Among the following pairs of complexes, in which case the value is higher for the first one? — Coordination Compounds Chemistry Question

💡 Solution & Explanation

Step 1: Recall the factors affecting the crystal field splitting energy (Δ_o): ligand field strength (CN^- > NH3 > H2O > F^-), oxidation state of metal (+3 > +2), and the transition series row (5d > 4d > 3d). Step 2: Compare the pairs: In (a) and (b), the second complex has a stronger-field ligand. In (c), the second complex has a higher metal oxidation state. Step 3: In (d), Rh^3+ belongs to the 4d series while Co^3+ belongs to the 3d series. Since 4d metals have larger d-orbital radial extension, they exhibit higher splitting (Δ_o) than 3d metals under the same conditions. Thus, Δ_o of [Rh(H2O)6]^3+ is higher than [Co(H2O)6]^3+.