Two types of lanthanide diruthenium phosphonate compounds, based on the mixed-valent metal-metal bonded paddlewheel core of Ru-2(hedP)(2)(3-) [hedp = 1-hydroxyethylidenediphosphonate, CH3C(OH)(PO3)(2)], have been prepared with the formulas Ln(H2O)(4)[Ru-2(hedP)(2)(H2O)2]center dot 5.5H(2)O (1 center dot Ln, Ln = La, Ce) and Ln(H2O)(4)[Ru-2(hedP)(2)(H2O)(2)]center dot 8H(2)O (2 center dot Ln, Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er). In both types, each Ru-2(hedP)(2)(H2O)(2)(3-) unit is linked by four Ln(3+)ions through four phosphonate oxygen (O-P) atoms and vice versa. The geometries of the {LnO(P4)} group, however, are different in the two cases. In 1 center dot Ln, the geometry of {LnO(P4)} is closer to a distorted plane, and thus a square-grid layer structure is found. In 2 center dot Ln, the geometry of {LnO(P4)} is better described as a distorted tetrahedron; hence, a unique PtS-type open-framework structure is observed. The channels generated in structures 2-Ln are filled with water aggregates with extensive hydrogen-bond interactions. The magnetic and electrochemical properties are also investigated.