Crystal packing energies

It is suggested that there are two possible conformations for the bridging cyclopropyl groups the syn form (Vila) observed in the crystal and the anti form (Vllb) that appears from minimum energy calculations to be more stable in solution (100). These differences and some of the angles seem to result from crystal packing energies in the solid state versus the less constricted form in solution. 

The physical state and melting point of a phosphonium salt are a function of the crystal packing energy, which in turn is controlled mainly by a combination of the asymmetry of the cation and anion as well as the shielding and or delocalizing of... 

The coefficients can be drawn from experimental values (but this is limited to the cases in which there is one site only for both A and B), from ad hoc calculations, or by a fitting of AE values. In the past, large use has been made of experimental AE values, derived, e. g., from crystal packing energies, but now the main sources are the variationally computed... 

The parameters in the original parameterization are adjusted in order to reproduce the correct results. These results are generally molecular geometries and energy differences. They may be obtained from various types of experimental results or ah initio calculations. The sources of these correct results can also be a source of error. Ah initio results are only correct to some degree of accuracy. Likewise, crystal structures are influenced by crystal-packing forces. 

The packing energy of an organic crystal can be easily calculated by a lattice sum over pairwise interactions. The potential parameters for these calculations are summarized in Table 15. The packing energy is usually a quite accurate estimate of the crystal sublimation energy. 

As already anticipated, the molecular surface we calculate is useful in describing condensed state properties. There is a steady linear relationship between Sn, and packing energy for organic crystals and the suiphoxide and suiphone compounds make no... 

In the gas phase, ions may be isolated, and properties such as stability, metal-ligand bond energy, or reactivity determined, full structural characterization is not yet possible. There are no complications due to solvent or crystal packing forces and so the intrinsic properties of the ions may be investigated. The effects of solvation may be probed by studying ions such as [M(solvent) ]+. The spectroscopic investigation of ions has been limited to the photoelectron spectroscopy of anions but other methods such as infrared (IR) photodissociation spectroscopy are now available. 

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