A novel lead-phosphonate, [Pb₂(HL)]·(NO₃)·2(H₂O) 1 (H₄L = H₂O₃PCH₂N(C₄H₈)NCH₂PO₃H₂ N,N′-piperazinebis(methylenephosphonic acid), so HL = O₃PCH₂NH(C₄H₈)NCH₂PO₃), has been hydrothermally synthesized and characterized by elemental analysis, IR, TG-DTA, and X-ray single-crystal diffraction. Compound 1 possesses a 2D cationic layer structure built from inorganic chains with three types of eight-membered rings arranged in an ABAC manner. In 1, both crystallographic distinct Pb(II) ions adopt three-coordination geometry, and a counter anion NO₃ ^– and two lattice water molecules occupy the voids between 2D layers. After the removal of solvent, the size of tunnel formed by 2D layers is 137.9 ų per unit cell, comprising 17.0% of the crystal volume based on the crystal structure. When the bond length of Pb–O(N) extended to 3.10 Å, a 3D metal–organic framework was constructed via long Pb–O(N) contacts, simultaneously accompanied by the hemi- to holo-directed transition in coordination geometry of Pb(II). Except for the long Pb–O contacts, a 3D supramolecular network is also formed by hydrogen bonds (N–H···O, O–H···O, and C–H···O), van der Waals forces as well as electrostatic interactions. The result of fluorescence measurements indicates that 1 shows a fluorescent emission band at 465 nm (λ_excitation = 215 nm).