A novel cobalt(II)-organic framework, [CO2(OH)(3,4-PBC)(3)](n) (I), has been acquired by the reaction of CoO with an unsymmetrical pyridylbenzoate ligand, 3-pyrid-4-ylbenzoic acid (3,4-PBC). Singlecrystal X-ray diffraction studies reveal that it is comprised of [CO4ll((mu 3)-OH)(2)] clusters linked by the unsymmetrical ligand 3,4-PBC, forming a novel helical double-layered metal-organic architecture. A significant overall antiferromagnetic behavior has been observed for this compound.