Synthesis, Crystal Structure and Magnetic Properties of Naphthalene-Based Cobalt Diphosphonates Compound.

Two new cobalt diphosphonates with formulae [Co₄(1,4-ndpa)₂(4,4'-bpy)₂] ⋅ 5H₂ O (1) and [Co(1,4-ndpaH)] ⋅ 1.5H₂ O (2) are isolated based on naphthalene scaffold, where 1,4-ndpa^4- 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 {PO₃ C}. These ladder-like chains are then connected with adjacent ladder-like chains through 1,4-ndpa^4- 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 {PO₃ C} are cross-linked by only 1,4-ndpaH^3- ligands into 3D open framework structures. Magnetic studies reveal that spinorbit coupling and/ or antiferromagnetic interaction of Co^II is observed in compound 1. [ABSTRACT FROM AUTHOR]