AMMONIA AND PHOSPHORTRICHLORIDE COMPLEXES

The structure analysis of nitrites, however, shows that they contain isolated NO groups in complexes of trivalent metals, e.g. in the alkali aluminates (KA102) that have the same bruto composition as the nitrites, the coordination, indeed, is higher. Here the AI3 ions are surrounded by six oxygen ions, a coordination number that is as to be expected for a really ionic compound. Hypochlorites ACIO, chlorites AC102, chlorates AG103, sulphites A2S03, etc., all have coordination numbers that are smaller than those to be expected in ionic compounds. 

Although the ions NOs, P04, S04 and C104 are not completely ionic, there is still an appreciable charge difference between the central atom and the oxygen atoms. Since, in all probability, the bonds are semipolar, the positive charges on the central atom are one for NO f and POf, two for SO and three for ClO s and it can be understood that, in spite of the covalency, the rules for the acid strength can still be applied. 

With some of the alkali- and alkaline-earth halides, ammonia forms complexes that, in their general behaviour, strongly resemble the hydrates. Since neither the positive nor the negative ions have unoccupied orbitals available for bond formation, it has to be assumed that in these ammoniates the ammonia is bonded by the electrostatic attraction of the ions of the halide on the dipole of the ammonia molecule. 

In the ammoniates of the halides of elements beyond the aluminium group, this dipole ion attraction may be replaced by the 

There are ammoniates of PtCl2, of halides of other platinum metals and of cobalt and nickel, too, some of which have been mentioned before in, Section 50. The cobalt complexes clearly show the importance of the completed d shells for the stability of the complex. Non complex compounds of trivalent cobalt are very unstable. Solutions of divalent cobalt in ammonia, however, are readily oxidized by air, because the NH3 complex of trivalent cobalt Co(NH3)6 3+ClT has eighteen electrons used in bond formation, whereas the ion Co(NH3) + would have nineteen electrons. 

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