Alkali metal halides dimers

The potential energy of alkali metal halide dimers... 

THE POTENTIAL ENERGY OF ALKALI METAL HALIDE DIMERS... 

Alkali metal halide dimers calculation of equilibrium bond distances and dissociation energies... 

ALKALI METAL HALIDE DIMERS CALCULATION OF EQUILIBRIUM BOND 77... 

Of great importance as precatalysts in organolanthanide-catalyzed processes are lanthanide hydrocarbyls containing the bulky bis(trimethylsilyl)methyl ligand. They are also the most suitable precursors for the preparation of the dimeric hydrides [(C5Me5)2Ln(/t-H)]2. Such compounds can be isolated completely free of coordinating solvents and alkali metal halides Eq. (2) [19-25. ... 

Chemiluminescence and photoluminescence in diatomic iron oxide, Rb2, and alkali-metal dimers with halogen atoms and metal vapour-oxidant flames,202 203 lifetime measurements of selectively excited states of diatomic hydrides,204 photodissociation of alkali-metal halide vapours,206 spin-orbit relaxation of the HTe ( 2IIi) radical,20 the photodecomposition of metal carbonyl anions such as [Mn(C04)] in the vapour phase,207 and the fluorescence of Rhodamine 6G in the vapour phase 208 have been studied in recent reports. In the last study it was concluded that an insufficient concentration of the fluorescing dye could be maintained in the vapour phase to permit laser action to occur. 

Simple alkali metal halide molecules, for example NaCl and KCl, are found in the vapors above heated samples of the solid compounds. These vapor species have been studied by IR spectroscopy of gases and matrices, and by gas electron diffraction. The studies show that planar rhombic dimers are also present. 

Alkali halide vapor consists mainly of monomers and dimers. As stated in Sec. 1-22, Linevsky developed a technique to isolate these monomers and dimers, produced at high temperature, in inert gas matrices. This technique has been used extensively to study the infrared spectra and structures of a number of inorganic salts. Some references on metal halide dimers are LiF)2. (LiCOz, (LiBr)2, and (NaX)2 (X = F, Cl, Br, and 1). These dimers are known to be cydic-planar (02 ). On the other hand, (T1X)2(X — F and Cl) are linear and symmetrical (Doo X-Tl-Tl-X). Such structures have been well known for (HgX)2 (X = C1, Br, and 1). The dimer LiO)2 is also cyclic-planar. However, (Nbl)2 is frans-planar (C2J,) in a Nj matrix but takes the cis structure upon complex formation with the Cr(CO)s group. ... 

Table 7 Values of internuclear distances and angles for dimers of alkali-metal halides...

While this is probably the best reference that can be found, it seems important to remark that ionic radii depend on the environment surrounding the ions, that is, on the force field in which the ions lie. Studies of the ion pairs formed in alkali metal halide vapour show that the distance between anion and cation may be 20 % smaller than the interionic distance for the same pair in the crystal. Dimers in the vapour phase have a distance between anion and cation which is intermediate between that in the monomer and that in the crystal. When an alkali salt melts, the first-neighbour distance may decrease up to... 

The alkali metal halides, MX, fonn solids at room temperature. The best known member of the family, NaCl, melts at 801°, the vapor pressure reaches 1 torr at 865°, and the melt boils at 1413°. The dominant species in gaseous alkali metal halides is the monomeric formula unit, MX(g), but smaller amounts of dimers (M2X2), trimers (M3X3) and tetramers (M4X4) have also been detected by mass spectroscopy. Information about the monomeric molecules obtained by spectroscopic studies at high temperatures is collected in Table 5.1 [1]. 

Table 5.2. Coordination numbers, C, Madelung constants, M, and calculated bond distance ratios, R R, for gaseous, monomeric alkali metal halides MX, gaseous square dimers M2X2, for cubic tetramers M4X4 and for MX crystals with rock-salt structures.

HEP readily reacts with hydrogen, chlorine, and bromine (but not iodine), by an addition reaction similar to other olefins [57-59]. Similarly, HE, HCl, and HER (but not HI), add to HEP. By reacting HEP with alcohols, mercaptans, and ammonia, hexafluoro ethers (CF3CFHCF20R), hexafluoro sulfides (CF3CFHCF2SR), and tetrafluoropropionitrile (CF3CFHCN) are obtained. Diels-Alder adducts have been identified fi om the reaction of anthracene, butadiene, and cyclopentadiene with HEP. Cyclic dimers of HEP can be prepared at 250-400°C under autogenous pressure [49]. Linear dimers and trimers of HEP can be produced catalytically in the presence of alkali metal halides in dimethylacetamide [48]. 

Vilcu and Misdolea [143] applied the significant structure theory and considered dimeric gaseous species too, obtaining acceptable values of the calculated constant volume heat capacity, but not of the constant pressure values. Contrary to these results, the constant pressure heat capacity calculated by Lu et al. [142] agreed with the experimental data, but the estimated critical temperatures were only 49-76 % of the values in Table 3.3, with opposite trends regarding the sizes of the anions. This was remedied by Cheng et al. [144] who applied a version of the significant structure theory to the estimation of thermophysical quantities for the same alkali metal halides as studied by Lu et al. [142] with acceptable success. 

In the reactions of 10.13a with alkali metal terr-butoxides cage expansion occurs to give the sixteen-atom cluster 10.15, in which two molecules of MO Bu (M = Na, K) are inserted into the dimeric structure. The cluster 10.13a also undergoes transmetallation reactions with coinage metals. For example, the reactions with silver(I) or copper(I) halides produces complexes in which three of the ions are replaced by Ag" or Cu" ions and a molecule of lithium halide is incorporated in the cluster. ... 

Simple transition metal halides react cleanly with alkali metal boratabenzenes. In this way sandwich-type complexes 32 of V (27), Cr (64), Fe (58), Ru (61), and Os (61) have been made. The corresponding nickel complexes seem to be nonexistent, quite in contrast to NiCp2 in attempted preparations, mixtures of diamagnetic C—C linked dimers were obtained (29). In the manganese case, high sensitivity to air and water has precluded preparative success until now. Some organometallic halides have added further variations to the main theme. The complexes 33 of Rh and 34 of Pt were obtained from [(COD)RhCl]2 and [Me3PtI]4, respectively (61). 

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