Synthesis, characterization, and X-ray crystal structures of cobalt(II) and cobalt(III) complexes of four topologically constrained tetraazamacrocycles
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. ISSN 0020-1693Full text not available from this repository.
Official URL: http://10.1016/S0020-1693(02)01080-0
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|
|Subjects:||Q Science > QD Chemistry|
|Divisions:||Faculty of Science > Chemistry|
|Journal or Publication Title:||INORGANICA CHIMICA ACTA|
|Publisher:||Elsevier Science SA|
|Date:||26 September 2002|
|Number of Pages:||12|
|Page Range:||pp. 91-102|
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