# Why does [Co(NO2)6]4- ion have 3 unpaired electron as opposed to 1?

Why does $$\ce{[Co(NO2)6]^4-}$$ ion have 3 unpaired electron as opposed to 1?

The book says that it has 3 unpaired electrons. I thought $$\ce{NO2-}$$ was a strong field ligand, making $$\ce{Co^2+}$$ a $$\ce{d^7}$$ low spin ion. Six electrons go in the $$\mathrm{t_{2g}}$$ orbital and 1 in the $$\mathrm{e_g}$$ orbital.

Please explain the bonding in this compound (preferably with a suitable MO diagram to go with it).

• You can't predict which ligand is strong or weak, there are many factors which can change this. – King Tut Feb 13 '18 at 12:32
• An easier method - instead of getting tangled in the mess of strong vs weak field ligand - would be to make deductions based on the compound's calculated paramagnetic moments. Unfortunately, a simple Google search yields too little information. Perhaps, the chemists with more efficient database searches can help out here? – Gaurang Tandon Mar 15 '18 at 15:51