cis-[CoCl2(NH3)4]+

First semester organic chemistry typically provides undergraduates their most thorough treatment of the topics of geometrical and optical isomerism, but organic chemistry is not the only context for these types of isomerism. Geometrical and optical isomerism are also important in coordination chemistry, the study of compounds formed between metal ions and neutral or negatively charged molecules to form a metal complex.

In other words, a coordination complex consists of a metal ion bonded to one or more groups of molecules, which, when bonded, are called its ligands. As with organic compounds, coordination complexes with different geometic arrangements of ligands are called geometric isomers whereas isomers whose structures are mirror images of each other are called optical isomers. It would be typical of the MCAT to ask a question about optical isomers but in the context of coordination chemistry to see if you can apply what you already know in a new context.