Synthesis And Properties Of Inorganic-organic Hybrid Compounds With Saturated Keggin-type Polyoxoanions

Polyoxometalates (POMs) are a unique class of inorganic metal-oxygen aggregates with particular interest in the fields of catalysis, surface science, and materials science because their chemical properties including redox potentials, acidities, and solubility in various media, can be finely tuned by choosing the appropriate constituent elements and countercations. One of the remarkable approaches in the construction of POM-based inorganic-organic hybrid materials is to combine the POMs with transition-metal compounds (TMCs). This strategy is anticipated to obtain new POM-based compounds with a variety of structural motifs and interesting properties, which should lead to new functional materials. POMs usually act as linkages and/or templates in the repoeted compounds.More recently, a comprehensive library of coordination networks incorporating electrophilic Ag(Ⅰ) species have attracted considerable interest owing to silver’s ability to form bonds with different donors simultaneously, a large radius, a wide variety of coordination geometries, and special photophysical and photochemical properties. Furthermore, the argentophilicity of Ag(Ⅰ) can form a [Ag-Ag]2+dimer, which provides opportunities to extend dimensions of structures. While a number of POM-based hybrid compounds have been assembled by the reactions of different transition-metal organic units with POMs, the use of silver ion to construct a POM-based inorganic-organic hybrid composite is still lacking. As the same time, the reports about POM-based compounds with alkali earth metal cations have reraly, especially with the metal of strontium. The appropriate design of organic ligands is undoubtedly a key element in assembling POM-based inorganic-organic hybrid compounds.4,4’-Bipyridine-N,N’-dioxide (dpdo) is an excellent organic ligand because of not only the longer spacer but also the small steric size, which avoids crowding at the metal centers and encourages high connectivity and a large volume of voids. Although the remarkable progress in the construction of dpdo-based MOFs has been made, there are relatively a few literature citations reported on the crystal engineering of POM species with dpdo ligand. Herein we report synthesis and characterization of seven interesting POM-based inorganic-organic hybric compounds constructed from M-dpdo (M=Ag, Sr) coordination species and saturated Keggin type polyoxoanions. All compounds have been structurally characterized by IR, elemental analysis, XRPD, thermogravimetric (TG) analyses and complete single crystal structure analyses. Moreover, the luminescent spectroscopy and photocatalytic activities for RhB degradation under UV light irradiation of products have also been investigated in detail. The text has divided into two chapters which were introduced as follows:(I) Four novel inorganic-organic hybric compounds:[Ag3(dpdo)3.5(DMF)(PW12O40)]·H2O (1),[Ag3(dpdo)5(DMF)2](PW12OH3OH (2),[Ag3(dpdo)5(DMF)2](PMo,2O4o)-4H2O (3) and [Ag4.5(dpdo)5(DMF)(BW12O4o)]·2H2O (4), have been synthesized by the reaction of the Keggin heteropolyanions,4,4’-bipydidine-N,N’-dioxide (dpdo) and AgNO3. Keggin polyoxoanions of3D frameworks1and4represent the feature of multiplicity interaction units not only to balance the charge of silver-dpdo building blocks as larger counteranions, but also to link the silver-dpdo building blocks through Ag…O interactions as the source of oxygen donors. Keggin polyoxoanions of 2D networks2and3acts as templates. And the compounds have been structurally characterized by IR, single-crystal X-ray diffraction and XRPD. The luminescent properties of compounds1-4were investigated in the solid state at room temperature and photocatalytic activities for RhB degradation under UV light have also been investigated. The degradation rate is46%and48%in RhB solution containing compounds1and2as catalyst, respectively.(Ⅱ) Three compounds, one-dimensional [Sri.s(dpdo)6(H20)7(PW12O40)2]·6H2O (5), two-dimensional [Sri.5(dpdo)2.5(H2O)2.5(DMF)(PMo12O40)]·2H2O (6) and one-dimensional [Sr2(dpdo)(H2O)9(SiW12O40)]H2o (7) have been synthesized by the reaction of the Keggin heteropolyanions,4,4’-bipydidine-N,N’-dioxide (dpdo) and Sr(NO3)2. The compounds have been structurally characterized by IR, single-crystal X-ray diffraction and XRPD. Keggin polyoxoanions of3D frameworks5-7acts as ligand to link Sr centers through terminal oxygen atoms. The luminescent properties of compounds5and7were investigated in the solid state at room temperature. And photocatalytic activities for RhB degradation under UV light have also been investigated. The degradation rate is71%in RhB solution containing compounds5as catalyst.