Syntheses And Properties Of Polymolybdate Hybrid Materials Decorated By Transition Metal And Flexible Multidentate N-containing Ligands

In this paper, a new series of organic-inorganic hybrid materials based on polymolybdates, transition metal ions and flexible multidentate N-containing ligands have been synthesized under hydrothermal conditions. The influence of the reaction conditions for the final products was investigated such as structure of the organic ligand, metal cations, and pH value. The study on synthetic conditions for these new compounds, topological analyses, and the exploration of relationships between structures and properties for these new materials are also carried out.Twenty-three new organic-inorganic hybrid compounds based on polymolybdates and transition metal ions have been successfully obtained by utilizing 1,3,5-tris(1,2,4-triazol-l-ylmethyl)-2,4,6-trimethyl benzene (ttb) and bis-[(pyridyl)-benzimidazole] ligands. Their structures have been determined by single crystal X-ray diffraction analyses, IR, XPRD, XPS, TGA and elemental analyses, In addition, the luminescent, electrochemical, and photocatalytic properties of some complexes have also been studied.1. Six organic-inorganic hybrid compounds based on octamolybdate building blocks and metal-organic fragments with flexible ttb ligand have been synthesized. [CuⅡ2(ttb)2(β-Mo8O26)(H2O)2]-2H2O (1) CuⅠ4(ttb)2(β-Mo8O26)(H2O) (2) [CuⅠ4(ttb)3(β-Mo8O26)3 (3) [Ni2(ttb)2(β-Mo8O26)(H2O)6]-2H2O (4) [Zn2(ttb)2(α-Mo8O26)(H2O)2] (5) [Ag4(ttb)2(β-Mo8O26)] (6)These complexes display fascinating 2D and 3D frameworks. Furthermore, compounds 1-3 exhibit 2-fold interpenetrating frameworks, respectively. The structural diversities of the complexes show that the ttb ligand, the electronic configuration of metal ion, and the coordination mode of the octamolybdate anion play important roles in the formation of the hybrid compounds.2. Eight octamolybdate-based hybrid compounds based on flexible opr, ope, obu, and mbu ligands{opr=1,1'-(1,3-propanediyl)bis[2-(2-pyridyl)benzimidazole], opr= 1,1'-(1,5-pentanediyl)bis[2-(2-pyridyl)benzimidazole], obu= 1,1'-(1,4-butanediyl)bis[2-(2-pyridyl)benzimidazole], and mbu= 1,1'-(1,4-butanediyl)bis[2-(3-pyridyl)benzimidazole]} have been designed and syntheszed. [CuⅠ4(opr)2(β-Mo8O26)]·2H2O (7) [CuⅡ4(ope)8(δ-Mo8O26)2]·4H2O (8) [CuⅡ2(obu)2(β-Mo8O26)]·2CH3OH·H2O (9) [Zn2(obu)2(β-Mo8O26)(H2O)2]·2H2O (10) [Co2(obu)3(β-Mo8O26)]·3H2O (11) [Ni2(obu)3(β-MogO26)]·3H2O (12) )2]-4H2O (13) [Ag4(mbu)2 (y-Mo8O26)] (14)Compounds 7-12 show 1D and 2D structures, respectively, while compounds 13 and 14 exhibit 3D and 2D frameworks, respectively. This result may be attributed to the different structure of the organic ligand. From the structures of the compounds 7-12, it can be seen that the coordination sites of the metal ions are occupied by the chelating group of the flexible ligands, and the polyanions bonded to metal ions is hindered. Thus, it is difficult to form high dimensional structures using chelating ligands.3. Four octamolybdate hybrid materials based on a flexible 1,1'-(1,4-butanediyl)bis[2-(4-pyridyl)benzimidazole] (pbu) ligand have been synthesized at different pH values under hydrothermal conditions. (H4pbu)(γ-Mo8O26)·2H2O (15) [Cu(H2pbu)(β-Mo8O26)(H2O)2]·3H2O (16) [Cu(H2pbu)(γ-Mo8O26)]·3H2O (17) [Cu(Hpbu)2(β-Mo8O26)] (18) Compound 15, which is hydrothermally prepared at pH≈1, exhibits a rare 1D molybdenum oxide chain. Compounds 16 and 17 are hydrothermally obtained at pH≈2.5. They show 2D and 3D frameworks, respectively. However, at pH≈3.5, the 1D chain structure of 18 is obtained. From the syntheses of these compounds, it can be seen that the pH value of the reaction system plays a crucial role in the assembly of polyoxometalate-based (POM) metal-organic frameworks.4. Three novel compounds coexisting different forms of polymolybdate have been successfully synthesized by using 1,1'-(1,3-propanediyl)bis[2-(4-pyridyl)benzimidazole] (ppr),1,1'-(1,5-pentanediyl)bis[2-(4-pyridyl)benzimidazole] (ppe), and mbu ligands. [Ag8(ppr)4(α-Mo8O26)(β-Mo8O26)(H2O)3]·H2O (19) CuⅠ3.1CuⅡ0.5(β-Mo8O26)0.5(ζ-Mo7ⅥMoⅤO26)0.5(mbu)2(H0.8mbu)0.5 (20) [Cu(H2ppe)2(γ-Mo8O26)]·(Mo6O19)·2H2O (21)Compounds 19 and 20 contain two kinds of (Mo8O26)4- isomers in the same crystal architecture, respectively. However, compound 21 is a rare example coexisting two kinds of (γ-Mo8O26)4- and (MO6O19)2- anion clusters. This result suggests that by rational reaction condition, assembly of POM-based coordination polymers may be controllable, so that a crystal structure of the coexistence two or more kinds of POMs can form.5. Two new low-nuclear polymolybdate clusters were successfully isolated by the introduction of flexible multidentate ligands and transition metal ions.[(H2ttb)2(ttb)2(Cd2Mo2oO64)(H20)2]·4H20 (22)[CuⅡ4(opr)2(Mo12O40)]·3H2O (23)Compound 22 contains a new "sandwich type" heteropolymolybdate clusters{Mo20Cd2}. In 23, the{Mo12} clucters are linked together through shared edges to form a 1D molybdenum oxide chain. Their successful isolation further riches the synthetic chemistry and structural chemistry of the polymolybdates.