Syntheses, Structures And Property Studies Of Coordination Polymers Based On A Purin-Containing Carboxylate Ligand

Metal-organic coordination polymers have attracted particular interests in coordination chemistry not only owing to their intriguing topology structures, but also owing to their practical applications in molecular recognition, nonlinear optical devices, biomimetic chemistry, asymmetric catalysis chemistry, ions exchange, adsorption, magnetic devices and enantiomorph separation. Directional synthesis of coordination polymers with certain properties through the self-assembly of the designed organic ligands with different configurations and metal ions is a current hot topic and an attractive challenge in coordination chemistry.The target ligand2-(6-oxo-6H-purin-1(9H)-yl)acetic acid (H2L) was synthesized via the substitution reaction of quantificational2'3'-dideoxyinosine, chloroacetic acid and sodium carbonate in water, and characterized by IR,'H NMR and elemental analysis.In this paper,10new coordination polymers were synthesized through the reactions of H2L and rare earth metals and transition metals, namely,[La(HL)2(NO3)(H2O)2]n (1),[Ce(HL)2(NO3)(H2O)2]n (2),[Co(HL)2(H2O)2]n·2nH2O (3),[Ni(HL)2(H2O)2]n·2nH2O (4),[Mn(HL)2(H2O)2]n·2nH2O (5),[Fe(HL)2(H2O)2]n·2nH2O (6),[Pb(HL)2(H2O)2]n(7),[Cd(HL)2(H2O)2]n(8),[CdL]n(9) and [ZnL]n (10), Single-crystal structural analysis reveals that1and2are isomorphous and crystallize in a monoclinic space group P21/m. In addition, they have nearly the identical coordination environment, spatial configuration and interwinding double helical chain, in which the Nimidazole atoms do not involve in coordination, and each helical chain structure is extended by the intermolecular hydrogen bond to form a3D supermolecular structure. Complexes3-6are isomorphous, too, and crystallize in a monoclinic space group P21/c. They have nearly the identical coordination environment, spatial configuration, and (4,4) topology structure, in which there is a pair of left and right helical chains in the same net where π-π weak interactions make the skeleton of the complex be more stable. A three dimensional supramolecular network forms through five different types of hydrogen bonds between two-dimensional layers due to the presence of coordinated water and lattice water. Complexes7and8are isomorphous, too, and crystallize in a monoclinic space group P21/m. They have nearly the identical coordination environment and spatial configuration of3-6. Of course, there are some differences between3-6and7-8. Firstly, they have different space groups. Scondly, only three different kinds of hydrogen bonds exist in7and one kind of hydrogen bond exists in8due to the absent of lattice water. Compounds9and10are isomorphous and crystallize in a monoclinic space group P21/c. They are3D coordination polymer with the identical coordination environment and spatial configuration of metal centers. In these structures, the imidazole group of each L2-link two metal centers to form an extended right-handed helical chain, and then those right-handed helical chains are further linked by one O atom of the carboxylic group of L2-ligand to produce a2D homochiral layer in the ab plane. Finally, the2D layers are further crosslinked by the other O atom of the carboxylic group of L2-ligand to produce the achiral3D networks.Ligands H2L possess a rigid skeleton with an imidazole group and a flexible carboxylic group, and display three coordination modes in these complexes. In complexes1-2, not only Ocarboxy1but also Ocarbony1of the ligands participate in coordination, and the Nimidazoie of the ligands do not participate in coordination due to the nature of the pro-oxygen coordination of the rare earth ion. In3-8the imidazole group of the ligands only uses one nitrogen atom to participate in coordination and the carboxylate group adopt monodentate mode. In9-10, the both imidazole and carboxylica groups of the ligand adopt the bridge mode, and thus the ligand is a μ4bridging spacer.Based on the crystal structure study, the relative properties of these synthesized coordination polymers, such as thermal stability and luminescent property, have been investigated.