Bis(benzimidazol-1-yl)methane dihydrate

The bis(benzimidazol-1-yl)methane molecule of the title compound, C15H12N4·2H2O, displays a trans conformation with a twofold axis running through the methylene C atom. Two adjacent water molecules are bonded to this molecule through O—H⋯N hydrogen bonds, forming a trimer. Adjacent trimers are connected together via C—H⋯O interactions, forming a chain running along the b-axis direction. Two such chains are joined together via π–π interactions [centroid–centroid distance = 3.556 (2) Å], forming double chains, which are connected via the water molecules through C—H⋯O associations, forming a sheet structure. The sheets are stacked on top of each other along the a-axis direction and connected through O—H⋯O and C—H⋯O interactions, forming a three-dimensional ABAB layer network structure.

The bis(benzimidazol-1-yl)methane molecule of the title compound, C 15 H 12 N 4 Á2H 2 O, displays a trans conformation with a twofold axis running through the methylene C atom. Two adjacent water molecules are bonded to this molecule through O-HÁ Á ÁN hydrogen bonds, forming a trimer. Adjacent trimers are connected together via C-HÁ Á ÁO interactions, forming a chain running along the b-axis direction. Two such chains are joined together viainteractions [centroid-centroid distance = 3.556 (2) Å ], forming double chains, which are connected via the water molecules through C-HÁ Á ÁO associations, forming a sheet structure. The sheets are stacked on top of each other along the a-axis direction and connected through O-HÁ Á ÁO and C-HÁ Á ÁO interactions, forming a three-dimensional ABAB layer network structure.   Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1; Ày þ 1; Àz þ 1; (ii) Àx; Ày; Àz þ 1; (iii) x þ 1; y þ 1; z þ 1; (iv) Àx þ 1; Ày; Àz þ 1. We gratefully acknowledge financial support by the Education Office Foundation of Zhejiang Province (project No. Y201017321) and the innovation project of Zhejiang A & F University.

Comment
Bridged imidazole derivatives can be used as multidentate N-donor ligands in constructing functioned coordination polymers, such as nonlinear optical materials (Chang et al., 2005), novel hybrid inorganic organic photoactive materials (Wen et al., 2006) and novel metal-organic frameworks (Fan et al., 2004;Abrahams et al., 2002). The ligands bearing alkyl spacers are a good choice of a N-donor ligand, and the flexible nature of the spacers allows the ligands to bend and rotate when coordinating to metal centers so as to conform to the coordination geometries of the metal ions. Significant progress has been achieved by us (Jin et al., 2007) and others (Ma et al., 2003) in this area.
However, the archived data on bridged benzimidazole derivatives bearing the methylene spacer have been rare. As an extension of our study in bridged imidazole derivatives, here in this paper, we report the structure of bis(benzimidazol-1yl)methane dihydrate.
X-ray diffraction analysis indicated that in the title compound there are one bis(benzimidazol-1-yl)methane and two lattice water molecules (Fig. 1). All bond distances and angles are in the normal range. The r.m.s. deviation of the benzimidazole ring bearing the N1 and N2 atoms is 0.0056 Å. The r.m.s. deviation of the benzimidazole ring bearing the N3 and N4 atoms is 0.00123 Å. Both benzimidazole rings make a dihedral angle of 106.9 (3)° with each other. The bis(benzimidazol-1-yl)methane displays trans conformation with a twofold axis running through atom C1. Two water molecules are bonded to the bis(benzimidazol-1-yl)methane molecule through O-H···N hydrogen bonds (Table 1) to form an adduct. These adjacent adducts are connected together via C-H···O interactions to form a one-dimensional chain running along the b axis direction.
There are two kinds of C-H···O associations (Table 1), one is arising from the N-CH-N of the benzimidazole moiety, another from the benzene C12-H12. In this chain the bis(benzimidazol-1-yl)methane molecules are parallelly arranged.
Two such chains were joined together via the π-π interactions to form a double chain structure (Cg(1)···Cg(2) i distance = 3.556 (2) Å, Cg(1) is the centroid of ring N1,N2, C9-C11, Cg(2) is the centroid of ring C10-C15, symmetry operation: (i) 1 -x, 1 -y, 1 -z). The bis(benzimidazol-1-yl)methane molecules at these two chains are arranged antiparallel. The double chains were connected together via the water molecules through the C-H···O associations to form a two-dimensional sheet extending along the direction forming a dihedral angle of ca 60 ° with the bc plane (Fig. 2). Such sheets were further stacked along the a axis direction via the O-H···O (between two water molecules with O···O separations of 2.911 Å) and C-H···O interactions to form a three-dimensional ABAB layer network structure.

Experimental
The starting material bis(benzimidazol-1-yl)methane was prepared according to the published procedure (Lavandera et al., 1988). A solid of bis(benzimidazol-1-yl)methane (24.8 mg, 0.10 mmol) in 10 ml of 95 percent EtOH was stirred at room temperature to dissolve it, then the solution was filtered into a test tube. The solution was left standing at room temperature for several days, colorless block crystals were isolated after slow evaporation of the solution in air at ambient temperature.
The crystals were collected and dried in air to give the title compound. isotropically. Other H atoms were positioned geometrically with C-H = 0.93-0.97 Å, and constrained to ride on their parent atoms with U iso (H) = 1.2 U eq (C). Fig. 1. The structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.