Thallium monohalides

The gas-phase molecular structures and dissociation energies of the seven monohalides MCI in Table 13 have all been determined by high-temperature spectroscopic studies. As expected, M-Cl bond distances increase, and the dissociation energies decrease as Group 13 is descended. Similarly Tl-X bond distances in the three thallium monohalides increase and the bond energies decrease as the halogen group is descended. 

Passing back to the boron group, if it is desired to form anhydrous chloride, it is necessary either to heat the element, or its oxide mixed with charcoal, in a current of chlorine, or, except in the case of boron, to prepare a double salt of the chloride with ammonium chloride, and to volatilise the latter after driving off the water the aqueous chlorides are formed by dissolving the oxides or hydroxides in hydrochloric acid. Thallium forms monohalides, sparingly soluble in cold water, and thereby attaches itself to the copper group. 

Certain metals, such as thallium, may give rise to two zero valent ions with different charges, e.g. Tl+ (5d10 6j2) and Tl3+ (5[Pg.328]

The most stable halides of boron and aluminum are the trihalides for thallium, the monohalides (TlX) are the most stable. Similarly, the most stable oxides of boron and aluminum are of the formula M2O3 for thallium, the most stable oxide is TI2O. Comment on this chemistry. 

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