SYNTHESIS AND CHARACTERIZATION OF COBALT CYCLIDENE COMPLEXES WITH LONG POLYMETHYLENE BRIDGES AND THEIR BINDING TO SMALL MOLECULES
UNSPECIFIED. (1993) SYNTHESIS AND CHARACTERIZATION OF COBALT CYCLIDENE COMPLEXES WITH LONG POLYMETHYLENE BRIDGES AND THEIR BINDING TO SMALL MOLECULES. INORGANIC CHEMISTRY, 32 (12). pp. 2736-2744. ISSN 0020-1669Full text not available from this repository.
The synthesis of four novel cobalt(II) cyclidene complexes with long polymethylene bridges is described. These complexes have been found to reversibly bind dioxygen in a manner similar to that of their shorter bridged analogs. Dioxygen affinities are reduced for bridge lengths exceeding that of octamethylene, an effect which has been correlated with the width of the cavity surrounding the dioxygen-binding site. Structural effects on small-molecule binding that are associated with the long bridge have been examined by comparison of the X-ray crystal structure of the undecamethylene-bridged cobalt(III) complex with the shorter bridged analogues. Bis(isothiocyanato)(2,3,15,16,17,24-hexamethyl-3,15,19,23,26,30-hexaazabicyclo- [15.7.7] hentriaconta-1,16,18,23,25,30-hexaene-kappa4N)cobalt(III) hexafluorophosphate crystallizes in space group P2(1) with a = 13.699(6) angstrom, b = 9.515(3) angstrom, c = 14.726(7) angstrom, and beta = 97.40(4)-degrees, and the structure was solved by the heavy-atom method to R = 0.053, R(w) = 0.058. The thiocyanate that is coordinated within the cavity is bent through steric interaction with the ligand and has bond lengths and angles closer to those of the externally bound thiocyanate than is true of analogous complexes with shorter bridges. The cavity width of the six-coordinate undecamethylene-bridged cobalt(III) complex is similar to that of the octamethylene-bridged complex, in contradistinction to the previous observation that the widths of vacant cavities decrease as the bridge length increases beyond (CH2)8. This clearly shows that that the longer bridged complexes are flexible enough to expand their cavities when a small molecule is coordinated to the metal center. The autoxidation of these cobalt(II) complexes has been found to depend on the dioxygen partial pressure and the axial base in a manner analogous to that of the shorter bridged derivatives. However, the rate of autoxidation is significantly greater for the complexes having longer bridges.
|Item Type:||Journal Article|
|Subjects:||Q Science > QD Chemistry|
|Journal or Publication Title:||INORGANIC CHEMISTRY|
|Publisher:||AMER CHEMICAL SOC|
|Official Date:||9 June 1993|
|Number of Pages:||9|
|Page Range:||pp. 2736-2744|
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