Coordination compounds are important :
1. Most of the elements in the periodic table are metals, and almost all metals form complexes
2. Many industrial catalysts are metal complexes, and these catalysts are important as a way to control reactivity
3. Transition-metal complexes are essential in biochemistry
a. Hemoglobin, an iron complex that transports oxygen in blood
b. Cytochromes, iron complexes that transfer electrons in cells
c. Complexes that are components of enzymes, the catalysts for all biological reactions
elements