Coordination Number and Hybridizations in Chemistry

Study Notes

Coordination Compounds

Chlorophyll, haemoglobin, and vitamin B12 are coordination compounds of magnesium, iron, and cobalt respectively.
Coordination compounds have various applications in metallurgical processes, industrial catalysts, analytical reagents, electroplating, textile dyeing, and medicinal chemistry.

Alfred Werner's Contributions

Alfred Werner, a Swiss chemist, formulated ideas about the structures of coordination compounds.
He prepared and characterized a large number of coordination compounds and studied their physical and chemical behavior using simple experimental techniques.

Definitions of Important Terms

A coordination entity constitutes a central metal atom or ion bonded to a fixed number of ions or molecules.
The central atom/ion is the atom/ion to which a fixed number of ions/groups are bound in a definite geometrical arrangement.
Ligands are the ions or molecules bound to the central atom/ion in the coordination entity.

Hybridization and Geometry

The geometry of a complex can be predicted from its magnetic behavior based on the valence bond theory.
In the diamagnetic octahedral complex [Co(NH3)6], the cobalt ion is in the +3 oxidation state and has the electronic configuration 3d6.
The complex has octahedral geometry and is diamagnetic due to the absence of unpaired electrons.
In the formation of this complex, the inner d orbital (3d) is used in hybridization, making it an inner orbital or low spin or spin-paired complex.

Influence of Ligands on Colour

The colour of a complex may be influenced by the ligand, as illustrated by the [Ni(H2O)6] complex, which forms when nickel(II) chloride is dissolved in water.
The addition of the didentate ligand ethane-1,2-diamine (en) to [Ni(H2O)6] results in a series of reactions and associated colour changes.

Colour of Some Gemstones

Ruby, a gemstone, is predominantly aluminium oxide (Al2O3) containing about 0.5-1% Cr ions (Cr3+), which are randomly distributed in positions normally occupied by Al.
The d–d transitions at these centres give rise to the colour of the ruby.

Description

Explore the concepts of coordination number, types of hybridizations, and predicting the geometry of complexes based on valence bond theory. Learn about different hybrid orbitals in space and their distributions.