Isomorphism and phase transition in triferrocenylboroxine and triferrocenylborazine

The crystal structures of triferrocenylboroxine, [Fe(3)(C(5)H(5))(3)(C(15)H(12)B(3)O(3))], (I), and triferrocenylborazine, [Fe(3)(C(5)H(5))(3)(C(15)H(15)B(3)N(3))], (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.