Cobalt ammines, interaction with

Cobalt(lll).—Complexes. Ammine complexes. Optical activity can be induced in the complexes [Co(NH3) ] and [Cofenlj] by means of outer-sphere association with chiral anions, e.g. (- - )-tartrate. Circular dichroism is observed in the d-d bands of the cations and it is suggested that this is due to (a) direct interaction between the chiral anion and the metal f/-orbitals and (b) the preferred conformation adopted by the inner-sphere ligands in the presence of a helical outer-sphere ligand. 

As an example of the first kind of outer-sphere complex formation, Werner (44) studied the interaction of thiocyanato complexes of cobalt (Ill)ammines with silver ions. In these complexes nitrogen is bound to the metal, and the sulfur atom in the thiocyanate group is free to complex... 

Cationic Complexes. Both Rh and Ir give cobalt-like ammines of the types [ML6]3 +, [MLsX]2+, and [ML4X2]+, of which [Rh(NH3)5Cl]Cl2 is a typical example. The salts are made in various ways, but usually by the interaction of aqueous solutions of RhCl3(aq) with the ligand. 

Such criteria cannot be simultaneously satisfied in the case of the NHa group. Studies have thus been undertaken to examine the mode of interaction of complexes where such a group is the potential bridging site. The reductions of penta-ammine cobalt complexes of urea, carbamate, N-cyanoguanidine [N=C—N=C(NH2)2l, and cyanamide (N=C—NHa), by chromium(n) involve an outer-sphere path with the exception of the carbamato-species, where, however, there is no evidence of a nitrogen-bonded chromium(in) species as product. The cyanamide-complex reaction follows the rate law... 

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