Are you sure the formula for the first compound in your equation is correct? Is it a neutral compound?
N2H4CO is urea, and it's a neutral ligand. CN is cyanide, an anionic ligand (charge -1)
So [Cr(N2H4CO)6]3[Cr(CN)6]3 would make sense: it's just Cr (III).
Check it, please, and I'll try to help you.