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Ch.21 - Transition Elements and Coordination Chemistry
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.21 - Transition Elements and Coordination ChemistryProblem 21.138e
Chapter 21, Problem 21.138e

In acidic aqueous solution, the complex trans-[Co(en)2Cl1]2+(aq) undergoes the following substitution reaction:
trans-[Co(en)2Cl1]+(aq) + H2O(l) → trans-[Co(en)2(H2O)Cl]2+(aq) + Cl–(aq)
The reaction is first order in trans-[Co(en)2Cl2]+(aq), and the rate constant at 25°C is 3.2×10–5 s–1.
e. Draw a crystal field energy-level diagram for trans-[Co(en)2Cl2]+ that takes account of the fact that Cl– is a weaker-field ligand than ethylenediamine.

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1
Identify the metal center and its oxidation state in the complex trans-[Co(en)_2Cl_2]^+.
Recognize that Cl^- is a weaker-field ligand compared to ethylenediamine (en), which affects the splitting of the d-orbitals.
Draw the octahedral crystal field splitting diagram, noting that the presence of weaker-field ligands like Cl^- results in a smaller splitting energy (Δ).
Label the d-orbitals in the diagram as t_2g (lower energy) and e_g (higher energy) levels, considering the octahedral geometry.
Populate the d-orbitals with electrons according to the electron configuration of Co^3+ (d^6), considering the weak-field nature of Cl^- which may lead to high-spin configuration.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Crystal Field Theory

Crystal Field Theory (CFT) explains the electronic structure of transition metal complexes by considering the effect of ligands on the d-orbitals of the metal ion. In an octahedral field, the d-orbitals split into two energy levels: the lower-energy t2g and the higher-energy eg orbitals. The extent of this splitting depends on the nature of the ligands, with stronger field ligands causing greater splitting. Understanding this concept is crucial for predicting the electronic transitions and colors of complexes.
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The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.

Ligand Field Strength

Ligand field strength refers to the ability of a ligand to split the d-orbitals of a central metal ion in a coordination complex. Ligands are classified as strong or weak field based on their ability to cause d-orbital splitting. Ethylenediamine (en) is a strong field ligand, leading to significant splitting, while chloride (Cl-) is a weak field ligand, resulting in less splitting. This concept is essential for understanding the stability and reactivity of metal complexes.
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Strong-Field Ligands result in a large Δ and Weak-Field Ligands result in a small Δ.

First-Order Reaction Kinetics

First-order reaction kinetics describes a reaction where the rate is directly proportional to the concentration of one reactant. In this case, the substitution reaction involving trans-[Co(en)2Cl2]+ is first-order with respect to the complex, meaning that as its concentration decreases, the rate of reaction also decreases. The rate constant, given as 3.2×10–5 s–1, allows for the calculation of reaction rates and is fundamental for understanding the dynamics of the substitution process.
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First-Order Reactions
Related Practice
Textbook Question

Spinach contains a lot of iron but is not a good source of dietary iron because nearly all the iron is tied up in the oxalate complex [Fe(C2O4)3]3-.

(d) Draw the structure of [Fe(C2O4)3]3-. Is the complex chiral or achiral?

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Textbook Question

In acidic aqueous solution, the complex trans-[Co(en)2Cl1]2+(aq) undergoes the following substitution reaction:

trans-[Co(en)1Cl2]+(aq) + H2O(l) → trans-[Co(en)2(H2O)Cl]2+(aq) + Cl–(aq)

The reaction is first order in trans-[Co(en)2Cl2]+(aq), and the rate constant at 25°C is 3.2×10–5 s–1.

(d) Is the reaction product chiral or achiral? Explain.

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Textbook Question

The complete reaction of 2.60 g of chromium metal with 50.00 mL of 1.200 M H2SO4 in the absence of air gave a blue solution and a colorless gas that was collected at 25°C and a pressure of 735 mm Hg. (e) When an excess of KCN is added to the solution, the color changes, and the paramagnetism of the solution

decreases. Explain.

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Textbook Question

Locate on the periodic table the transition elements with the following electron configurations. Identify each element.

(a) [Ar] 3d74s2

(b) [Ar] 3d54s1

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Textbook Question

Locate on the periodic table the transition elements with the following electron configurations. Identify each element.

(c) [Kr] 4d25s2

(d) [Xe] 4f36s2

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Textbook Question

Look at the location in the periodic table of elements A, B, C, and D. What is the electron configuration of the transition metal in each of the following ions?

(c) C3+

(d) DO42-

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