24. Transition Metals and Coordination Compounds

Complete the exercises below.

The coordination complex [Cr(CO)₆] forms colorless, diamagnetic crystals that melt at 90 °C

c. Given that [Cr(CO)₆] is colorless, would you expect CO to be a weak-field or strong-field ligand?

Based on the wavelength of maximum absorption of the cobalt complexes, arrange the following ligands in a spectrochemical series from weakest-field to strongest-field ligand.

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(a) Cl^- < NCS^- < H₂O < NH₃

(b) Cl^- < NCS^- < H₂O < NH₃

(d) Cl^- < H₂O < NCS^- < NH₃

Complete the exercises below.

As shown in Figure 23.26, the d-d transition of [Ti(H₂O)₆]³⁺ produces an absorption maximum at a wavelength of about 500nm .

a. What is the magnitude of ∆ for [Ti(H₂O)₆]³⁺ in kJ/mol?

b. How would the magnitude of ∆ change if the H₂O ligands in [Ti(H₂O)₆]³⁺ were placed with NH₃ ligands?

Complete the exercises below. A classmate says, “A weak-field ligand usually means the complex is high spin.” Is your classmate correct? Explain.

Complete the exercises below.

For a given metal ion and set of ligands, is the crystal-field splitting energy larger for a tetrahedral or an octahedral geometry?

The [Ti(NCS)6]3- ion exhibits a single absorption band at 544 nm. Calculate the crystal field splitting energy ∆ in kJ/mol. In NCS- a stronger or weaker field ligand than water? Predict the color of [Ti(NCS)6]3-.

Chromium forms three isomeric compounds A, B, and C with percent composition 19.52% Cr, 39.91% Cl, and 40.57% H2O. When a sample of each compound was dissolved in water and aqueous AgNO3 was added, a precipitate of AgCl formed immediately. A 0.225-g sample of compound A gave 0.363 g of AgCl, 0.263 g of B gave 0.283 g of AgCl, and 0.358 g of C gave 0.193 g of AgCl. One of the three compounds is violet, while the other two are green. In all three, chromium has coordination number 6. (c) Which of the three compounds is likely to be the violet one? Explain.