Chiral recognition and conglomerate crystallization induced by self-organization of cobalt(III) complexes of a tripodal ligand containing three imidazole groups.
Chiral recognition and conglomerate crystallization induced by self-organization of cobalt(III) complexes of a tripodal ligand containing three imidazole groups.
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DOI：
10.1021/ic070286
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发表时间：
2007-09
影响因子：
4.6
通讯作者：
Hirofumi Nakamura;Y. Sunatsuki;M. Kojima;N. Matsumoto
中科院分区：
文献类型：
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作者：
Hirofumi Nakamura;Y. Sunatsuki;M. Kojima;N. Matsumoto
报道了反阴离子对手性识别诱导钴（III）配合物砾岩结晶的影响。以三（2-氨基乙基）胺和4-甲酰基咪唑为原料，以1:3摩尔比缩合制备了含有三个咪唑基团的三[2-{（咪唑-4-酰基）甲基}氨基]乙基胺（H3L）非手性三足配体。H3L与反式-[CoIIICl2(py)4]+反应生成手性（δ或λ） [CoIII(H3L)]3+配合物。形式上的半质子化配合物[CoIII(H(1.5)L)]X（1.5）。nH2O （X = Cl, Br， I, BF4, ClO4，或PF6）是通过控制[Co(H3L)]3+的不配位咪唑nhh基团的去质子化合成的。在半质子化配合物晶体中，具有相同绝对构型的[Co(H3L)]3+和[Co(L)]两种组分通过咪唑-咪唑酸氢键连接，形成扩展的同手性二维片状结构，该结构由六核单元和三角空洞组成。有两种堆叠方式：一种是通过同手性堆叠，另一种是通过异手性堆叠。当反离子的大小较小（即X = Cl, Br， I，或BF4）时，相邻的具有相同手性的同手性片层堆叠形成同手性晶体（砾岩）。对于大阴离子（即ClO4-和PF6-），由δ对映体组成的同手性片和由λ对映体组成的同手性片交替堆叠，形成异手性晶体（外消旋晶体）。光学活性λ -[Co(H(1.5)L)](ClO4)（1.5）。以Lambda-[Co(H3L)]3+为原料合成H2O，并与外消旋配合物的晶体结构进行了比较。有两个相互冲突的因素控制着晶体结构：骨骼密度；通道的大小。二维薄片在同手性晶体中比在异手性晶体中排列得更紧密。然而，在同手性晶体中，容纳反离子的通道更小，阴离子之间的空间拥塞随着阴离子尺寸的增加而增加。该异手性晶体具有柔性的之字形通道结构，并且通道的大小可以增加以容纳较大的阴离子。因此，具有大阴离子的配合物（即ClO4-和PF6-）优先形成异手性晶体而不是同手性晶体。
The effect of a counteranion on chiral recognition inducing conglomerate crystallization of a cobalt(III) complex is reported. An achiral tripodal ligand involving three imidazole groups, tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H3L), was prepared by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 mole ratio. The reaction of H3L and trans-[CoIIICl2(py)4]+ afforded the chiral (Delta or Lambda) [CoIII(H3L)]3+ complex. The formally hemideprotonated complexes [CoIII(H(1.5)L)]X(1.5).nH2O (where X = Cl, Br, I, BF4, ClO4, or PF6) were synthesized by controlled deprotonation of the uncoordinated imidazole NH groups of [Co(H3L)]3+. In crystals of the hemideprotonated complex, two components, [Co(H3L)]3+ and [Co(L)], with the same absolute configuration are linked by imidazole-imidazolate hydrogen bonds to form an extended homochiral 2D sheet structure, which is composed of a hexanuclear unit with a trigonal void. There are two ways of stacking the sheets: One is via homochiral stacking, and the other is via heterochiral stacking. When the size of the counterion is small (i.e., X = Cl, Br, I, or BF4), adjacent homochiral sheets with the same chirality are stacked to form a homochiral crystal (conglomerate). With large anions (i.e., ClO4- and PF6-), a homochiral sheet consisting of Delta enantiomers and a sheet consisting of Lambda enantiomers are stacked alternately to give a heterochiral crystal (a racemic crystal). Optically active Lambda-[Co(H(1.5)L)](ClO4)(1.5).H2O was synthesized from Lambda-[Co(H3L)]3+, and the crystal structure was compared to that of the racemic complex. There are two conflicting factors governing the crystal structure: the skeletal density; the size of the channels. The 2D sheets are more closely packed in the homochiral crystal than in the heterochiral crystal. However, the channels, where the counterions are accommodated, are smaller in the homochiral crystal, and the steric congestion between the anions increases with increasing anion size. The heterochiral crystal has a flexible, zigzag channel structure, and the size of the channels can increase to accommodate larger anions. Thus, complexes with large anions (i.e., ClO4- and PF6-) preferentially form heterochiral crystals rather than homochiral crystals.