[Foobarz]

Ok so in my AP Chemistry study book (Princeton Review 2012 ed.) it says "Transition metal ions form complex ions with those species. It doesn't matter how many of them you place on the transition metal, as long as you get the charge on the complex ion right."

So does that mean I can write Fe(CN)₆^4- as Fe(CN)₄^2-?

[AWK]

Fe²⁺ forms different complexes with CN^- containibg from 1 to 6 cyanide groups, ie FeCN⁺, Fe(CN)^3-, and so on. All species exist in solution, at least in minute amount irrespective on mutual concentration of Fe(II) and cyanide ions. Since cyanide forms strong complex with iron cation then always Fe(CN)₆^4- exists. But in the case of SCN^- which forms much weaker complex with Fe(III) one can expected only 5 SCN^- groups at iron cation.

[Foobarz]

So a cation can form many different complexes at a same time? And I can use any one of those complexes, as long as the charge is correct?