Among the following, species expected to show fluxional behaviour are
(a)$[\mathrm{NiCl_4}]^{2-}$ (tetrahedral)
(b)$\mathrm{IF}_{7}$ (pentagonal bipyramidal)
(c)$[\mathrm{CoF_6}]^{3-}$ (octahedral)
(d)$\mathrm{Fe(CO)_5}$ (trigonal bipyramidal)
Answer
Answer: B ✓ checked by 4AB · confidence high
Answer: (B) IF₇ and (D) Fe(CO)₅.
Explanation
Answer: (B) IF₇ and (D) Fe(CO)₅ — Five- and seven-coordinate species interconvert their axial and equatorial ligands easily: Berry pseudorotation in Fe(CO)₅ and a pseudorotation (Bartell) motion in IF₇. Rigid tetrahedral and octahedral complexes are not fluxional.