Syntheses, Structures And Properties Of Metallo-Organic Complexes Based On A Hypoxanthine Carboxylic Acid Ligands

The research of coordination chemistry in biomedical field has drawn increasing attention compared with the past decades because of the selective synthesis of specific ligand and the investigation upon the self-assembly of coordination supermolecules which will provide a basis for the development of medicine. The complexes mentioned in this paper were originally designed by using raw materials whose composition is similar to that of DNA, and through a further derivation an organic ligand containing N-heterocycle and carboxylic acid groups was finally gotten. The targeted ligand,2-(6-oxo-6H-purin-1(9H)-yl) propionic acid (H2L), is a multifunctional ligand and has multiple coordination atoms. By trying to reaction with various rare earth metal salts and the transition metal salts to obtain unique complexes, and it has been further proceeded to study upon the synthesis methods, structures and the relative properties.This paper has ultimately obtained two rare earth metal complexes and four transition metal complexes, namely,[La(HL)3(H2O)2]n·H2O (1),[Ce(HL)3(H2O)2n·4nH2O (2),[Co(HL)2(H2O)2]n (3),[Cd(L)H2O]n (4),[Pb(HL)(C2O4)0.5(H2O)]n·2nH2O (5), and [Zn(L)]n (6). Complexes1and2have similar structure, and crystallize in a monoclinic space group P21/c. In the1-D chain structure, the coordination atoms all are O atoms, the Nimidazole atoms and N pyrimidyl atoms do not involve in coordination. The differences between the two are that complex1was synthesed by evaporation at normal temperatures whereas complex2was produced by a diffusion method. The3-D supramolecular structures of both compounds are formed by the complicated hydrogen bonds and π-π stacking interactions. Complexes3-5all are2-D structures. Complex3crystallizes in the orthorhombic space group Pcab. The hexacoordinated metal ions are in the center of a slightly distorted octahedron, and the2-D structure is composed by two-sized nets. Complex4belongs to monoclinic space group P21/c, the Cd(Ⅱ) centers are in a five-coordinated environment, in which the two imidazole nitrogen atoms of ligand involved in the coordination. The2-D structure of4contains two different rings. Complex5also crystallizes in a monoclinic space group P21/c, and the metal nodes Pb(II) are in a eight-coordinated environment ligated by eight oxygen atoms from carboxyls of L and oxalate ligand. Complex6is a3-D network structure, and crystallizes in a monoclinic system P21/c space group. The central metal Zn(II) adopts a four-coordinated mode and locates in a distorted tetrahedral environment coordinated with two carboxyl oxygen atoms and two imidazole nitrogen atoms, respectively.Ligand H2L displays four coordination modes in the above complexes. In1,2and5, only carboxyl oxygen atoms participate in the coordination, with partial carboxyls in a chelating mode and the others in a monodentate mode. All carboxyl groups in L in complex3only adopt monodentate coordination in combination with the coordination of imidazole nitrogen to make L act as bridge ligand. It’s worth saying that two Nimidazoie atoms are participated in the coordination. In complexes4and6, H2L ligands adopt the μ3and μ4bridge mode, respectively. As to say the properties, the two complexes exhibit a relatively rare thermal stability, which may relate to their coordination modes.The N2adsorption experiments show that complexes1and2only have surface adsorption and failed to get to the microporosity of networks. The magnetic studies of complex3show that complex3has antiferromagnetism.