Incommensurate Phase in Λ-cobalt (III) Sepulchrate Trinitrate Governed by Highly Competitive N-H⋅⋅⋅O and C-H⋅⋅⋅O Hydrogen Bond Networks.

Phase transitions in molecular crystals are often determined by intermolecular interactions. The cage complex of [Co(C H N )]  ⋅ 3 NO is reported to undergo a disorder-order phase transition at T ≈133 K upon cooling. Temperature-dependent neutron and synchrotron diffraction experiments revealed satellite reflections in addition to main reflections in the diffraction patterns below T . The modulation wave vector varies as function of temperature and locks in at T ≈98 K. Here, we demonstrate that the crystal symmetry lowers from hexagonal to monoclinic in the incommensurately modulated phases in T