Ligand L (4,5-bis[(2′-hydroxyethyl)thio]1,3-dithiole-2thione) which crystallizes in the monoclinic system (P2
1
/n) displays a 1-D network generated by a succession of
intra
-molecular and
inter
-molecular hydrogen bonds. Weak
π-π and S
⋯S interactions are also observed in the supramolecular structure. Reaction of L with one equivalent of mercury(II) iodide affords the adduct [HgI
2
L] (la). The crystal structure of this complex shows that coordination occurs exclusively via the sulfur atom of the thione function (C=S). The ligation on HgI
2
induces a change of the hydrogen bond pattern generated by the hydroxyl substituents: only intermolecular hydrogen bonds are present, organizing the adduct 1a in form of centrosymmetrical dimers in the solid state. The propensity of HgI
2
to build-up chains via
μ
2
-iodo ligand may be at the origin of the modification of the hydrogen bond network.