An orthorhombic polymorph of 10,11-dihydrocarbamazepine

Abstract

The title compound (systematic name: 10,11-dihydro-5H-dibenz[b,f]azepine-5-carboxamide), C15H14N2O, is shown to crystallize as an orthorhombic polymorph to complement the known monoclinic form. The molecular conformations of both forms are very similar, involving a bent conformation for the seven-membered azepine ring and an overall ;butterfly' shape. The molecules assemble into chains by way of N-H...O bonds and N-H...pi interactions in both crystal modifications. The two polymorphs appear to form due to different van der Waals interactions between the layer-like sheets of molecules.

Crystal polymorphism in a carbamazepine derivative: Oxcarbazepine

“…This is thought to allow for the optimization of the hydrogen bonding in a chain motif 13. All three structures of dihydrocarbamazepine also exhibit an analogous hydrogen bonding scheme to OCB, as they all form hydrogen bonded chains 7–9. The hydrogen bonding in all four of the carbamazepine polymorphs favor an anti‐dimer motif,6 whereas the structure of epoxycarbamazepine displays a twisted syn‐dimer configuration 18.…”

“…Carbamazepine (CBZ) (Fig. 1), an important anticonvulsant, exhibits four structurally characterized polymorphs,6 whereas its dihydro derivative (10,11‐dihydrocarbamazepine) is trimorphic 7–9. Its keto‐derivative, oxcarbazepine (OCB) (Fig.…”

Polymorphic Phase Transitions in Carbamazepine and 10,11‐Dihydrocarbamazepine

“…This is a consequence of the alignment of the molecules relative to each other in the crystal and so the distances between them. The dominant intermolecular force in the structure of polymorph II is hydrogen bonding between one hydrogen from the amide group and the oxygen of an adjacent molecule (Figure S2 and Figure a). This is in fact the only hydrogen bonding throughout the lattice, and while relatively weak for an H‐bond with an H⋅⋅⋅O distance of 2.206 Å is the strongest interaction holding the crystal together.…”

“…The dominant intermolecular force in the structure of polymorph II is hydrogen bonding between one hydrogen from the amide group and the oxygen of an adjacent molecule (Figure S2 and Figure a). This is in fact the only hydrogen bonding throughout the lattice, and while relatively weak for an H‐bond with an H⋅⋅⋅O distance of 2.206 Å is the strongest interaction holding the crystal together. An amide proton of the second molecule forms a similar H‐bond with the oxygen of a third adjacent DHC molecule, and so strings of molecules are formed in one direction.…”

“…10,11‐dihydrocarbamazepine has four known polymorphs, three of which display a catemeric H‐bonded motif similar to that of CBZ V. In contrast, the most recently discovered form (IV) has a dimer motif similar to that seen in CBZ forms I–IV. There has been little research into DHC, with no studies reported into the phase transitions between polymorphs or describing their behaviour upon heating.…”