Metal halide molecules

It is a fundamentally important point that the reaction (12) involving abstraction of a hydride ion from the monomer by a cation is essentially different from Kennedy s reaction (6) in which the neutral metal halide molecule acts as a hydride ion abstractor [12]. 

For floppy systems, such as many metal halide molecules, the rg/re differences may be even much greater than those listed in Table 3. Alkaline earth metal, zinc, and transition metal dihalides, for example, have been extensively investigated by gas-phase electron diffraction (see e.g., [33-36]). The structure determinations have involved a joint electron diffraction/vibrational spectroscopic analysis (cf. [37]). Depending on the model potential used, and among them on the manner in which anharmonic effects are taken into account, even the r distances are rather different. This is illustrated by the data of Table 4. The re distances obtained from experimental data applying various model potentials [32] have the following... 

Large-amplitude, low-frequency intramolecular vibrations may lower the molecular symmetry of the average structure from the higher symmetry of the equilibrium structure. Some examples from metal halide molecules are shown in Figure 3-47. 

Figure 3-47. Equilibrium versus average structures of simple metal halide molecules with low-frequency, large-amplitude deformation vibrations.

Simple aUcah 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. 

Halides.—Theoretical calculations have been performed on both alkali-metal halide molecules and crystals. " In an analysis of the dipole moments of alkali-metal halide molecules, the extent of effective charge transfer was found to vary from 0.76 (Lil) to 0.99 (CsF), in an order that is predictable from the Periodic Table. 

It is seen that all the calculated dipole moments are higher than the true, experimental values. The average deviation between estimate and experiment amounts to 32% of the experimental value, so it is clear that the charge distribution in alkali metal halide molecules deviates significantly from that predicted from the spherical ion model. 

BOND DISTANCES IN ALKALI METAL HALIDE MOLECULES... 

The bond in a gaseous alkali metal halide molecule may be ruptured in such a way that one obtains two neutral atoms ... 

Bond distances in alkali metal halide molecules... 

The most straightforward way to describe the strength of the M-Cl bonds in a gaseous metal halide molecule MX/t is probably to use the mean bond energy, MBE, which is obtained by dividing the standard energy of atomization with the number of M-X bonds k ... 

For the catalyst systems using metal halides, the optimum ratio of metal/IL was sometimes observed to be 2 [18,19,24]. This may be explained by simultaneous activation of two epoxide molecules by one metal halide molecule and two IL molecules (Scheme 6). Zinc tetrahalide ILs also showed notable activity for the reaction. Similar cooperative actions of the Zn center of [ZnX2Y2]2" (Lewis acid) and a halide anion (Lewis base) liberated from the dianion were proposed for the epoxide ting opening [15,16,21]. 

Scheme 6. Simultaneous activation of two epoxide molecules by one metal halide molecule and two IL molecules.

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