Circular Dichroism and Stereochemistry of Tetranuclear Cobalt(III) Complexes of Hexol Type. I. Dodecaammine-hexa-μ-hydroxotetracobalt(III) Ion, [Co{(OH)2Co(NH3)4}3]6+

From the circular dichroism spectra of optically active dodecaammine-hexa-μ-hydroxo-tetracobalt(III) ion, (+)589-[Co{(OH)2Co(NH3)4}3]6+, measured in the visible and ultraviolet region in several solvents such as 0.01M-HCl and 0.17M-Na2SeO3, the d–d transitions of the complex are assigned in consideration of the ion-pairing effect. The absolute configuration of (+)589 isomer is assigned as Δ based upon a negative sign of the Ea component for the CoO6 chromophore. The circular dichroism change by the ion-pairing is attributed to the vicinal effect of chiral oxygen centers stereospecifically produced by the ion-pair formation, and the importance of the oxygen chirality is discussed on the basis of the time-course of circular dichroism change in the solutions.

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