Low-spin hexadentate cobalt(II) and cobalt(III) complexes of the hexathioether cage (1,8-dimethyl-3,6,10,13,16,19-hexathiabicyclo[6.6.6]icosarie) have been synthesised, their redox and spectral properties have been investigated, and the encapsulation of the cobalt(II) ion has been established by an X-ray crystal structure determination, which shows the metal ion to be coordinated to six thioether sulphur atoms at distances ranging from 2.265(3) to 2.354(2)Å.