Question

Hemoglobin in our bodies exists in two predominant forms. One form, known as oxyhemoglobin, has O2 bound to the iron and the other, known as deoxyhemoglobin, has a water molecule bound instead. Oxyhemoglobin is a low-spin complex that gives arterial blood its red color, and deoxyhemoglobin is a high-spin complex that gives venous blood its blue color.

Part A
Would you categorize O2 as a strong- or weak-field ligand?
strong-field ligand
weak-field ligand
Part B
Explain these observations in terms of crystal field splitting.

Answer 1

Oxygen is a strong-field ligand. Crystal field splitting explains that strong-field ligands cause a large splitting, resulting in a low-spin complex and giving arterial blood its red color, while weak-field ligands cause a smaller splitting, resulting in a high-spin complex and giving venous blood its blue color.

Step-by-step explanation:

Oxygen is categorized as a strong-field ligand.

In crystal field splitting, when the ligands approach the metal ion, the electrons in the metal d orbitals are repelled. The ligand field splits the d orbitals into two sets of orbitals, known as the t2g and eg sets. The energy difference between these two sets determines the color of the complex. Ligands that cause a large splitting, like strong-field ligands, result in a large energy difference and therefore absorb light in the visible spectrum, giving rise to color. In the case of oxyhemoglobin, the O2 ligand is a strong-field ligand and causes a large splitting, resulting in a low-spin complex that gives arterial blood its red color. On the other hand, deoxyhemoglobin, with the water molecule ligand, is a weak-field ligand and causes a smaller splitting, resulting in a high-spin complex that gives venous blood its blue color.

Answer 2

O2 is categorized as a weak-field ligand in the context of crystal field splitting.

Step-by-step explanation:

O2 would be categorized as a weak-field ligand. In crystal field splitting, ligands can be categorized as either strong-field or weak-field based on their ability to cause electron pairing in the d orbitals of the metal ion. Strong-field ligands cause greater splitting of the d orbitals, resulting in higher energy and eventually electron pairing, while weak-field ligands cause less splitting and a lower energy difference between the d orbitals.