Circular dichroism and stereochemistry of tetranuclear cobalt(III) complexes of hexol type. I. Dodecaammine-hexa-μ-hydroxo-tetracobalt(III) Ion, [Co{(OH)2Co(NH3)4}3]6+

From the circular dichroism spectra of optically active dodecaammine-hexa-hydroxo-tetracobalt(III) ion, ( + )589-[Co{(OH)2Co(NH3)4}3]6+, mcasurcd in the visible and ultraviolet region in several solvents such as O.OIM-HCI 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 Eα 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.