The histidine bound haem group of succinate dehydrogenase, an electron carrier in the mitochondrial electron transfer chain. The large semi-transparent sphere indicates the location of the iron ion.

Coordination chemistry is essential to understanding the properties of metallic cofactors in enzymes and oxygen transporters.

Coordination complexes are molecules that possess a metal center bound to atoms, ions, or molecules (ligands) that donate electrons to the metal. The importance of coordination chemistry for the new MCAT derives from the common occurrence of metals as cofactors for many enzymes and other proteins such as hemoglobin. Understanding how the availability of the d subshell of transition metals for electron exchange in catalysis or electron transfer processes such as in cytochromes and iron-sulfur complexes is one of the most important insights to gain in biochemistry. Another aspect of coordination chemistry for focus is the behavior polydentate ligands in living systems (λ-carboxy glutamate in blood clotting) and on the molecular biology benchtop (EDTA).

WikiPremed Resources

Coordination Chemistry Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Coordination Chemistry
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Be prepared to define a coordination complex and describe its components.

Understand what distinguishes a coordinate covalent bond.

Be able to distinguish monodentate and polydentate ligands.

Be familiar with chelating agents and the process of chelation.

Have a basic sense of how the inner-outer hybrid model involving d orbital hybridization explaining coordination complex structure has been superseded by crystal field and ligand field theory.

Be able to account for d-orbital splitting in ligand field theory and explain why coordination complexes are often intensely colored.

Understand the role that complex ion formation can play in affecting the solubility of weak electrolytes.

Be prepared to describe the importance of coordination chemistry to many biochemical processes.

Suggested Assignments

Review terminology from coordination chemistry using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Study the web resources for coordination chemistry.

Conceptual Vocabulary for Coordination Chemistry

A complex is a molecule or ensemble formed by the combination of ligands and metal ions.
Coordinate covalent bond
A coordinate covalent bond is a type of covalent bonding between two atoms in which both electrons shared in the bond come from the same atom.
Lewis base
A Lewis base is any molecule or ion that can form a new coordinate covalent bond, by donating a pair of electrons.
A ligand is an atom, ion, or molecule donating one or more of its electrons through a coordinate covalent bond to one or more central atoms or ions
Coordination number
Coordination number is defined as the total number of neighbors of a central atom in a chemical compound.
Inorganic chemistry
The field of inorganic chemistry covers all chemical compounds except the myriad organic compounds, which are the subjects of organic chemistry.
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal.
Chelation is the binding or complexation of a bi- or multidentate ligand.
18-Electron rule
Arising from the size of the valance shell of a transition metal, the 18-electron rule is a rule of thumb used primarily in transition metal chemistry for characterizing and predicting the stability of metal complexes.
Bridging ligand
A bridging ligand is an atom or a polyatomic entity that connects two or more metal centres in a complex.
Ligand field theory
Applying molecular orbital theory to transition metal complexes, ligand field theory describes the bonding in coordination complexes.
Crystal field theory
Though not describing bonding, crystal field theory represents a reasonanbly successful model for describing the electronic structure of transition metal compounds which are coordination complexes.
Trigonal bipyramid molecular geometry
A trigonal bipyramid is a molecular geometry with one atom at the center and 5 more at the corners of a triangular dipyramid.
Inclusion compound
In host-guest chemistry an inclusion compound is a complex in which one chemical compound the host forms a cavity which molecules of a second compound the guest are located.
Clathrate compound
A clathrate or cage compound is a chemical substance consisting of a lattice of one type of molecule trapping and containing a second type of molecule.
Sandwich compound
A sandwich compound in organometallic chemistry is any chemical compound containing a metal atom oriented between two arene units.
Advanced terms that may appear in context in MCAT passages
Octahedral molecular geometry
Octahedral molecular geometry describes a molecular geometry in which 6 ligands are symmetrically arranged around a central atom in an arrangement having the form of an octahedron.
Coordination polymer
Coordination polymer is the term given to a metal coordination compound where a ligands bridge between metal centres to create an infinite array of metal centres.
Transition metal carbene complex
A transition metal carbene complex in organometallic chemistry is a compound bearing a formal carbon-metal bond.
The spinels are any of a class of minerals which crystallize in the isometric system with an octahedral habit.