Mercury(II) complexes which have a bulky cholyl amide group at the ortho or para position of benzenethiolate, Hg[S-2-{C23H36(OH)(3)}CONHC6H4](2) (1) With an intramolecular NH ... S hydrogen bond and Hg[S-4-{C23H36(OH)(3)}CONHC6H4](2) (2), were synthesized to prepare an aqueous micellar solution. A hydrated Hg(II) ion was formed from the Hg(II) thiolate complexes, 1 and 2, at the ligand dissociation point (pH 4.0 and 4.9, respectively) near the pK(a) values (5.7 and 7.0, respectively) of the corresponding thiols. The hydrated Hg(II) ion was detected by the formation of Hg(0) species reduced with Na2S2O4 in an aqueous micellar solution. The NH ... S hydrogen bond lowers the pK(a) value of the conjugated thiol to protect the Hg-S bond from dissociation by water under neutral conditions.