Question

Describe the general behavior of d orbitals in an octahedral field (splitting pattern). You can either explain it using the Molecular orbital model or the Crystal Field Model. (explain the splitting and why, don’t just tell me that they split into two groups). What makes a ligand a strong field ligand, while another one a weak field ligand? For example why are H2O ligands generally regarded as weak field splitters, while NH3 ligands are strong field splitters? Why carbonyls are considered strong field splitters?

PLEASE EXPLAIN AND SHOW YOUR WORK

Answer 1

d orbitals are of five

d_XY, d_xz, d_YZ, d_XZ,dx²-Y² and  d_z²

these orbitals are aligned in the form of shown.

dx²-Y² and  d_z²these orbitals are aligned along the axis while others are arranged between the orbitals.these orbital shows the cloud of electrons at the same energy level.

so in octahedral ligand field , assuming that ligand aproach the metal through the axis,

the orbitals cloud align on the axis will face more  than the other ones in between the axis repulsion because of the approach of the ligand through axis.and so there will be splitting in energy level.and one which face more repulsion will be raised into higher energy than the other. dx²-Y² and  d_z² wil occupy a higher energy level than the other three orbitals.

the energy difference between these two splited energy levels in shown as delta⁰.orbitals at the same energy level is called as degenerate orbitals.

now, matter of strong and weak field ligands is about how strong the approaching ligands and also about the energy of orbitals of ligand and that of metal interacts.

H₂O

in this ligand the electron donar atom is oxygen there for we need to compare see the orbital structure of oxygen atom.they donat electrons from filled P orbital of orbital to the empty d orbitals of the metal.that is interaction is Pi-dpi

as we see ligand p orbital (arranged lower to metal orbital due to high electro negativity of ligand than that of metal) interact with metal orbital t2g orbital and form a bonding two energy orbital and t2g^* orbital is the one new formed orbital on interaction of ligand and metal which now acts like t2g of figure shown before. so we see energy delta⁰ has been reduced when metal and ligand orbital interacted.and so ligands which undergo this kind of interaction which finally reducec delta⁰ are called weak field ligand.

NH₃ AND CO

considering the orbitals of these ligands. we see they are less elctro negativ compared to metal so their orbitals are arranged at higher position that that of metal.

here we can see the interaction causes th eenergy difference of eg-t2g^* is increased.these ligands are pi accepting orbitals.they increase the delta⁰ to a verry high energy .