机译:酰胺氧作为配位基团-四-乙酰胺取代的环的金属离子络合特性-结晶图谱,NMR,分子力学和热力学研究
, a = 9.490(1) Angstrom, b = 12.464(2) Angstrom, c = 12.998(2) Angstrom, alpha = 99.070(1)degrees, beta = 107.67(1)degrees, and gamma = 108.24(1)degrees. There is an unusual distortion in the coordination geometry of the complexes. There are two sets of metal-to-oxygen bond lengths for each complex; Zn(II) has two oxygens, placed opposite each other in the approximately square arrangement defined by the four oxygen donor atoms at about 2.19 Angstrom and two at 3.23 Angstrom, Cd(II) has two at 2.34 and two at 2.64 Angstrom, and Ca(II) has two at 2.40 Angstrom and two at 2.42 Angstrom. Molecular mechanics calculations suggest the Cd(II) and Zn(II) structures represent six coordination of four nitrogens and two of the oxygens, while the two long bonds represent van der Waals contacts with a possible electrostatic component. Approach of the oxygen donors to the metal ion is controlled by the van der Waals radii of the oxygens. C-13 NMR studies give rates of helicity interchange of the complexes Zn(II) > Hg(II) > Cd(II) > Ca(II) Pb(II). This order is discussed in terms of the difference in bond lengths between the two sets of oxygen donors. A stability constant study gave logK(1) values in 0.1 M NaNO3 and 25 degrees C: Cu(II), 16.3; Zn(II), 10.47; Ca(II), 7.54; Sr(II), 6.67; Ba(II), 5.35; Hg(II), 14.53; La(III), 10.35; Gd(III), 10.05. For Cd(II) and Pb(II), the complexes were fully formed even at pH 0.3, and only a lower limit of 19 for logK(1) could be set. Selectivity of DOTAM for metal ions is discussed in terms of coordinating properties of the amide oxygen donor and geometric requirements of the DOTAM ligand. [References: 56]
上,a = 9.490(1)埃,b = 12.464(2)埃,c = 12.998(2)埃,alpha = 99.070(1)度,beta = 107.67(1)度,gamma = 108.24 (1)度。配合物的配位几何形状存在异常畸变。每个络合物有两组金属-氧键长度; Zn(II)具有两个氧,以四个方的氧供体原子在约2.19埃和两个在3.23埃处定义的近似正方形排列彼此相对放置,Cd(II)在2.34埃和两个在2.64埃处具有两个氧,并且Ca (II)在2.40埃处有两个,在2.42埃处有两个。分子力学计算表明Cd(II)和Zn(II)结构代表四个氮和两个氧的六个配位,而两个长键代表与可能的静电成分的范德华接触。氧供体接近金属离子的过程由氧的范德华半径控制。 C-13 NMR研究给出了配合物Zn(II)> Hg(II)> Cd(II)> Ca(II) Pb(II)的螺旋交换率。根据两组氧气供体之间键长的差异来讨论此顺序。稳定性常数研究给出了在0.1 M NaNO3和25摄氏度下的logK(1)值:Cu(II),16.3;锌(II),10.47; Ca(II),7.54; m / z。锶(II),6.67; Ba(II),5.35; n。 Hg(II),14.53; Hg(II),14。 La(III),10.35; Gd(III),10.05。对于Cd(II)和Pb(II),即使在pH 0.3时也能完全形成络合物,并且只能将logK(1)的下限设置为19。根据酰胺氧供体的配位性质和DOTAM配体的几何要求,讨论了DOTAM对金属离子的选择性。 [参考:56]
UNIV WITWATERSRAND DEPT CHEM WITWATERSRAND 2050 SOUTH AFRICA;
Size-based selectivity; Coordination chemistry; Neutral oxygen; Ligand design; Dynamic properties; Aqueous-solution; Macrocycles; Complexation; Stability; Lanthanum(iii);
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