Color of compounds
Since color is only seen in complex ions containing transition metals, the partially filled d orbitals are probably the cause of the colors. Normally d-orbitals in transition metals have uniform energy levels. However when transition metals form coordination complexes, ligands can produce energy level gaps by d-orbital splitting. Some ligands produce wide gaps and are called strong field ligands while those that produce small gaps are called weak field ligands. How much the d-orbitals split depends on the geometry of the complex, and the ligands. Electrons can be promoted from lower d-orbitals to higher energy level d-orbitals from absorbing electromagnetic radiation. When the electromagnetic radiation passes through the transition metal complex, we see the wavelength or color being transmitted.
Colors of major transition metal ions are shown below:
Colors of major transition metal ions are shown below:
http://www.wou.edu/las/physci/ch462/tmcolors.htmhttp://www.compoundchem.com/wp-content/uploads/2014/03/Transition-Metal-Ion-Colours-Aqueous-Complexes.png