The CORRECT order of the soft character (as per HSAB principle) of the central metal ion is · ABC26IN0340

Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Coordination – General · Exam: GATE 2005-2021 · Marks: 2 · Difficulty: Hard

The CORRECT order of the soft character (as per HSAB principle) of the central metal ion is
(a)$\left[\mathrm{CrO}_{4}\right]^{2-}<\left[\mathrm{CrCl}_{4}\right]<\left[\mathrm{Cr}(\text { bipy })_{3}\right]<\left[\mathrm{Cr}(\mathrm{CO})_{5}\right]^{2-}$
(b)$\left[\mathrm{CrCl}_{4}\right]^{-}<\left[\mathrm{Cr}(\text { bipy })_{3}\right]<\left[\mathrm{CrCO}_{4}\right]^{2-}<\left[\mathrm{Cr}(\mathrm{CO})_{5}\right]^{2-}$
(c)$\left[\mathrm{CrCO}_{4}\right]^{2-}<\left[\mathrm{Cr}(\text { bipy })_{3}\right]<\left[\mathrm{Cr}(\mathrm{CO})_{5}\right]^{2-}<\left[\mathrm{CrCl}_{4}\right]^{-}$
(d)$\left[\mathrm{CrCl}_{4}\right]^{-}<\left[\mathrm{CrCO}_{4}\right]^{2-}<\left[\mathrm{Cr}(\mathrm{CO})_{5}\right]^{2-}<\left[\mathrm{Cr}(\text { bipy })_{3}\right]$
Answer
Answer: A ✓ checked by 4AB · confidence medium
Explanation
Softness increases as the oxidation state falls and the ligands become more π-acidic: CrO₄²⁻ (Cr VI) < CrCl₄⁻ (Cr III) < Cr(bipy)₃ (Cr 0) < [Cr(CO)₅]²⁻ (Cr −II) (a).

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