The utility of the water-soluble (HOCH2)(2)PCH2CH2P(CH2OH)(2) ligand (dhmpe) in generating 19-electron complexes in aqueous solution was tested. in buffered aqueous solutions at pH 2, the ligand reacts with 17-e1ectron radicals generated by photolysis of water-soluble [(CpCH(2)CH(2)NH(3)(+))(2)Mo-2(CO)(6)][NO3-](2) to form 19-electron adducts. The formation of 19-electron adducts was established by disproportionation of [(CpCH(2)CH(2)NH(3)(+))(2)Mo-2(CO)(6)][NO3-](2) and by the reduction of methyl viologen, both standard indicators of 19-electron adduct formation. The crystal structures of the (HOCH2)(2)PCH2CH2P(CH2OH)(2) ligand and of one of its complexes, [Ni(dhmpe)(2)]Cl-2, were determined.