Each cis-bis(ethylenediamine) cobalt centre can have Δ or Λ helicity. Combining the centres gives homochiral ΔΔ and ΛΛ forms, which are a mirror-image pair and optically active. Opposite-helicity combinations require attention to the bridge arrangement and symmetry; their treatment leads to the alternative count in the grading. The official answer explicitly accepts 2 OR 4, both retained as discrete alternatives rather than a continuous 2–4 interval.
More Transition Metals: Coordination chemistry – structure and isomerism, theories of bonding (VBT, CFT, and MOT). Metal-metal multiple bonds. Energy level diagrams in various crystal fields, CFSE, applications of CFT, Jahn-Teller distortion. Electronic spectra of transition metal complexes: spectroscopic term symbols, selection rules, Orgel and Tanabe-Sugano diagrams, nephelauxetic effect and Racah parameter, charge-transfer spectra. Magnetic properties of transition metal complexes. Ray-Dutt and Bailar twists, Reaction mechanisms: kinetic and thermodynamic stability, associative, dissociative substitution and redox reactions. questions
