Complementary Colors & Absorption Spectra

Spectral Relationship:

$$E_{\text{absorbed}} = \frac{h \cdot c}{\lambda_{\text{absorbed}}} \implies \lambda_{\text{absorbed}} \propto \frac{1}{\Delta_o} \quad (\text{Observed Color} = \text{Complementary Color})$$

Concept: $$d\text{-}d$$ transitions occur when an electron in a lower $$t_{2g}$$ orbital absorbs a specific wavelength of visible light to jump to an upper $$e_g$$ orbital. The color transmitted or reflected by the coordination compound is the complementary color of the light absorbed.

Notation:

• h = Planck's constant; c = Speed of light;
• $$\lambda_{\text{absorbed}}$$ = Wavelength of light absorbed;
• Larger $$\Delta_o$$ (stronger ligand field) shifts absorbed light to shorter wavelengths (higher frequency / blue region), rendering the observed color shifted toward longer wavelengths (yellow/red region).