Solubility relationships, size and

When an aqueous solution containing Ni2+ has a solution containing CN added to it, [Ni(CN)4]2 is produced  

It is known that if CN- is present in large excess, another cyanide ion adds to the [Ni(CN)4]2 to form [Ni(CN)s]3-. However, when K+ is added to the solution in an attempt to isolate solid K3[Ni(CN)5], the result is K2[Ni(CN)4] and KCN  

Many complex ions that form in solutions, [Ni(CN)5]3 being one of them, are not particularly stable. Consequently, any technique that produces a more stable environment for such an ion becomes a factor to consider in synthesis. This case illustrates the importance of understanding general rules regarding the favorable interactions of species of similar size and charge. 

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