Exploring hydrogen-bond capable backbone and ligating topologies: Co(II) coordination polymers derived from mixed ligand systems

Three new coordination polymers namely {[Co(H2O)2(phthalate)(μL1)]·2.36H2O}n 1, {[Co(H2O)4(μL2)Co(H2O)2(phthalate)2]·H2O}n 2 and {[Co(H2O)4(μL3)Co(H2O)2(phthalate)2]·1.12H2O}n 3 [L1=N-(4-pyridyl)isonicotinamide, L2=N-(3-pyridyl)isonicotinamide, L3=N-(4-pyridyl)nicotinamide] have been synthesized and characterized by single crystal X-ray diffraction, elemental analyses, IR, X-ray powder diffraction and thermogravimetric analyses. 1 and 2 crystallize in monoclinic P21/n space group with cell dimensions a=8.2460(8) Å, b=13.5199(14) Å, c=19.609(2) Å, β=100.161(2)°, Z=4 and a=10.6653(8) Å, b=7.9952(6) Å, c=24.7444(17) Å, β=102.3790(10)°, Z=4, respectively. 3 crystallizes in monoclinic space group P21/c with a=11.6556(8) Å, b=8.0359(6) Å, c=23.6344(17) Å, β=103.4040(10)° and Z=4. The metal centres in all the structures are hexacoordinated displaying slightly distorted octahedral geometry. Axial sites of the metal centres in all the cases are occupied by the nitrogen atoms of the bidentate ligands (L1, L2 and L3) whereas the equatorial sites are occupied by the oxygen atoms coming from phthalate and water molecules. All the structures show 1D polymeric open framework capable of occluding hydrogen bonded guests such as water molecules.