Received 11 October 2004
Isomeric nitrophthalimides: sheets built from N-HO and C-HO hydrogen bonds
aSchool of Chemistry, University of St Andrews, Fife KY16 9ST, Scotland,bDepartment of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland, and cInstituto de Química, Departamento de Química Inorgânica, Universidade Federal do Rio de Janeiro, 21945-970 Rio de Janeiro, RJ, Brazil
Molecules of 3-nitrophthalimide, C8H4N2O4, are linked into sheets by a combination of one N-HO hydrogen bond [HO = 1.99 Å, NO = 2.8043 (14) Å and N-HO = 176°] and two independent C-HO hydrogen bonds [HO = 2.36 and 2.56 Å, CO = 3.1639 (16) and 3.4386 (16) Å, and C-HO = 142 and 153°], and these sheets are linked into pairs by a single - stacking interaction. Molecules of isomeric 4-nitrophthalimide are linked into sheets by a combination of one three-centre N-H(O)2 hydrogen bond [HO = 2.14 and 2.55 Å, NO = 2.974 (3) and 3.231 (3) Å, N-HO = 151 and 131°, and OHO = 76°] and two independent two-centre C-HO hydrogen bonds [HO = 2.38 and 2.54 Å, CO = 3.257 (4) and 3.452 (4) Å, and C-HO = 156 and 168°].
The isomeric title compounds 3-nitrophthalimide, (I), and 4-nitrophthalimide, (II), contain, within very compact molecules, a wide variety of potential hydrogen-bond donors and acceptors (Fig. 1). Both N-H and C-H bonds provide potential donors, while carbonyl and nitro O atoms and the arene ring all provide potential acceptors, although there is aet al., 1995; Desiraju & Steiner, 1999). In addition, aromatic - stacking interactions and non-bonded dipolar interactions (Allen et al., 1998) involving both carbonyl and nitro groups are possible, in principle.
In the event, the supramolecular structure of (I) (Fig. 1) is dominated by a two-centre N-HO hydrogen bond, in which the acceptor is a carbonyl O atom, and two independent C-HO hydrogen bonds, one involving a carbonyl O atom and the other a nitro O atom as acceptor. By contrast, the supramolecular structure of (II) (Fig. 2) is dominated by one asymmetric three-centre N-H(O)2 hydrogen bond, involving both of the carbonyl O atoms as the acceptors, and two independent two-centre C-HO hydrogen bonds, one involving a carbonyl O atom and the other a nitro O atom as acceptor.
In isomer (I), each of the independent hydrogen bonds (Table 1) can be regarded as producing a one-dimensional substructure (Gregson et al., 2000), all parallel to the  direction but all generated by different symmetry operations; the combination of these three motifs generates a sheet. The formation of the sheets in (I) is most readily analysed by considering, in turn, the action of each hydrogen bond. Amine atom N1 in the molecule at (x, y, z) acts as a hydrogen-bond donor to carbonyl atom O1 in the molecule at ( + x, y, - z), so producing a C(4) chain running parallel to the  direction and generated by the a-glide plane at z = (Fig. 3).
At the same time, aryl atom C6 in the molecule at (x, y, z) acts as a hydrogen-bond donor to the second carbonyl O atom, O2, in the molecule at (-1 + x, y, z), thus generating by translation a C(7) chain along . The combination of the two motifs having carbonyl acceptors generates a column of R32(14) rings across z = (Fig. 3). Finally, aryl atom C5 at (x, y, z) acts as a hydrogen-bond donor to nitro atom O41 in the molecule at (- + x, y, - z), so forming a C(5) chain along , this time generated by the a-glide plane at z = . The combination of the two motifs involving aryl H atoms generates a column of R33(15) rings across z = (Fig. 3). Neither of the rings utilizes all three independent hydrogen bonds. However, the combination of all three hydrogen bonds generates a (010) sheet in which columns of R33(14) rings across z = n + (n = zero or integer) alternate with columns of R33(15) rings across z = n + (n = zero or integer) (Fig. 3). Four sheets of this type pass through each unit cell, and the sheets are linked weakly into pairs by a single aromatic - stacking interaction.
The C3-C8 aryl rings in the molecules at (x, y, z) and (-x, -y, 1 - z) are strictly parallel, with an interplanar spacing of 3.309 (2) Å; the ring-centroid separation is 3.758 (2) Å, corresponding to a centroid offset of 1.781 (2) Å (Fig. 4). These two molecules lie in the (010) sheets within the domains 0.02 < y < 0.31 and -0.21 < y < -0.02, respectively, and these two sheets are thus linked into a bilayer. The formation of the bilayer is reinforced by a dipolar interaction between the negatively polarized nitro atom O42 in the molecule at (x, y, z) and the positively polarized carbonyl atom C1 in the molecule at ( - x, -y, + z), which forms part of the sheet in the domain -0.21 < y < -0.02. The COi distance [symmetry code: (i) - x, -y, + z] is 2.980 (2) Å and the COi-Ni angle is 135.9 (2)°. However, there are no direction-specific interactions between adjacent bilayers
In isomer (II), the hard and soft hydrogen bonds independently generate two one-dimensional substructures, each in the form of a chain of rings, and these chains combine to form sheets. Amine atom N1 in the molecule of (II) at (x, y, z) acts as a hydrogen-bond donor to carbonyl atoms O1 and O2 in the molecules at (2 - x, - + y, - z) and (2 - x, + y, - z), respectively. These two interactions (Table 2) are the strong and weak components of a markedly asymmetric, but essentially planar, three-centre interaction. The sum of the angles at atom H1 is 358°. Together these interactions produce a chain of edge-fused R22(8) rings running parallel to the  direction and generated by the 21 screw axis along (1, y, ) (Fig. 5).
In addition, aryl atoms C4 and C7 in the molecule at (x, y, z) act as donors, respectively, to atoms O1 and O51 in the molecules at (-1 + x, -1 + y, z) and (1 + x, 1 + y, z), so generating two individual C(6) chains, whose combined action generates by translation a C(6)C(6)[R22(10)] chain of rings (Bernstein et al., 1995) running parallel to the  direction (Fig. 6). The combination of the  and  chains generates a (001) sheet, which is modestly reinforced by a dipolar interaction between the negatively polarized atom O2 at (x, y, z) and the positively polarized atom C2 at (1 - x, - + y, - z). The O2C2ii distance is 2.906 (3) Å [symmetry code: (ii) 1 - x, - + y, - z] and the C2-O2C2ii angle is 156.1 (2)°, indicating an interaction whose geometry is intermediate between the perpendicular motif I and the sheared motif III described by Allen et al. (1998). The two molecules involved in this interaction lie in the  chains along (1, y, ) and (, y, ), so that this dipolar interaction generates a motif along  within the (010) sheet. There are no direction-specific interactions between adjacent sheets.
The bond distances and angles within the molecules of (I) and (II) present no unusual values. The dihedral angle between the planes of the aryl ring and the nitro group is 31.6 (2)° in (I) and 8.0 (2)° in (II), so that each molecule has point group C1; this is sufficient to render the molecules of both isomers chiral. Isomer (I) crystallizes in the centrosymmetric space group Pbca, as a racemate with equal numbers of both conformational enantiomers present in each single-crystal domain. Isomer (II) crystallizes in space group P212121 as a fully ordered structure, having only one conformational enantiomer present in each single-crystal domain.
| || Figure 1 |
The molecule of isomer (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
| || Figure 2 |
The molecule of isomer (II), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
| || Figure 3 |
A stereoview of part of the crystal structure of isomer (I), showing the formation of a (010) sheet containing alternating columns of R33(14) and R33(15) rings.
| || Figure 4 |
Part of the crystal structure of isomer (I), showing the - stacking interaction that links the (010) sheets into pairs. For clarity, H atoms have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (-x, -y, 1 - z).
| || Figure 5 |
Part of the crystal structure of isomer (II), showing the formation of a chain of edge-fused rings along . For clarity, H atoms bonded to C atoms have been omitted. Atoms marked with an asterisk (*), a hash (#), a dollar sign ($) or an ampersand (&) are at the symmetry positions (2 - x, + y, - z), (2 - x, - + y, - z), (x, -1 + y, z) and (x, 1 + y, z), respectively.
| || Figure 6 |
Part of the crystal structure of isomer (II), showing the formation of a chain of rings along . Atoms marked with an asterisk (*) or a hash (#) are in the molecules at (1 + x, 1 + y, z) and (-1 + x, -1 + y, z), respectively.
Commercial samples of 3- and 4-nitrophthalimide were obtained from Aldrich, and crystals suitable for single-crystal X-ray diffraction were grown from solutions in ethyl acetate [for (I)] and acetone [for (II)].
Space group Pbca for (I) and P212121 for (II) were uniquely assigned from the systematic absences. All H atoms were located from difference maps and then treated as riding atoms, with C-H distances of 0.95 Å and N-H distances of 0.82 Å in (I) at 120 (2) K, and C-H distances of 0.93 Å and N-H distances of 0.92 Å in (II) at 291 (2) K, and with Uiso(H) values of 1.2Ueq(C,N). In the absence of any significant anomalous scattering, the Flack (1983) parameter for isomer (II) was indeterminate (Flack & Bernardinelli, 2000), and it was not possible to establish the absolute configuration (Jones, 1986). Accordingly, the Friedel equivalent reflections were merged prior to the final refinements.
For compound (I), data collection: COLLECT (Hooft, 1999); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT; data reduction: DENZO and COLLECT. For compound (II), data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN. For both compounds, program(s) used to solve structure: OSCAIL (McArdle, 2003) and SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: OSCAIL and SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).
Supplementary data for this paper are available from the IUCr electronic archives (Reference: SK1783 ). Services for accessing these data are described at the back of the journal.
The authors thank a referee for helpful comments on conformational enantiomerism. X-ray data were collected at the EPSRC X-ray Crystallographic Service, University of Southampton, England; the authors thank the staff for all their help and advice. JNL thanks NCR Self-Service, Dundee, for grants which have provided computing facilities for this work. JLW thanks CNPq and FAPERJ for financial support.
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