| To design and synthesize framework materials linked by well-defined building blocks is still a challenge to the solid-state inorganic and material chemists. Polyoxometalates (POMs) have received considerable attention due to their diverse structures and unusual properties, with potential applications in fields such as catalysis, magnetism, optics and medicine. As a continuation of the hydrothermal synthesis of various polyoxometalates, we are trying to construct higher-dimensional framework from the metal-oxygen clusters through different bridging groups, especially transition metal complexes. Although various preparation methods have been proposed to obtain such metal-oxide clusters, the preparation of these complexes still remains elusive and often is described as self-assembly.During our research for the metal-oxygen clusters, we synthesized some decorated metal-oxygen clusters, vanadates, tungstates, the cluster based on tungstate-vanadium and gave much attention on supramolecular assemblies based on polyoxometalates. On the bases of X-ray structural analyses, some compounds have been characterized by IR, XPS, ESR spectra. The magnetic properties of some compounds have also been studied, which would take a role in the explorations of structures and functions for the compounds.1. V-O clustersAll of compounds [Mn(bpy)V(bpy)V3O11] (1),γ-[Cu(bpy)V2O6] (2), [Zn(phen)3][V2O6]·10H2O (3),β-[Cu(2,2′-bpy)V2O6] (4), Zn(2,2′-bpy)V2O6 (5), Ni(2,2′-bpy)(H2O)V2O6 (6), [Zn(2,2′-bpy)3]2[V4O12]·11H2O (7) are composed of vanadium and transition metal-organic ligand. Compound 1 crystallized in the monoclinic, space group P21/n, a = 7.0738 (7) Aa, b = 33.236(3) A, c =11.0043(11) A,β= 102.453(2) o, V= 2526.3(4) A3, compound 1 can be described as a 1-D double-chain structure with [V4O11]2– cyclic clusters providing the vanadate building blocks which are linked by Mn(2,2′-bpy)2+ cations. To the best of our knowledge, it is the first example that bpy units coordinate to different transition metals in one molecule. Compound 2 crystallized in the monoclinic, space group P21/c, a = 8.1044(6) A, b =17.3844(13) A, c=9.6523(7) A,β=106.0630(10)o, V=1306.82(17) A3. As we know, there have been two isomers of the Cu(bpy)V2O6. The structure of 2 can be described as a copper-vanadium oxide ribbon, decorated with bpy groups projecting above and below the ribbon. The ribbon is constructed from rings of corner-sharing vanadium (V) tetrahedra linked through copper square pyramids. It is noteworthy that there areπ-πstacking interactions between bpy groups from adjacent chains. Therefore, the 1-D copper-vanadate chain are arranged in interesting two-dimensional supramolecualr arrays viaπ-πstacking interactions of bpy groups. Compound 3 crystallized in the triclinic, space group P-1, a=12.489(3) A, b=13.492(3) A, c=14.672(3) A,α=81.84(3) o,β=68.73(3)o,γ=74.71(3)o, V=2219.3(8) A3, 2-D water sheet with big holes filled by the"naked"[V4O12]4– clusters is found in 3 and between adjacent phen groups of different Zn complexes there exist multipleπ-πinteractions in the form of face-to-face. Theπ-πstacking interactions lead to a 2-D supramolecular sheet. Compound 4 crystallized in the monoclinic, space group C2/c, a =18.9896(11)A, b=10.5886(6) A, c=19.7955(12) A,β=94.7000(10) o, V=3967.0(4) A3. Compound 4 can be described as [V6O18]6– corner-sharing hexanuclear rings linked through [Cu(bpy)]24+ dimers. Compound 5 crystallized in the triclinic, space group P-1, a=8.0719(4)A, b=8.2122(5) A, c=10.3501(4) A,α=72.332(3) o,β=84.562(3) o,γ=76.878(3) o, V=636.41(6) A3. In 5, [Zn(2,2′-bpy)]2+ cations connect [V4O12]2- anions into 2-D sheet. Compound 6 crystallized in the orthorhombic, space group Pca2(1), a=9.1625(18) A, b=10.510(2) A, c=14.328(3) A, V=1379.7(5) A3. There exist [VO3]n2n- 1-D chains which incorporate with Ni(2,2′-bpy)(H2O)2+ cations to generate the 2-D sheet. Compound 7 crystallized in the monoclinic, space group C2/c, a=21.9753(18) A, b=14.0610(10) A, c=23.8671(18) A,β=106.216(5)o, V=7081.4(9) A3. 3-D supramolecular network was found and [Zn(2,2′-bpy)3]2+ cations filled in the 1-D channels.2. High-dimensional transition metal substituted tungstates{[Ni(enMe)2]2[Ni(enMe)2(H2O)]2[As2VW18VINi4(enMe)2O68]}·2H3O·2H2O (8) crystallized in the triclinic, space group P-1, a=13.3055(7)A, b=13.8637(7)A, c=17.0327(9)A,α=68.1790(10) o,β=71.4860(10)o,γ=88.2780(10) o, V=2752.0(2)A3. Compound 8 is a novel high-dimensional transition metal substituted tungstate linking through transition metal coordination fragments which has been sucessfully synthesized by a hydrothermal method. The successful synthesis of 8 suggests that preparation of high-dimensional extended solid frameworks which are composed of transition metal substituted POMs and transition coordination fragments will be feasible, and they will form a new interesting field of POMs and will represent a new family of organic-inorganic hybrid materials.3. Capped Keggin/pseudo-Keggin type compoundsCompounds [Cu(en)2(H2O)]2[Cu(en)2]2[AsW2VIW7VV7IVO44]·2H2O (9), (H2en)2[AsW9VIWVV4IVO42] (10),[Ni(enMe)2]4{Ni(enMe)2[Ni(enMe)2(H2O)AsW6VIW4VV4IVO42]2}·6H2O (11) and [Ni(enMe)2]4{Ni(enMe)2[Ni(enMe)2(H2O)AsMo4VIMo4VV8IVO44]2}·8H2O (12) have been synthesized hydrothermally. Compound 9 crystallized in the triclinic, space group P-1, a=12.879(3)A, b=12.934(3)A, c=13.916(3)A,α=81.27(3)o,β=62.97(3)o,γ=61.85(3)o, V=1814.8(7)A3. Compound 10 crystallized in the monoclinic, space group P21/n, a=11.144(2)A, b=20.522(4)A, c=12.441(3)A,β=115.85(3)o, V=2560.5(9)A3. Compound 11 crystallized in the monoclinic, space group P21/n, a=19.765(4)A, b=13.618(3)A, c=27.096(5)A,β=93.63(3)o, V=7279(3)A3. Compound 12 crystallized in the monoclinic, space group P21/c, a= 19.649(3)A, b = 13.590(2)A, c = 33.857(4)A,β= 125.475(6)o, V =7362.6(18)A3. Compounds 9 and 12 are tetra-capped pesudo-Keggin type; compounds 10 and 11 are bi-capped Keggin type. Compounds 9 and 10 represent high-dimensional configuration; compounds 11 and 12 are dimers. In the case of organic ligands with approximate steric hinderess, the formation of these compounds may be controlled by the type and quantity of transition metals.4. High-dimensional supramolecular architectures based on simple polyoxometalatesCompound [4,4′-Hbpy]2[Ni(4,4′-bpy)2(H2O)4][AsW11VIWVO40]·4H2O(13) crystallized in the monoclinic, space group C2/c, a=21.309(4) A, b=15.303(3) A, c = 24.247(5) A,β= 106.47(3)o, V = 7582(3) A3. Compound [4,4′-H2bpy]2[PMo9VIMo3VO40]·2H3O (14) crystallized in the monoclinic, space group P21/c, a=11.504(2) A, b=12.104(2) A, c=18.435(6) A,β=114.15(2)o, V=2342.3(9) A3. Compound [4,4′-H2bpy]2[β-Mo8VIO26] (15) crystallized in the monoclinic, space group P21/c, a=10.728(2) A, b=15.198(3) A, c=14.661(5) A,β=133.076(17)o, V=1746.1(8) A3. Comparing the three compounds, when use the same organic ligands, the different type of cluster anions and different quantitative water molecules determine the different structures. Hydrogen bonding interactions between inorganic framework and organic molecules play important roles in the formation of high-dimensional supramolecular network.5. In this paper, I investigate the influence of the pH value, temperature, the ratio of reactants, the type of reducer, the steric hinderess of the ligand and the type of the secondary transition metals which contribute to the formation of the single crystal. These research and discussion will be beneficial to understand the speciality of metal-oxo clusters, and will lay a foundation for realizing the semi- or directional synthesis of the metal-oxo clusters.
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