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

Abstract

AbstractBoron‐capped hexachlorine‐containing cobalt(II) clathrochelates were prepared by means of template condensation of dichloroglyoxime (Cl2GmH2) 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 CoIIICoIICoIII 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(Cl2Gm)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 multitemperature X‐ray diffraction data showed that the cobalt(II) clathrochelates undergo gradual and incomplete ${1 \over 2}$ ↔ 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 α‐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 α‐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.