Quinquedentate Coordination of 6-Methyl-1,11-dithia-4,8-diazacyclotetradecan-6-amine to Cobalt(III). X-Ray Crystal Structure of the [Co(N₃S₂)(OOCCH₃)] (ClO₄)₂.H₂O Complex

Abstract

The pendant arm macrocycle 6-methyl-1,11-dithia-4,8-diazacyclotetradecan-6-amine (7) can coordinate to cobalt(III) as a quinquedentate N₃S₂ ligand . Spectroscopy indicated a geometry with the macrocycle folded and the pendant amine and the unidentate donor in cis dispositions for the [Co(7) Cl ]²⁺ and [Co(7)(OOCCH₃)]²⁺ products isolated. An X-ray crystal structure analysis of [Co(7)(OOCCH₃)](ClO₄)₂.H₂O characterized the cis stereochemistry. The complex crystallized in the Pbca space group, a 10.620(9), b 13.926(9), c 32.35(2)Ǻ, and analysis defined a distorted octahedral geometry with the primary and two secondary nitrogen donors occupying an octahedral face with relatively short Co-N bonds [1.937(7)-1.950(7)Ǻ], the acetate ion [Co-O 1.905(6)Ǻ] trans to one of the secondary amine donors and thioether donors [Co-S 2.223(3), 2.227(3)Ǻ] trans to the other nitrogen donors. Significant angle distortions occur around the metal ion. Base hydrolysis of the chloro complex is slow and stereoretentive , with a rate constant of 1.08×10³ dm³ mol^-1 s^-1 at 25°C, 15-fold faster than for the pentaaza analogue.