As a model of the active site of [NiFe] hydrogenases, a dinuclear nickel - ruthenium complex [Ni(xbsms) Ru(CO)(2)Cl-2] was synthesized and fully characterized. The three-dimensional structure reveals a nickel center in a square-planar dithioether-dithiolate environment connected to a ruthenium moiety via a Ni(mu-SR)(2)Ru bridge. This complex catalyzes hydrogen evolution by electroreduction of the weakly acidic Et3NH+ ions in N,N-dimethylformamide and is therefore the first functional bioinspired model of [ NiFe] hydrogenases.