The Synthesis, Structure And Nature Of Arsenite Heteropoly Compounds

Heterpolyoxometalates have received much attention due to their fascinating variety of structure and chemical composition, and potential applications in catalysis, materials science, environmental protection and medicine. The synthesis design, structure properties of novel large polyoxometalates and derivatives of known polyoxometalates are interesting and remain a challenge.This thesis is devoted to the topic of the synthesis and structural characterization of polytungstate ions containing arsenic (IE). The lone pair of electrons on the As (HI) inhibits formation of the classic Keggin structure. This open structure may be used to construct novel large species by linking with inorganic or organic groups, such as transition metal cations, lanthanide cations, PhSn3+ and so on. Altogether eight new type heterpolyoxometalates including sandwich type heteropolytungstate and big cyclic polyanion have been synthesized and characterized structurally. Their formulas are as follows:The results of the crystal structure analysis show that among the compounds (I)(II) (III) (IV), the structure of anion reveals a arrangement of two (a-B-AsW9)moieties enclosing one, two or three M(L)2+. The compound (V) consists of threenew (AsW8O31) subunits related through a C3 axis and joined up by three extra(WO(H2O))group. Each (WO(H2O)) joints two AsW8O31 subunits by sharing two cis oxygen atoms with each other, the polyanion [{WO(H2O)}3(AsW8O31)3]21- has approximately D3h symmetry. The compound (VI) shows that the four S2 sites of the big cyclic ligand [As4W40O140]28- are occupied by two Na+ and two Ni2+ respectively, the third Ni2+ locates outside the cyclic [As4W4oO140]28- and connects with one Od, its coordination number is six. the compounds (VII) show that show that the central site S1and two opposite S2 sites of the big cyclic ligand [As4W40O140]28- are occupied by one Ln3+ and two Ni2+ respectively, five molecular waters coordinate to Ln3+. The compounds (VIII) show that two opposite S2 sites of the big cyclic ligand [As4W40O140]28- are disorderly occupied by one VO3+ and one Ni(H2O)2+, and other two are occupied by two Na+ connected by a bridging water.Most of the compounds have been investigated with IR, UV-Vis spectra and element analysis. TG-DTG have also been recorded for the compounds (I) (IV) (V) and (VI). The magnetic properties of the compounds (I) and (VIII) have been studied. The compound (V) was also characterized by 183 W NMR. Finally, some of hydrogen-bond interaction are discussed.