Studies On Synthesis,Structure And Properties Of Organoimido Derivatives Of Polyoxometalates

The early transition metals(V,Nb,Ta,Mo,W) themselves or combining with each others or other elements are able to form molecular metal-oxide cluster anions, commonly referred to as polyoxometalates or polyoxoanions. Those species are remarkable for their important optical, electronic, magnetic, catalytic and medical properties owing to their nanometer-sized shapes and electronic structures involving d-π orbits and d-π electrons. On the other hand, molecular structures of organic compounds are easy to be sheared and modified, particularly, organic conjugated molecules are novel electrically and optically active materials and their molecular structures and properties are also easily controlled. Therefore, the molecular natures of these two types of materials offer the opportunity to generate covalently bonded molecular hybrids where the interaction of delocalized π or p electrons of the organic moiety with d electrons of the cluster may bring exciting synergitic effects and novel materials with excellent properties. Best of all, organoimido derivatives of polyoxometalates with the typical structures of organoimido groups bonded at an octahedral metal center and consistent in a substantial degree of Mo ≡ N triple bond character were synthesized by Maatta' method. Beside these, an alternative way to efficiently construct novel hybrid molecular materials containing covalently bonded metal-oxygen clusters and organic conjugated segments has also been discovered. In summary, studies on synthesis, structure and properties of organoimido derivatives of polyoxometalates, will promote the development of polyoxometalate chemistry, and also discover a novel kind of organic-inorganic hybrids with novel structures and unusual properties. This is very important in theoryand application.With N,N'-dicyclohexyl-carbodiimide (DCC) as dehydrating agent, the synthesis way of organoimido derivatives of polyoxometalates is studied in detail in this dissertation. Lindqvist hexamolybdates and their derivatives were modified via the reaction of [ a -Mo8O26]4* with aromatic amines or other amines, which are also important building blocks for constructing novel organic-inorganic hybrids based on polyoxometalates by controllable organic synthesis technology such as the nucleophilic reaction, thus a novel kind of organic-inorganic hybrids with novel structures and unusual properties is obtained, which will contribute to be optical, electronic, magnetic, catalytic and medical materials.On the basis of the Maatta's direct modified method with organoimido, a novel reaction routine to organoimido derivatives of polyoxometalates has been developed, which is the Aromatic Amine halides' method. And six new organoimido derivatives of polyoxometalates were synthesized via this reaction routine. These six new organoimido derivatives of polyoxometalates can be described with a general chemical formula:(Bu4N)2[Mo6Oi8 (=NR) ].(R=: o-ClQH*, m-ClQsEU, P-CIQH4, p-BrC6H4, 0-CH3QH4, o-CNC6H4).The optimum reaction conditions such as the amount of each raw material and the reaction time can be obtained by monitoring the reaction system with UV-Vis Spectra. In this thesis, by comparing UV-Vis spectroscopy of the product under different conditions, a favorable routine has been obtained and is given in below: A mixture of (Bu4N)4[ a -Mo8O26] (1.0 mmol), Aromatic Amine hydrochloride (RC6H4NH2 ? HC1 2.0 mmol, 1.5 equiv ) and N,N'-dicyclohexyl-carbodiimide (DCC) (3.4 mmol) was refluxed(81-84°C) in anhydrous acetonitrile (10 mL) for about 6h.Moreover, A novel bifunctionalized arylimido derivative of hexamolybdate was synthesized according to the literature procedure where the aromatic amine hydrochloride was not existed in the reaction mixture. By comparison of the synthesis routine of imido and bifunctionalized derivative of [Mo6Oic>]2" with each other, the possible reaction mechanism was suggested. In the novel reaction routine to organoimido derivatives of polyoxometalates, an aromatic amine hydrochloride salt(instead of Yf) is added into the reaction, and contributed to catalyze the reaction, andprevent the side reaction to take place, such as the redox reaction.The structures of these four new organoimido derivatives of polyoxometalates were initially obtained according to X-rays single crystal structure analysis. Most of those compounds crystallized in monoclinic space group P2(l)/n. An important feature that should be pointed out here is the dimerization of cluster anions of these new organoimido derivatives of polyoxometalates in the solid state through the ji - 31 stacking of parallel phenyl rings of two neighboring cluster anions. The existence of k - % interactions between the pairs of cluster anions has not been mentioned up to date. Moreover, the molecular structure of compound (Bu4N)2[Mo6O17 (=NR) 2], (R=o-CH3C6H4, 7) has also been confirmed by single-crystal X-ray diffraction. There is also dimerization of the cluster anions of 7 through k-tl stacking between parallel phenyl rings on two neighboring hexamolybdate cluster anions in the crystal. The existence of the supramolecular n - jt interactions between the pairs of cluster anions is clearly indicated by the short vertical phenyl ring separation of 2.9752A. It is interesting that four such dimers form a supramolecular ring-like structure by linking the dimers with each other via C-H—O hydrogen bonding between a C-H group( C(3)-H(3),0.93A) of one aromatic ring attached to the cluster anion and a terminal oxo group(O(3)) on neighboring cluster anion (C(3)-H(3)—O(3)i, 3.311 A). Such a structural feature has not been mentioned since the phenylimido derivative of hexamolybdate was reported.The composition and structures features of these compounds have also been confirmed by IR and 'H-NMR spectroscopy. The peaks in IR and ] H-NMR spectra of these compounds were also attributed via comparing the corresponding peaks of raw materials. Some factors, such as inductive and conjugative effects, which have an influence on IR and 1 H-NMR spectra of these organoimido derivatives of polyoxometalates, have also been discussed. It is very useful to confirm the compositions and structures of these compounds.The UV-Vis Spectra of these organoimido derivatives of polyoxometalates have been studied in depth, and their characters have also been confirmed. There is a good linear relationship between the shift of UV-Vis absorptions(A A max) and conjugated effect of the p-substituted...