Crystal structures of 2-[3,5-bis(bromomethyl)-2,4,6-triethylbenzyl]isoindoline-1,3-dione and 2-{5-(bromomethyl)-3-[(1,3-dioxoisoindolin-2-yl)methyl]-2,4,6-triethylbenzyl}isoindoline-1,3-dione

The title compounds, C23H25Br2NO2 (1) and C31H29BrN2O4 (2), crystallize in the space group P21/n with two and one molecules, respectively, in the asymmetric unit of the cell. The molecular conformation of these compounds is stabilized by intramolecular C—H⋯O hydrogen bonds and C—H⋯N or C—H⋯π interactions. The crystal structure of 1 features a relatively strong Br⋯O=C halogen bond, which is not observed in the case of 2. Both crystal structures are characterized by the presence of C—H⋯Br hydrogen bonds and numerous intermolecular C—H⋯O hydrogen-bonding interactions.


Structural commentary
Compounds 1 and 2, the structures of which are illustrated in Fig. 1, were found to crystallize in the monoclinic space group P2 1 /n. In the case of compound 1, the asymmetric unit of the cell consists of two crystallographically non-equivalent molecules (1-A and 1-B). Molecule 1-A displays a conformation with a fully alternating arrangement of the substituents above and below the plane of the central benzene ring [ab 0 ab 0 ab 0 pattern, a = above, b = below (a 0 /b 0 = Et above/below); see Koch et al., 2017;Schulze et al., 2017]. In molecule 1-B, one of the ethyl groups is disordered over two positions with an occupancy of 0.820 (6) for the major disorder component; the two disorder positions are related by rotation of approximately 180 about the C4-C11 bond. The molecules display similar conformations, as illustrated by the molecular leastsquares overlay shown in Fig. 2. The dihedral angle between the phthalimide moiety and the benzene ring is 82.27 (14) (molecule 1-A) and 83.78 (13) (molecule 1-B). The conformation of the molecules appear to be stabilized by intramolecular C-HÁ Á ÁO C hydrogen bonds (Tables 1 and 2 Table 1 Hydrogen-bond geometry (Å , ) for 1.

Figure 1
Perspective view of 1 and 2 including the labelling of non-hydrogen atoms. Displacement ellipsoids are drawn at a 50% probability level.

Figure 2
Least-squares overlay of 1-A and 1-B with an r.m.s. deviation of 0.0089 Å . The hydrogen atoms are omitted for clarity.
The crystal structure of compound 2 contains one molecule in the asymmetric unit of the cell. The two phthalimide groups of the molecule point in opposite directions, showing inclination angles of 70.27 (16) and 79.10 (16) with respect to the plane of the central aromatic ring. The three-dimensional arrangement of substituents along the periphery of the benzene ring follows an ab 0 ba 0 ab 0 pattern, in which the bromomethyl group, one phthalimidomethyl unit and one ethyl group are directed towards one face of the benzene ring, whereas the three remaining substituents point in the opposite direction. This conformation is stabilized by intramolecular C ethyl -HÁ Á ÁO C (2.45, 2.50 Å ) and C ethyl -HÁ Á Á interactions [d(HÁ Á ÁCg) 2.80, 2.85 Å ].

Supramolecular features
In the crystal of compound 1, the distance of 3.220 (3) Å between Br2B and the oxygen atom O1A of an adjacent molecules (symmetry code: 1 + x, y, z) is considerably shorter than the sum of the van der Waals radii of the atoms (3.37 Å ; Bondi, 1964); this, as well as the well-defined bond geometry [/C-BrÁ Á ÁO = 171.34 (11) ] indicates the presence of a relatively strong BrÁ Á ÁO halogen bond (Table 3). This C-BrÁ Á ÁO C interaction is assisted by a C-HÁ Á ÁBr bond [d(HÁ Á ÁBr) = 2.92 Å , /C-HÁ Á ÁBr = 141.6 ], so that atom Br2B acts as a bifurcated binding site (see Fig. 3). The atoms Br1B and Br2A are involved in the formation of C ethyl -HÁ Á ÁBr interactions with distances of 2.86 and 3.00 Å , respectively (/C-HÁ Á ÁBr = 123 and 158 ). The two independent molecules are involved in a different way in the molecular association. The phthalimide group of molecule 1-B participates in the formation of C-HÁ Á Á contacts with HÁ Á ÁCg distances of 2.62 and 2.96 Å , whereas the phthalimide moiety of the second molecule is involved in the formation of an offset face-to-face interaction [d(CgÁ Á ÁCg) = 3.75 Å , symmetry code: Àx, 1 À y, 1 À z]. In addition, the crystal packing is characterized by the presence of several C-HÁ Á ÁO hydrogen bonds (2.35-2.43 Å ; Table 1). The different types of non-covalent bonds in the crystal generate a three-dimensional supramolecular network.
As a result of the presence of two phthalimide units in compound 2, its crystal structure is dominated by C-HÁ Á ÁO bonds [d(HÁ Á ÁO) = 2.49-2.59 Å ; Table 2] in which all oxygen atoms participate. The fragment of the packing structure shown in Fig. 4 shows that atoms O1 and H10A take part in the formation of an inversion-symmetric supramolecular ring motif with graph-set motif R 2 2 (10) (Etter, 1990;Bernstein et al., 1995; such a ten-membered supramolecular motif has, for example, been recognized in some crystal structures of fluorene derivatives bearing phthalimidomethyl groups, see  Packing excerpt of 1 showing C-BrÁ Á ÁO C and C-HÁ Á ÁBr halogen and hydrogen bonds, respectively (dashed lines). Hydrogen atoms of subunits that are excluded from intermolecular interactions are omitted for clarity. Table 3 Halogen bonds in 1.  Koch et al., 2014) in each of the 2-, 4-and 6-positions of the benzene ring. Furthermore, a 1,3,5-trisubstituted benzene derivative, namely 3,5-bis(phthalimidomethyl)phenyl-tert-butyldimethylsilyl ether (WIKRAK; Domínguez et al., 2007), has been found. In the case of IDOBIO and LOFBIT, the molecules adopt a conformation in which two phthalimidomethyl groups and one methoxy or bromomethyl group are directed towards one face of the benzene ring. The phthalimidomethyl groups of the 1,3,5-trisubstituted benzene derivative adopt a trans geometry.