Absorption Spectra of [Cu(H2O)6]+2 Complex Ion

Absorption Spectra of [Cu(H2O)6]+2 Complex Ion

Absorption Spectra of [Cu(H2O)6]+2 Complex Ion

Absorption Spectra of [Cu(H2O)6]+2 Complex Ion

There is nine electrons in d-orbital of Cu+2 ion (d9 system). Therefore, the spectroscopic term for the ground state of Cu+2 ion is 2D. In the ground state, six electrons occupy the lower t2g orbital and three electrons in higher eg orbital (i.e. T2g6 eg3) and a hole may be considered in eg orbitals. on absorption of radiation, the electron gets excited to eg orbital from t2g orbital (i.e. T2g5 eg4) and now a hole may be considered in T2g orbital.
The hole in the T2g orbitals may be placed in any of the three orbitals. Therefore, the configuration is triply degenarate and the term corresponding to this configuration is 2T2g. Thus, the energy of 2eg is lower than that of 2T2g. In other words, 2eg state is ground state and 2T2g is excited state. Therefore, There is a hole transition from 2Eg to 2T2g which is similar to electron transition and can be represented as 2T2g2Eg. This is opposite of the order of energies of the orbitals (T2g lower energy than Eg energy).
Absorption Spectra of [Cu(H2O)6]+2 Complex Ion
Therefore, absorption band of [Cu(H2O)6]+2 complex in electronic spectra is observed as broad band at 12,500cm due to J-T-distortion.
Due to J-T distortion, 2E2g state splits into B1g lower energy and A1g higher energy and 2T2g state splits into B2g lower energy and Eg higher energy as shown below. There are four electronic transition may occur from B1g to A1g, B2g and Eg state and also from 2T2g2Eg but this transition is very poor. So, only three absorption bands overlap together and becomes a broad band.
Electronic transiton of [Cu(H2O)6]+2 Complex Ion
Electronic spectra of [Cu(H2O)6]+2 Complex Ion