Question 20.10: Draw crystal field energy-level diagrams, and predict the nu......
Draw crystal field energy-level diagrams, and predict the number of unpaired electrons for the following complexes:
(a) [FeCl_{4}]^{-} (tetrahedral) (b) [PtCl_{4}]^{2-} (square planar)
STRATEGY
Begin with the energy-level diagrams in Figure 20.32, and remember that nearly all tetrahedral complexes are high-spin (small Δ) while square planar complexes have a large energy gap (large Δ) between the x² – y² orbital and the four lower-energy orbitals.
(a) The five d electrons of Fe^{3+} ([Ar] 3d^{5}) are distributed between the higher- and lower-energy orbitals as shown below. Because Δ is small in tetrahedral complexes, [FeCl_{4}]^{-} is high-spin with five unpaired electrons.
(b) Pt^{2+} ([Xe] 4f^{14} 5d^{8}) has eight d electrons. Because Δ is large in square planar complexes, all the electrons occupy the four lower-energy d orbitals. There are no unpaired electrons, and the complex is diamagnetic.
