The Compounds Derived From Lacunary Dawson-Type Tungstophosphates: Syntheses, Structures And Properties

Our work is focused on the design and preparation of new polyoxometalate compounds based on the lacunary Dawson type tungstophosphates which react to various metal compounds or metal-organic complexes. The study on sythetic conditions and rules for these new copounds and the exploration of relationships between structures and properties for these new compounds are also carried out.Several new polyoxometalate compounds have been synthesized on the basis of water solution synthesis methods or hydrothermal technique and structurally characterized by elemental analyses, IR,TG, EPR,UV-vis,NMR and single crystal X-ray diffractions. The thermal stabilities, magnetic properties and electrochemical behavior of these compounds have been studied.1. Interaction of the hexa-lacunary polyanion precursor [α-H₂P₂W₁₂O₄₈]12- with the FeIII in aqueous solution results in the formation of an equatorial tri-iron substituted Wells-Dawson type compound: K₄Cs₂Fe₂[P₂W₁₅(FeOH)₃O₅₉]·22H₂O (1)Compound 1 was characterized by IR, elemental, single-crystal X-ray diffraction, thermogravimetric, magnetic, as well as electrochemical analyses. The [P2W15(FeOH)3O59]12- polyoxoanion can be viewed as a derivative of parent [α-P₂W₁₈O₆₂]6- polyoxoanion by removal of three belt W=O groups and then inhabited by three Fe=OH groups. The compound 1-modified carbon paste electrode (1-CPE) presents good electrocataltic activity not only toward the reduction of nitrite, which is attributed to the function of tungstophosphate, but also toward the oxidation of ascorbic acid, which is primarily attributed to the function of FeIII. The magnetic properties of 1 have been studied by magnetic susceptibility and magnetization measurement and fitted according to an isotropic exchange model. 1 exhibits strong antiferromagnetic spin exchange interactions between the FeIII centers.2. Interaction of the lacunary lacunary Dawson type tungstophosphate precursors with main group metal elements in aqueous solution results in the formation of new Wells-Dawson type polyanions clusters: K₁₀[H₆{P₂W₁₃O₅₁}₂Sb₄]·21H₂O (2) [(CH₃)2NH₂]5[H₂{P₂W₁₇SbO₆₁}]·18H₂O (3)A sandwich-type anionic cluster of a new lacunary building block [P2W13O51]14- has been prepared: 2 was synthesized in one-pot self-assembly reaction of [H₂P₂W₁₂O₄₈]12- with C₄H₄KO₇Sb·0.5H₂O. The compound 3 is an antimony(III) substituted Wells-Dawson type tungdstophosphate. They have been characterized by single-crystal X-ray analysis, IR, thermogravimetric analysis, elemental analysis, UV, NMR and electrochemistry. 2 represents the first dimetric, antimony-containing polyoxoanion derived from vacant Dawson-type tungstophosphate. In contrast to the tetrahedrally coordinated P (V) and As (V) of the same main group, Sb (III) give new structural information because of the stereochemical effect of the lone pair electrons located on top of the trigonal pyramid. Examination of cyclic voltammograms displays a good electrocatalytic activity toward the reduction of nitrite. The polyanion 2 is stable in solution, as shown by UV spectra and 31P NMR spectroscopy. Due to the excellent stability of 2, it is promising to use 2 as a new polyoxometalate precursor to research its extensional structures.3. Interaction of the lacunary lacunary Dawson type tungstophosphate precursors with metal-organic complexes in hydrothermal condition results in the formation of new hybrid compounds with multinuclear magnetic clusters(Phen = 1, 10-phenanthroline, bdc = 1,4-benzenedicarboxylate): [Cu₂(Phen)₄Cl][Cu₂(Phen)₃(H₂O)Cl][P₂W₁₈O₆₂]·H₂O (4) [Cu₇(Phen)₇(H₂O)4Cl₈][P₂W₁₈O₆₂]·6H₂O (5) K₂[{(CuPhen)₂Cl₂}₂(bdc)]2[P₂W₁₈O₆₂]·6H₂O (6)Three novel hybrid compounds containing multinuclear CuII complex cations, have been obtained in hydrothermal conditions and characterized by IR, elemental, thermogravimetric, magnetic, electrochemical and single-crystal X-ray diffraction analyses. The main structural feature to these compounds is the presence in different copper-Phen complex moieties which compose new multinuclear copper-Phen complexes linked by Cl and bdc ligands. The Cu-Cl-Cu angles of binuclear and heptanuclear copper-Phen complexes are close to 180o and 90o, respectively. This difference induces that 3 and 4 exhibit antiferromagnetic and ferromagnetic spin exchange interactions between the CuII centers, respectively. The magnetic behavior of 5 is unusual and interesting, indicative of a strong antiferromagnetic interaction admixture with a ferromagnetic interaction. The 4-CPE and 4-CPE display good electrocatalytic activity toward the reduction of nitrite. This work reveals that appropriate combination of materials, size and ratio of anion and cation, and hydrothermal synthetic conditions can lead to the formation of POM-based complexes with different structural and functional characteristics.4. Interaction of the lacunary lacunary Dawson type tungstophosphate precursors with metal-organic complexes in hydrothermal condition results in the formation of new 1D chain hybrid compounds(bpy = bipyridine): (4,4'-H₂bpy)₄[{Cu(4,4'-Hbpy)₂(4,4'-bpy)}{P₂W₁₈O₆₂}]·7H₂O (7) [Cu(2,2'-bpy)]₂ [H₂P₂W₁₈O₆₂]·8H₂O (8)Two new 1D chain hybrid compounds have been obtained in hydrothermal conditions. Compounds 7 is constructed by {Cu(4,4'-Hbpy)2(4,4'-bpy)}_nⁿ⁺ chain and Dawson type polyanion cluster [P₂W₁₈O₆₂]^6-. Compound 8 show one-dimensional chain formed by two[Cu(2,2'-bpy)₂]²⁺ and [H₂P₂W₁₈O₆₂]^4-.