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How is the oxidation state of a central metal found from a coordination compound’s formula?

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Structural diagram of the vitamin B12 coenzyme molecule, highlighting its organometallic core with five nitrogen-cobalt bonds and one cobalt-carbon bond at the center, surrounded by complex organic groups. — coordination compound Coordination compounds contain a central metal atom surrounded by nonmetal atoms or groups of atoms, called ligands. For example, vitamin B₁₂ is made up of a central metallic cobalt ion bound to multiple nitrogen-containing ligands.

To determine the oxidation state of a central metal in a coordination compound, you must account for the charges of the ligands and the overall charge of the complex ion or molecule.1

The oxidation state is calculated using the following logic:

Identify the overall charge: The sum of the oxidation state of the central metal and the charges of all attached ligands must equal the total charge of the coordination entity.1
Determine ligand charges: Assign the appropriate charge to each ligand (e.g., neutral molecules like water or ammonia have a charge of 0, while anions like cyanide (CN⁻) or fluoride (F⁻) carry their respective negative charges).12
Solve for the metal: Use the formula:
$Overall Charge = (Oxidation State of Metal) + \sum (Charges of Ligands)$

For example, in the hexaaquanickel(2+) ion, [Ni(H₂O)₆]²⁺, water is neutral (0) and the total charge is +2, meaning the nickel ion is in the +2 oxidation state. In the hexacyanoferrate(3−) ion, [Fe(CN)₆]³⁻, each of the six cyanide ligands has a charge of −1; therefore, the iron must be in the +3 oxidation state to result in an overall charge of −3.1