Abstract: A complex ion containing rhodium, Rh.sub.2 (1,3-diisocyanopropane).sub.4.sup.2+ is called "rhodium bridge." Because of the nature of its molecular structure, it is deep blue in water solution. Irradiation of the blue complex between 500 and 600 nm leads to direct reduction of the protons in water to hydrogen gas. In this reaction rhodium bridge is converted to a yellow form, in which each of the two rhodiums has lost one electron. The H.sub.2 -producing visible photoreaction of rhodium bridge can be utilized in a solar-driven water splitting cycle.