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Chemistry LibreTexts

24: Complex Ions and Coordination Compounds

  • 24.1: Werner’s Theory of Coordination Compounds
    A metal complex consists of a central metal atom or ion that is bonded to one or more ligands, which are ions or molecules that contain one or more pairs of electrons that can be shared with the metal. Metal complexes can be neutral, positively charged, or negatively charged. Electrically charged metal complexes are sometimes called complex ions. A coordination compound contains one or more metal complexes.
  • 24.2: Ligands
    A metal ion in solution does not exist in isolation, but in combination with ligands (such as solvent molecules or simple ions) or chelating groups, giving rise to complex ions or coordination compounds. These complexes contain a central atom or ion, often a transition metal, and a cluster of ions or neutral molecules surrounding it. Ligands are ions or neutral molecules that bond to a central metal atom or ion. Ligands act as Lewis bases and the central atom acts as a Lewis acid.
  • 24.3: Complex Ion Nomenclature
    Coordination complexes have their own classes of isomers, different magnetic properties and colors, and various applications (photography, cancer treatment, etc), so it makes sense that they would have a naming system as well. Consisting of a metal and ligands, their formulas follow the pattern [Metal Anions Neutrals]±Charge, while names are written Prefix Ligands Metal(Oxidation State).
  • 24.4: Isomerism in Coordination Complexes
    Two compounds that have the same formula and the same connectivity do not always have the same shape. There are two reasons why this may happen. In one case, the molecule may be flexible, so that it can twist into different shapes via rotation around individual sigma bonds. This phenomenon is called conformation, and it is covered in a different chapter. The second case occurs when two molecules appear to be connected the same way on paper, but are connected in two different ways in three dimens
  • 24.5: Bonding in Complex Ions: Crystal Field Theory
    Crystal field theory treats interactions between the electrons on the metal and the ligands as a simple electrostatic effect. The presence of the ligands near the metal ion changes the energies of the metal d orbitals relative to their energies in the free ion. Both the color and the magnetic properties of a complex can be attributed to this crystal field splitting. The magnitude of the splitting depends on the nature of the ligands bonded to the metal.
  • 24.6: Magnetic Properties of Coordination Compounds and Crystal Field Theory
    The magnetic properties of a compound can be determined from its electron configuration and the size of its atoms. Because magnetism is generated by electronic spin, the number of unpaired electrons in a specific compound indicates how magnetic the compound is. In this section, the magnetism of the d-block elements (or transition metals) are evaluated. These compounds tend to have a large number of unpaired electrons.
  • 24.7: Color and the Colors of Complexes
    When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed.
  • 24.8: Aspects of Complex-Ion Equilibria
    A complex ion forms from a metal ion and a ligand because of a Lewis acid–base interaction. The positively charged metal ion acts as a Lewis acid, and the ligand, with one or more lone pairs of electrons, acts as a Lewis base. Small, highly charged metal ions have the greatest tendency to act as Lewis acids, and consequently, they have the greatest tendency to form complex ions.
  • 24.9: Acid-Base Reactions of Complex Ions
  • 24.10: Some Kinetic Considerations
    Transition metal complexes which undergo rapid substitution of one ligand for another are labile, whereas complexes in which substitution proceed slowly or not at all are inert. For an inert complex, it is a large activation energy which prevents ligand substitution. Inert complexes are therefore kinetically stable compounds.
  • 24.E: Exercises