Answer to Question #342542 in Inorganic Chemistry for Newton

Question

Explain in detail the Crystal Field Theory. Using

examples where applicable, how does the theory

explain the following for a transition metal complex;

1.The structure.

2.Colours behavior

3.Compound formation

4.Magnetic properties

Prepare and submit a one-page rep

Answer 1

For each complex, predict its structure, whether it is high spin or low spin, and the number of unpaired electrons present.

1. [CoF₆]^3−
2. [Rh(CO)₂Cl₂]^−

Given: complexes

Asked for: structure, high spin versus low spin, and the number of unpaired electrons

Strategy:

1. From the number of ligands, determine the coordination number of the compound.
2. Classify the ligands as either strong field or weak field and determine the electron configuration of the metal ion.
3. Predict the relative magnitude of Δ_o and decide whether the compound is high spin or low spin.
4. Place the appropriate number of electrons in the d orbitals and determine the number of unpaired electrons.

Solution

1. A With six ligands, we expect this complex to be octahedral.

B The fluoride ion is a small anion with a concentrated negative charge, but compared with ligands with localized lone pairs of electrons, it is weak field. The charge on the metal ion is +3, giving a d⁶ electron configuration.

C Because of the weak-field ligands, we expect a relatively small Δ_o, making the compound high spin.

D In a high-spin octahedral d⁶ complex, the first five electrons are placed individually in each of the d orbitals with their spins parallel, and the sixth electron is paired in one of the t_2g orbitals, giving four unpaired electrons.

1. A This complex has four ligands, so it is either square planar or tetrahedral.

B C Because rhodium is a second-row transition metal ion with a d⁸ electron configuration and CO is a strong-field ligand, the complex is likely to be square planar with a large Δ_o, making it low spin. Because the strongest d-orbital interactions are along the x and y axes, the orbital energies increase in the order d_z2d_yz, and d_xz (these are degenerate); d_xy; and d_x2−y2.

D The eight electrons occupy the first four of these orbitals, leaving the d_x2−y2. orbital empty. Thus there are no unpaired electrons.