Tris-Dioximate Cobalt(I,II,III) Clathrochelates: Stabilization of Different Oxidation and Spin States of an Encapsulated Metal Ion by Ribbed Functionalization

Boron-capped hexachlorine-containing cobalt(II) clathrochelates were prepared by means of template condensation of dichloroglyoxime (Cl(2)GmH(2)) with boron-containing Lewis acids on a cobalt(II) ion matrix. The nucleophilic substitution of the reactive chlorine atoms of these macrobicyclic tris-dioximates with thiolate anions gave the hexasulfide cobalt(II) and dodecasulfide (CoCoCoIII)-Co-III-Co-II mono- and bis-clathrochelates. The treatment of the hexachlorine-containing cobalt(II) precursors with primary aliphatic amines afforded hexaamine cobalt(III) clathrochelates. The reduction of these precursors led to the clathrochelate [Co(Cl(2)Gm)(3)(BR)(2)](-) anions, which were isolated as the salts with bulky organic cations. The relative stability of these cobalt(I) complexes accounted for a strong electronic effect of six electron-withdrawing ribbed chlorine substituents. Superconducting quantum interference device (SQUID) magnetometry, EPR, and multi-temperature X-ray diffraction data showed that the cobalt(II) clathrochelates undergo gradual and incomplete. 3/2 spin transition. The Jahn-Teller distortion of the low-spin encapsulated cobalt(II) ion causes its shift in the direction of one of the three chelate alpha-dioximate fragments. The anisotropic displacement parameters were used to estimate the ordering of the molecular species, and the superposition of two Jahn-Teller distorted structures was found in a crystal. The cyclic voltammetry (CV) data showed the influence of the substituents in alpha-dioximate fragments on the redox potentials of an encapsulated cobalt ion. The electron-withdrawing ribbed substituents stabilize the cobalt(I) oxidation state of this ion because of electron-density delocalization on their ribbed substituents, whereas the electron-donating amine groups stabilize the cobalt(III) oxidation state.