Two new cobalt diphosphonates with formulae ［Co4(1,4-ndpa)2(4,4′-bpy)2］·5H2O (1) and ［Co(1,4-ndpaH)］·1.5H2O (2) are isolated based on naphthalene scaffold, where 1,4-ndpa4- represents deprotonation of 1,4-naphthalene diphosphonic acid and 4,4′-bpy is 4,4′-bipyridine. The cobalt atoms are four coordinated with distorted tetrahedral geometries in both 1 and 2. Compound 1 displays a three dimensional framework structure containing ladder-like chains made up of corner-sharing tetrahedra {CoNO3} and {PO3C}. These ladder-like chains are then connected with adjacent ladder-like chains through 1,4-ndpa4-and 4,4′-bpy ligands respectively. Lattice water molecules fill the gaps in the skeleton by hydrogen bond. Compound 2 has a different type of chain structure, where the inorganic chains composed of corner-sharing {CoO4} and {PO3C} are cross-linked by only 1,4-ndpaH3- ligands into 3D open framework structures. Magnetic studies reveal that spin-orbit coupling and/or antiferromagnetic interaction of CoII is observed in compound 1.