Crystal structure of 3-[({2-[bis(2-hydroxybenzyl)amino]ethyl}(2-hydroxybenzyl)amino)methyl]-2-hydroxy-5-methylbenzaldehyde

The molecular structure of a non-symmetric structure based on a tetrasubstituted ethylenediamine backbone consists of three hydroxybenzyl groups and one 2-hydroxy-5-methylbenzaldehyde group bonded to the N atoms of the diamine unit. The ethylenediamine skeleton shows a regular extended conformation, while the phenol arms are randomly oriented but governed by hydrogen bonds.

The non-symmetric title molecule, C 32 H 34 N 2 O 5 , is based on a tetrasubstituted ethylenediamine backbone. The molecular structure consists of three hydroxybenzyl groups and one 2-hydroxy-5-methylbenzaldehyde group bonded to the N atoms of the diamine unit. The ethylenediamine skeleton shows a regular extended conformation, while the spatial orientation of the phenol arms is governed by hydrogen bonds. In the 2-hydroxy-5-methylbenzaldehyde group, an intramolecular S(6) O-HÁ Á ÁO hydrogen bond is observed between the alcohol and aldehyde functions, and the neighbouring phenol arm participates in an intramolecular S(6) O-HÁ Á ÁN hydrogen bond. The third phenol group is involved in a bifurcated intramolecular hydrogen bond with graph-set notation S(6) for O-HÁ Á ÁN and O-HÁ Á ÁO intramolecular hydrogen bonds between neighbouring amine and phenol arms, respectively. Finally, the fourth phenol group acts as an acceptor in a bifurcated intramolecular hydrogen bond and also acts as donor in an intermolecular hydrogen bond, which connects inversionrelated molecules into dimers with R 4 4 (8) ring motifs.

Chemical context
The preparation of non-symmetric compounds has always been of interest in organic synthesis, as well as in coordination chemistry. Compounds containing tetrasubstituted ethylenediamine groups have attracted significant interest because of their coordination versatility towards metal ions, their easy preparation and their biological activity (Musa et al., 2014). With respect to medical applications, high in vitro cytotoxic activity of free ethylenediamine-type compounds against different types of cancer cells, such as HL-60 leukemic and B16 human melanoma cells lines, has been reported (Dencic et al., 2012;Lazić et al., 2010). In addition, metal complexes containing substituted ethylenediamine have also found valuable applications in pharmacological research as potential anticancer agents (Ansari et al., 2009), radiopharmaceuticals for tumor imaging (Boros et al., 2011;Price et al., 2012) and artificial nucleases (Raman et al., 2011). In this paper, we report the synthesis and crystal structure of the non-symmetric molecule 3- [({2-[bis(2-hydroxybenzyl)amino]ethyl}(2-hydroxybenzyl)amino)methyl]-2-hydroxy-5-methylbenzaldehyde, (I), which is a potential hexadentate ligand with an N 2 O 4 -donor set which could stabilize complexes containing high-oxidation-state metal ions, such as Tc III , Ga III and In III ions, that are widely used in radiopharmaceuticals for diagnostic imaging and related research.

Structural commentary
Compound (I) is a non-symmetric molecule based on a tetrasubstituted ethylenediamine backbone (Fig. 1). The structure consists of three hydroxybenzyl groups and one 2hydroxy-5-methylbenzaldehyde group bonded to nitrogen atoms of the diamine unit. The ethylenediamine skeleton shows a regular extended 'zigzag' conformation [with an N1-C2-C3-N4 torsion angle of 174.78 (13) ], while the pendant phenol arms are randomly oriented but governed by hydrogen bonds (Table 1). Three intramolecular hydrogen bonds with an S(6) graph-set motif are observed in the molecular structure of (I) (Fig. 2). One of these occurs between the neighbouring alcohol and aldehyde groups. In addition, intramolecular O-HÁ Á ÁN and O-HÁ Á ÁO interactions, which include bifurcated hydrogen bonds, are observed, involving O-H functions as donors and the amine sites and one phenolic oxygen atom as acceptors. All bond lengths and angles found for (I) are in the expected range for organic compounds (Bruno et al., 2004).

Supramolecular features
In the crystal of (I), inversion dimers with R 4 4 (8) ring motifs are formed by pairs of O-HÁ Á ÁO hydrogen bonds (Fig. 3, Table 1). The approximate planes of the ring motifs of the dimers are arranged as stacks along [010] (Fig. 4). Nostacking interactions are observed.  (Wang et al., 2011b). All of these structures are symmetric molecules and the phenol groups have an additional one or two substituents in the para and ortho positions with respect to the O-H function. As observed in (I), the spatial orientations of the phenol arms are influenced by intra-and intermolecular hydrogen bonding. There are no significant differences in the geometrical parameters; The molecular structure of (I), with displacement ellipsoids drawn at the 40% probability level. Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) Àx þ 1; Ày; Àz.

Figure 2
The intramolecular hydrogen bonds (dashed lines) observed in (I).
however, the crystal packing shows distinguishable threedimensional arrangements due to differences in molecular symmetry and intermolecular interactions.

Special details
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 > 2σ(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.