The crystal structures of mercury oxosalts are described with isolation of oxocentered tetrahedrul groups [OHg₄]. The bond topology of the oxocentered polycations is more diversified and rich than the motifs of canonic polyhedra in “classical” crystal chemistry and often is a more striking illustration of the unique nature of the structure of compounds from this class. The relative stability of the oxocentered polyions indicates that they play an important role in structure formation and possibly exist in various natuml media, making it appropriate to consider these groups in analysis of mercury transfer processes occurring in nature. The oxocentered approach proved to be useful for establishing structure-property type correlations and promotes the understanding and predicting the anisotropy of physical properties.