Oxyhemoglobin, with an O2 bound to iron, is a low-spin Fe(II) complex; deoxyhemoglobin, without the O₂ molecule, is a high-spin complex.

(a) Assuming that the coordination environment about the metal is octahedral, how many unpaired electrons are centered on the metal ion in each case?

(b)What ligand is coordinated to the iron in place of O₂ in deoxyhemoglobin?

(c) Explain in a general way why the two forms of hemoglobin have different colors (hemoglobin is red, whereas deoxyhemoglobin has a bluish cast).

(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 binding of carbon monoxide and O₂ to hemoglobin?

(e) CO is a strong-field ligand. What color might you expect carboxyhemoglobin to be?