EQUILIBRIUM AND THERMODYNAMIC STUDY OF THE AQUEOUS COMPLEXATION OF 1,4,7-TRIAZACYCLONONANE-N,N',N''-TRIACETIC ACID WITH PROTONS, ALKALINE-EARTH-METAL CATIONS, AND COPPER(II)
EQUILIBRIUM AND THERMODYNAMIC STUDY OF THE AQUEOUS COMPLEXATION OF 1,4,7-TRIAZACYCLONONANE-N,N',N''-TRIACETIC ACID WITH PROTONS, ALKALINE-EARTH-METAL CATIONS, AND COPPER(II)
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DOI：
10.1021/ic00263a029
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发表时间：
1987-08-12
影响因子：
4.6
通讯作者：
ZOMPA, LJ
中科院分区：
文献类型：
--
作者：
BEVILACQUA, A;GELB, RI;ZOMPA, LJ
用pH电位滴定法测定了1，4，7-三氮杂环壬烷-Ar，N，N，N”-三乙酸（H_3T）与H ~+，Mg ~（2+），Ca ~（2+），Sr ~（2+）和Ba ~（2+）反应的温度依赖性平衡常数。此外，H_3T与Cu ~（2+）的反应用pH电位法和分光光度法进行了研究。平衡常数数据用于通过范特霍夫分析计算各种反应的0和5。对热力学数据的解释得出几个结论：（1）T2 34”的第一和第二质子化反应似乎局限于氮中心，而第三和第四质子的加入则涉及羧酸基团。(2)Mg ~（2+）与T_3 ~-的络合作用不同于其它碱土金属离子。T_3 ~+与Mg ~（2+）仅形成4 ~ 5个键，而同类离子可能形成6个键。然而，MgT-是IIA族（223族）金属络合物中最稳定的，这显然是因为形成较少但较强的金属-配体键。(3)Cu 2+与T3 '形成异常稳定的1：1配合物。质子化形式的复合物是占主导地位的pH范围从0到2.7。根据现有的热力学、光谱和X射线晶体学数据，讨论了碱土金属和Cu 2+与T3 '的配合物的稳定性和性质，并与其他多氨基多羧酸的稳定性和性质进行了比较。
pH potentiometric titrations are employed to estimate temperature-dependentequilibrium constants for reactions of the amino acid l, 4, 7-triazacyclononane-Ar, lV,, A"-triacetic acid (H3T) with H+, Mg2+, Ca2+, Sr2+, and Ba2+. Additionally, reactions of H3T with Cu2+ are studied by both pH potentiometry and spectrophotometry. Theequilibrium constant data serve to calculate 0 and 5 for the various reactions via a van’t Hoff analysis. Interpretation of the thermodynamic data leads to several conclusions:(1) First andsecond protonation reactions of T2 34" seem localized to nitrogen sites while addition of a third and fourth proton involve carboxylate groups.(2) Mg2+ complexation of T3" is distinct from that of the other alkaline-earth-metal ions studied. It appears that T3" formsonly four or five bonds with Mg2+ whereas the congener ions likely form six bonds. MgT" is however the most stable of the group IIA (group 223) metal complexes apparently because of the formation of fewer but stronger metal to ligand bonds.(3) Cu2+ forms an unusually stable 1: 1 complex with T3". The protonated form of the complex is dominant in the pH range from 0 to 2.7. Thestability and properties of alkaline-earth-metal and Cu2+ complexes with T3" are discussed and compared to those of other polyamino polycarboxylic acids in the light of the available thermodynamic, spectroscopic, and X-ray crystallographic data.