Determine the Effective Atomic Number (EAN) of the Cobalt atom in the stable polynuclear complex Dic — Coordination Compounds Chemistry Question

💡 Solution & Explanation

For polynuclear complexes, an additional rule applies: each metal-metal bond ($\delta$ -bond) contributes 1 electron to each of the bonded metal atoms (or 2 electrons total to the system). In $Co_2(CO)_8$, the two Co atoms share $8$ CO ligands evenly (either via bridges or symmetrically) and have one $Co-Co$ bond. Calculation for one Co atom: Atomic number ($Z$) = 27. Oxidation state = 0. Electrons from $4$ CO ligands per Co = $4 \times 2 = 8$. Electron from the $Co-Co$ bond = $1$. $EAN = 27 - 0 + 8 + 1 = 36$.