colours of transition metals

why are the colours of different transition metal complexes different?

• d orbitals have different e/d orbital Es are split

• e^- move to excited state/higher E d orbitals

• e^- absorb visible light

• colour seen is that from complementary colours that are reflected not absorbed

give the eqn for calculating the difference in E and state what each symbol corresponds to:

ΔE = h ν = hc / λ, where:

• ΔE: energy absorbed / J

• h: Planck’s constant = 6.63 × 10^-34 Js

• v (Greek letter nu): freq of light absorbed / Hz

• c: speed of light = 2.998 × 10⁸ ms^-1

• λ: wavelength of light absorbed / m

give 3 factors which might affect the colour of a transition metal complex:

• change in oxidation state

• change in coordination number

• change in ligand

how can we use colorimetry to determine the concentration of transition metal ions in a solution of unknown concentration?

1. add an appropriate ligand to intensity colour

2. make up solutions of some known concentrations and measure absorbance

3. plot calibration curve of of absorbance v conc

4. measure absorbance of coloured complex and find conc from graph