Monohalides gaseous

The reverse reaction to give the gaseous species AlX(g) at high temperature accounts for the enhanced volatility of AIF3 when heated in the presence of A1 metal, and the ready volatilization of A1 metal in the presence of AICI3. Using calculations of the type outlined on p. 82 the standard heats of formation of the crystalline monohalides AIX and their heats of disproportionation have been estimated as ... 

Like AIX (p. 233), GaF and InF are known as unstable gaseous species. TTie other monohalides are more stable. GaX can be obtained as reactive sublimates by treating GaXs with... 

Special synthetic routes are necessary to gain access to the metastable monohalides of A1 and Ga, since they are thermodynamically unstable at room temperature toward disproportionation into A1 metal and A1X3 or Ga metal and GaX3. First, the gaseous MX species, that are thermodynamically stable at high temperatures,22 have to be synthesized. A variety of methods are available for their preparation, some of which are shown in equations (a)-(c) of Scheme 2. 

A method for the synthesis of Al and Ga clusters has been described by Schnepf and Schnockel (2002) which is based on the preparation of the gaseous monohalides subsequently isolated in metastable solutions at — 78°C. The halogen atoms are substituted by bulky groups and, in a parallel disproportionation reaction, large Al (or Ga) clusters are formed. 

New thermodynamic data have also been reported for the gaseous rare earth monohalides (Yokozeki and Menzinger, 1976). The dissociation energies of SmF, SmCl and YbF (DJ Sr 121,100,124 kcal/mol, respectively) have been obtained from molecular beam chemiluminescence measurements. 

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