Cobalt(III) complexes of a tripodal ligand containing three imidazole groups: Properties and structures of racemic and optically active species

Hirofumi Nakamura, Megumi Fujii, Yukinari Sunatsuki, Masaaki Kojima, Naohide Matsumoto

Research output: Contribution to journalArticle

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Abstract

The complex [Co(H3L)](ClO4)3·H 2O (1), where H3L {tris[2-(4-imidazoylmethylideneamino) ethyl]amine} is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 molar ratio, was synthesized and optically resolved by fractional crystallization of the diastereomeric salt with [Sb2{(R,R)-tart}2]2- [(R,R)-tart = (2R,3R)-tartrate(4-) ion]. From the less soluble part, Λ-[Co(H2L)][Sb2-{(R,R)-tart}2] ·4H2O (2) was isolated. Starting from 2, two optically active complexes, Λ-[Co(H3L)](ClO4)3·1. 5H2O (Λ-1) and Λ-[Co(L)] (Λ-3), were obtained. The crystal structures of these complexes are compared with those of the racemic structures. Λ-1 shows an unusually strong circular dichroism (λ = 488 nm, Δε = -7.74 M-1 cm-1) in the first d-d absorption band region. The effects of deprotonation-reprotonation of the uncoordinated imidazole NH groups of Λ-[Co(H3L)]3+ on the UV/Vis and CD spectra and on the cyclic voltammograms were studied in methanol. Although the deprotonation-reprotonation reactions are reversible, the redox couple for the completely deprotonated species [CoIII/II(L)] 0/- is not observed.

Original languageEnglish
Pages (from-to)1258-1267
Number of pages10
JournalEuropean Journal of Inorganic Chemistry
Issue number8
DOIs
Publication statusPublished - Mar 2008

Fingerprint

Deprotonation
Cobalt
Ligands
Crystallization
Amines
Methanol
Absorption spectra
Condensation
Salts
Crystal structure
Ions
imidazole
perchlorate
tartaric acid
Oxidation-Reduction
tris(2-aminoethyl)amine

Keywords

  • Chiral resolution
  • Cobalt
  • Crystal structure
  • N ligands
  • Schiff bases
  • Tripodal ligands

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Cobalt(III) complexes of a tripodal ligand containing three imidazole groups : Properties and structures of racemic and optically active species. / Nakamura, Hirofumi; Fujii, Megumi; Sunatsuki, Yukinari; Kojima, Masaaki; Matsumoto, Naohide.

In: European Journal of Inorganic Chemistry, No. 8, 03.2008, p. 1258-1267.

Research output: Contribution to journalArticle

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abstract = "The complex [Co(H3L)](ClO4)3·H 2O (1), where H3L {tris[2-(4-imidazoylmethylideneamino) ethyl]amine} is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 molar ratio, was synthesized and optically resolved by fractional crystallization of the diastereomeric salt with [Sb2{(R,R)-tart}2]2- [(R,R)-tart = (2R,3R)-tartrate(4-) ion]. From the less soluble part, Λ-[Co(H2L)][Sb2-{(R,R)-tart}2] ·4H2O (2) was isolated. Starting from 2, two optically active complexes, Λ-[Co(H3L)](ClO4)3·1. 5H2O (Λ-1) and Λ-[Co(L)] (Λ-3), were obtained. The crystal structures of these complexes are compared with those of the racemic structures. Λ-1 shows an unusually strong circular dichroism (λ = 488 nm, Δε = -7.74 M-1 cm-1) in the first d-d absorption band region. The effects of deprotonation-reprotonation of the uncoordinated imidazole NH groups of Λ-[Co(H3L)]3+ on the UV/Vis and CD spectra and on the cyclic voltammograms were studied in methanol. Although the deprotonation-reprotonation reactions are reversible, the redox couple for the completely deprotonated species [CoIII/II(L)] 0/- is not observed.",
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AB - The complex [Co(H3L)](ClO4)3·H 2O (1), where H3L {tris[2-(4-imidazoylmethylideneamino) ethyl]amine} is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 molar ratio, was synthesized and optically resolved by fractional crystallization of the diastereomeric salt with [Sb2{(R,R)-tart}2]2- [(R,R)-tart = (2R,3R)-tartrate(4-) ion]. From the less soluble part, Λ-[Co(H2L)][Sb2-{(R,R)-tart}2] ·4H2O (2) was isolated. Starting from 2, two optically active complexes, Λ-[Co(H3L)](ClO4)3·1. 5H2O (Λ-1) and Λ-[Co(L)] (Λ-3), were obtained. The crystal structures of these complexes are compared with those of the racemic structures. Λ-1 shows an unusually strong circular dichroism (λ = 488 nm, Δε = -7.74 M-1 cm-1) in the first d-d absorption band region. The effects of deprotonation-reprotonation of the uncoordinated imidazole NH groups of Λ-[Co(H3L)]3+ on the UV/Vis and CD spectra and on the cyclic voltammograms were studied in methanol. Although the deprotonation-reprotonation reactions are reversible, the redox couple for the completely deprotonated species [CoIII/II(L)] 0/- is not observed.

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