44 



SECTIONAL ADDRESSES 



and both these compounds exhibit the same evolution ot gas as does 

 monoethylenediaminotetra-w-propyldibromodigold on being heated to 

 their mehing points. Other cases of the initial production of free radicals 

 will be mentioned and their production from compounds containing 

 two 4-covalent auric gold atoms in the molecule always results in the 

 simultaneous production of a mixed auric-aurous compound in which 

 the gold atoms are 4-covalent and 2-covalent respectively. Such 

 decompositions as those just described raises the question of the possibility 

 of establishing the existence of chlorine and bromine derivatives of gold 

 having the formula AU2X4 (formerly written as AuXg and given as examples 

 of bivalent gold). Such halides would be mixed auric and aureus com- 

 pounds having the constitution : 



X X 



\ / ^^ 

 Au Au 



/ ^ / 

 X X 



and they may be produced as intermediate products in the decomposi- 

 tion — not completely reversible — of the trihalides to the monohalides. 



The first stable salt to be isolated in this series of organic gold com- 

 pounds was the colourless highly crystalline auric compound ethylene- 

 diaminodiethylgold bromide, 



Br 



which with its homologues has proved of utility in the preparation of 

 the dialkyl and diaryl compounds. Although evidence of the formation 

 of the analogous ammonia and pyridine compounds 



Br 



has been obtained they are too unstable (owing to loss of one molecule 

 of the volatile base resulting in the formation of the non-electrolytes 

 already mentioned) to be isolated. The corresponding co-ordination 

 compound of diethylmonobromogold with the asymmetrical N-diethyl- 

 ethylenediamine is of special interest (Brain and Gibson 1938). The 

 interaction of these two substances in molecular proportions results in 

 the production of a colourless crystalline compound soluble in water 

 and also soluble in benzene. The compound therefore appears to be 

 both a salt and a non-electrolyte. Bearing in mind that the co-ordinating 

 power of tertiary amines is less than that of primary amines it might be 



