Orientational disorder in Lambda-cobalt(III) sepulchrate trinitrate.

The crystal structure of Lambda-(1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane)cobalt(III) trinitrate, Co(C(12)H(30)N(8))(3), consists of a sepulchrate moiety that serves as a macrobicyclic nitrogen cage for the Co(3+) cation, which is six-coordinated by N atoms, and three nitrate anions. The Co-sepulchrate group lies on a threefold axis (site symmetry 32), as do two symmetry-related and ordered nitrate groups (site symmetry 3), with which it is connected via N-H...O hydrogen bonds [Co-N = 5.1452 (12) A]. The third nitrate group is disordered as a result of symmetry requirements around the origin (site symmetry 32), and is further away from the Co-sepulchrate cage [Co-N = 6.3160 (8) A]. The structure is described by applying orientational disorder over six equivalent orientations for the disordered nitrate group, which is considered as an ideal planar molecule of regular trigonal geometry with its molecular plane rotated out of the ab plane and the molecular centre of gravity slightly shifted away from the origin. This new model for disorder clearly improves a previous crystal structure determination.