Crystal structure of catena-poly[[[bis(1-benzylimidazole-κN)copper(II)]-μ-sulfato-κ2 O:O′-[tetrakis(1-benzylimidazole-κN)copper(II)]-μ-sulfato-κ2 O:O′] N,N-dimethylformamide disolvate dihydrate]

The crystal structure of the title compound comprises polymeric chains formed by two independent copper(II) polyhedra, [CuN2O2] and [CuN4O2], which are linked by sulfate anions and stabilized by extended hydrogen-bonding, C—H⋯π and π–π interactions.


Chemical context
The exploration of new transition-metal coordination polymers (CPs) is still an ongoing process since this class of molecular materials presents interesting properties and potential applications in adsorption, catalysis, storage, and photoluminescent sensing (Engel & Scott, 2020;Liu et al., 2021;Baruah, 2022;Ma & Horike, 2022). For the design and synthesis of new CPs, metal ions and bridging ligands play an important role, because they influence structural topologies, dimensionalities, and possible functions (Du et al., 2013). In this context, we focused on the copper(II) ion and O-donor sulfate ) and N-donor heterocyclic aromatic ligands for the current study. Copper(II) compounds show interesting electronic and magnetic properties, accompanied by various structural topologies, physical properties and applications (Das & Pal, 2001;Gao & Liu, 2022). The sulfate anion can act as a bridging ligand due to its versatile coordination modes supporting the increase of structural dimensionalities of the CPs (Yotnoi et al., 2014). The presence of mono-and/or bidentate N-donor heterocyclic aromatic imidazole derivatives as ligands in CPs is generally found to increase the extended structures and the stability of the crystal structures through supramolecular interactions such asstacking and C-HÁ Á Á bonding (Krinchampa et al., 2016;Assavajamroon et al., 2019). As previous studies suggest, there is limited research reported for Cu II CPs constructed from mixed sulfate and N-donor imidazole derivatives, for example [Cu(L) 2 (-O 2 SO 2 )] n where L = imidazole (Fransson & Lundberg, 1972;Kumar et al., 2014) and L = N-methylimidazole (Liu et al., 2003). During the current study, we used the imidazole derivative, 1-benzylimidazole (bzi), to investigate its influence on supramolecular interactions in the resulting network.

Structural commentary
The asymmetric unit of the solvated coordination polymer {[Cu(bzi) 3 (-O 2 SO 2 )]ÁH 2 OÁDMF} n comprises two Cu II ions with site symmetry 1 (Wyckoff letters b and d), three bzi molecules (see Fig. S1 in the supporting information), a coordinating sulfate anion, one water and one DMF solvent molecule (Fig. 1). The environments of the two Cu II cations are different. Cu1 is surrounded by two nitrogen donor atoms from two monodentate bzi ligands and two oxygen donor atoms of two different sulfate bridging ligands, resulting in an [N 2 O 2 ] coordination set with a square-planar shape and Cu1-N1 and Cu1-O1 bond lengths of 1.9951 (14) and 1.9564 (12) Å , respectively; the bite angles around Cu1 are in the range 89.25 (6)-90.75 (6) . Cu2 is coordinated by four nitrogen donor atoms from four monodentate bzi ligands and two oxygen donor atoms of two different sulfate bridging ligands, resulting in an [N 4 O 2 ] coordination set with a typically Jahn-Teller-distorted octahedral shape with bond lengths of Cu2-N3 = 2.0210 (15), Cu2-N5 = 2.013 (15) Å , and Cu2-O2 = 2.4912 (12) Å . Both Cu II sites are alternatively connected by bis-monodentately binding and bridging sulfate ligands, -2 O,O 0 , leading to a chain-like structure extending parallel to the c axis, as shown in Fig. 2. The Cu1Á Á ÁCu2 distance within a chain is 6.1119 (4) Å .

Supramolecular features
The crystal structure of the title compound is consolidated by weak interactions such as hydrogen-bonding, C-HÁ Á Á and interactions. Non-classical C-HÁ Á ÁO hydrogen-bonding interactions are found between the C-H donor groups of the Asymmetric unit of the title compound with displacement ellipsoids drawn at the 30% probability level.

Figure 2
Side (a) and top (b) views of the chain-like structure of the title compound extending parallel to the c axis. Hydrogen atoms bound to carbon atoms as well as solvent water and DMF molecules were omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ).

Spectroscopic characterization
The FT-IR spectrum of the title compound ( Fig. S5 in the supporting information) exhibits the characteristic broad bands (centered at 3454 cm À1 ) assigned to the O-H stretching vibration of the solvent water molecule hydrogenbonded to the DMF solvent molecule. Characteristic bands of the bzi ligand are observed at 3142 cm À1 for the aromatic C-H stretching, at 1523 and 1453 cm À1 and in the range of 700-500 cm À1 for the C C, C-N stretching and C-H bending, respectively (Assavajamroon et al., 2019). The strong bands at 1675, 1116 and 713 cm À1 are due to the asymmetric stretching of the bridging sulfate ligand (Wang et al., 2014). The solid-state diffuse reflectance spectrum of the title compound ( Fig. S6 in the supporting information) shows a broad asymmetric band with max at 602 nm (16.60 kK) and a shoulder at about 756 nm (13.24 kK). These bands might be assigned to electronic d ! d transitions, (d xy , d xz , d yz ) ! d x 2 -y 2 and d z 2! d x 2 -y 2, corresponding to a distorted octahedral conformation.

Figure 4
View of interchaininteractions in the title compound along the a axis.

Figure 5
View of the three-dimensional supramolecular network of the title compound. Solvent water and DMF molecules are omitted for clarity.

PXRD and thermal analysis
The plots of the experimental and simulated powder X-ray diffraction (PXRD) patterns of the title compound ( Fig. S7 in the supporting information) show a good match, confirming reproducibility and phase purity. The thermal stability of the title compound has been investigated by means of thermogravimetric analysis with the temperature in the range 303-1073 K under a nitrogen atmosphere. Based on the results (Fig. S8 in the supporting information), the title compound is stable to about 371 K. Above this temperature, the compound starts to decompose by a mass loss of 13%, which corresponds to the loss of solvent water and DMF molecules. The second step of mass loss (65%) corresponds to the release of the remaining coordinating bzi and sulfate ligands. Further increasing the temperature leads to another mass loss (22%) until CuO forms as the final product.

Database survey
According to a search of the Cambridge Structural Database (CSD; version 5.41, November 2019 update; Groom et al., 2016), there are some one-dimensional Cu II coordination polymers containing the sulfate anion as a bridging ligand together with N-donor imidazole-based ligands. The ones most closely related to the title compound are [Cu(imida-zole) 4 SO 4 ] (TIMZCU02; Kumar et al., 2014) and [Cu(Nmethylimidazole) 4 (SO 4 )] (IJEBII; Liu et al., 2003). These two Cu II coordination polymers have the same octahedral [N 4 O 2 ] coordination set around the Cu II ion, while those of the title compound contain alternatively two different Cu II polyhedra, as discussed in the Structural commentary.

Synthesis and crystallization
A methanolic solution (5 ml) of bzi (0.6329 g, 4.0 mmol) was dropped slowly into a methanolic solution (5 ml) of CuSO 4 Á5H 2 O (0.2491 g, 1.0 mmol) under continuous stirring at 333 K over a period of 10 min, resulting in a blue solution. The solution was then filtered and allowed to evaporate slowly under atmospheric conditions at room temperature. After seven days, the solution became viscous, and 10 ml of DMF were added to the solution under continuous stirring at 333 K over a period of 5 min. Stirring was continued until the solution became clear. Finally, the solution was filtered and allowed to evaporate slowly in air at room temperature. Blue crystals of the title compound were obtained within a day (yield 38%, 93.4 mg, based on the Cu II salt).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All C-bound H atoms were calculated and refined using a riding model, with C-H = 0.93 Å for aromatic H atoms (0.97 Å for methyl H atoms), and U iso (H) = 1.2U eq (C) [U iso (H) = 1.5U eq (C)]. The O-bound H atoms of the water molecule were located in a difference-Fourier map, and were refined with an O-H bond length of 0.85 Å , and with U iso (H) = 1.5U eq (O).  program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010).

κN)copper(II)]-µ-sulfato-κ 2 O:O′] N,N-dimethylformamide disolvate dihydrate]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.39 e Å −3 Δρ min = −0.35 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.