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Ch.23 - Transition Metals and Coordination Chemistry
All textbooksBrown 14th EditionCh.23 - Transition Metals and Coordination ChemistryProblem 83
Chapter 23, Problem 83

Complete the exercises below. Oxyhemoglobin, with an O₂ bound to iron, is a low-spin Fe(II) complex; deoxyhemoglobin, without the O₂ molecule, is a high-spin complex. d. A 15-minute exposure to air containing 400 ppm of CO causes about 10% of the hemoglobin in the blood to be converted into the carbon monoxide complex, called carboxyhemoglobin. What does this suggest about the relative equilibrium constants for the binding of carbon monoxide and O₂ to hemoglobin? e. CO is a strong-field ligand. What color might you expect carboxyhemoglobin to be?

Verified step by step guidance
1
Step 1: Understand the context of the problem. Hemoglobin can bind to different ligands, such as O₂ and CO, forming oxyhemoglobin and carboxyhemoglobin, respectively. The problem involves comparing the binding affinities of these ligands to hemoglobin.
Step 2: Analyze part (d). The fact that a small concentration of CO (400 ppm) can convert 10% of hemoglobin to carboxyhemoglobin suggests that CO has a higher binding affinity to hemoglobin than O₂. This implies that the equilibrium constant for the binding of CO to hemoglobin is greater than that for O₂.
Step 3: Consider the implications of part (d). A higher equilibrium constant for CO binding means that the reaction of hemoglobin with CO is more favorable compared to O₂, indicating a stronger interaction between CO and hemoglobin.
Step 4: Analyze part (e). CO is described as a strong-field ligand, which typically causes a larger splitting of the d-orbitals in the metal center. This can affect the color of the complex due to changes in the wavelengths of light absorbed.
Step 5: Predict the color of carboxyhemoglobin. Strong-field ligands like CO often result in low-spin complexes, which can absorb light in the visible spectrum differently than high-spin complexes. This could lead to a color change, potentially making carboxyhemoglobin appear a different color than oxyhemoglobin, possibly more towards the red or brown spectrum.

Key Concepts

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

Ligand Field Theory

Ligand Field Theory explains how the presence of ligands around a metal ion affects its electronic structure and energy levels. In the case of hemoglobin, the binding of O₂ or CO alters the spin state of the iron center, influencing its color and reactivity. Strong-field ligands, like CO, cause greater splitting of the d-orbitals, leading to low-spin configurations, while weak-field ligands result in high-spin configurations.
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Strong-Field Ligands result in a large Δ and Weak-Field Ligands result in a small Δ.

Equilibrium Constants

Equilibrium constants (K) quantify the ratio of the concentrations of products to reactants at equilibrium for a reversible reaction. In the context of hemoglobin, the relative equilibrium constants for the binding of CO and O₂ indicate the preference of hemoglobin for one ligand over the other. A higher K value for CO compared to O₂ suggests that CO binds more strongly to hemoglobin, which is critical for understanding the toxic effects of carbon monoxide.
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Equilibrium Constant K

Color and Coordination Complexes

The color of coordination complexes, such as carboxyhemoglobin, arises from the electronic transitions of d-electrons in the metal ion when exposed to light. The specific wavelengths of light absorbed depend on the ligand field strength and the arrangement of ligands around the metal. Since CO is a strong-field ligand, carboxyhemoglobin is expected to exhibit a distinct color, often appearing bright red due to the specific d-d transitions that occur in the low-spin state.
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Coordination Complexes Example
Related Practice
Textbook Question

Carbon monoxide, CO, is an important ligand in coordination chemistry. When CO is reacted with nickel metal, the product is [Ni(CO)4] which is a toxic, pale yellow liquid.

a. What is the oxidation number for nickel in this compound?

b. Given that [Ni(CO)4] is a diamagnetic molecule with a tetrahedral geometry, what is the electron configuration of nickel in this compound?

c. Write the name for [Ni(CO)4] using the nomenclature rules for coordination compounds.