2,2′,2′′-(Nitrilotrimethylene)tris(1H-benzimidazol-3-ium) trinitrate

In the title compound, C24H24N7 3+·3NO3 −, the cation exhibits a distorted propeller-like conformation in which the benzimidazolium fragments form dihedral angles of 9.4 (1), 10.7 (1) and 19.1 (1)° with each other. In the crystal, intermolecular N—H⋯O hydrogen bonds link cations and anions into double ribbons propagated in [100]. Weak intermolecular C—H⋯O interactions further consolidate the packing.


Comment
The tripodal ligands derived from the Schiff-base condensation with tris(2-aminoethyl)amine (H 3 ntb) are of particular interest since the benzimidazole ring in a terpyridine-like ligand allows easy derivation and incorporation in segmental di-and trileptic ligands used as building blocks in self-assembling processes (Zheng et al., 2007). A blue-emitting LED device was fabricated using one ntb cerium complex (Zheng et al., 2007) et al., 2005).the ntb adopts a tripodal 'mode to form hydrogen bonds with a solvent water molecule via N-H···O and O-H···N hydrogen bond. As a part of our study of the assembly of supramolecular aggregates with ntb-related compounds, we report here the synthesis and crystal structure of the title compound (I).
In (I) (Fig. 1), the three free N atoms were all pronated, and ntb adopts a tripodal mode to form strong N-H···O hydrogen bonds (Table 1) with O atoms of three nitrate anions building the 1-D chains along the a axis. In the cation, three benzimidazole rings form in pairs the dihedral angles in the region 9.4 (1) to 19.1 (1)°. There are also some weak C-H···O inter-and intramolecular interactions, which further stabilize the structure of (I).

Experimental
Tris(2-aminoethyl)amine was prepared from the condensation reaction between nitrilotriacetate and 1,2-diaminobenzene in diethylene glycol (yield 73%). Single crystals of (I) suitable for X-ray analysis were obtained by slow evaporation from a 50% nitric acid solution at room temperature.

Refinement
C-bound H atoms were geometrically positioned with C-H distances of 0.93-0.97 Å. and refined as riding, with U iso (H) = 1.2 U eq (C). N-bound H atoms were located in difference Fourier maps and refined isotropically, with N-H bond length restrained to 0.87 (2) Å.  supplementary materials sup-3

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.