Twelve-coordinated sulfate hydrogen bonding interactions in water-containing Fe(II) system, [Fe-0.5(H2O)(3)](2)SO4 center dot H2O (1), are reported herein. The X-ray single-crystal structural characterization suggests that the SO42- anion is coordinated by a total of twelve O-H center dot center dot center dot O hydrogen bonds from coordinated or free water molecules, with each sulfate O atom accepting three H-bonds in water-containing Fe(II) system. A well-defined cyclic (10) H-bonding motif is found in the sulfate - water clusters, which is extended into 2D sulfate - water H-bonding sheet. An 1D infinite [SO42--H2O](n) chain is further cross-linked with the 2D H-bonding sheet above mentioned to form a 3D sulfate - water hydrogen bonding network stabilized by the O-H center dot center dot center dot O hydrogen bonds interactions. The sulfate saturated coordination of 12 hydrogen bonds from water molecules in its first hydration shell is confirmed by X-ray crystallography. GRAPHICAL ABSTRACT The X-ray single-crystal structural characterization suggests that the SO42 anion is coordinated by a total of twelve O-H center dot center dot center dot O hydrogen bonds from coordinated or free water molecules, with each sulfate O atom accepting three H-bonds in water-containing Fe(II) system. The H-bonding interactions in the sulfate -water chains are also studied. [GRAPHICS] .