ja0123960_si_001.cif (182.2 kB)
Spontaneous Resolution Induced by Self-Organization of Chiral Self-Complementary Cobalt(III) Complexes with Achiral Tripod-Type Ligands Containing Three Imidazole Groups
dataset
posted on 2002-01-05, 00:00 authored by Ikuko Katsuki, Yuri Motoda, Yukinari Sunatsuki, Naohide Matsumoto, Toshio Nakashima, Masaaki KojimaThe progression from synthetically achiral ligand and metal ion, to isolated chiral metal complex,
to homochiral two-dimensional (2D) assembly layer, and finally to conglomerate is presented. The cobalt(III) complexes of achiral tripod-type ligands involving three imidazole groups with the chemical formulas
[Co(H3L6)](ClO4)3·H2O (6) and [Co(H3L7)](ClO4)3·0.5H2O (7) were synthesized, where H3L6 = tris[2-(((imidazol-4-yl)methylidene)amino)ethyl]amine and H3L7 = tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. Each complex induces the chirality of clockwise (C) and anticlockwise (A) enantiomers
due to the screw coordination arrangement of the achiral tripod-type ligand around the Co(III) ion. The fully
protonated (6, 7), the formally hemi-deprotonated (6‘, 7‘), and the fully deprotonated (6‘ ‘, 7‘ ‘) complexes
were obtained as good quality crystals by adjusting the pH of the solutions. The crystal structures were
determined by single-crystal X-ray analyses. There is no intermolecular network structure in the fully
protonated complexes (6, 7). The fully deprotonated complexes (6‘ ‘, 7‘ ‘) form a hydrogen-bonded network
structure, in which the C and A enantiomers coexist and are connected through a water molecule. The
formally hemi-deprotonated species [Co(H1.5L6 or 7)]1.5+, which functions as a self-complementary chiral
building block, generates equal numbers of protonated and deprotonated molecules by an acid−base
reaction to form an extended 2D homochiral layer structure consisting of a hexanuclear structure with a
trigonal void as a unit. The 2D structure arises from the intermolecular imidazole−imidazolate hydrogen
bonds between [Co(H3L6 or 7)]3+ and [Co(L6 or 7)]0, in which adjacent molecules with the same chirality are
arrayed in an up-and-down fashion. In the crystal lattices of the perchlorate salts (6‘, 7‘), the perchlorate
ions are located in the cavity, and the homochiral layer consisting of C enantiomers and the adjacent layer
consisting of A enantiomers are stacked alternately to give an achiral crystal. The chloride salt of the hemi-deprotonated complex [Co(H1.5L6)]Cl1.5·4H2O (6a‘) is found to be a conglomerate, in which the chloride
ions are positioned in the intermediate region of the double layer, and layers with the same chirality are
well stacked by adopting the up-and-down layer's shape to generate channels, and so form a chiral crystal.
The circular dichroism (CD) spectrum of 6a‘ showed a positive peak and a negative peak at 480 and 350
nm, respectively, and the spectrum of another crystal showed an enantiomeric CD pattern, providing further
evidence of spontaneous resolution on crystallization.
History
Usage metrics
Categories
Keywords
2 D structure2 D homochiral layer structuredeprotonated moleculesimidazole groupschloride saltmetal ionhexanuclear structureH 3 L 6H 3 L 7perchlorate saltsSpontaneous Resolution InducedC enantiomersdeprotonated complexeschloride ionsImidazole Groupsscrew coordination arrangementchiral crystal7achiral crystalnetwork structureprotonated complexes350 nm6homochiral layerchiralitychemical formulasquality crystalsassembly layerCoenantiomeric CD pattern1.5crystal structuressynthetically achiral ligandwater moleculecrystal latticeschiral metalperchlorate ions
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC