text: As studied in coordination chemistry, metal ions (usually transition metal ions) exist in solution bound to ligands,  In many cases, the coordination sphere defines geometries conducive to reactions either between ligands or involving ligands and other external reagents.
  A well known metal-ion-templating was described by Charles Pedersen in his synthesis of various crown ethers using metal cations as template. For example, 18-crown-6 strongly coordinates potassium ion thus can be prepared through the Williamson ether synthesis using potassium ion as the template metal.
  Metal ions are frequently used for assembly of large supramolecular structures. Metal organic frameworks (MOFs) are one example. MOFs are infinite structures where metal serve as nodes to connect organic ligands together. SCCs are discrete systems where selected metals and ligands undergo self-assembly to form finite supramolecular complexes, usually the size and structure of the complex formed can be determined by the angularity of chosen metal-ligand bonds.