The preparation of the bivalent complex of ruthenium, hexammineruthenium( 11) chloride [RuIL( NH,),] CI,. is described. This compound is a powerful reducing agent and this property is exemplified in many of the reactions which have been studied. The isolation of the compound has made it possible to prepare several ammine complexes of ruthenium not previously described and has opened routes to known complexes previously difficult of, preparation. Its reaction with sodium chloroaurate which, under certain conditions, leads to the oxidation of ruthenium to the octavalent state, is particularly noteworthy.FEW ammine complexes of ruthenium(I1) such as are reported here l y 2 have been described. Some trichelate complexes 3 s 4 of bipyridyl (bipy) , [Ru11bipy3]Clg or terpyridyl (terpy), [RuII(terpy),]Cl, are known. Gleu and his collaborators5 prepared a series of ammonia complexes of ruthenium(I1) containing five, four, or two ammine groups, the remaining groups in the complexes being six-co-ordinate , mainly comprising sulphur-containing radicals such as SO,2-, SO,H-, or SO,. Typical compounds are [ RUI~(NH,)~(SO~H),] , Na4[RuI1(NH,),-(SO,),( S0,H)J ,6H,O , [RuII ( NH3)4( SO,) C1J C1 , and [RuII-During investigations into electrodeposition of platinum-group metals, it was found impossible to deposit ruthenium from electrolytes containing the ammine Int. Conf. Co-ord. Chem., Chem. SOC. Special Publ., 1959, (NHJ5 (SO,) IC1,-