A second monoclinic polymorph for 3-amino-1-(4-methoxyphenyl)-9,10-dihydrophenanthrene-2,4-dicarbonitrile

The title compound, C23H17N3O, has been previously described in a monoclinic P21/c polymorph with Z = 4 [Asiri, Al-Youbi, Faidallah, Ng & Tiekink (2011). Acta Cryst. E67, o2449]. In the new monoclinic P21/n form, with Z = 8, there are two independent molecules, A and B, in the asymmetric unit. In both molecules, the cyclohexa-1,3-diene ring has a screw-boat conformation, whereas it is a distorted half-chair in the original polymorph. There is a fold in each molecule, as indicated by the dihedral angle between the benzene rings of the 1,2-dihydronaphthalene and aniline residues of 33.19 (10)° (molecule A) and 30.6 (10)° (molecule B). The methoxybenzene ring is twisted out of the plane of the aniline residue to which it is connected [dihedral angles = 49.22 (10) and 73.27 (10)°, in A and B respectively]. In the crystal, the two independent molecules self-associate via N—H⋯N hydrogen bonds, generating a 12-membered {⋯HNC3N}2 synthon. These are connected into a supramolecular tape in the (-101) plane by N—H⋯O(methoxy) interactions. In the P21/c polymorph, supramolecular layers are formed by N—H⋯N and N—H⋯O interactions.

In the P2 1 /c polymorph of (I), the conformation matches more closely a distorted half-chair.
For the first independent molecule, the benzene rings of the 1,2-dihydronaphthalene and methoxybenzene residues form dihedral angles of 33.19 (10) and 49.22 (10)°, respectively, with the amino-benzene ring, indicating non-planarity in the fused ring system and a twist of the methoxybenzene out of the plane of the benzene ring to which it is connected. The comparable angles for the second independent molecule are 30.6 (10) and 73.27 (10)°, respectively. Figure 2 shows an overlay diagram for the three independent molecules of (I) characterized in the two polymorphs.
In the crystal structure of (I) the two independent molecules self-associate via N-H···N hydrogen bonds to generate 12membered {···HNC 3 N} 2 synthons, Fig. 3 and Table 1. One of the amino-H atoms forms a hydrogen bond to a methoxy-O atom leading to the formation of a supramolecular tape along [1 0 1], Fig. 3 and Table 1. The fourth independent amino-H atom does not participate in a significant intermolecular interaction. In the previously described P2 1 /c form of (I), supramolecular arrays with a zigzag topology were formed through N-H···N hydrogen bonds, leading to {···HNC 3 N} 2 synthons, as well N-H···O(methoxy) hydrogen bonding.

Refinement
Carbon-bound H-atoms were placed in calculated positions [C-H = 0.95 to 0.99 Å, U iso (H) = 1.2 to 1.5U eq (C)] and were included in the refinement in the riding model approximation. The N-H atoms were located in a difference Fourier map, and were refined with a distance restraint of N-H = 0.88±0.01 Å; their U iso values were refined. Owing to poor agreement, the (1 0 1) and (0 2 1) reflections were omitted from the final cycles of refinement.

Figure 1
The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.  Overlay diagram of the two independent molecules of (I) and the polymorph of (I). The molecules have been aligned so that nitrile-N atom closest to the partially saturated ring, amino-N and the C atom diagonally opposite to the amino-N atom have been superimposed. Colour code: red = N1-molecule of (I), green = N4-molecule (inverted) of (I) and blue = polymorph of (I). 3-amino-1-(4-methoxyphenyl)-9,10-dihydrophenanthrene-2,4-dicarbonitrile