FIG. 19.3 A cross section of the electron density difference in the CoiNCyi ¡on in a plane bisecting opposite edges of the CoN6 octahedron

FIG. 19.4 The electron density differences in (a) the cation and (b) the anión of [Co(NH3)6]3+[Co(CN)6]3~

19.2 Metal-polychalcogenide compounds 19.2.1 Metal-polysulfur compounds Just as sulfur itself forms rings reflecting its preferred bond and dihedral angles, so do we find rings containing polysulfur units bonded to metal atoms. As both the metals and the sulfur chain are reasonably flexible in their steric demands, a wide variety of compounds is found. The metal can either be part of the ring system (which is the most common situation), or coordinated to it.