Isomorphism and phase transition in triferrocenylboroxine and triferrocenylborazine

The crystal structures of triferrocenylboroxine, [Fe-3(C5H5)(3)(C15H12B3O3)], (I), and triferrocenylborazine, [Fe-3(C5H5)(3)(C15H15B3N3)], (II), are isomorphous. At room temperature, the space group is Cmc2(1) and the molecules have crystallographic m symmetry. A reversible phase transition occurs at 283 (2) K for (I) and at 263 (5) K for (II). In the low-temperature phase, the space group of both compounds is P2(1) and the molecules no longer have internal symmetry. Intermolecular C-H...pi interactions are enhanced in the low-temperature phase.