Received 13 September 2011
Two polymorphs of N1,N4-bis(5-hydroxypenta-1,3-diynyl)-N1,N4-diphenylbenzene-1,4-diamine
The title compound, C28H20N2O2, forms two conformational polymorphs, (I) and (II), where the molecular structures are similar except for the orientation of the two hydroxy groups. In (I), which was obtained by slow evaporation from chloroform, the two hydroxy groups have an anti conformation. The molecules form a sheet structure within the ac plane, where the hydroxy groups form zigzag hydrogen bonds. In (II), which was obtained by slow evaporation from acetonitrile, the two hydroxy groups have a syn conformation. The molecules form a double-sheet structure within the ab plane, where the hydroxy groups form 4-helix hydrogen bonds.
Benzene-1,4-diamines show electron-donating ability and are able to act as -conjugated linkers. Acetylene derivatives which have amino groups as substituents are named ynamines, and they are known to be unstable because of their high reactivity. In the course of our research into ynamine compounds (Okuno et al., 2006), we succeeded in the preparation and characterization of the title compound, which incorporates an N,N'-diethynylbenzene-1,4-diamine skeleton. The molecule is a key unit in the formation of two-leg ladder polydiacetylenes by solid-state polymerization. We also found conformational polymorphism (Bernstein, 2002) dependant on the recrystallization solvent of the title compound, shown in the orientation of the hydroxy groups. Either crystal could be obtained independently, as judged by powder X-ray diffraction. In order to clarify the difference in the hydrogen-bonding patterns and crystal packings caused by the different hydroxy-group orientations, the crystal structures of the two polymorphs, (I) and (II), were determined.
Displacement ellipsoid plots of the two polymorphs are shown in Fig. 1. The bond lengths and angles of both polymorphs are almost similar (Tables 1 and 3). These structural geometries are consistent with those of the reported ynamines (Galli et al., 1988, 1989; Mayerle & Flandera, 1978; Okuno et al., 2006).
In (I), the structures around the N atoms, viz. the N1/C1/C7/C19 (r.m.s. deviation = 0.010 Å) and N2/C4/C13/C24 planes (r.m.s. deviation = 0.003 Å), are planar. The dihedral angles between the plane of the C1-C6 ring and the N1/C1/C7/C19 and N2/C4/C13/C24 planes are 49.15 (8) and 31.92 (8)°, respectively. A large residual density of 0.65 e Å-3 is located near atom C28, which has rather elongated displacement ellipsoids. This is presumably due to thermal motion of the hydroxymethyl group.
In (II), the structures around the N atoms, viz. the N1/C1/C7/C19 (r.m.s. deviation = 0.045 Å) and N2/C4/C13/C24 planes (r.m.s. deviation = 0.007 Å), are planar. The dihedral angles between the C1-C6 ring and the N1/C1/C7/C19 and N2/C4/C13/C24 planes are 57.36 (8) and 46.98 (8)°, respectively.
In both polymorphs, intramolecular conjugation between the two diacetylene units, i.e. overlap of p- or -orbitals, is estimated by the value of cos2, where is the torsion angle between the two orbitals. Even in the case of the smallest cos2 with = 57.36° in (II), the value is 0.29, suggesting the two diacetylene units are conjugated effectively.
We now discuss the differences between the molecular structures in the two polymorphs. A significant difference between the structures of (I) and (II) is the orientation of the hydroxy groups to the C23/N1/N2/C28 planes. The hydroxy groups in (I) have an anti conformation, while those in (II) have a syn conformation (Fig. 2), affording different types of intermolecular hydrogen bonds and different molecular packing structures. There are no significant - or C-H interactions.
The molecules in (I) and (II) form similar sheet structures, which are parallel to the ac and ab planes, respectively. In (I), the hydrogen bonds connect two sheets above and below (Fig. 3) to give zigzag intermolecular hydrogen bonds. The H atoms of both hydroxy groups are disordered and there are four types of O-HO hydrogen bonds (Table 2). Therefore, two kinds of zigzag intermolecular hydrogen bonds are observed, which are distinguished by black and grey lines in Fig. 4. When the structure of (I) was solved in the P21/c space group without disorder, the distances between the O-bound H atoms became too close, because the hydrogen-bonded pair of molecules are related by inversion symmetry. The remaining peaks around the O atoms were also high, indicating the existence of disorder. The possibility of solving the structure in the space group P21 was examined carefully, but the disorder was still present, as indicated by large peaks around the O atoms.
In (II), intermolecular hydrogen bonds are limited within two sheets (Table 4), giving double-sheet structures (Fig. 5). The hydrogen-bonding pattern was classified as a 4-helix (Fig. 4) (Taylor & Macrae, 2001).
| || Figure 1 |
The asymmetric units of (a) polymorph (I) and (b) polymorph (II) of the title compound, showing the atom-numbering schemes. Displacement ellipsoids are drawn at the 50% probability level. The disordered H atoms in polymorph (I) are identified by suffixes A and B.
| || Figure 2 |
Views of (a) polymorph (I) and (b) polymorph (II), projected along the N1N2 direction, with the benzene rings horizontal.
| || Figure 3 |
A view of the hydrogen-bonding interactions in (I) (dashed lines). [Symmetry codes: (i) -x + 1, -y + 1, -z + 1; (ii) x - 1, -y + , z + ; (iii) -x + 1, y - , -z + ; (iv) x - 1, y, z.]
| || Figure 4 |
Schematic presentations of (a) the zigzag hydrogen-bonding network of (I) and (b) the 4-helix hydrogen-bonding network of (II). The hydrogen bonds involving the disordered H atoms of (I) are identified by black and grey lines. [Symmetry codes: (i) -x + 1, -y + 1, -z + 1; (ii) x - 1, -y + , z + ; (iii) -x + 1, y - , -z + ; (iv) x - 1, y, z; (v) x + 1, y + 1, z; (vi) -x + 3, y + , -z + ; (vii) -x + 2, y + , -z + ; (viii) x, y + 1, z.]
| || Figure 5 |
A view of the hydrogen-bonding interactions in (II) (dashed lines). [Symmetry codes: (i) x + 1, y + 1, z; (ii) -x + 3, y + , -z + ; (iii) -x + 2, y + , -z + ; (iv) x, y + 1, z.]
The title compound was prepared according to the method of Tabata et al. (2012). A suspension of copper(I) chloride (0.81 g, 7.8 mmol) in acetone (15 ml) was degassed by argon bubbling for 30 min, and then tetramethylethylenediamine (TMEDA; 400 µl, 2.6 mmol) was added and the suspension stirred for 30 min. The supernatant solution containing the CuCl-TMEDA catalyst was transferred to a mixture of N1,N4-diethynyl-N1,N4-diphenylbenzene-1,4-diamine (1.00 g, 3.24 mmol) and 2-propyn-1-ol (2.7 ml, 45 mmol) in acetone (63 ml) at 253 K. The solution was stirred for 2 d under an oxygen atmosphere. The solvent was evaporated and the residue extracted with dichloromethane (200 ml). The solution was washed with 5% ammonium hydroxide (300 ml) and the water layer was extracted twice with dichloromethane (200 ml). The combined organic layer was washed with water (300 ml) and dried over anhydrous sodium sulfate. After the solvent had evaporated, the residue was purified by gel permeation chromatography to give the title compound as a white powder (yield 0.68 g, yield 50%). Slow evaporation from solutions in chloroform or acetonitrile gave polymorphs (I) and (II), respectively.
In polymorph (I), the C-bound H atoms, except for those on atoms C23 and C28, were obtained from a difference Fourier map and refined isotropically. The H atoms on C23 and C28 were placed in idealized locations (C-H = 0.99 Å) and were refined as riding on their parent C atoms, with Uiso(H) = 1.2Ueq(C). The O-bound H atoms were obtained from a difference Fourier map and found to be disordered. The occupancies of these H atoms were fixed at 0.5. The O-bound H-atom positions were refined with the restraint O-H = 0.84 (2) Å (DFIX instruction in SHELXL97; Sheldrick, 2008), with Uiso(H) = 1.2Ueq(O1 and O2). Similar U restraints (SIMU instruction in SHELXL97) and approximately isotropic restraints (ISOR instruction in SHELXL97) were applied to atoms C22, C23, C27, C28, O1 and O2, with an effective s.u. of 0.005 Å2. Restraints (SADI instruction in SHELXL97) were applied to the CH distances C23H1A/H1B and C28H2A/H2B, the O-H bond lengths O1-H1A/H1B and O2-H2A/H2B, and the C-O bond lengths C23-O1 and C28-O2, with an effective s.u. of 0.004 Å. A planarity restraint (FLAT instruction in SHELXL97) was applied to the groups C23/O1/H1A/O1i [symmetry code: (i) -x + 1, -y + 1, -z + 1], C23/O1/H1B/O2ii [symmetry code: (ii) -x + 2, y - , -z + ], C28/O2/H2A/O1iii [symmetry code: (iii) -x + 2, y + , -z + ] and C28/O2/H2B/O2iv [symmetry code: (iv) -x + 2, -y + 2, -z].
In polymorph (II), the H atoms were obtained from a difference Fourier map. All H atoms, except H4, H6 and H14, were refined isotropically. The positions of H4, H6 and H14 were refined, although their Uiso(H) values were fixed at 1.2Ueq(C).
For both compounds, data collection: APEX2 (Bruker, 2010); cell refinement: APEX2; data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: enCIFer (Allen et al., 2004).
Supplementary data for this paper are available from the IUCr electronic archives (Reference: UK3036 ). Services for accessing these data are described at the back of the journal.
This work was supported by Research for Promoting Technological Seeds from the Japan Science and Technology Agency (JST). The authors thank Dr Yoza of Bruker AXS for helpful discussions.
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