompper [51] were the only structurally characterized salts with simple halide anions until Imakubo recently described an extensive series of Cl" and Br" salts from several ortho-diiodo tetrathiafulvalene, tetraselena-fulvalene and dithiadiselenafulvalene derivatives (Scheme 8) [62], The X-ray crystal structure analysis of the nine salts described there show a variety of halogen bonded motifs, demonstrating the adaptability of the supramolecu-lar interactions to other structural requirements imposed by the nature of the heteroatoms (O, S, Se) in the TTF frame. Indeed, in (EDT-TTF-l2)2X-(H20)2 (X = Cl, Br), a bimolecular motif (Fig. 6) associates two partially oxidized EDT-TTF-I2 molecules with one Br" anion and one water molecule. 

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