54 SECTIONAL ADDRESSES 



are two ways in which the two compounds may be linked together in the 

 complex. In the one case, the gold atoms may be connected thus : 



Br 



^ \ 

 Au Au 



^ / 



Br 



the aurous gold atom having four valencies — two co-ordinately attached 

 bromine atoms (shown), a co-ordinately attached sulphur (of dibenzyl- 

 sulphide) atom and a covalently attached bromine atom — tetrahedrally 

 disposed, while the auric gold atom has its four valencies in a plane, 

 three being covalent links attached to bromine atoms and a co-ordinate 

 link from the sulphur atom of dibenzylsulphide. The dissociation of 

 the complex in non-aqueous solvents might then be explained by the 

 particular disposition of the co-ordinate Br -> Au links since, in the stable 

 mixed aurous-auric compounds already known and some of which have 

 been referred to above, such linkages are alternately disposed thus : 



Br 



Au Au 



K / 

 Br 



In the other case arising from suggestion {a) the solid complex may 

 consist of alternate auric and aurous units linked together by co-ordination 

 of a bromine atom from the former to the latter, each aurous unit being 

 linked to two auric units. The simplest possible molecule would thus 

 be a ring containing two auric and two aurous units thus : 



Br SBz2 



I \ 



BzgS^Au— Br-»Au— Br 



I - t 

 Br Br 



I I 



Br— Au-^Br -Au^SBz2 



t I 



SBz2 Br 



If, in this case, the four valencies (three co-ordinate and one covalent) 

 of the aurous gold atoms are as we would expect tetrahedrally disposed, 

 the structure becomes much more complicated than is represented by 

 the above plane diagram. Arising from suggestion (6), there is the 

 possibility that in the solid state an auric unit becomes linked to an aurous 

 unit by the bromine atom of the latter becoming co-ordinately linked to 

 the gold atom of the former. The auric atom now becomes 5-covalent 

 and its five valencies may assume a pyramidal configuration whereas the 

 four valencies of the auric atom had a planar configuration. This would 

 appear to cause the minimum displacement of atoms in the two units 



