Transition of electrons between t2g and eg to give colour of coordination compounds

Question

In the case of a hexaaquairon (III) complex, the iron (III) ion has 5 electrons, each singly occupying one d orbital. As the d orbitals are occupied, the vacant 4s, 4p and 4d orbitals are hybridised to give 6 sp3d2 orbitals to be used to overlap with the atomic orbitals of the ligands to do coordinative covalent bond. In this case since the t2g and eg orbitals are not completely filled transition can take place to give colour.

But in case of [Cr(H2O)6]+3. there will be 3 single electrons in 3 orbitals t2g. and all the other orbitals will be hybridized d2sp3. And according to what I understand, there will be coordinate covalent bonds between the lone pair of electrons of the ligands and these hybridized orbitals, meaning that these orbitals will be filled. So, how the electrons will transfer from the t2g orbitals to any higher filled orbital? thus, How could this compound have a color?

Answer 1

So, how the electrons will transfer from the t2g orbitals to any higher filled orbital?

This concept of t2g and eg comes in crystal field theory.

According to NCERT chemistry class 12 it is written that:

The crystal field theory (CFT) is an electrostatic model which considers the metal-ligand bond to be ionic arising purely from electrostatic interactions between the metal ion and the ligand.

Ligands would cause splitting of d orbitals but they do not transfer there electrons to these t2g and eg orbitals and hence electrons are free to jump in them.

Apart from CFT, other theories like LFT also tell the same thing that: t2g and eg orbitals are not occupied by ligands.