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Synthesis, characterization, and X-ray crystal structures of cobalt(II) and cobalt(III) complexes of four topologically constrained tetraazamacrocycles
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Hubin, Timothy J., Alcock, Nathaniel W., Clase, Howard J., Seib, Lawrence L. and Busch, Daryle H. (2002) Synthesis, characterization, and X-ray crystal structures of cobalt(II) and cobalt(III) complexes of four topologically constrained tetraazamacrocycles. INORGANICA CHIMICA ACTA, 337 . pp. 91-102. doi:10.1016/S0020-1693(02)01080-0 ISSN 0020-1693.
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Official URL: http://10.1016/S0020-1693(02)01080-0
Abstract
The high spin Co2+ complexes of 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1), 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane (2), 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (3), and racemic-4,5,7,7,11,12,14,14-octamethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (4) have been synthesized and characterized by X-ray crystallography. The Co(III) complexes of 1-3 were also prepared by the chemical oxidation of the Co(II) complexes. The X-ray crystal structures of Co(1)Cl-2, Co(3)Cl-2, and [Co(3)Cl-2]PF6 demonstrate that the ligands enforce a distorted octahedral geometry on Co(II) and Co(III) with two cis sites occupied by chloro ligands. In contrast, the Co(II) complex of 4 is five-coordinate with trigonal bipyramidal geometry. The methyl groups substituted on the carbon atoms of ligand 4 define a shallow cavity, allowing only one chloride ligand to bind to the chelated metal ion. This difference in coordination geometry causes Co(4)Cl+ to be much more difficult to oxidize (E-1/2 = 1.176 V vs. SHE) than the octahedral Co(II) complexes of 1-3 (E-1/2 from -0.157 to 0.173 V vs. SHE). The Co(III) complexes of 1-3 have three absorbances in their electronic spectra, while typical cis-Co(III)N4X2 complexes have only two. This additional splitting of energy states is attributed to the increased distortion from octahedral resulting from the short ethylene cross-bridge on the macrobicyclic ligands. (C) 2002 Elsevier Science B.V. All rights reserved.
Item Type: | Journal Article | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry | ||||
Journal or Publication Title: | INORGANICA CHIMICA ACTA | ||||
Publisher: | Elsevier Science SA | ||||
ISSN: | 0020-1693 | ||||
Official Date: | 26 September 2002 | ||||
Dates: |
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Volume: | 337 | ||||
Number of Pages: | 12 | ||||
Page Range: | pp. 91-102 | ||||
DOI: | 10.1016/S0020-1693(02)01080-0 | ||||
Status: | Peer Reviewed | ||||
Publication Status: | Published |
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