Here's why:

* Iron (Fe) has a common oxidation state of +2 or +3.

* Cyanide (CN) has a charge of -1.

* To balance the charges, you would need either:

* Fe(II) with two cyanide ions (Fe(CN)2), which is a neutral compound, or

* Fe(III) with three cyanide ions (Fe(CN)3), which is also a neutral compound.

Therefore, FeCN2 is not a valid chemical formula.

It's important to remember that chemical formulas must follow the rules of charge balance and represent real compounds.