| Polyoxometalates(POMs)compose of early transition metal ions by point-,edgeand lessly face-sharing O atoms,and possess rich structural compositions and versatile physical and chemical properties.In order to improve the application values of POM,we use the functional ligand to modify POMs.There are two methods can be applied,the first method is to replace the cations of POMs by cationic surfactants,the second method is to attach organic components directly on polyanion through covalent bond,the merit for the latter method is that it is easy to control the decoration site and provide a confirmed combined type.It is very important for rich structural compositions.In this paper,based on Anderson-Evans POMs,we made detailedly research about triol ligands covalently decorated on this type of POMs.By selecting Cu and Co as heteroatoms,we synthesized a series of triol ligands covalently modified Anderson-Evans clusters,in addition with the investigations on the structures transformation between different decoration types.And we have also obtained one type of the intermediates of Anderson-Evans POMs by controlling the ratio of the starting materials,and realized their transformation to corresponding triol ligand decorated Anderson-Evans polyanions.Firstly,by using a [(n-C4H9)4N]4[Mo8O26] precursor cluster as the starting materials,a series of triol ligand organically modified χ-isomer Anderson-Evans POMs with CuII as heteroatom were obtained with the functional groups of-CH3,-CH2CH3,-OH,and-NO2.When the Mo source was changed as [(n-C4H9)4N]2[Mo2O7],however,a triol ligand decorated Anderson-Evans cluster in δ/χ fashion was obtained,which is an important supplement of the types of triol ligand modification on clusters.By changing the solvent from acetonitrile to methanol,we realized a secondary organic modification on μ3-O and obtained a triol ligand/methanol co-decorated Anderson-Evans POM.By analyzation of the reaction process,we found that acidity-base environment play a key role for sites and types of triol ligand decoration on Anderson-Evans POMs.The acidic environment benefits for the protonation of μ2-O and forms χ-isomers,while a little basic environment is easy to obtain δ/χ-isomer.By utilizing this theory,we succeeded in transformation between different decorations.Secondly,by selecting cobalt possessing variable valences as heteroatom,we synthesized a series of CoII/CoIII-centered Anderson-Evans POMs.Single-crystal X-ray structural analysis reveals that four decoration manners of organic ligands occur on the mother polyanion [CoII/III(OH)6Mo6O18]4-/3-.They are(1)double-sided χ/χ-isomer and(2)double-sided δ/χ-isomer with CoII central heteroatom,and(3)single-sided δ-isomer and(4)double-sided δ/δ-isomer with CoIII central heteroatom.By controlling reaction condition,a gradual oxidation process from CoII to CoIII happened in the air,where CoII-centered double-sided δ/χ-isomer was obtained at beginning and then transformed into CoIII-centered double-sided δ/δ-isomer as the final product.When electron-withdrawing group-NO2 substituted triol ligand was used to replace CH3C(CH2OH)3,the oxidation process was found to be accelerated.A further investigation showed that this oxidation process can be blocked with the addition of acid.Accompanying the triol ligands’ decoration on Anderson-Evans POMs and oxidation of central heteroatom,the co-decoration of other components was also acquired.In the presence of excess acetic acid,an unprecedented single-sided δ-isomer attaching with an acetate ligand covalently on the other side by replacing one μ3-O atom in aqueous solution was obtained.By conducting the reaction with mother cluster [(n-C4H9)4N]3[Co(OH)6Mo6O18] in methanol,a co-decoration of triol ligand and methanol in double-sided δ/δ-isomer was achieved,which has never been reported in B-type Anderson-Evans POMs.The results demonstrated that the kind and valence of heteroatom and solvent can both influence the types of triol ligand decoration on Anderson-Evans POMs.Thirdly,for further investigation on the reaction process of triol ligand modified Anderson-Evans POMs,we designed and synthesized a series of triol ligand modified {M2Mo6}(M=Cu2+,Co2+,Ni2+,Zn2+)clusters by controlling rations of starting materials.This type of clusters can transform to their corresponding triol ligand decorated Anderson-Evans POMs in double-side χ/χ isomer by adding of additional Mo source.Because these {M2Mo6} clusters have the starting materials with those for synthesis of corresponding Anderson-Evans POMs and can transform to latter by adding of Mo source,so they can be seen as one type of the intermediates.Taking CuII as an example,we did a further investigation for the transformation under different Mo source and acidity-base environment,and obtained a novel triol ligand/methanol co-decoration double-side δ/χ structure Anderson-Evans POM.This study presented here offers a new approach for exploring the reaction process of triol ligand modification on Anderson-Evans POMs.In a word,in this thesis we mainly study triol ligand decorated Cu-or Co-centered Anderson-Evans POMs.By selecting different Mo sources and solvent environments,we succeed in synthesis a series of organic-inorganic hybrid,including a new double-side δ/χ decoration types.We have also realized the transformations between different structures and illuminated the reaction mechanism.Here,we afford a large number of instances about triol ligand decoration on Anderson-Evans POMs,which is an important reference for the further study in this area.In addition,the mechanism proposed here also can guide the further study on organic components covalently decorated Anderson-Evans POMs. |
