Protonation and Zn(II) coordination by dipyridine-containing macrocycles with different molecular architecture. A case of pH-controlled metal jumping outside-inside the macrocyclic cavity.
Protonation and Zn(II) coordination by dipyridine-containing macrocycles with different molecular architecture. A case of pH-controlled metal jumping outside-inside the macrocyclic cavity.
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具有不同分子结构的含联吡啶大环化合物的质子化和 Zn(II) 配位。
DOI：
10.1021/ic001381k
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发表时间：
2001
影响因子：
4.6
通讯作者：
B. Valtancoli
中科院分区：
文献类型：
--
作者：
C. Lodeiro;A. Parola;F. Pina;C. Bazzicalupi;A. Bencini;A. Bianchi;C. Giorgi;A. Masotti;B. Valtancoli
报道了大环配体4,4'-(2,5,8,11,14-五氮杂[15])-2,2'-联吡啶（L3）的合成，该配体含有连接2,2'-二吡啶片段的4,4'-位置的五胺链。用电位法、紫外可见法和荧光发射法研究了连接2,2‘-二吡啶的6,6’位的同一五胺链的L3和大环L2的质子化作用和Zn（II）的络合作用。在L2中，所有的氮给体原子都聚集在大环腔内，而在L3中，杂芳氮原子位于大环腔外。两种配体在水溶液中形成单核和双核Zn（II）配合物。在含L2的单核Zn（II）配合物中，金属在大环腔内配位，与杂芳氮给体和脂肪链上的三个胺基结合。从[ZnL2]（2+）配合物的晶体结构可以看出，两个苯基氮不配位，在微酸性pH值下，配合物易于质子化。考虑到单核[ZnL3]（2+）配合物，金属被封装在腔内，而不是由二吡啶单元配位。配合物的质子化发生在脂肪族多胺链上，并引起金属在腔外的移位，与杂芳香氮结合。
The synthesis of the macrocyclic ligand 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridylophane (L3), which contains a pentaamine chain linking the 4,4'-positions of a 2,2'-dipyridine moiety, is reported. Protonation and Zn(II) complexation by L3 and by macrocycle L2, containing the same pentaamine chain connecting the 6,6'-positions of 2,2'-dipyridine, were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. While in L2 all the nitrogen donor atoms are convergent inside the macrocyclic cavity, in L3 the heteroaromatic nitrogen atoms are located outside. Both ligands form mono- and dinuclear Zn(II) complexes in aqueous solution. In the mononuclear Zn(II) complexes with L2, the metal is coordinated inside the macrocyclic cavity, bound to the heteroaromatic nitrogen donors and three amine groups of the aliphatic chain. As shown by the crystal structure of the [ZnL2](2+) complex, the two benzylic nitrogens are not coordinated and facile protonation of the complex takes place at slightly acidic pH values. Considering the mononuclear [ZnL3](2+) complex, the metal is encapsulated inside the cavity, not coordinated by the dipyridine unit. Protonation of the complex occurs on the aliphatic polyamine chain and gives rise to translocation of the metal outside the cavity, bound to the heteroaromatic nitrogens.