The colour in the coordination compounds can be readily explained in terms of crystal field theory. Consider, for example, the complex [Ti(H_(2)O)_(6)]^(3+), which is violet in colour. This is an octahedral complex where the single electron [Ti^(3+) is a 3d^(1) system] in the metal d-orbital is in the t_(2g) level in the ground state of the complex. The next higher state available for the electron is the empty e_(g) level. If light corresponding to the energy of blue-green region is absorbed by the complex, it would excite the electron from t_(2g) level to the e_(g) level (t_(2g)^(1)e_(g)^(0)to t_(2g)^(0)e_(g)^(1)). Consequently, the complex appears violet in colour. The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. It is important to note that in the absence of ligand, crystal field splitting does not occur and hence the substance in colourless. For example, removal of water from [Ti(H_(2)O)_(6)]Cl_(3) on heating renders it colourless. Similarly, anhydrous CuSO_(4) is white, but CuSO_(4).5H_(2)O is blue in colour. Why is anhydrous CuSO_(4) white but CuSO_(4) dissolved in water gives a blue solution ?

The colour in the coordination compounds can be readily explained in t

1.	The colour in the coordination compounds can be readily explained in terms of crystal field theory. Consider, for example, the complex [Ti(H_(2)O)_(6)]^(3+), which is violet in colour. This is an octahedral complex where the single electron [Ti^(3+) is a 3d^(1) system] in the metal d-orbital is in the t_(2g) level in the ground state of the complex. The next higher state available for the electron is the empty e_(g) level. If light corresponding to the energy of blue-green region is absorbed by the complex, it would excite the electron from t_(2g) level to the e_(g) level (t_(2g)^(1)e_(g)^(0)to t_(2g)^(0)e_(g)^(1)). Consequently, the complex appears violet in colour. The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. It is important to note that in the absence of ligand, crystal field splitting does not occur and hence the substance in colourless. For example, removal of water from [Ti(H_(2)O)_(6)]Cl_(3) on heating renders it colourless. Similarly, anhydrous CuSO_(4) is white, but CuSO_(4).5H_(2)O is blue in colour. Why is anhydrous CuSO_(4) white but CuSO_(4) dissolved in water gives a blue solution ?
Answer» Solution :In the absence of WATER (ligands), there is no splitting and no excitation of electrons. HENCE it is WHITE. When dissolved in water, they act as ligands, splitting of ORBITALS takes PLACE and excitation of electrons takes place and colour is produced.