Hemoglobin exists in two predominant forms in our bodies.

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 darker color. Explain these observations in terms of crystal field splitting. Would you categorize O₂ as a strong- or weakfield ligand?