A monometallic and kinetically inert complex of a ditopic open ligand as a tight polyaza cage
作者:Valeria Amendola、Luigi Fabbrizzi、Carlo Mangano、Anna Manotti Lanfredi、Piersandro Pallavicini、Angelo Perotti、Franco Ugozzoli
DOI:10.1039/a909756b
日期:——
The new ligand L has been prepared by appending three 2,2′-bipyridine molecules to a tren (tris(2-aminoethyl)amine) unit. It binds a Fe2+ cation with its three bipyridines, imparting to it an octahedral co-ordination. The obtained [FeL]2+ molecular cation has a closed shape, whose nature has been ascertained by X-ray diffraction studies on the complex [Fe(HL)][PF6]3. The tren unit can thus be described as one half of a bis-tren cage. The kinetic inertness of the complex between Fe2+ and the three bipyridines has been verified: in the pH 2–12 range the [FeII(bipyR)3] unit is stable and plays only an architectural role. According to this it has been possible to determine the protonation and complexation constants (in the presence of 1 equivalent of Cu2+) of the tren fragment, which is in fact able to interact with protons and metal cations, behaving as a tight and rigid half of a bis-tren ligand. High percentages (70–100%) of the [FeLHn](n + 2)+ species can be found in sharp pH ranges, while, in the presence of 1 equivalent of Cu2+, the metal-containing species [FeCu(HL)]5+, [FeCuL]4+, [FeCuL(OH)]3+ and [FeCuL(OH)2]2+ exist in the pH 2–12 range, each one prevailing in distinct pH intervals, reaching high percentages (70–100%). The variation of the spectral and electrochemical properties of the [Fe(bipyR)3] fragment have been studied as a function of pH, and related with the protonation degree or complexation of the tren unit.
新的配体L是通过在tren(三(2-氨基乙基)胺)单元上附加三个2,2′-联吡啶分子制备的。它用三个联吡啶结合Fe2+阳离子,使其呈八面体配位。得到的[FeL]2+分子阳离子具有封闭形状,其性质已通过复合物[Fe(HL)][PF6]3的X射线衍射研究确定。因此,tren单元可以描述为双tren笼的一半。Fe2+和三个联吡啶之间的复合物的动力学惰性已经得到验证:在pH 2-12范围内,[FeII(联吡啶)3]单元是稳定的,只起结构作用。根据这一点,可以确定tren片段的质子化和络合常数(在1当量的Cu2+存在下),事实上,tren片段能够与质子和金属阳离子相互作用,表现为双tren配体的一半,紧密而刚性。在尖锐的pH范围内,可以发现高比例(70-100%)的[FeLHn](n + 2)+物种,而在1当量的Cu2+存在下,含金属物种[FeCu(HL)]5+、[FeCuL]4+、[FeCuL(OH)]3+和[FeCu