Mononuclear Zn, Cd, and Hg 1,2-benzenedithiolates with intramolecular NH center dot center dot center dot S hydrogen bonds, [M-II{1,2-S-2-3,6-(RCONH)(2)C6H2}(2)](2-) (R = CH3, t-Bu; M = Zn, Cd, Hg), were synthesized and characterized by X-ray analysis and spectral measurements. The presence of intramolecular NH center dot center dot center dot S hydrogen bonds was established by the IR spectra. Hg-199 and Cd-113 nuclear magnetic resonance showed a stabilized four-thiolate coordinated structure and suggested the influence of the NH center dot center dot center dot S hydrogen bonds to p pi(Hg)-p pi(S) interactions. The NH stretching bands show that the NH center dot center dot center dot S hydrogen bonds in Cd and Hg complexes are stronger than those in the corresponding Zn complex. These results are supported by theoretical, calculations. The experimental and theoretical results suggested that the NH center dot center dot center dot S hydrogen bond influences the efficient capture of toxic Cd and Hg ions by metallothioneins.