Studies On The Syntheses, Structures And Performances Of Transition Metal-Hydroxyl Polycarboxylate Coordination Polymers

The coordination polymers of metal-polycarboxylates have diverse topology structures and potential applications in many fields. In this paper, the hydroxyl polycarboxylic acids (malic acid, citric acid and tartaric acid) have been been employed to act as the building units, which have excellent chelating ability, hydrophilic nature and biological properties. Under water-alcohol mixed solvothermal conditions with the mild temperature (160-180oC), fifteen coordination polymers of transition metal-hydroxyl polycarboxylates with two-and three-dimensional structures were designed and synthesized, and three new compounds with nitrogen-containing carboxylates were also obtained. The X-ray single-crystal structures of these compounds were determined and characterized by elemental analysis, IR, XPS and EPR spectra. The thermal analyses and magnetic properties for most of the compounds have also been studied. In these compounds, most of the hydroxyl polycarboxylate ligand exhibit new coordination modes which have not been reported in previous literatures and the antiferromagnetic, ferromagnetic and antiferromagnetic interactions are exist respectively between the metal ions. I Transition metal-malate coordination polymers Four matate-bridging coordination polymers, {[M(Hmal)(H2O)]·H2O}n,M = CoII(1), NiII(2) 0.3CoII/0.7NiII(3) and {[Mn(Hmal)(H2O)2]·H2O}n (4),H3mal = malic acid,have been synthesized from weak acidic solutions by solvothermal technique. Compounds 1 , 2 and 3 are isostructural three-dimensional coordination polymers, and the malate coordinated to the metal ions by adopting μ3-pentadentate mode with all of the five oxygen atoms parcipating in the coordination, which is a type of new mode found firstly by us. Both α-and β-carboxylates adopt the syn-anis confirmation. In compound 4, the malates adopt μ3-tetradentate coordination mode connecting the Mn(II) ions together to generate the two-dimensional layers, which are linked to form three-dimensional network. The magnetic data analysis indicate that compounds 1-4 are antiferromagnetic, ferromagnetic, ferrimagnetic and antiferromagnetic. II Transition metal-malate-4,4′-bipy coordination polymers Three new three-dimensional coordination polymers containing matate and 4,4′-bpy as mixed bridging ligands, [M(Hmal)(4,4′-bipy)0.5]n, M = CoII (5), NiII (6) and 0.3CoII/0.7NiII (7), H3mal = malic acid, have been synthesized from weak acidic solutions by solvothermal technique. Compounds 5-7 possess three-dimensional structures, and the metal ions are interconnected by the malate bridging ligand to form 2D layers, which are linked together by different 4,4′-bipy molecules to form three-dimensional network. The malate act as the μ3-pentadentate ligand in 5-7 as same as in 1-3, but the coordination positions and confirmation are different in them. In compounds 5-7, the α-carboxylates coordinated to the metal ions with anis-anis confirmation and -carboxylates with syn-anis confirmation. The magnetic data analysis indicate that compounds 5 and 7 are antiferromagnetic, and 6 is antiferromagnetic. III Transition metal-citrate coordination polymers Five two-and three-dimensional coordination polymers containing citrate as bridging ligands have been synthesized under solvothermal condition, they are {K[Mn(Hcit)(H2O)]}n (8), {[KMn3(OH)(Hcit)2(H2O)]·2H2O}n (9), {K(H2O)2}4 {[Co(H2O)4]2[Co4(cit)4]}n (10), {[K(H2O)2]2[Co2Co4(cit)4]·2H3O·6H2O}n (11) and {[K(H2O)2]2[M2M4(cit)4]·2H3O·8H2O}n, M = 0.7Co/0.3Ni (12). In compounds 8-12, the citrate ligand coordinate to the metal ions with diverse modes, μ3-pentadentate, μ5-heptadentate, μ4-pentadentate, μ5-octadentate and μ5-octadentate, and they are all new coordination modes which are not found in previous litereatures. Compounds 8 and 9 possess three-dimensional supramolecular networks with potassium ions and hydrogen bond linking the two-dimensional Mn-citrate layered structures, respectively. Compounds 10 and 11 possess porous zeolite–like structures, which are constructed from the [Co4(cit)4]8-cubane clusters linked by six-and four-coordinated cobalt ions, respectively. It is firstly reported that the [Co4(cit)4]8-cluster anion act as the secondary building unit. Compound 12 have similar structure with 11 except the difference in lattice water molecules. The magnetic data analysis indicate that compounds 8 and 9 are antiferromagnetic, and 11 and 12 are ferromagnetic. IV The Polymers containing citrate and nitrogen-containing ligands A novel coordination polymer containing the citrate and 4,4′-bipy as mixed ligands {[Ni3(Hcit)2(4,4′-bipy)2(H2O)3]·H2O}n (13) and a new tetramer [Cu4(cit)2 (im)4(H2O)4] (14) have been synthesized from weak acidic solutions under solvothermal conditions.