Tris(1H-benzimidazol-2-ylmethyl)amine methanol trisolvate

In the title solvate, the tertiary amine adopts a stair-like conformation, with all imine and amine groups forming N—H⋯O and O—H⋯N hydrogen bonds with the lattice methanol molecules.

The structure of the tertiary amine tris(1H-benzimidazol-2-ylmethyl)amine (C 24 H 21 N 7 , abbreviated ntb) has been previously reported twice as solvates, namely the monohydrate and the acetonitrile-methanol-water (1/0.5/1.5) solvate, both with the tripodal conformation formed via multiple hydrogen bonds. Now, we report the trimethanol adduct, ntbÁ3CH 3 OH, where the amine has the stair conformation featuring one benzimidazole group oriented in the opposite direction from the other two. The asymmetric unit contains one-half amine, completed through the mirror plane m in space group Pmn2 1 to form the ntb molecule, with the H atom for each imidazole moiety equally disordered between both N sites available in the imidazole ring. The asymmetric unit also contains one and a half methanol molecules, one being placed in general position with the hydroxy H atom disordered over two sites with occupancy ratio 1:1, while the other lies on the m mirror plane, and has thus its hydroxy H atom disordered by symmetry. As in the previously reported solvates, all imine and amine groups of the ntb molecules and the methanol molecules are involved in N-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds. In the title compound, however, the involved H atom is systematically a disordered H atom provided by an imidazole group or a methanol molecule.

Structure description
The tertiary amine tris(1H-benzimidazol-2-ylmethyl)amine (abbreviated ntb in the literature) is a molecule that can act as a tetradentate ligand through its three imine N atoms and the central amine one, exhibiting thus a versatile and rich coordination chemistry, where the molecule adopts a tripodal coordination mode to the metal (e.g. data reports Nakata et al., 1997;Kwak et al., 1999;Rheingold & Hammes, 2015). In addition, it is a potential hydrogen-bond donor through its three NH amine groups (Su et al., 2000). Similar tripodal behaviour has been found in ntb solvent adducts such as the monohydrate, C 24 H 21 N 7 ÁH 2 O, and the acetonitrilemethanol-water (1/0.5/1.5) solvate, C 24 H 21 N 7 ÁC 2 H 3 NÁ-0.5CH 4 OÁ1.5H 2 O. In both cases, ntb forms two N-HÁ Á ÁO and one O-HÁ Á ÁN hydrogen bonds with a solvent water molecule (Zhang et al., 2005). In addition, the imine N atoms of the benzimidazolyl arms can be protonated with HNO 3 , and the resulting trication then adopts a stair arrangement, where the N atoms of the benzimidazolium fragments interact with anions NO 3 À through N-HÁ Á ÁO hydrogen bonds (Cui, 2011). The present report deals with a new ntb solvate. When this amine is crystallized from methanol solution, the solvate ntbÁ3CH 3 OH is obtained, in space group Pmn2 1 . The ntb molecule has one benzimidazolyl arm placed over the mirror m plane (N2/C1Á Á ÁC5 group), while the other crystallographically independent arm (N3/N4/C6Á Á ÁC13 group) is placed in general position (Fig. 1). As a consequence, instead of the common tripodal molecular geometry (approximate point group: C 3v ), the ntb molecule adopts a stair-like conformation (point group: C s ), with one benzimidazole group oriented in the opposite direction from the other two (Fig. 2). The imidazol H atom of the arm bisected by the mirror plane, H2, is disordered by symmetry so that the -bond of this imidazole ring is delocalized over C2 . . . N2 and C2 . . . N2 i bonds [symmetry code: (i) 1 À x, y, z], with a bond length of 1.342 (3) Å . The same kind of delocalization is observed in the other ntb arm, with the imidazolic H atom equally disordered over N3 and N4, and identical bond lengths C7 . . . N3 and C7 . . . N4 of 1.338 (4) and 1.335 (4) Å . In other words, amine and imine sites in ntb are indistinguishable (Fig. 2). As clearly observed in Fig. 1, the methanol molecules of crystallization are recognized by the ntb molecule in a similar way as in the previously described ionic compound ntbÁ3HNO 3 (Cui, 2011). The methanol molecules are sandwiched between two ntb arms, in order to form three O-HÁ Á ÁN and three N-HÁ Á ÁO hydrogen bonds (Table 1), with OÁ Á ÁN separations spanning a short range, from 2.722 (4) to 2.767 (3) Å . Given that all imidazolic H atoms are disordered, the same holds for hydroxy H atoms: the first methanol molecule C14-O1 lies in the mirror m plane, with its H atom disordered by symmetry (H1); the second methanol molecule, C15-O2, placed in general position, has its hydroxy H atom disordered over two sites, H2A and H2B, with half occupancy (Fig. 2). With this arrangement, any physically unreasonable HÁ Á ÁH contact is avoided, despite all heteroatoms, except N1, being involved in efficient hydrogen bonds. The complete adduct ntbÁ3CH 3 OH thus features three similar ring motifs R 2 2 (10) sharing the central N1 atom (Fig. 2).
The supramolecular structure is further extended by onedimensional stacks of ntb molecules in the [011] direction. The stair conformation adopted by ntb allows rather closeinteractions between benzimidazole rings along the stacks: mean plane separations for neighbouring rings along a stack are 3.782 (2) and 3.454 (2) Å for the N2/C2-C5 and N3/N4/ C7-C13 benzimidazole rings, respectively.

Figure 2
View of the title compound rotated by ca 90 in comparison with Fig. 1, showing the stair-like conformation for ntb. All H atoms bonded to heteroatoms are shown. Green H atoms are disordered by symmetry, while purple H atoms are positionally disordered, all having the same half occupancy. The orange line is the trace of the m mirror normal to the a axis. Table 1 Hydrogen-bond geometry (Å , ). (4) 156 (3) Symmetry code: (i) Àx þ 1; y; z.

Figure 1
Molecular structure of the title compound, with displacement ellipsoids for non-H atoms at the 50% probability level. For all disordered H atoms, a single site was retained, in order to emphasize the O-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds (dotted lines). Non-labelled atoms are generated by the symmetry operation 1 À x, y, z.

Synthesis and crystallization
The title compound was prepared through the solid-solid condensation reaction of nitrilotriacetic acid (1 g, 5.2 mmol) and o-phenylenediamine (1.7 g, 15.7 mmol), both reactants contained in a round-bottom flask provided with a septum connected to the outside through a needle, which was maintained at 463-473 K in a sand bath for 1 h. As the heating progressed, a dark-brown solution formed, which solidified when the temperature returned to 298 K. Then, 0.7 g of activated carbon and 20 ml of methanol were added and the mixture refluxed for 2 h. The still hot mixture was filtered in a

Special details
Refinement. All C-bonded H atoms were placed in calculated positions and refined as riding atoms, while H atoms bonded to N (H2, H3, H4) and O sites (H1, H2A, H2B) were found in difference maps, and refined with free coordinates and occupancy fixed to 1/2. Corresponding bond lengths were restrained to O-H = 0.85 (2) and N-H = 0.90 (2) Å.