Potentiometric and spectroscopic study of copper(II) and nickel(II) complexes of trans-dioxopentaaza macrocycles in aqueous solution
作者:Mathieu W. A. Steenland、Ilse Dierck、Gerrit G. Herman、Bart Devreese、Werner Lippens、Jozef Van Beeumen、André M. Goeminne
DOI:10.1039/a703762g
日期:——
The trans-dioxopentaaza macrocycles 2,6-dioxo-1,4,7,10,13-pentaazacyclopentadecane (L1) and 2,6-dioxo-1,4,7,11,14-pentaazacycloheptadecane (L2) have been prepared. Their protonation and metal-binding properties with Cu2+ and Ni2+ have been investigated in 0.10 mol dm–3 KNO3 (aq) at 25.0 °C by potentiometric pH-metry, calorimetry (in part), electronic absorption and IR spectroscopy. Metal-ion complexation promotes the deprotonation and the co-ordination of the amide nitrogens, resulting in neutral complexes with four nitrogen donors and a MLH–2 stoichiometry at pH 8. Additional complexes with stoichiometry MHL, ML and MLH–1 complete the complexation set. The overall stability constants of the complexes were calculated. The electronic spectra support a tetragonal co-ordination of Cu2+ and a square-planar co-ordination of Ni2+ in the MLH–2 complexes leaving one amino group unco-ordinated. It is suggested that the planar trigonal nature of the co-ordinated amido nitrogens in trans position to each other in the equatorial plane around Ni2+ or Cu2+ structurally prevents the fifth nitrogen donor from binding at an axial site. The NiL2H–2 complex exhibits a yellow-to-blue conversion equilibrium.
已合成了转二氧五氮的大环化合物2,6-二氧-1,4,7,10,13-五氮环五烯烃(L1)和2,6-二氧-1,4,7,11,14-五氮环十七烯烃(L2)。在25.0°C的0.10 mol dm⁻³ KNO₃(aq)中,通过电位法pH计、热量测定(部分)、电子吸收和红外光谱研究了它们的质子化和与Cu²⁺及Ni²⁺的金属结合性质。金属离子络合促进了氨基氮的去质子化和配位,导致pH 8时形成具有四个氮供体及MLH–₂化学计量比的中性络合物。进一步的络合物具有MHL、ML和MLH–₁的化学计量,完善了络合物的集合。计算了络合物的整体稳定常数。电子光谱支持Cu²⁺在MLH–₂络合物中的四方配位,以及Ni²⁺的方平面配位,其中一个氨基未参与配位。研究表明,在Ni²⁺或Cu²⁺周围的赤道平面中,配位的氨基氮呈平面三角形结构,这在结构上阻止了第五个氮供体在轴向位点的结合。NiL₂H–₂络合物表现出黄色到蓝色的转化平衡。