The synthesis, structure, and solution properties of a water-soluble (alkanethiolato)nickel complex, NiL(S2(Me)N3(Pr)) (1) are described. Structure 1 is mononuclear, despite the lack of bulky substituents near the sulfurs, and is the first example of a five-coordinate nickel alkanethiolate complex. Evidence for intermolecular S...H interactions in the solid state, and H-bonding in protic solvents, suggests that Ni-bound thiolates have an affinity for protons and can therefore act either as proton storage sites or as participants in the promotion of heterolytic H-2 cleavage in the metalloenzyme hydrogenase.