Valence Bond Approach: structure, color & magnetic properties of CN Complexes

Coordination number is the number of ligands that surround the metal ion and are linked to it through sigma bonds.

The square planar geometry has a hybridisation of either dsp² and sp²d. The orbitals involved here are s, px, py and dx² - y². We can clearly see that there is no involvement of z-direction.
Hence it is based on the z-exclusion principle.

A monodentate ligand is a ligand that donate electrons to the central metal ion from its one site.
A minimum of 4 such ligands is required for the formation of a tetrahedral (sp³ hybridisation) or square planar (dsp² hybridisation) complex.

A low spin complex is formed when the ligands are of strong field strength whereas high spin is characterised by weak field strength.
In K²NiF⁶ , Ni is in +4 oxidation state with d⁶ electronic configuration.Here fluoride acts as a strong field ligand resulting in low spin complex.
In a strong field, all of the electrons in d⁶ are paired up, leaving zero unpaired electrons, corresponding to a zero magnetic moment.
Note: When metal is in +4 oxidation state all ligands act as strong field ligands.

The cuprammonium ion is [Cu(NH₃)₄]²⁺.The copper is in +2 oxidation state with the electronic configuration of 3d⁹. The hybridisation takes place in the following manner:

The dsp² hybridization corresponds to square planar shape.

When the two orbitals have identical stability or energy, the one which is more directionally concentrated would form a stronger bond.

The p-orbital is in the shape of a Dumbbell. It has 2 lobes that are pointing in opposite directions.

According to VBT, when two atoms come closer to each other with opposite electron spins, due to mutual rearrangements (or overlapping) of their electron clouds, energy changes are produced.

The Valence Bond Theory was developed in 1927 by Heitler and London.

The s-orbital is spherically symmetric in shape so it does not show preference to any direction. It is the same from all the directions.