As discussed above, TiCl 4 is coordinatively unsaturated. Reaction by the associative mechanism allows the Ti to gain more electrons first by associating with a molecule of water before dissociating a Cl ligand. This equilibrium lies to the right. Very briefly explain your answer to the previous question. Ethylenediamine is a sronger ligand than water, so the complex with en thermodynamically more stable than the hexaaqua complex.
Color arises when a molecule absorbs some portion of the visible spectrum.
The remaining light is perceived by the eye and brain to have the complimentary color to that which the molecule absorbs. Alternately, the complex could be absorbing all light that is not red, leaving only red photons for the eye and brain to perceive. The photon energy is convewrted into electron energy by electron promotion. In the case of a transition metal complex, this is a promotion from a lower-energy d orbital to one of higher energy. The energy gap between these orbitals is termed the crystal field splitting energy.