Molecular Structure and Thermochemistry of Tin Dibromide Monomers and Dimers. A Computational and Electron Diffraction Study

Abstract

The molecular structure of tin dibromide was investigated by high-level computational methods and gasphase electron diffraction. The structural and vibrational characteristics of both SnBr 2 and Sn 2 Br 4 were determined by computations. To reach an agreement between computed and experimental bond lengths for SnBr 2 , very large bases and correlated methods are needed. For the dimer Sn 2 Br 4 , two low-energy geometries were found, one with C s and the other with C 2V symmetry, the former with somewhat lower energy. Thermodynamic functions for gaseous SnBr 2 and Sn 2 Br 4 and their dimerization reaction have been calculated on the basis of the computed structures.

Vapor phase tin diiodide: its structure and thermodynamics, a computational study

“…1 These structures were calculated at higher computational levels as well and their geometrical parameters are given in Table 2. These two structures are very similar to the ones found stable for tin dichloride and dibromide [5,[11][12][13], perhaps one difference can be mentioned: for the C 2v -symmetry isomer the central four-membered ring puckers towards the terminal iodines, while in the tin dichloride and dibromide dimers this puckering is in the opposite direction; obviously the large size of the iodine atoms being the reason. The terminal bond lengths of the dimer are about 0.02-0.04 Å longer than the corresponding monomer bonds, and the bridging bonds are considerably, about 0.16-0.18 Å , longer than the terminal bonds-as expected.…”

“…The density functional calculations consistently gave several hundredths of an angstrom larger bond lengths and also somewhat larger bond angles than the MP2 calculations. We had a similar experience with our calculations of the SnBr 2 structure [12]. Since the MP2 and CCSD(T) computed geometries of the monomer agreed much better with the experimental results than the density functional ones, our discussion is based on these results.…”

“…The general consensus about metal dihalide dimer structures used to be that they have a D 2h -symmetry halogen-bridged structure. However, as recent computational results show, this does not apply to the tin dihalides in that the stereochemical activity of the lone electron pair on tin does have its influence on the dimer structure just as it does on the structure of the monomer [5,[11][12][13][14]. Two different structures were found for these dimers, one with C s and the other with C 2v symmetry, usually with the lower-symmetry structure being the ground state.…”

Magdolna Hargittai’s inorganic structures

“…Magdi and her co-workers found structures that were fully consistent with the presence of such lone pairs. Figure 6 demonstrates the models [14,15]. The two structures are of very similar energies, therefore, if they appear in the vapor phase, probably both would appear.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 18, 2007) and the discipline

“…Thermodynamic calculations show that, although the geometry of the dimer is very different from the usual D 2h symmetry arrangement of metal dihalide dimers, this difference hardly has any effect on thermodynamic functions of the dimer. Related studies of gaseous tin dichloride [300,301] and dibromide [302] were earlier reported and in addition, Br/I exchange enthalpies in related mixed tin dihalide dimers have also been investigated [303].…”