Coordination compounds are those compounds that consist of a central metal atom or ion surrounded by ligands. The bonding in these compounds is different from the bonding seen in simple covalent or ionic compounds.



The coordination number of a metal in a coordination compound refers to the number of ligands attached to the metal. The geometry of the compound is determined by the arrangement of these ligands. The two most common geometries are:

• Octahedral - six ligands arranged around the central metal atom in a symmetrical manner.


• Tetrahedral - four ligands arranged around the central metal atom in a symmetrical manner.

The bonding in coordination compounds can be explained by two theories:

• Crystal Field Theory - This theory explains the bonding in terms of the interaction between the metal ion and the ligands. According to this theory, the ligands create a crystal field around the metal ion. This field splits the d orbitals of the metal ion into two sets - a lower energy set and a higher energy set. The energy difference between these sets is called the crystal field splitting energy (Δ). The electrons from the ligands then fill the lower energy d orbitals, resulting in a complex with a net magnetic moment.


• Valence Bond Theory - This theory explains the bonding in terms of the overlap of the metal ion's d orbitals with the ligand's orbitals. According to this theory, the metal ion's d orbitals hybridize with the ligand's orbitals to form a set of hybrid orbitals. These hybrid orbitals then overlap with the ligand orbitals to form a set of covalent bonds. The geometry of the complex is determined by the shape of these hybrid orbitals.

The bonding between the metal ion and the ligands can be explained by two types of forces:

• Electrostatic Forces - These forces arise due to the attraction between the opposite charges of the metal ion and the ligands. The metal ion has a positive charge, while the ligands have a negative charge due to the lone pairs of electrons present on them.


• Covalent Bonding - This type of bonding arises due to the overlap of the metal ion's d orbitals with the ligand's orbitals. This overlap results in the formation of a set of covalent bonds between the metal ion and the ligands.

In conclusion, the bonding in coordination compounds is complex and involves a combination of electrostatic forces, covalent bonding, and crystal field splitting. The geometry of the compound is determined by the number and arrangement of the ligands attached to the metal ion.