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X-ray structural study of a zinc(II) inclusion complex of a phenolate-pendant cyclam (1992)

Kimura, Eiichi ; Kurosaki, Hiromasa ; Koike, Tohru ; [et al.]

Springer

Journal of inclusion phenomena and macrocyclic chemistry 12 (1992), S. 377-387

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ISSN: 1573-1111

Keywords: Charles Pedersen ; crown ethers ; phenol-pendant cyclam-zinc(II) complex ; crystal structure

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract The molecular structure of phenol-pendant cyclam-zinc(II) complex,4a, has been determined by X-ray structure analysis. Crystals of4a · ClO4 · CH3OH (C16H27N4OZn · ClO4 · CH3OH) are monoclinic, space groupP21/nn, with four molecules in the unit cell of dimensionsa=31.198(2) Å,b=8.426(1) Å,c=8.214(1) Å, andβ=93.96(1)°. The structure was solved by the heavy atom method and refined anisotropically toR=0.044,R w=0.062 for 1551 independent reflections. The complex assumes a five-coordinate, square pyramidal geometry, where zinc(II) is surrounded by the cyclam moiety in a planar fashion with the pendant phenolate anion occupying an axial position. An extremely short Zn-O(phenolate) bond distance of 1.983(5) Å, in conjunction with the 0.288 Å displacement of Zn(II) above the cyclam N4 plane toward the phenolate, accounts for the extremely low pK a value of 5.8 for the pendant phenol. These facts about4a, in comparison with the previous findings for the Ni(II) (4b) and Cu(II) complexes (4c) with the same ligand, illustrate well the characteristics of zinc(II) ion coordination properties.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01053875

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Structure and O2 uptake properties of a novel nickel(II) complex of pyridyl-pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane] (1997)

Kimura, E. ; Sasada, Masatoshi ; Shionoya, Mitsuhiko ; [et al.]

Springer

JBIC 2 (1997), S. 74-82

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ISSN: 1432-1327

Keywords: Key words Nickel complex ; DNA cleavage ; O2 activation ; Biomimetic chemistry ; Macrocyclic polyamine

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Abstract Novel potentially five-coordinate pyridyl–pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (H2L) and its homologs (6-methyl and 6,6-dimethyl derivatives)] have been synthesized to study nickel(II) complexation. A purple nickel(II) complex with a deprotonated amide (NiHL) was isolated from aqueous equimolar solution of H2L and Ni(ClO4)2. A yellow nickel(II) complex with two deprotonated amides (NiL) was crystallized from an H2O/CH3CN solution of H2L and Ni(OH)2. The X-ray crystal study of NiL showed a square-planar nickel(II) complex with the pyridyl–pendant remaining uncoordinated. It is concluded from the visible absorption and NMR study of NiL in aqueous solution that the four-coordinate NiL is in equilibrium with a five-coordinate square-pyramidal nickel(II) complex with the apical coordination of the pyridyl–pendant. A voltammetric study disclosed a low nickel(II/III) redox potential of +0.29 V vs SCE for NiL at pH 9.5 and 25 °C with 0.10 M Na2SO4. The nickel(II) complex NiL absorbed an equimolar amount of O2 at pH 9.5 and 25 °C, and the O2 was activated to cleave plasmid DNA.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s007750050108

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