A coordination complex may be defined as a compound that results from the combination of two or more stable chemical species and retains its identity in the solid as well as the dissolved state.
The cation to which one or more neutral molecules or ions are coordinated is called the central ion.
The molecules or ions so attached are called ligands.
The atom in the ligand which can donate the electron pair is called the donor atom.
The total number of ligands attached to a central ion is called the coordination number of that ion.
The central ion together with molecules or ions coordinated to it constitutes what is termed a coordination complex.
Isomerism in coordination compounds:
The compounds having the same molecular formula but different structures and hence different physical and chemical properties are called isomers.
The phenomenon of the existence of such compounds is known as isomerism.
Isomerism in coordination compounds may be divided into two main types, Structural isomerism, and Stereo isomerism.
Structural isomerism is in five types Ionisation isomerism, Hydrate isomerism, Coordination isomerism, Linkage isomerism, and coordination position isomerism.
In ionization isomerism, the difference arises from the positions of groups within or outside the coordination sphere. therefore these isomers give different ions in the solution.
In Hydrate isomerism, arises from the replacement of a coordinated group with water of hydration.
The coordination isomerism is observed in the case of compounds comprising of both cationic and anionic complexes.
In linkage isomerism, there are two atoms that can donate their lone pairs, for example, in the Nitrogen atom as well as the Oxygen atom can donate their lone pairs. If Nitrogen donates its lone pair, one particular compound will be formed. If Oxygen does a different compound is obtained.
Coordination position isomerism is exhibited by bridged complexes and results from the different placement of ligands.
Stereo isomerism is in two types Geometric isomerism and Optical isomerism.
In geometric isomerism, the atoms have different spatial arrangements, and it is also known as cis-trans isomerism.
In optical isomerism, are certain substances that can rotate the plane of polarised light, and the optically active isomers of a compound that rotate the plane of polarised light equally but in opposite directions are called enantiomers.
and is a type of ionization isomer.
Here, the difference arises from the positions of groups within or outside the coordination sphere. therefore these isomers give different ions in the solution.