SYNTHESIS AND CRYSTAL STRUCTURES OF A POLIAZA RECEPTOR MACROLIGAND: 1,3-BIS(2-NITROBENZYLIDENEAMINO)PROPAN-2-0L

The asymmetric unit of the title compound C11H16N,0 5 , contains one molecule of the compound (L3) ( 1,3-bis(2-nitrobenzylideneamino )propan-2-ol). The molecule shows a chiral C atom but the absolute structure was not possible to be determined by X-ray diffraction. The molecule shows intermolecular hydrogen bonding involving the hydroxy group and an imine nitrogen atom of a symmetry related molecule. The molecular distribution shows weak interactions between oxygen atoms of the nitro groups and two different C-H groups of benzene rings. The extended weak H bond formation, using the N0 2 groups, probably gives a more stable crystal structure. The molecule represents a precursor of a polyaza macrocylic ligands.


lntroduction
The new Schiff base acyclic ligand in the title compound {L3), has been synthesized as a receptor and a chemical precursor of a variety of acyclic and macrocyclic multidentate ligands and metal complexes [1][2][3][4].
The polydentate azamacroligands have been of considerable interest in terms of structure chemistry, affinity with heavy metals and environmental and technological applications [5][6][7][8]. During the past years an extensive work has been carried out in the synthesis of this type of compounds which has culminated in the production of materials used in the extraction of heavy metals, as a catalyst, in the construction of diodes and molecular memories [9][10][11] is why the importance of both its synthesis as determining its structure on this applications can predict.

Synthesis
AII the reactants used to obtain the ligand were analytic grade from Sigma-Aldrich Chemical Company lnc., USA. IR spectra were measured on an IR-FT Nicolet 550 Model Magna-IR Spectrometer and ATR-FT Perkin Elmer Spectrum 1. Elemental analyses (C, H, N) were performed using a Perkin Elmer lnstruments Series 11 2400 CHNS-O. Single crystals diffraction data were collected on a Siemens P4 diffractometer.
In arder to obtain L3, 1,3-Diaminopropan-2-ol (penOH) (3.61 g) was added to a dissolution of 2nitrobenzaldehyde (DNB) (12.08 g) in ethanol (80 mL). The mixture was stirring for 25 minutes anda yellow salid carne out. The salid was filtered off, and purified. Suitable crystals were obtained as colorless plates from ethanol solution by slow evaporation of the solvent at 298 K. The title compound was characterized by IR (KBr disc) and elemental analysis, which are in agreement with the X-ray structure.

X-ray diffraction
Pertinent crystal data and other crystallographic parameters are listed in Table 1. Diffraction data were collected at room temperature (294-298 K) using the Mo-K radiation (=0.71073 A), through standard procedures [12]. Raw data were corrected far absorption effects, either using suitable 41-scans data [13], ora Gaussian face-indexed correction, if available [14].

Crystal data 1,3-Bis(2-nitrobenzylideneamino)propan-2-ol
Data collection Refinement of F2 against ali reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors (gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.
Ali 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.
Hydrogen atoms bonded to C atoms were included in calculated positions, using the riding method, with C-H distances constrained to 0.93 (aromatic CH) and 0.97 A (methylene CH 2 ) and Uiso(H) = 1.2Ueq( carrier C). The Hydrogen atom of the OH group was not constrained but let it refined isotropically.
The molecule shows a chiral atom, C9, but the absolute structure was not possible to be determined because the compound is organic with no heavy atoms in it. The molecule shows an intermolecular hydrogen bond involving the OH group and a symmetry related N atom of an imine group (O3-H3B···N3 2.23 (8) A). There exist two weak H bond between a C-H of a benzene ring with symmetry related O of NO2 group (N1-O2···H3C 2.489 and N4-O4···H15A 2.450 A respectively) as shown in Fig 1 b. The extended weak H bond formation, using the NO 2 groups, probably gives a more stable crystal structure. The X-ray structure agree well with elemental analysis.
(b) Figure 1a. Molecular structure of (1). Displacement elli¡:,_,u,u::> c11tl arawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. 1 b. Molecular packing structure of (1) showing hydrogen bond and two week interactions between O of nitro groups and H atoms of a C-H groups of the benzene rings (dashed bonds).

Acknowledgments
Authors thank to PAICYT of the UANL, for support of this work [project number CA-1260-06].

5.Appendix
The following data are included in Appendix Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (A2) Atomic displacement parameters (A2) Geometric parameters (A, º)