Four octahedral complexes of Co(III) are formed with four different monodentate ligands: CN ⁻ , NH ₃ , H ₂ O , and F ⁻ (not necessarily in that order). The absorption wavelengths of these four complexes are recorded as 310 nm , 475 nm , 600

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Four octahedral complexes of Co(III) are formed with four different monodentate ligands: CN ⁻ , NH ₃ , H ₂ O , and F ⁻ (not necessarily in that order). The absorption wavelengths of these four complexes are recorded as 310 nm , 475 nm , 600 nm , and 700 nm . Let Complex A be the one that absorbs light at 700 nm . The square of the spin-only magnetic moment (in B.M. ² ) of Complex A is ________.

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The energy of absorbed light is inversely proportional to its wavelength ( E = hc ). The complex absorbing the longest wavelength ( 700 nm ) will have the smallest crystal field splitting energy ( ₀ ). According to the spectrochemical series, the order of ligand field strength is F ⁻ Therefore, the weakest ligand F ⁻ corresponds to the smallest ₀ , making Complex A [ CoF ₆]³⁻ . The central metal ion Co ³⁺ has a 3 d ⁶ electronic configuration. Since F ⁻ is a weak field ligand, the pairing energy is greater than ₀ ,

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