| As a new type of functional material,titanium oxide clusters(TOCs)has become one of the focus of research because of its novel structure and unique properties.It is one of the key research contents in the field of coordination chemistry and material chemistry.At present,the research on titanium oxide clusters is mainly focused on four aspects:first,the synthesis of pure titanium oxide clusters with new structures;secondly,the synthesis of titanium oxide clusters modified by organic small molecules;third,the synthesis of metal-doped titanium oxide clusters;The fourth is the synthesis of titanium oxide cluster frame compounds.Among them,many organic ligands modified titanium oxygen clusters have been synthesized and paticularly some functional organic ligand modified titanium oxo clusters have attracted more and more attention.Therefore,aromatic carboxylic acids,including salicylic acid(H2sal),5-sulfosalicylic acid(H3ssal),5-aminosalicylic acid(H4asal)and 3-sulfobenzoic acid(3-H2sb),and 1,10-phenanthroline(1,10-phen),2,2-bipyridine(2,2-bipy)as neutral ligands,are selected to synthesize novel titanium oxygen clusters.These clusters were characterized by infrared spectroscopy,ultraviolet spectroscopy,elemental analysis,thermal stability analysis and fluorescence analysis,and their photocatalytic or electrocatalytic properties or catalytic oxidation properties of thioether were studied.The main work of this paper includes the following six aspects:(1)In this paper,the structure,properties and applications of metal oxygen clusters are briefly introduced.Secondly,the research status of the simple titanium oxygen cluster,the organic ligand modified titanium oxygen cluster,the transition metal doped titanium oxygen cluster and the titanium oxygen cluster frame compound are reviewed.(2)The titanium oxo cluster[Ti4O4(sal)4(phen)4]·12H2O(1)modified by salicylic acid/1,10-phenanthroline was successfully synthesized by solution evaporation method.The crystal structure shows that complex 1 is composed of one{Ti4O4} structural unit,four sal2-anions and four Phen molecules,which together form a distortedplane quadrangle.H2sal was protonated completely,and both hydrogens on hydroxyl and carboxyl groups were removed.In addition,it was characterized by elemental analysis,infrared spectroscopy,thermogravimetric analysis,fluorescence spectra,UV diffuse reflectance spectroscopy,and the catalytic properties of the photocatalytic reaction of methyl orange were also investigated.(3)[Ti6O8(Hssal)2(Phen)6(H20)4]·40H·21H20(2)and[Ti4O4(Hssal)4(Phen)4]· 18H2O.4NH3(3)were successfully synthesized by the solution volatilization method.The crystal structure shows that complexes 2-3 is composed of titanium oxide unit,acidic ligand H3ssal and neutral ligand Phen.Complex 2 is a six core structure made up of {Ti6O8} structural units,and complex 3 is a four core structure composed of {Ti4O4} structural units.In addition,H3ssal in complexes 2 and 3 only removed two hydrogen and retained hydrogen on hydroxyl group.The complexes 2 and 3 were characterized in detail in many aspects,such as infrared spectrum,UV spectroscopy,molar conductivity,and the catalytic oxidation of MPS and PPS was carried out.The results showed that the complexes 2 and 3 showed good catalytic performance.Paticularly,complex 2 integrate the advantages of both homogenous and heterogeneous catalysts,as it showed not only excellent catalytic performance,but also good recyclability in the oxygenation of organic sulfide.The further study of its mechanism found that the presence of 4 coordination H2O molecules and 4OH-ions in complex 2 could easily be exchanged with oxidant H2O2 to produce active intermediates,which may be the reason for the catalytic efficiency of complex 2 to be higher than that of complex 3.In addition,two ligand complexes[(H3ssal)(Phen)](4)and[(H3ssal)(Phen)]·H20(5)were obtained.(4)Through the solution evaporation method,5-amino salicylic acid/1,10-phenanthroline modified titanium oxo cluster[Ti4O4(H2asal)4(phen)4]·16H2O(6)was successfully synthesized.Crystal structure determination shows that complex 6 is similar to complex 1,and is also composed of {Ti4O4} structure unit,4 H2asal2-anions,4 phen molecules,forming a twisted plane quadrangle together,and H4asal removal of two hydrogen on hydroxyl and carboxyl groups,preserving 2 hydrogen on the amino-group.The complex 6 was characterized by elemental analysis,IR and thermogravimetric analysis,and electrochemical behavior of dopamine(DA)on the surface of complex 6 modified glassy carbon electrode was studied.Under the optimal conditions,the oxidation current and concentration of dopamine have a good linear relationship with the concentration of 1.0×10-6-7.0×10-5 mol/L,the correlation coefficient is 0.9928,the detection limit is 2.0×10"7mol/L.Therefore,the modified electrode prepared by complex 6 has good stability and reproducibility,and can be used for the electrochemical determination of DA.(5)Ti(phen)(OC2HS)2Cl2(7)was successfully synthesized by the solution volatilization method,and the structure of the complex 7 was characterized by single crystal diffraction,IR,1H and 13C NMR,elemental analysis and thermogravimetric analysis.The catalytic performance of the catalyst in the catalytic oxidation of thioether was investigated under different reaction conditions with the synthesized complex 7 as the catalyst and hydrogen peroxide(H2O2)as the oxidizing agent.By optimizing the experimental conditions such as temperature,solvent,catalyst and oxidant,we found that at room temperature and the medium of methanol,the complex can catalyze methyl phenyl sulfide to methyl phenyl sulfoxide.Further expansion of the reaction substrate,the results showed that the catalyst showed high conversion rate(95-100%)and excellent selectivity(92-100%)in the oxidation of a series of thioethers with different structures,different electronic effects and space hindrance effects.In addition,the mechanism of catalytic reaction has been speculated briefly.(6)Two 3-sb-1,10-phen/-2,2-bipy modified titanium oxide clusters[Ti8O12(3-sb)2(3-Hsb)4(phen)6(H20)6]4H20· 4CH3OH(8)and[Ti8O11(3-sb)2(2,2-bi)6(H2O)io]·Cl· 3-sb· 3(3-Hsb)· 16H2O(9)were successfully synthesized by solution evaporation method.Single crystal X-ray analysis shows that both clusters are cubic structures consisting of eight titanium atoms.Complex 8 is a closed cubic skeleton structure composed of {Ti8O12} units,while complex 9 is an open cubic skeleton structure composed of {Ti8O11} units.In addition,3-sb ligand in complex 8 coordinates with Ti(?)via sulfonic SO3H,while carboxyl COOH remains free.In complex 9,3-sb ligand bridges with Ti(?)via COOH.The selective oxidation of organic sulfides was studied in detail with complexes 8 and 9 as catalysts.The results show that both complexes 8 and 9 exhibit excellent catalytic performance at room temperature,and the catalytic activity of complex 9 is higher than that of complex 8,which may be due to the supramolecular assembly and stacking effects. |
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