Poly[bis[μ2-4,4′-bis(imidazol-1-ylmethyl)biphenyl-κ2 N:N′]dichloridonickel(II)]

The crystal structure of a two-dimensional metal–organic compound constructed from 4,4′-bis[(1H-imidazol-1-yl)methyl]-1,1′-biphenyl (BIMB) and nickel ions is described. Each BIMB ligand adopts a linear linker to connect Ni2+ ions, forming a layer with an sql network. In the crystal, neighboring layers repeat in an ABAB stacking mode, and weak intermolecular C—H⋯Cl hydrogen bonds between alternate layers lead to a three-dimensional, twofold interpenetrated, supramolecular framework with a pcu topology net.


Structure description
Over the last two decades, imidazole and its derivatives have attracted a lot of attention as N-heterocyclic aromatic ligands, since they can easily form metal-imidazole frameworks with special luminescent, magnetic and favorable gas-adsorption abilities (Banerjee et al. 2008;Zhang et al. 2012;Zhu et al. 2012;Chen et al. 2014). As an extended imidazole-type linker, the flexible ligand 4,4 0 -bis[(1H-imidazol-1-yl)methyl]-1,1 0 -biphenyl (BIMB) exhibits a geometrical diversity with cis or trans conformations, leading to diverse structures of coordination compounds. Until now, most reported metal-organic compounds based on BIMB ligands have employed organic multicarboxylates as coligands because BIMB is a neutral ligand and another anion is needed to balance the charge requirement to form a neutral framework. Common inorganic anions such as Cl À , Br À , I À , NO 3 À , SO 4 2À , N 3 À , etc. can also be used as co-ligands to balance the charge requirement. However, only ten examples of neutral, BIMB-based metal-organic compounds have been reported [according to the Cambridge Structural Database (CSD, Version 5.43 with update of March, 2022; Groom et al., 2016) with inorganic anions as coligands.

data reports
The asymmetric unit of the title compound, [NiCl 2 (C 20 H 18 N 4 ) 2 ] n , contains one half nickel(II) ion, two half BIMB ligands and one chloride ion (Fig. 1). The nickel(II) ion sits on an inversion center and is coordinated by four imidazole nitrogen atoms from four different BIMB ligands [Ni-N = 2.100 (3)-2.108 (3) Å ] and two chloride ions [Ni-Cl = 2.4793 (11) Å ], forming a slightly distorted octahedral geometry. In the crystal, the BIMB ligands have twofold rotational symmetry, being bisected by rotation axes, and the biphenyl groups are not coplanar, with dihedral angles of 33.21 (10) and 35.4 (10) between the ring planes. The dihedral angles between the imidazole ring plane and the average plane of the biphenyl group are 87.71 (14) and 81.93 (14) . Each BIMB ligand exhibits a cis-conformation relative to the average plane of the biphenyl group, and acts as a linear linker between Ni 2+ ions, which gives a corrugated two-dimensional layer structure with an sql (square lattice) network as illustrated in Fig. 2. The layers stack in an -ABAB-mode, and the Ni 2+ ion in one layer is located at the center of the grid of adjacent layers. Thus, there are no residual solvent-accessible voids in this compound. Alternate layers between A-A or B-B layers are further linked by C-HÁ Á ÁCl hydrogen bonds (Table 1, Figs. 3 and 4) to form a three-dimensional, twofold interpenetrated, supramolecular framework with a pcu (primitive cubic) topology network (Fig. 5).
The structure of the title compound is isomorphous to that of the cadmium(II) compound, whose structure has been studied at 200 K (Zhao et al. 2003). This structural similarity of the Cd II and Ni II compounds is somewhat unexpected in view of the different effective radii of these ions (Shannon & Prewitt, 1969, 1970, which causes the differences between M-N distances [Cd--N = 2.339 (2)-2.364 (2) Å in the cadmium(II) compound]. It should also be noted that the title compound was easily obtained within one day using solvothermal conditions, whereas the cadmium(II) compound was obtained after several weeks using a slow-diffusion method.

Figure 3
The packing of the title compound viewed along the b axis. H atoms are omitted for clarity.

Figure 4
View of the C-HÁ Á ÁCl hydrogen bonds (dashed lines) between alternate layers along the c axis. H atoms not involved in hydrogen bonding are omitted.

Synthesis and crystallization
A mixture of NiCl 2 ÁH 2 O (24 mg, 0.1 mmol), BIMB (62 mg, 0.2 mmol) and DMF (6 ml) was added to a 20 ml glass vial and then ultrasonicated for 1 minute. The vial was capped tightly and placed in an oven at 120 C. After 12 h, the vial was removed from the oven and allowed to cool to room temperature. The light-green transparent needle-like crystals were collected by filtration, washed with DMF and dried under ambient conditions. About 34 mg of product was obtained (44% yield based on BIMB ligand). The phase purity of the bulk sample was verified by powder X-ray diffraction (PXRD). The experimental and simulated powder XRD patterns of the title compound are displayed in Fig. S1 of the supporting information. Their peak positions are in good agreement with each other, indicating the phase purity of the title compound (slight intensity mismatches due to preferred orientation are observed).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Funding information
Funding for this research was provided by: the Research Training Program (KX2021018) for College Students of Yunnan Normal University.

Figure 5
The twofold interpenetrated supramolecular framework with a pcu topology network connected by C-HÁ Á ÁCl hydrogen bonds (shown as dashed lines). Computer programs: CrysAlis PRO (Rigaku OD, 2015), SHELXT2014/5 (Sheldrick, 2015a), SHELXL2018/3 (Sheldrick, 2015b) and DIAMOND (Brandenburg, 1999 where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.61 e Å −3 Δρ min = −0.27 e Å −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. All H atoms were placed in idealized positions (C-H = 0.93 Å for aromatic H; C-H = 0.97 Å for methylene H) and refined as riding atoms with U iso (H) = 1.2U eq (C).