Tris{2-[(2-aminobenzylidene)amino]ethyl}amine

The title Schiff base, C27H33N7, is a tripodal amine displaying C 3 symmetry, with the central tertiary N atom lying on the threefold crystallographic axis. The N—CH2—CH2—N conformation of the pendant arms is gauche [torsion angle = 76.1 (3)°], which results in a claw-like molecule, with the terminal aniline groups wrapped around the symmetry axis. The lone pair of the apical N atom is clearly oriented inwards towards the cavity, and should thus be chemically inactive. The amine NH2 substituents lie in the plane of the benzene ring to which they are bonded. With such an arrangement, one amine H atom forms an S(6) motif through a weak N—H⋯N hydrogen bond with the imine N atom, while the other is engaged in an intermolecular N—H⋯π contact involving the benzene ring of a neighbouring molecule related by inversion. The benzene rings also participate in an intramolecular C—H⋯π contact of similar strength. In the crystal structure, molecules are separated by empty voids (ca 5% of the crystal volume), although the crystal seems to be unsolvated.

The title Schiff base, C 27 H 33 N 7 , is a tripodal amine displaying C 3 symmetry, with the central tertiary N atom lying on the threefold crystallographic axis. The N-CH 2 -CH 2 -N conformation of the pendant arms is gauche [torsion angle = 76.1 (3) ], which results in a claw-like molecule, with the terminal aniline groups wrapped around the symmetry axis. The lone pair of the apical N atom is clearly oriented inwards towards the cavity, and should thus be chemically inactive. The amine NH 2 substituents lie in the plane of the benzene ring to which they are bonded. With such an arrangement, one amine H atom forms an S(6) motif through a weak N-HÁ Á ÁN hydrogen bond with the imine N atom, while the other is engaged in an intermolecular N-HÁ Á Á contact involving the benzene ring of a neighbouring molecule related by inversion. The benzene rings also participate in an intramolecular C-HÁ Á Á contact of similar strength. In the crystal structure, molecules are separated by empty voids (ca 5% of the crystal volume), although the crystal seems to be unsolvated.
Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97. Recently, the research line of receptors with the ability to extract metal salts has grown in relevance, because of the harmful effects that anions and cations have in health and the environment. A class of such receptors includes polyamines, in which cations and anions are found in separate sites in a zwitterionic form of the ligand. As a consequence, the efficiency for solvent extraction of metal salts may be modulated trough pH adjustment (Wenzel, 2008). In these compounds, the metal ion coordinates in the deprotonated moiety, while the anion is associated to the protonated pendant groups (Bernier et al., 2009;Galbraith et al., 2006). The Schiff base condensation is a useful route to obtain polyamines including suitable structural characteristics in order to act as polytopic ligands. Some recent reports highlighted important applications of this type of compounds (Zibaseresht & Hartshorn, 2005;Mercs et al., 2008).
We report herein on the synthesis (Fig. 1) and crystal structure of a new Schiff base, which, we hope, will allow to bond both cations and anions, depending on the pH. The molecule (Fig. 2) is a tripodal tertiary amine NR 3 where R contains imine functionality. The tripodal N atom is placed on a 3-fold axis in a trigonal cell (C 3 point symmetry). The pendant arms R are gauche, as reflected by torsion angle N1-C2-C3-N4, 76.1 (3)°, and the lone pair on N1 is directed toward the cavity formed by the arms. Similar arrangements giving claw-like molecules were observed in related tertiary amines, although in less symmetric Laue groups (e.g. Weibel et al., 2002;Işıklan et al., 2010). In some instances, closely related tripodal NR 3 molecules approximate the C 3 symmetry but with R arms lying in a plane rather than forming a closed cavity (McKee et al., 2006). Glidewell et al. (2005) showed that the molecular conformation for this class of amines is determined mainly by direction-specific intra-and intermolecular interactions. In the case of the title amine, NH 2 groups in the aniline moieties are engaged in both intra and intermolecular interactions: H12A forms a weak hydrogen bond with the imine atom N4, while H12B affords an intermolecular N-H···π contact, also of limited strength. The last significant contact is intramolecular: the C7-H7 aromatic group gives a C-H···π contact with the next arm in the molecule.
As mentioned, all non bonding contacts are rather weak. As a consequence, molecules are not densely packed in the crystal, and voids of ca 60 Å 3 are available for solvent insertion. However, attempts to include non-diffracting solvent in the structural model using SQUEEZE (Spek, 2009) were unsuccessful. The chemical formula was thus left as unsolvated.

Experimental
To a dissolution of 2-nitrobenzaldehyde (0.020 mol) in ethanol (60 ml), were added 11.114 g (0.20 mol) of iron, 90 µl of hydrochloric acid and 15 ml of distilled water. Immediately the mixture was refluxed for 90 min. The mixture was filtered off using Hyfo supercell, and the solvent was distilled, affording a yellow oil (Fig. 1, IL). In order to obtain the title molecule

Refinement
Amine H atoms H12A and H12B were found in a difference map and refined with free coordinates. Other H atoms were placed in idealized positions and refined as riding to their parent C atoms, with bond lengths fixed to 0.97 (methylene) or 0.93 Å (aromatic). Isotropic displacement parameters for H atoms were calculated as U iso (H) = 1.2U eq (carrier atom). A set of 21 reflections with F o << F c (probably because of a diffractometer instability) were omitted in least-squares refinement. Fig. 1. Synthetic route for the title compound. Fig. 2. ORTEP-like view of the title molecule, with displacement ellipsoids at the 30% probability level. H atoms have been omitted for clarity, and only the asymmetric unit is completely labeled. Other atoms are generated by symmetry codes A: 2 -y, 1 + x -y, z and B: 1 -x + y, 2 -x, z.