Crystal structure of 2,2′-{[(2-nitrobenzyl)azanediyl]bis(propane-3,1-diyl)}bis[1H-isoindole-1,3(2H)-dione]

The structure of the title compound exhibits a folded conformation with the three arms all on the same side of the tertiary N atom. The crystal packing features π–π interactions.


Chemical context
The coordination chemistry of tripodal tetramine ligands has been reviewed and includes structures with pendant arms that are symmetric or asymmetric with respect to the presence of aliphatic and aromatic donor atoms (Blackman, 2005). The ligands coordinate transition metals or lanthanide ions using all four nitrogen donor atoms. Tripodal amines have also been shown to coordinate to anions (Bose et al., 2011;Bazzicalupi et al., 2009;Kuswandi et al., 2006). The title compound is an intermediate for the synthesis of an asymmetrical tripodal tetramine. After removal of the phthalimide protecting groups and reduction of the nitro group, the title compound will become a tripodal ligand with two arms that contain aliphatic nitrogens and one with an aromatic nitrogen (Keypour et al., 2008a,b). Phthalimide compounds are of interest themselves because they have the tendency to exhibit a variety of supramolecular interactions in the solid state. These include n-, -, dipole-dipole, hydrogen bonding, and other supramolecular interactions (Howell et al., 2003;Barrett et al., 1995). ISSN 2056-9890

Structural commentary
In the title compound ( Fig. 1), the planes of the two phthalimide units (N1/C1-C8 and N3/C15-C22) make a dihedral angle of 12.18 (12) . The dihedral angles between the benzyl plane and the phthalimide units are 68.08 (7) and 67.71 (7) . This orientation creates a cavity around which the three arms are arranged. The bridgehead nitrogen (N2) is located 2.104 (2) Å away from the plane created by the other three nitrogen atoms.

Database survey
A search of the Cambridge Structural Database (version 5.41, update of October 2020; Groom et al., 2016) for related compounds with a phthalimide unit gave 2623 hits. A search for the skeletal structure of N(CH 2 CH 2 CH 2 N) 3 resulted in 149 entries. Similar off-setstacking was seen in another compound with two phthalimide groups (REVYUM; Barrett et al., 1995). However, it was shown that an intramolecular hydrogen bond between phthalimide groups resulted in nostacking (VEHRUW; Brycki et al., 2006). More recently, a urea compound with two phthalimides showedstacking and intramolecular hydrogen bonding (PONZEZ; Medrano et al., 2014). Three structures with only one phthalimide group have also showninteractions (VIDTUA; Brovarets et al., 2018;PAVHUR;Yang et al., 2012;SAGTIF;Shao et al., 2012). Another compound has been reported that has two phthalimide-protected nitrogens with two carbon spacers versus three for the title compound, a benzyl group, and a trityl sulfide (WOJSIZ; Flö rke et al., 2014). The dihedral angle between the planes of the phthalimide units is significantly different from the title compound at 77.86 (3) . The crystal packing of this structure shows hydrogen bonding but notstacking.

Synthesis and crystallization
The title compound was prepared by using a previously reported method (Keypour et al., 2008a) The molecular structure of the title compound, showing 50% probability ellipsoids.   (2.6 g, 15 mmol), and potassium carbonate (1.8 g, 13 mmol) were heated at 433 K for one h to give the title compound. Crystals suitable for X-ray analysis were slowly grown from chloroform.

2,2′-{[(2-Nitrobenzyl)azanediyl}bis(propane-3,1-diyl)}bis[1H-isoindole-1,3(2H)-dione]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.