No. of unpaired electrons = ; Hence paramagnetic Magnetic moment (Using spin only formula) µ s = n(n+ ) = ( + ) = . BM Colour of the complex and crystal field splitting energy: Most of the transition metal complexes are coloured. A substance exhibits colour when it absorbs the light of a particular wavelength in the visible region and transmit the rest of the visible light.
When this transmitted light enters our eye, our brain recognises its colour. The colour of the transmitted light is given by the complementary colour of the absorbed light. For example, the hydrated copper(II) ion is blue in colour as it absorbs orange light, and transmit its complementary colour, blue. A list of absorbed wavelength and their complementary colour is given in the following table.
Wave length(λ) of absorbed light (Å) Wave number( ν ) of the absorbed light (cm- ) Colour of absorbed light Observed Colour 25000 Violet Yellow 21053 Blue Orange 19608 Green Red 17544 Yellow Violet 16949 Orange Blue 15385 Red Green The observed colour of a coordination compound can be explained using crystal field theory. We learnt that the ligand field causes the splitting of d orbitals of the central metal atom into two sets (t 2g and e g ). When the white light falls on the complex ion, the central metal ion absorbs visible light corresponding to the crystal filed splitting energy and transmits rest of the light which is responsible for the colour of the complex. Yellow - nm Green - nm Blue - nm Indigo - nm Violet - nm Red - nm orange - nm Figure .
Colour Wheel - Complementary colours are shown on opposite sides. XII U5 Coordination XII U5 Coordination - - - - This absorption causes excitation of d-electrons of central metal ion from the lower energy t 2g level to the higher energy e g level which is known as d-d transition. Let us understand the d-d transitions by considering [Ti(H O) ] + as an example. In