# Iron(iii) hexacyanoferrate(ii) has formula Fe4[Fe(CN)6}3. I want to know where this 4 along with Fe came from ? Also there is 3 outside the square bracket ?? HOW ?

Iron(III) hexacyanoferrate(III) has formula Fe4[Fe(CN)6]3 .
The 4 along with Fe came as it is the charge above the coordination sphere and the 3 outside the square bracket is the charge on the Fe outside the coordination sphere. It exist as Fe3+ [Fe(CN)​6]4-. When they both combine, Fe4[Fe(CN)6]3 is formed.

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