hw to find a coordination number ( plsssss help)?

Question

i hav my exams next week and i dnt knw how to find the coordiantaon number , pls hlp me , pls suggest if there is any formula or shortcut , pls help me [K4[Fe(CN)6] pls help me in finding the coordination number of this compound?

Answer 1

It's six. There's logic to it, but if you're so far gone, just count the number othings inside the square brackets. In this case, [Fe(CN)6]: there are 6 CN's, so the coordination number is six. If it was Fe(CO)5 there'd be 5 CO's, so the coordination number is 5. The K in your example is a counterion that just balances the charge, and that's why people write it outside the square brackets usually.

If you actually care about understanding it, the topic to study is molecular orbital theory, which would tell you that Fe2+ almost always forms octahedral compounds where the coordination number is 6, just as Ni2+ almost always forms square planar compounds, with a coordination number of 4, etc. etc. etc.