Two copper diphosphonates were hydrothermally synthesized using ethylenediphosphonic and p-xylenediphosphonic acids, synthesized according the Arbuzov method. The structure of (Cu I I (H 2 O)) 2 {O 3 P-CH 2 -CH 2 -PO 3 } already described from powder data, was solved from single crystal data. Its symmetry is monoclinic (space group P2 1 /c (no. 14)) with lattice parameters a=8.0670(4) 9, b=7.5889(4) 9, c=7.3997(4) 9, β=116.281(2) o , V=406.18(4) 9 3 , Z=2. The structure of (Cu I I (H 2 O)) 2 {O 3 P-CH 2 -(C 6 H 4 )-CH 2 -PO 3 } was solved by powder X-ray diffraction (space group P2 1 /c (no. 14)) with lattice parameters a=10.812(1) 9, b=7.577(1) 9, c=7.412(1) 9, β=92.34(1) o , V=606.7(2) 9 3 , Z=2. Both structures are built up from identical inorganic layers covalently linked by the organic chains which act as pillars. The inorganic layers contain dimers of edge-sharing CuO 4 (H 2 O) square pyramids linked by the PO 3 C tetrahedra. Both compounds are antiferromagnetic at 4(1) K.