A study of the vapour-phase equilibria over tin(II) chloride

Structure and Thermodynamics of the Tin Dichloride DimerA Computational Study

“…Consequently, it may seem plausible that during the vaporization process it is the dimers and not the monomers that evaporate. This is supported by the fact that according to the thermodynamic measurements the heat of sublimation of dimers is about the same as that of monomers in the crystalline phase (see Table of ref ). It is reasonable to assume that the dissociation of the dimers into monomers takes place in the vapor phase and the monomer−dimer equilibrium is being established there.…”

“…The equilibrium constants for the dimerization were taken from Table 6 of the paper of O'Brien and Mucklejohn, 11 who studied the vapor-phase equilibria over SnCl 2 by a combination of different experimental techniques. (Note that the equilibrium constant for the dimerization is the reciprocal of their value given for the dissociation reaction.)…”

“…This should not be surprising, since the temperature dependence of K p changes drastically with increasing temperature (see Figure 4 in ref 11). The dissociation enthalpy of Sn 2 Cl 4 in the vapor in equilibrium with the crystalline phase below the melting point (518 K) was also determined by O'Brien and Mucklejohn, 11 and an average value of 82 ( 12 kJ mol -1 was obtained at 494 K, which is smaller than the value above the melting point of tin dichloride. Since individual K p values are not given in the paper, it was not possible to calculate ∆ r H°m(298.15) by the third-law evaluation method.…”

“…The mass spectra of SnCl 2 have also been studied repeatedly, mostly because of its importance in high-pressure discharge lamps. ,− Although the conclusions of these studies are not the same, it seems that there is only a very small fraction of dimeric molecules in the vapor over solid and molten SnCl 2 and that the mole fraction of the dimer decreases with temperature, at least in the measured temperature range of about 600−900 K.…”

Thermochemistry of tetrabromoditin and bromoiodotin gaseons

“…However, the two values are significantly higher than the values reported for the dissociation of (SnCl2)2(g): 495 K) = 82 ± 12 kJ mol"1 (ref 31) and A,//°m(298.15 K) = 95.4 kJ mol"1 (ref 32). The influence of the different temperature on the value from ref 31 is negligible. The comparatively low enthalpy values for the dissociation of (SnCl2)2(g) are in contradiction to the increase of electronegativity in the order I, Br, and Cl.…”