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Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

Why do we need to name the compounds?

How would your teacher call you and your best friend if you both didn’t have any names? Similarly, the naming of coordination compounds(complex nomenclature) is important to provide an unambiguous method to represent and describe formulas and names of coordination compounds systematically.

Also, it becomes very important while you deal with isomers. We follow a few rules of the International Union of Pure and Applied Chemistry (IUPAC) system while naming these compounds. In a nutshell, the rules are as follows:

In Coordination Compounds, 

  • within the coordination entities, we list down the central atom/ion first followed by the ligands.
  • After this, we list down the ligands in alphabetical order.
  • We write the formula of coordination entity in square brackets.
  • Ligand abbreviations are to be enclosed in parentheses.
  • We must not keep any space between the ligands and the metal within a coordination sphere.
  • The charge on the cation(s) should be equal to the charge of the anion(s).

Now, let us look at these rules of complex nomenclature in greater details, along with suitable examples:

  1. Rule 1: While naming a coordination compound, we always name the cation before the anion. This rule does not count the fact of whether the complexion is cation or anion.
    Example: 
    Na[Co(NH)4(Cl)2]: Na is to be named first followed by [Co(NH)4 (Cl)2], i.e. Sodium tetramminedichlorocoblatate(I)
    [Co(NH)4(Cl)2]SO4[Co(NH)4(Cl)2] is to be named first followed by SO4, i.e Tetraamminedichlorocobalt(0) sulphate.
  2. Rule 2: When we see that there are multiple types of ligands present in any coordination compound, we name the ligands in alphabetic order after by the name of central metal atom/ion.
    - Name of the anionic ligands ends with ‘o’.
    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET- For neutral ligands, their common name is used as such e.g.
    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET
    Question for Nomenclature of Coordination Compounds
    Try yourself:Identify the correct formula for hexaaquamanganese(II) ion.
    View Solution
  3. Rule 3: If the names of the ligands have a numerical prefix, then we use the terms bis, tris, tetrakis. This will represent the ligand to which they refer is placed in parentheses.
    For example, we name [NiCl2(PPh3)2] as dichloridobis(triphenylphosphine)nickel(II)
    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET
  4. Rule 4: After naming the ligand in alphabetic order, we name the central metal atom/ion.
    - If the complex ion is a cation, we name the metal the same as the element.
    - If the complex is an anion, the name of metal ends with the suffix -ate for Latin name.
    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET
    Question for Nomenclature of Coordination Compounds
    Try yourself:The correct way of naming Co in [CoCl2(en)2]+ is ________
    View Solution
  5. Rule 5: We give the oxidation state of the metal in the complex as a roman numeral in parentheses.
  6. Rule 6: We name the neutral complex molecule similar to that of the complex cation.
  7. Rule 7: There are some ligands like NO2, CN that are attached to the central metal atom/ion through different atoms. We name them as follows:

    M-NO2 → nitro

    M-ONO →  nitrito

    M-SCN →  thiocyanato

    M-NCS →  isothiocyanato

  8. Rule 8: If any lattice component such as water or solvent of crystallisation is present, these follow their name, and are preceded by the number of these groups in Arabic numericals. These rules are illustrated by the following examples.

    (a) Complex cations

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    IUPAC name

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    (b) Complex anions

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    (c) Organic groups

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    (d) Bridging groups

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

    (e) Hydrates

    AlK(SO4)2. 12H2O

    Aluminium potassium sulphate 12-water
  9. Writing the formula of a coordination compound: 

  10. When writing the formula of complexes, the complex ion should be enclosed by square brackets. The metal is named first, then the coordinated groups are listed in the order: negative ligands, neutral ligands, positive ligands (and alphabetically according to the first symbol within each group).
  11. [M negative ligands, Neutral ligands, positive ligands]Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET

Question for Nomenclature of Coordination Compounds
Try yourself:Which of the following is the correct formulation of the entity according to IUPAC?
View Solution

The document Nomenclature of Coordination Compounds | Chemistry Class 12 - NEET is a part of the NEET Course Chemistry Class 12.
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FAQs on Nomenclature of Coordination Compounds - Chemistry Class 12 - NEET

1. Why is it important to name coordination compounds?
Ans. Naming coordination compounds is important because it allows scientists and chemists to communicate effectively about the specific compounds they are working with. A systematic naming system ensures that everyone understands the composition and structure of the compound, facilitating research, communication, and understanding in the field of coordination chemistry.
2. What are the rules for naming coordination compounds?
Ans. The rules for naming coordination compounds follow a systematic approach. The cation or positive ion is named first, followed by the anion or negative ion. The ligands, which are the molecules or ions surrounding the central metal atom, are named next in alphabetical order. Finally, the central metal atom is named and its oxidation state indicated in Roman numerals (if necessary).
3. How does naming coordination compounds help in their identification?
Ans. Naming coordination compounds helps in their identification by providing information about their composition and structure. The systematic naming system allows scientists to identify the central metal atom, ligands, and their arrangement, which in turn provides insights into the chemical and physical properties of the compound. This information is crucial for understanding the behavior and potential applications of coordination compounds.
4. Are there any exceptions to the rules of naming coordination compounds?
Ans. Yes, there are exceptions to the rules of naming coordination compounds. Some common exceptions include using special names for certain ligands (e.g., ammonia instead of amines) and using ligand names in their non-systematic form (e.g., water instead of aqua). These exceptions are based on historical usage and convenience but still follow the general principles of naming coordination compounds.
5. Can the same coordination compound have multiple names?
Ans. Yes, the same coordination compound can have multiple names. This can occur due to historical naming conventions, regional preferences, or different languages. However, it is important to note that regardless of the name used, the systematic naming system provides a standardized and unambiguous way to identify coordination compounds across different disciplines and regions.
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