Complexation of Metal Ions, Including Alkali-Earth and Lanthanide(III) Ions, in Aqueous Solution by the Ligand 2,2′,6′,2"-Terpyridyl
Complexation of Metal Ions, Including Alkali-Earth and Lanthanide(III) Ions, in Aqueous Solution by the Ligand 2,2′,6′,2"-Terpyridyl
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DOI：
10.1021/ic101742x
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发表时间：
2011-04-04
影响因子：
4.6
通讯作者：
Hancock, Robert D.
中科院分区：
文献类型：
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作者：
Hamilton, Joanna M.;Anhorn, Michael J.;Hancock, Robert D.
用紫外可见光谱法测定了配体2,2′，6′，2”-三吡啶基（terpy）在水溶液中的一些金属离子络合性质。研究发现，在pH值高于5的情况下，在加入氯化钠或氯化钠等电解质以控制离子强度的情况下，terpy以中性配体的形式形成沉淀，这可以从大的光散射峰中得到证明。因此，确定了terpy的质子化常数。为避免沉淀，离子强度(mu) = 0，分别为4.32(3)和3.27(3)。用碱土金属离子Mg-II， Ca-II, Sr-II， Ba-II和Ln（III) （Ln =镧系）离子La-III， Gd-III, Lu-III）在pH > 5.0下用金属离子溶液滴定2 × 10(-5) M游离铽，测定了其对数K-1值。测定了Zn-II、Cd-II和Pb-II的Log K-1 （terpy）。通过跟踪金属离子和质子之间的竞争作为ph的函数。所有这些金属离子的络合物形成伴随着自由三角的宽pi-pi*跃迁的显着锐化，这归因于络合物形成影响配体振动，在自由配体中，配体与pi-pi*跃迁耦合，从而使它们变宽。结果表明，各种金属离子的对数K-1（terpy）与金属离子的对数K-1（NH3）值具有良好的相关性。后者既包括实验对数K-1（NH3）值，也包括之前通过密度、泛函理论计算预测的对数K-1（NH3）值。[Ni(terpy)(2)][Ni(CN)(4)]中心点CH3CH2OH中心点H2O(1)的结构如下：三斜，P (1) / bar, a = 8.644(3)埃，b = 9.840(3)埃，c = 20.162(6)埃，alpha = 97.355(5)度，beta = 97.100(5)度，gamma = 98.606(5)度，V = 1663.8(9)埃(3),Z = 4，最终R = 0.0319。两个Ni-N键与三萜配体的中心N给体的平均能级为1.990(2)埃，而四个外围Ni-N键的平均能级为2.107（10）埃。三元配合物的M-N键长度的差异是较小金属离子配合物的典型特征，而对于较大的金属离子，这种差异则相反。讨论了金属离子大小对多吡啶基配体选择性的影响，以及以吡啶基为芳香基团的配体具有较大的刚性。
Some metal-ion-complexing properties of the ligand 2,2',6',2 ''-terpyridyl (terpy) in aqueous solution are determined by following the pi-pi* transitions of 2 x 10(-5) M terpy by UV-visible spectroscopy. It is found that terpy forms precipitates when present as the neutral ligand above pH similar to 5 in the presence of electrolytes such as NaClO4 or NaCl added to control the ionic strength, as evidenced by large light-scattering peaks. The protonation constants of terpy are thus determined at. the ionic strength (mu) = 0 to avoid precipitation and found to be 4.32(3) and 3.27(3). The log K-1 values were determined for terpy with alkali-earth metal ions Mg-II, Ca-II, Sr-II, and Ba-II and Ln(III) (Ln = lanthanide) ions La-III, Gd-III, and Lu-III by titration of 2 x 10(-5) M free terpy at pH > 5.0 with solutions of the metal ion. Log K-1 (terpy) was determined for all, Zn-II, Cd-II and Pb-II. by following the competition between the metal ions and protons as a function of the pH. Complex formation for all of these metal ions was accompanied by marked sharpening of the broad pi-pi* transitions of free terpy, which was attributed to complex formation affecting ligand vibrations, which in the free ligand are coupled to the pi-pi* transitions and thus broaden them. It is shown that log K-1(terpy) for a wide variety of metal ions correlates well with log K-1(NH3) values for the metal ions. The latter include both experimental log K-1(NH3) values and log K-1(NH3) values predicted previously by density, functional theory calculation. The structure of [Ni(terpy)(2)][Ni(CN)(4)]center dot CH3CH2OH center dot H2O (1) is reported as follows: triclinic, P (1) over bar, a = 8.644(3) angstrom, b = 9.840(3) angstrom, c = 20.162(6) angstrom, alpha = 97.355(5)degrees, beta = 97.100(5)degrees, gamma = 98.606(5)degrees, V = 1663.8(9) angstrom(3), Z = 4, and final R = 0.0319. The two Ni-N bonds to the central N donors of the terpy ligands in 1 average 1.990(2) angstrom, while the four peripheral Ni-N bonds average 2.107(10) angstrom. This difference in the M-N bond length for terpy complexes is typical of the complexes of smaller metal ions, while for larger metal ions, the difference is reversed. The significance of the metal-ion size dependence of the selectivity of polypyridyl ligands, and the greater rigidity of ligands based on aromatic groups such as pyridyl groups, is discussed.