Four new transition metal(II) diphosphonates with a 3D supramolecular structure, M(hedpH₂)₃·3NH₂(CH₃)₂NH(CH₃)₃·3H₂O (M = Mn (1), Co (2), Ni (3), Zn (4); hedpH₄ = 1-hydroxyethylidenediphosphonate acid) have been synthesized under mixed-solvothermal conditions and structurally characterized. Compounds 1–4 are isomorphous and adopt a three-dimensional supramolecular network structure containing {M(hedpH₂)₃}⁴⁻ cluster units. The interconnection of {MO₆} and {CPO₃} polyhedra via corner-sharing forms a {M(hedpH₂)₃}⁴⁻ cluster, and these isolated clusters are extended by hydrogen bonds to form a two-dimensional layer structure, which are further connected through hydrogen bonding interactions to give rise to a 3D supramolecular structure. Surface photovoltage spectroscopy (SPS) of compounds 1–4 indicates that it possesses positive SPV response in the range of 300–600 nm and shows p-type semiconductor characteristic. Luminescence properties of the four compounds have also been studied.