A coordination complex comprises a core atom or ion called the coordination centre, which is usually metallic, and a surrounding array of bonded molecules or ions called ligands or complexing agents. Many metal-containing compounds, particularly those containing transition metals (elements in the d-block of the Periodic Table, such as titanium), are coordination complexes. A dative bond, also known as a coordinate bond, develops when a Lewis base and a Lewis acid combine. Coordination is the word describing the donation of a Lewis base to a Lewis acid without any other bonding modifications. Coordination complexes can be subcategorized into the cationic, anionic and neutral complexes.

Coordination chemistry is concerned with the reactivity and characteristics of complexes comprising single metal atoms or small groups of metal atoms.

Coordination Complexes’ Nomenclature

The following are the rules for designating a coordination complex:

• The ligands are mentioned well before metal ions while naming a complex ion.
• In the following order, give a list of the ligands: neutral, negatives, positive. If many ligands with the same charged type exist, they are named alphabetically.
• The number of repetitions of several monodentate ligands is indicated by a prefix: di-, tri-, tetra-. Bis-, tris-, and other ligands are received by polydentate ligands.
• -ido is the suffix for anions. Whenever the anion ends in “-ate,” this replaces the last “e,” and “-ide” is replaced by this.
• With a few exclusions, neutrality ligands are assigned their customary names: NH3 became ammine, H2O will become aqua or aqua, CO becomes carbonyl, and NO has now become nitrosyl.
• Put the words of both the central atom/ion in the box. The central atom’s name will end in -ate if the composite is an anion, and its Latin word must be used if it is accessible (except for mercury).
• If the oxidation state of something like the central atom requires to be provided (when there are numerous options or zero), put it in parenthesis as a Roman number (or 0).
• Separate the terms “cation” and “anion” at the end.

Examples of Naming Coordination Compounds

• [NiCl4]2-    

Tetrachloronickelate(II) ion. Inside the parentheses the complex ion is formed, an anion. The suffix -ate must be added to the metal’s name.

• [Pt (NH3)2]Cl4 

Diamminedichloroplatinum. This molecule is completely neutral. The ligands have a total charge of -4. As a result, the oxidation number of platinum is +4.

• [Pt (NH3)2Cl2]Cl2  

Chloride of diamminedichloroplatinum(II). The concentration of ions and atoms is the same in this case. The brackets and the platinum’s differing oxidation number result in a considerably distinct name.

•  [Ag (NH3)2]Br :-  

Diamminesilver(I) bromide.      This molecule is completely neutral. The ligands have a total charge of -1. As a result, the oxidation number of silver is +1.

•  Ni (CO)4 :-   

Tetracarbonylnickel(0). This molecule is completely neutral. The ligands have a total charge of 0. As a result, the oxidation number of nickel is 0.

•  K2 [Cd(CN)4]     :-   

Potassium tetracyano cadmate(II)  . This molecule is completely neutral. The ligands have a total charge of -2. As a result, the oxidation number of cadmium is +2.

•  [Co (H2O)6] [Ag (CN)2]3  :- 

Hexaaquacobalt(III) dicyanoargentate(I). This molecule is completely neutral. The ligands have a total charge of -3 in case of cobalt complex and -1 in case of silver complex. As a result, the oxidation number of cobalt is +3 and of silver is +1.

Conclusion

A coordination complex is made up of a core atom or ion called its coordination centre, which is usually metallic, and an encircling array of bonded molecules or ions called complexing or ligands agents. Coordination complexes are metal-containing compounds that contain transition metals . And there are various rules to name the coordination complexes which we have discussed above.