Syntheses, Structures And Properties Of Oxo-centered Carboxylate-bridged Multinuclear Complexes

Transition-metal carboxylate chemistry has played a key role in the conceptual development of modern inorganic chemistry. In particular, the complexes containing metal-oxo-carboxylate fragments have recently received much attention in many respects, reasons for this phenomenon is that they provide structural models for the active sites of various metalloproteins and enzyme. Investigations have indicated that complexes containing metal-oxo-carboxylate fragments hold the balance role in the design of new molecular-base magnetic materials as well as medication.In 1965, Figgis and Robertson determined the first structure of the chromium(â…¢) 'basic acetate' complex by crystal X-ray diffraction. This can prove it is a trinuclear chromium(â…¢) oxo-centerded complex. Theμ₃-oxgen atom is the common vertex of the coordination octahedral around the three Cr^â…¢atoms. Each Cr^Ⅲ…Cr^â…¢vector is further bridged by twoη¹:η¹:μ₂-MeCO₂^- groups. Besides chromium, other metals show the same kind of structure, e.g. Fe, V, Rh, Ru, with the general formula [M₃(μ₃-O)(μ-RCO₂)₆L₃]·X.In this thesis ten oxo-centered carboxylate-bridged trinuclear iron(â…¢) and chromium(â…¢) complexes with formic acid,glacial acetic acid,propionic acid,monochloroacetic acid and sodium benzoate as ligand. Deep red single crystals of one dinuclear iron(â…¢) complex were obtained with 2,2'-bpy and NaN₃ as ligands; and deep red single crystals of four trinuclear iron(â…¢) complexes were obtained with pyrazine,ethanol and monochloroacetic acid as ligands. Their structures have been ascertained by C,H,N element analysis, Infrared spectrum and X-ray single crystal diffractometer.In the lnfared spectrum of the complexes, there are strong absorptions in～834 cm^-1 which can be ascribed to the antisymmetric vibration of the Fe-O-Fe unit in dinuclear iron complexes, and there are strong absorptions in～670 cm^-1 which can be ascribed to the Fe₃O unit in trinuclear iron complexes. The different date of antisymmetric vibration and symmetric vibration of carboxylate show bridged model.The structural analysis of complexes [Fe₃O(CH₃CO₂)₆(Pz)₂(H₂O)]CIO₄·2CH₃CN·2H₂O,[Fe₃O(PhCO₂)₆(Pz)₂(H₂O)]ClO₄·0.5CH₂Cl₂90.5C₅H₁₂ and [Fe₃O(PhCO₂)₆(CH₃CH₂OH)₃]ClO₄ shows that there exist complicated strong hydrogen bonds resulted in novel 2-D supramolecular network. There are strongÏ€-Ï€stacking interaction between molecules in the dinuclear complex [Fe₂O(PhCO₂)₂(2,2'-bpy)₂-(N₃)₂]·H₂O. The complex of (Et₃NH)₃[Fe₃O(μ-CH₂ClCO₂)₆(CH₂ClCO₂)₃]ClO₄ exits strong hydrogen bonds, and [Fe₃O(μ-CH₂ClCO₂)₆(CH₂ClCO₂)₃]^2- has been quite scarce in papers. The ligand of (4,4'-bpyH₂)Cl₂ shows one dimension link by strong hydrogen bonds.The cyclic voltammogram of the complexes [Fe₃O(CH₃CO₂)₆(H₂0)₃]NO₃,[Fe₃O(PhCO₂)₆(H₂O)₃]NO₃,[Fe₃O(CH₃CO₂)₆(Pz)₂(H₂O)]ClO₄-2CH₃CN·2H₂O,[Fe₃O(PhCO₂)₆(Pz)₂(H₂O)]ClO₄-0.5CH₂Cl₂·0.5C₅H₁₂ and [Fe₃O(PhCO₂)₆(CH₃CH₂OH)₃]·ClO₄ shows a quasi-reversible reduction process character, the wave of cyclic voltammogram is slightly cathodically shifted when the axial stronger donor replaces the axial weaker donor.