The colors of transition metal complexes depend on the metal and the ligand. Most copper complexes are blue. Cobalt complexes can be any color, depending on the ligand. For example, cobalt chloride dissolved in ammonia can be red, purple, green or yellow depending on the complex formed, says Purdue University. In general, solutions of nontransition metal compounds are colorless.
Transition metal complexes can absorb energy from visible light, and this causes an electron to shift from a lower energy d-orbital to a higher energy d-orbital. When the metal absorbs photons of particular wavelengths from light, the light passing through the metal exhibits a color caused by the removal of those photons, says Western Oregon University. Most transition metal complex solutions are colorful, while most other solutions are not. This is due to the ability of the metals to absorb energy and shift their electrons, says Chemguide.
Transition metals form complexes with various ligands in solution. These complexes may be referred to as coordination complexes, transition metal complexes or Lewis acid-bases, says Purdue University.
Transition metals have features commonly identified in metals – they are malleable, and they conduct heat and electricity. They are called transition metals because of their location in the periodic table in between two groups of non-metals, says Perdue University. They have incompletely filled d-orbitals.