B.— CHEMISTRY 47 



presence of concentrated acids. The corresponding salts with the halogen 

 acids, hydrocyanic acid and thiocyanic acid have, however, not been 

 obtained. 



(c) Cyano derivatives of organic gold compounds (Gibson, Burawoy and 

 Holt 1935, Burawoy, Gibson, Hampson and Powell 1937). 



By the direct action of silver cyanide on the dialkylmonobromogold 

 compounds, the corresponding cyano derivatives are easily prepared. 

 These compounds have unique properties and the detailed investigation 

 of the ethyl and w-propyl compounds have revealed a number of interesting 

 features in connexion with the general chemistry of gold. 



The dialkylmonocyanogold compounds are colourless highly crystalline 

 non-electrolytes, soluble in hydrocarbon solvents, and their molecular 

 weights in freezing bromoform are four times those required by their 

 empirical formula. These compounds, therefore, unlike any other gold 

 compounds so far described contain four atoms of tervalent gold in the 

 molecule. In the molecule of such compounds, the gold atoms must be 

 attached to the carbon atoms of the cyanogen groups and the nitrogen 

 atoms must be co-ordinated to neighbouring gold atoms. 



Constitution (I) (R = Et, Pr") indicating a symmetrical twelve atom 

 planar ring structure is the only possible one in keeping with the stereo- 

 chemical configuration of the cyanogen group, with the small dipole 

 moment — \i = 1-47 d in carbon-tetrachloride at 25° for the «-propyl 

 compound — with the 4-covalency of auric gold atoms and, as will be 

 pointed out later, with the results of X-ray crystallographic investigation. 



R R 



1 I 



R— Au— C=N^Au— R 



f I CN CN 



N C 



R— Au^N=C— Au— R 



I 1 



R R 



R— Au^NHa— C2H4— H.N^Au— R 



N I I 



I R R 



II 



CN 



III 



