Dichloridobis[2-(pyridin-2-yl-κN)-1H-benzimidazole-κN 3]nickel(II) monohydrate

The crystal structure of the nickel(II) dichloride complex of the ligand 2-(pyridin-2-yl)-1H-benzimidazole is described.

In the title complex, [NiCl 2 (C 12 H 9 N 3 ) 2 ]ÁH 2 O, a divalent nickel atom is coordinated by two 2-(pyridin-2-yl)-1H-benzimidazole ligands in a slightly distorted octahedral environment defined by four N donors of two N,N 0chelating ligands, along with two cis-oriented anionic chloride donors. The title complex crystallized with a water molecule disordered over two positions. In the crystal, a combination of O-HÁ Á ÁCl, O-H.ÁO and N-HÁ Á ÁCl hydrogen bonds, together with C-HÁ Á ÁO, C-HÁ Á ÁCl and C-HÁ Á Á interactions, links the complex molecules and the water molecules to form a supramolecular threedimensional framework. The title complex is isostructural with the cobalt(II) dichloride complex reported previously [Das et al. (2011). Org. Biomol. Chem. 9, 7097-7107].

Structure description
Transition-metal-catalyzed transfer hydrogenation (TH) is an effective method of reducing ketones to the corresponding secondary alcohols . Generally, the method is operationally simple, selective, and sources hydrogen from alcohols, thus avoiding high pressures of H 2 gas . Several transition-metal complexes have been studied in catalytic TH and have been used on laboratory and industrial scales. Complexes of precious metals (Rh, Ir, and Ru) have been the preferred catalysts for TH owing to their high activity and commercial availability (Raja et al., 2012;Wang et al., 2015;Li et al., 2015). With growing concern surrounding the economic and environmental impact of using precious metals in chemistry, a renewed interest in Earth-abundant metal catalysis has prompted our research into TH catalysts featuring first-row transition metals, such as iron, cobalt, or nickel (Morris, 2009; Garduñ o & García, 2017; Abubakar data reports et al., 2018;Chen et al., 2010). Recognizing that nickel(II) complexes of chiral bis(phosphines) have been utilized in asymmetric TH, we turned our attention to nickel(II) complexes of the commercially available ligand 2-(pyridin-2yl)-1H-benzimidazole.
The asymmetric unit of the title complex consists of a Ni II ion coordinated by two 2-(pyridin-2-yl)-1H-benzimidazole ligands bound in a 2 -N,N arrangement, along with two cisoriented anionic chloride donors (Fig. 1). The complex crystallized as a monohydrate with the water molecule disordered over two sites (Fig. 1). The metal center adopts a slightly distorted octahedral geometry. The pyridyl N-donor atoms are trans-disposed [N1-Ni1-N4 = 170.66 (8) ], while the chloride ligands are cis-disposed [Cl2-Ni1-Cl1 = 93.04 (2) ]. The disordered water molecules are linked to the complex molecule by O-HÁ Á ÁCl hydrogen bonds, and water H atom H2B is directed to the centroid of the C7-C12 ring ( Fig. 1, Table 1).
In the crystal, extensive hydrogen bonding is observed involving the disordered water molecule, the ligand NH groups and the chloride ions ( Fig. 2a and 2b and Table 1). The result is the formation of a supramolecular three-dimensional network (Fig. 3). There are also C-HÁ Á ÁO and C-HÁ Á Á interactions present (Table 1) Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Hydrogen-bonding networks involving, (a) the discorded water molecule, and (b) the N-HÁ Á ÁCl hydrogen bonds. For clarity, only the H atoms involved in hydrogen bonding (dashed lines; Table 1) have been included.

Figure 3
A view along the c axis of the crystal packing of the title complex. For clarity, only the H atoms involved in hydrogen bonding (dashed lines; Table 1) have been included.

Figure 1
The molecular structure of the title complex, with atom labeling. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are shown as orange dashed lines and the O-HÁ Á Á interaction as a red arrow (Table 1).

Synthesis and crystallization
The reaction scheme for the synthesis of the title complex is given in Fig. 5. A solution of 2-(pyridin-2-yl)-1H-benzimidazole (0.15 g, 0.78 mmol) in ethanol (5 ml) was added dropwise to a stirring ethanolic solution of bis(triphenylphosphine)nickel(II) dichloride (0.50 g, 0.76 mmol). The mixture was stirred at room temperature for 24 h. The resulting mixture was concentrated and the product isolated by addition of diethyl ether (5 ml) giving a light-brown solid. Yield: 0.27 g (68%

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The complex crystallized as a monohydrate with the water molecule disordered over two sites (O1 and O2); occupancies fixed at 0.5 each.

Figure 5
Reaction scheme for the synthesis of the title complex.