Skip to main content
Chemistry LibreTexts

Isomers

  • Page ID
    521
  • [ "article:topic-guide", "Structural Isomers", "Isomers", "Stereoisomers", "showtoc:no" ]

    There are several types of this isomerism frequently encountered in coordination chemistry and the following represents some of them. Isomers that contain the same number of atoms of each kind but differ in which atoms are bonded to one another are called structural isomers, which differ in structure or bond type. For inorganic complexes, there are three types of structural isomers: ionization, coordination, and linkage and two types of stereoisomers: geometric and optical.

    Structural isomers, as their name implies, differ in their structure or bonding, which are separate from stereoisomers that differ in the spatial arrangement of the ligands are attached, but still have the bonding properties. The different chemical formulas in structural isomers are caused either by a difference in what ligands are bonded to the central atoms or how the individual ligands are bonded to the central atoms. When determining a structural isomer, you look at: (1) the ligands that are bonded to the central metal, and (2) which atom of the ligands attach to the central metal. Below is a quick look at the different types of structural isomers. The highlighted ions are the ions that switch or change somehow to make the type of structural isomer it is.

    • Optical Isomers in Inorganic Complexes
      Optical isomers are related as non-superimposable mirror images and differ in the direction with which they rotate plane-polarised light. These isomers are referred to as enantiomers or enantiomorphs of each other and their non-superimposable structures are described as being asymmetric.
    • Stereoisomers: Geometric Isomers in cis-platin
      Two compounds that have the same formula and the same connectivity do not always have the same shape. If the molecules appear to be connected the same way on paper, but differ in three dimensional space, then they are called stereoisomers.  One simple example of stereoisomers from inorganic chemistry is diammine platinum dichloride. This important compound is sometimes called "platin" for short.
    • Stereoisomers: Geometric Isomers in Transition Metal Complexes
      The existence of coordination compounds with the same formula but different arrangements of the ligands was crucial in the development of coordination chemistry. Two or more compounds with the same formula but different arrangements of the atoms are called isomers. Because isomers usually have different physical and chemical properties, it is important to know which isomer we are dealing with if more than one isomer is possible.
    • Stereoisomers: Geometric Isomers in Transition Metal Complexes II
      Geometric Isomers are isomers that differ in the arrangement of the ligands around the metal or the central atom. In other words, these isomers differ from each other based on where the ligands are placed in the coordinate compound. This will be much easier to understand as examples will be considered. There are 2 main types of geometric isomers:
    • Stereoisomers of Complex Metal Complexes
      Stereoisomers are isomers that have the same molecular formula and ligands, but differ in the arrangement of those ligands in 3D space.
    • Structural Isomers: Coordination Isomerism in Transition Metal Complexes
      Coordination isomerism occurs compounds containing complex anionic and cationic parts can be thought of as occurring by interchange of some ligands from the cationic part to the anionic part. Hence, there are two complex compounds bound together, one with a negative charge and the other with a positive charge. In coordination isomers, the anion and cation complexes of a coordination compound exchange one or more ligands.
    • Structural Isomers: Ionization Isomerism in Transition Metal Complexes
      Ionization isomers are identical except for a ligand has exchanging places with an anion or neutral molecule that was originally outside the coordination complex. The central ion and the other ligands are identical. For example, an octahedral isomer will have five ligands that are identical, but the sixth will differ. The non-matching ligand in one compound will be outside of the coordination sphere of the other compound.
    • Structural Isomers: Linkage Isomerism in Transition Metal Complexes
      Linkage isomerism occurs with ambidentate ligands that are capable of coordinating in more than one way. The best known cases involve the monodentate ligands: SCN- / NCS- and NO2- / ONO-. The only difference is what atoms the molecular ligands use to attach to the central ion.