COORDINATION COMPOUND

These are molecular entities that consist of a central metal atom or ion bonded to surrounding molecules or ions known as ligands

Central metal ion are Lewis acid that accept electron pair from ligands . They act as coordinating centre that forms coordinating covalent bond with the ligands . They are often referred to as transition metals and they have vacant d orbital which enable them to receive electron pair from ligands

Ligands are Lewis base that donate electron pairs to central metal ions to form covalent bonds. They are classified based on several factors

  • Neutral — water and ammonia

  • Charged — chlorine and cyanide

  • Number of donor atoms {dentate)

  1. Mono dentate

  2. Poly dentate


Types of coordination compound

  1. Based on type of ligand

Homoleptic—one type of ligand

Heteroleptic —more than one type of ligand

2.Based on overall charge of the Complex

Neutral— has no charge

Cationic — positive charge

Anionic — negative charge

3.Ligand denticity

Monodentate— donate one pair of electron or ione pair

Polydentate— multiple ion pair or electron pairs



Properties of coordination compound

  • Color — it is coloured due to electronic transition within the d orbital of the central ion . It is also due to charge transfer transition

  • Magnetic properties — this is due to the number of unpaired electrons in the d orbital .of the centre metal ions

  1. Para magnetic — contains one or more unpaired electrons that are attached to magnetic field

  2. Diamagnetic —all paired electrons that are weekly repelled by magnetic field



Coordination number and geometry of coordination compound

Coordination number is the number of ligand donor atoms attached to the central metal ion. This influences the geometry ( structure).

These geometry includes

  1. Octahedral has a coordination number of 6 ligands are symmetrically arranged around the central metal ion

  2. Tetrahedral coordination number 4 ligands are arranged at the corners of a tetrahydron

  3. Square planar coordination number 4 ligands are arranged in a square plane around the central metal ion

  4. Linear coordination number 2 ligands are arranged in a straight line