Mono- and tri-chlorides of the Group 13 elements

At high temperatures the gaseous trichlorides suffer partial decomposition to form monochlorides and CI2  

The standard reaction enthalpies are positive, the standard reaction entropies negative the amount of monochloride increases with increasing temperature and decreasing pressure. For a given temperature and pressure the equilibrium shifts to the right as the group is descended from boron to indium. 

Thallium trichloride can be made, but decomposes at temperatures above 40°C to yield the solid monochloride and chlorine gas  

The mass spectra of the gas formed by evaporation of solid TICI3 shows that it contains significant amounts of the monochloride and chlorine in addition to the trichloride. 

We shall refer to a Group 13 atom that forms three single bonds as predicted by the Lewis electron pair model as Lewis-valent and to a Group 13 atom that forms just one single bond as subvalenl. M-Cl bond distances and bond dissociation energies of the gaseous 

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Table 11.1. Gaseous, monomeric mono- and tri-chlorides of the Group 13 elements M-Cl bond distances, R (in pm), and bond energies, Dq or MBE (in kJ mol ). The Tl-Cl bond distance and the mean bond energy of TICI3 are unknown, presumably because of the low stability of the gaseous trichloride relative to the monochloride. Gaseous monomeric trimethyl derivatives M-C bond distances and mean bond energies. ...

Gaseous, monomeric mono- and tri-chlorides of the Group 13 elements ... 

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