The binding abilities of a series of ionizable calixarenes towards three
lanthanides (Pr
3+
, Eu
3+
and Yb
3+
) and one
actinide (Th
4+
) have been established in methanol by
potentiometric measurements. The calixarenes result from progressive
substitution of the phenolic hydrogens of
p-tert-butylcalix[4]arene by carboxylic acid functions.
Calixarene derivatives with mixed carboxylic and ester functional groups,
as well as
octa-O-carboxymethyl-p-tert-butylcalix[8]arene
and the two oxa-derivatives,
tetra-O-carboxymethyl-p-tert-
butyltetrahomodioxacalix[4]arene and
tri-O-carboxymethyl-p-tert-
butylhexahomotrioxacalix[3]arene have also been studied. The formation of
1 : 1 species partially protonated
[M(H
z
L)] and totally deprotonated (ML) as well as
methoxo species [ML(OMe)
z
}] has been
established with lanthanides. Additional binuclear complexes and their
methoxo forms have been found in some cases. With thorium the mononuclear
ML and MHL complexes are mainly formed in addition to the corresponding
methoxo species at high pH. For a given ligand, the stability of the
complexes increases with the cationic charge: complexes of thorium are more
stable than those of lanthanides, which are themselves generally more
stable than the corresponding alkaline-earth- and alkali-metal complexes.
The predominance of electrostatic interactions in the binding is further
confirmed by a linear relationship between the stability of mononuclear
complexes (log β
110
) and the total basicity of the ligands
(ΣpK
ai
). The
p-tert-butylcalix[8]arene octaacid and the
p-tert-butylcalix[4]arene monoacid are respectively the
best complexing agents for the lanthanides and thorium. The monoacid
derivative shows significant Yb
3+
/Eu
3+
and
Th
4+
/Eu
3+
selectivities in appropriate pH
ranges.
在
甲醇中,通过电位测量法确定了一系列可电离
钙钛矿与三种
镧系元素(Pr 3+ 、Eu 3+ 和 Yb 3+ )和一种
锕系元素(Th 4+ )的结合能力。对叔丁基
钙并[4]烯的
酚羟基逐渐被
羧酸功能取代,从而产生了
钙并烯。
此外,还研究了具有混合
羧酸和酯官能团的
钙烯烃衍
生物,以及八-O-羧甲基-对叔丁基
钙[8]烯和两种氧杂衍
生物,即四-O-羧甲基-对叔丁基四氢二氧杂
钙[4]烯和三-O-羧甲基-对叔丁基六氢三氧杂
钙[3]烯。研究证实,
镧系元素可形成 1 : 1 的部分质子化[M(H z L)]和完全去质子化(ML)物种以及甲氧基物种[ML(OMe) z }]。在某些情况下,还发现了其他双核配合物及其甲氧基形式。对于
钍,除了在高 pH 值条件下形成相应的甲氧基外,还主要形成单核 ML 和
MHL 配合物。对于给定的
配体,络合物的稳定性随阳离子电荷的增加而增加:
钍的络合物比
镧系元素的络合物更稳定,而
镧系元素的络合物通常比相应的碱土
金属和碱
金属络合物更稳定。 单核络合物的稳定性(log β 110)与
配体的总碱性(ΣpK ai)之间的线性关系进一步证实了静电相互作用在结合中的主导地位。对叔丁基
钙[8]烯八酸和对叔丁基
钙[4]烯单酸分别是
镧系元素和
钍的最佳络合剂。单酸衍
生物在适当的 pH 值范围内具有显著的 Yb 3+ /Eu 3+ 和 Th 4+ /Eu 3+ 选择性。