Alkaline earth dihalides

Many of these conclusions from vibrational spectroscopy have been confirmed by other techniques, such as diffraction methods. This is also true for some alkaline-earth dihalides, which were investigated as matrix-isolated species by IR and Raman spectroscopy and studied in the gas phase with the help of electron diffraction e.g., MgC electron diffraction in the gas phase d Mxcn = 219 pm, a = 180° (Gershikov and Spiridonov, 1981) matrix-isolated MgCl2 V] = 327 cm", vi = 93 cm, v, = 601 cm (Lesieki and Nibler, 1976). The bonding and the structures of all alkaline-earth metal dihalides have been discussed in detail (Spoliti et al., 1980). 

Table 12 Calculated equilibrium structures of alkaline earth dihalides EX2 ...

Efremova and Matizen (11) reported that the phase transition for SrF occurs over a short temperature interval (1421-1484 K). There are no discontinuities in their enthalpy data in this temperature range. Other alkaline earth dihalides (1J ), which have the calcium fluoride structure, are known to exhibit similar behavior, and this fact would seem to rule out the possibility that the observed transition resulted wholly from impurities. We speculate that the two crystalline forms, a and 0, of SrPg are practically... 

Syntheses that exploit the solubility of the alkaline-earth metals in liquid ammonia have proven practical for alkoxide work, as they generate high yields, reaction rates, and purity (Table 8, Equation (3)). In a refinement of this approach, Caulton and co-workers have used dissolved ammonia in an ethereal solvent, usually THF, to effect the production of a number of alkoxides of barium, and this method has also been examined with calcium and strontium (Table 8, Equations (4a) to (4c)). Displacement reactions using alkali metal alkoxides and alkaline-earth dihalides (Table 8, Equation (5)), and between alkaline-earth hydrides or amides and alcohols (Table 8, Equations (6) and (7)), have been examined, but alkali-metal halide impurities, incomplete reactions, and unexpected equilibria and byproducts can affect the usefulness of these approaches. 

The molecular structures of the gas-phase alkaline-earth dihalides have been a source of continuing interest. Gas-phase electron diffraction (GED) and mass spectrometric (MS) measurements confirm that the vapor phase structure of BeCl2 at 274 °C is mostly that of a linear monomer, with a thermal average Be—Cl distance of 1.798(4) A. A small amount (2.5%) of a halide-bridged dimer form is also present, however, with Be—Clterm= 1-83(1) A, Be— Clbridg= 1-97(2), and Cltem—Be—Clbridg= 134(4)°. Dimers (ca. 1%) have also been detected in M 2 vapor. ... 

The group IIA metals are oxidized by halogens and all the alkaline earth dihalides are known h... 

The gaseous molecules of the alkaline-earth dihalides are also 16-electron molecules, but are presumably ionic rather than covalent molecules some are linear, as expected, others apparently non-linear (p. 373). 

For a recent contribution to the study of non-VSEPR structures of alkaline earth dihalides see Levy, J. B. Hargittai, M. J. Phys. Chem. 2000, 104, 1950-1958 and references therein. 

Kim, Y.S. and Gordon, R.G. (1974) Theory of binding in ionic crystals Application to alkali-halide and alkaline-earth dihalide crystals Phys. Rev. B9, 3548-3554. 

---