Nomenclature of Coordination Compounds

A coordination compound can be described as any substance with a chemical structure wherein the non-metal atoms surround the central metal atoms. One of the primary uses of coordination compounds is as catalysts. Coordination compounds are also known as coordination complexes. The ions or molecules surrounding the central metal atom are called ligands or complexing agents. In this nomenclature of coordination compounds notes, you will learn about coordination compounds nomenclature, properties of coordination compounds, and other related topics.

Properties of coordination compounds 

To understand coordination compounds nomenclature we must look at their properties. Some of the properties of coordination compounds are mentioned below:

• The coordination complexes will have a magnetic nature if the coordination centre is metal by nature. This happens because of unpaired electrons.
• The unpaired electrons absorb light, leaving coordination compounds that are produced by transition elements coloured. For instance, complexes that have iron(II) can reflect pale green and green colours. However, the coordination compounds with iron (III) would be yellowish-brown or brown.
• Coordination compounds that have some specific ligands can help in the transformation of molecules in a stoichiometric or catalytic manner.
• Complex compounds exhibit much chemical reactivity. Complex compounds can be a part of outer-sphere electron transfer reactions and inner sphere electron transfers as well.

Coordination complex and double salts

Coordination complex

In an aqueous solution, they are incompletely ionizable. They present a completion that doesn’t exhibit complete ionisation.

Potassium Ferrocyanide is an example. Potassium ferrocyanide ionises to give [Fe(CN)6]-4 and K+.

Double salts

In an aqueous solution, they are completely ionizable. Potash alum is an example. Potash alum is K2SO4.Al2(SO4)3.24H2O, which, when ionised, gives Al+3, K+, and SO2-4.

Coordination complexes types

Coordination complexes are of several types, which are mentioned below:

Neutral complexes

The coordination sphere in the neutral complex is neither an anion nor a cation. [Ni(CO)4] is an example of a neutral complex.

Anionic complexes

The coordination sphere here is an anion. K4[Fe(CH)6] is an example of ionic complexes.

Cationic complexes

The coordination sphere here is a cation. [Co(NH3)6]Cl3 is an example of a cationic complex.

Heteroleptic complexes

Heteroleptic complexes contain different ligands. [Co(NH3)5Cl]SO4 is an example of a heteroleptic complex.

Homoleptic complex

Homoleptic complexes contain similar ligands. K4[Fe(CN)6] is an example of a homoleptic complex.

Polynuclear complexes

The coordination sphere in the polynuclear complexes consists of multiple transition metal ions. 

Mononuclear complexes

The coordination sphere in mononuclear complexes consists of one transition metal ion. K4[Fe(CN)6] is an example of a mononuclear complex.

Rules for the naming of coordination compounds 

Some standard rules are to be followed in the process of naming coordination compounds. These rules are mentioned below:

1. Ligands are to be written before the central metal ion.
2. When multiple ligands surround the coordination centre, the naming of ligands is done via alphabetical order. This alphabetical arrangement of names of ligands isn’t disturbed by numerical prefixes that should be applied to ligands.
3. When the counter ion follows the coordination compound, the anionic entity should be written after the cationic entity.
4. When coordination compounds have several monodentate ligands, the prefixes are of this type: tetra-, tri- di- and so on.
5. Central ion’s oxidation state should be mentioned with Roman numerals, which are enclosed in parentheses.
6. When the central metal ion has several polydentate ligands, the prefixes are of this type: tris-, bis-, etc.
7. Whenever a central metallic atom’s name is written, preference is always given to the Latin of that metal. Mercury is an exception. 
8. When writing anion’s name, it should end with ‘o’. It usually replaces ‘e.’ For example, sulphate anion should be written sulphate. Similarly, chloride anion should be written as chloride.
9. The name of the central metal atom is written after writing the name of ligands. In case the complex has an anionic charge, ‘-ate’ is written as a suffix.
10. Some neutral ligands are given specific names in the naming of coordination compounds: H2O (aqua), NO (nitrosyl), NH3 (amine), CO(carbonyl).

These were all the rules of the naming of coordination compounds.

Nomenclature of coordination compounds examples

Some of the nomenclatures of coordination compounds examples are mentioned below:

• tetra carbonyl nickel (O): [Ni(CO)4]
• Potassium hexagon candies ferrate (II): K4[Fe(CN)6
• Tetra hydroxide zincate (II) ion: [Zn(OH)4]-2
• Tetra cyanide nickelate (II) ion: [Ni(CN)4]-2

Ligands in the nomenclature of coordination compounds

To understand the nomenclature of coordination compounds, it is important to know what ligands are. Ligands are nothing but the atoms that surround the central ion. Ligands act as Lewis’s base. They are also known as coordination complexes.

Types of ligands

Here are some types of ligands, along with their examples. They have been differentiated based on the nature of the bond present between the central atom and ligand. 

• Cationic ligands: example of cationic ligands is NO+
• Neutral ligands: Examples of neutral ligands are CO, H2O, NH3
• Anionic ligands: example of anionic ligands is NO+

Here are some examples of ligands that are used very commonly:

• pyridine C5H5N
• Dinitrogen N2
• Dioxygen O2
• Carbonyl CO
• Nitrosyl NO
• Aqua H2O
• Ammine NH3
• Acetate CH3COO-
• Carbonate CO32-
• Cyano CN-
• Hydroxo OH-
• Oxo
• Floro F-
• Bromo Br-

Isomerism in the nomenclature of coordination compounds

Two or more compounds have different atom arrangements, but identical chemical formulas are called isomers. Because of different atomic arrangements, coordination compounds have two kinds of isomerism: structural isomerism and stereoisomerism.

Coordination compounds play an important role in making polypropylene and polyethylene. 

Conclusion

This is all that you need to know about coordination compounds nomenclature. A coordination compound is a substance with a chemical structure wherein the non-metal atoms surround the central metal atoms. Coordination compounds are important as they play a key role in making compounds like polypropylene and polyethylene.