Question 20.12: Drawing Crystal Field Energy-Level Diagrams for Tetrahedral ......
Drawing Crystal Field Energy-Level Diagrams for Tetrahedral and Square Planar Complexes
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.
