Metal complexes in medicine: an overview and. Updated Drug Design P erspectiv e. Ravinderpal Kour Sodhi and Satya Paul. Department of Chemistry, University of Jammu, Jammu - India. The colors of transition metal complexes often vary between solvents. The color of the complex depends on the ligand. For example, it is pale green in water, but forms a dark green precipitate in concentrated hydroxide solution, carbonate solution, or ammonia. forms a pink solution in water, but a blue-green precipitate. Transition metal-ligand molecular complexes are emerging as useful paradigms in materials science. Transition metal complexes have various electronic configurations and d-metal oxidation states. This chapter reviews redox reactions between complexes of different metals. A redox reaction between transition metal complexes, having adjacent stable oxidation states, usually occurs as a simple one-equivalent change. For post-transition and actinide elements, where there is usually a difference of two between,