2,2′-(Iminodimethylene)dibenzimidazolium bis(perchlorate) methanol solvate

In the title compound, C16H17N5 2+·2ClO4 −·CH3OH, the dihedral angle between the two benzimidazolium ring systems is 34.6 (1)°. The anions and solvent molecules are linked to the cation by N—H⋯O hydrogen bonds. In the crystal structure, the combination of N—H⋯O and O—H⋯O hydrogen bonds results in two-dimensional layers running parallel to the (010) plane; these are in turn linked by π–π interactions, forming a three-dimensional network.


Related literature
Data collection: SMART (Bruker, 2001); cell refinement: SAINT-Plus (Bruker, 2001); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: PLATON.  -(benzimidazol-2-ylmethyl)]amine (IDB) and its analogs have been utilized extensively in the synthesis of various metal complexes to mimic certain biological activities; these include superoxide dismutase (Liao et al., 2001), DNA probe (Girasolo et al., 2000), alkaline phosphatase (Young et al., 1995). In IDB, each benzimidazole (bzim) arm possesses one imine N atom, one amine NH group and, at the centre, an NH group. The two imine N atoms can chelate metal ions, while the three NH groups can act as hydrogen bond donors. In the absence of metal coordination, the two imine N atoms can also act as hydrogen bond acceptors. The easily formed coordination and hydrogen-bonding interactions allow the central acyclic -CH 2 -NH-CH 2 -unit to possess various steric arrangements. In our and other reported organic complex analogs (Meng et al., 2006a;Meng et al., 2006b;Meng et al., 2005;Zheng et al., 2005;Liu et al., 2004;Tarazon Navarro et al., 2003) we find that IDB preferentially adopts a more extended conformation, with the two bzim groups pointing away from each other. However, in most examples of metal-complexes it adopts a more crowded conformation, with the two bzim units bending towards the same side of the central acyclic linkage (Berends & Stephan, 1984;Xu et al., 2007;Adams et al., 1990). With the aim of gaining more insight into the influence of solvents and anions on the crystal structure, we have synthesized H 2 IDB 2+ .2ClO 4 -.CH 3 OH and report its molecular and supramolecular structure in this communication.
The two imine N atoms on both bzim arms are protonated, as confirmed by the residual electron peaks around the imine determined at low temperature by Tarazon Navarro & McKee (2003). In the title compound, the dication adopts a somewhat folded conformation and the dihedral angle between two bzim groups is 34.6 (1)°. This angle is comparable with those in Two imine N atoms (N2 and N5) act as hydrogen bond donors, via atoms H2A and H5A, respectively, to atoms O8/O9 and O4/O5, thereby generating four hydrogen bonds, each two forming an R 2 1 (4) ( Fig.1) motif (Bernstein et al., 1995). The other two N atoms (N3 and N4) on bzim also act as hydrogen bond donors, forming intermolecular hydrogen bonds of R 1 2 (10) motif, to the methanol solvent molecule. The methanol molecule donates its hydroxyl H atom to atom O6, forming a relatively strong O-H···O hydrogen bond. There is a pseudo-mirror plane passing through the central NH group and the solvent C and O atoms.
In the crystal structure, the component ions are assembled into a three-dimensional network by a combination of N-H···O, O-H···O hydrogen bonds and π-π interactions which can be analyzed in terms of several substructures. Firstly, by the six cooperative hydrogen-bonding interactions (Table 1), the discrete dications, anions and methanol molecules are supplementary materials sup-2 joined together, forming a relatively independent neutral unit. These neutral units are linked together by N1···O7 (-1/2 + x,1/2 -y,-1/2 + z) and O1···O6 (1/2 + x,1/2 -y,-1/2 + z) hydrogen bonds related by the n-glide plane at y =1/4, forming a two-dimensional layer parallel to the (010) plane in the domain of -0.259 < y < 0.759 (Fig.2). Secondly, by π-π stacking interactions, adjacent two-dimensional layers are interlinked into a simple three-dimensional network. The geometric details of the π-π stacking interactions are listed in Table 2. A CSD (Version 1.9, September 2006 release; Allen, 2002;Bruno et al., 2002) study indicates that π-π stacking interactions play a critical role in stabilizing the crystal structures of organic and metal-organic compounds containing poly-bzim groups. For instance, in HIDB + .ClO 4 - (Liu et al., 2004), the N-H···N and N-H···O hydrogen bonds link the component ions into one-dimensional chains. However, π-π stacking interactions between adjacent bzim groups link the molecules into a three-dimensional network.

Experimental
All the reagents and solvents were used as obtained without further purification. Bis(benzimidazol-2-yl-methyl)amine (IDB) was prepared according to the method described by Adams et al. (1990). 2 g of the powdered title compound were dissolved in 15 ml methanol and adjusted to pH 5 using HClO 4 . Colorless crystals were obtained as blocks by slowly evaporating the solvent over a period of several days.

Refinement
H atoms bonded to C atoms were located in difference maps and subsequently treated as riding, with C-H distances of

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.