Which is low spin complex? — Coordination Compounds Chemistry Question

💡 Solution & Explanation

Step 1: Octahedral complexes with strong-field ligands like CN^- and NO2^- exhibit a large crystal field splitting energy (δ_o > Pairing energy, P). Step 2: This large splitting forces the d-electrons to pair up completely in the lower energy t_2g orbitals before entering the higher eg orbitals, forming low-spin complexes. Step 3: Since [Fe(CN)6]^3- (d^5, low spin), [Co(NO2)6]^3- (d^6, low spin), and [Mn(CN)6]^3- (d^4, low spin) all utilize strong-field ligands, they are all classified as low-spin complexes. Thus, option (d) is correct.