catena-Poly[[tetrakis(3,5-dimethyl-1H-pyrazole-κN 2)copper(II)]-μ2-sulfato-κ2 O:O′]: crystal structure and Hirshfeld surface analysis of a CuII coordination polymer

The title coordination pyrazole-containing coordination polymer, was synthesized using a one-pot reaction of copper powder, anhydrous copper(II) sulfate and 3,5-dimethyl-1H-pyrazole (Hdmpz) in acetonitrile under ambient conditions. The crystal structure is built up from packed parallel polymeric chains, which are stabilized by an extensive hydrogen-bond network, which forms with the participation of bridging sulfate ligands.

The title coordination polymer, [Cu(SO 4 )(C 5 H 8 N 2 ) 4 ] n , was synthesized using a one-pot reaction of copper powder, anhydrous copper(II) sulfate and 3,5dimethyl-1H-pyrazole (Hdmpz) in acetonitrile under ambient conditions. The asymmetric unit can be described as a chain consisting of four [Cu(SO 4 )(Hdmpz) 4 ] formula units that are connected to each other by a 2sulfato-bridged ligand. The octahedral coordination geometry (O 2 N 4 ) of all copper atoms is realized by coordination of four pyrazole ligands and two sulfate ligands. Four pyridine-like N atoms of the pyrazole ligands occupy the equatorial positions, while two oxygen atoms of two sulfate ligands are in axial positions. As a result of the sulfate ligand rotation, there is a pairwise alternation of terminal O atoms (which are not involved in coordination to the copper atom) of the SO 4 tetrahedra. The CuÁ Á ÁCu distances within one asymmetric unit are in the range 7.0842 (12)-7.1554 (12) Å . The crystal structure is built up from polymeric chains packed in a parallel manner along the b-axis direction. Hirshfeld surface analysis suggests that the most important contributions to the surface contacts are from HÁ Á ÁH (74.7%), HÁ Á ÁO/OÁ Á ÁH (14.8%) and HÁ Á ÁC/ CÁ Á ÁH (8.2%) interactions.

Chemical context
The synthesis, structure and properties of metal complexes, including coordination polymers, is an important area of chemical research. The nature of the anion, which is part of a coordination compound, is one of several factors that has a great influence on the final structural topology of the complexes (Mondal et al., 2009;Mahmoudi et al., 2007;Kwak et al., 2008;Balić et al., 2018). A large number of coordination compounds have been synthesized and studied due to the development of supramolecular chemistry and the study of self-assembly of metal complexes with organic molecules, such as pyrazoles. These molecules have long been recognized as useful ligands for studying transition-metal coordination chemistry (Mihailov et al., 1974;Nicholls et al., 1971;Reedijk, 1971Reedijk, , 1970aReedijk & Smit, 1971;Singh et al., 1973;ten Hoedt et al., 1982). Pyrazole-based ligands are used to construct supramolecular architectures due to the presence of a pyrrole NH group in the pyrazole ring, which is not necessarily coordinated by a metal atom, but may act as a donor of hydrogen bonds. In addition, substituents on the pyrazole ring can also be involved in hydrogen-bond interactions. These facts are very important because there is a noticeable influence of hydrogen bonding on coordination compound assembly (Di Nicola et al., 2007;Brewer et al., 2020;Burrows et al., 2011). The crystal packing of coordination polymers also depends on the different solvents employed, although not necessarily incorporating the solvents as crystallization molecules . Reaction of a metal salt with an organic ligand is a popular way for the synthesis of coordination compounds, including metal coordination polymers (Gogoi et al., 2019;Shen et al., 2004), but there are many types of coordination compounds and the methods of synthesis are varied (House et al., 2016). In this article we report the preparation of the coordination polymer catena-poly [[tetrakis(3,5-dimethyl-1H-pyrazole-N 2 )copper(II)]-2 -sulfato-2 O:O 0 ] using the direct synthesis method, which is based on oxidative dissolution of a powdered metal in the presence of an organic ligand (Kokozay et al., 2018;Li et al., 2021).

Structural commentary
The title coordination polymer crystallizes in the orthorhombic Pna2 1 space group. The asymmetric unit is a chain consisting of four [Cu(Hdmpz) 4 SO 4 ] formula units ( Fig. 1) that are connected to each other by a 2 -sulfato-bridged ligand along the b-axis direction (Fig. 2). Each mononuclear unit [Cu(Hdmpz) 4 SO 4 ] consists of four 3,5-dimethyl-1Hpyrazole molecules, which are coordinated in a monodentate way, and one sulfate ligand that is connected by one oxygen atom to the copper ion. The octahedral coordination environment of each copper atom consists of four pyridine-like nitrogen atoms of Hdmpz ligands, which occupy the equatorial positions, and two oxygen atoms of two SO 4 ligands, which are in axial positions. The difference in lengths of the axial Cu-O and equatorial Cu-N bonds is at least 0.235 Å . Bond lengths between the central atom and the nitrogen atoms in the equatorial position are approximately the same [in the range 2.028 (6) to 2.054 (6) Å ]. The N1, N3, N5 and N7 nitrogen atoms slightly deviate from of the equatorial plane [by À0.088 (3) Å for N1, 0.069 (3) Å for N3, 0.067 (3) Å for N5 and À0.086 (3) Å for N7]. The Cu1 atom is out of the equatorial plane, formed by four nitrogen atoms, by 0.038 (3) Å . The N-Cu-N angles are practically right angles, in the range of 88.0 (2)-91.2 (2) . The intermetallic CuÁ Á ÁCu distances between two neighboring [Cu(Hdmpz) 4 SO 4 ] fragments within one asymmetric unit are in the range 7.0842 (12)-7.1554 (12) Å while the interchalcogenic SÁ Á ÁS distances are in the range 7.166 (2)-7.223 (2) Å . Bridging oxygen atoms of sulfate ligands, which bind [Cu(Hdmpz) 4 SO 4 ] formula units, are arranged in a spiral along the b axis (Fig. 3).
The molecular structure of the complex is stabilized by weak intramolecular hydrogen bonds in which hydrogen donors are carbon atoms (-CH 3 groups at the 3 and 5 positions of the pyrazole ring) and pyrrole-like nitrogen atoms of NH groups, while hydrogen acceptors are pyridine-like nitrogen atoms of the neighboring pyrazole ligands and O and S atoms of the sulfate ligands. Significant contributions to the hydrogen-bond network are made by N-HÁ Á ÁO hydrogen bonds with lengths in the range of 2.022 (5) to 2.437 (4) Å .

Figure 3
The spiral arrangement of the bridging oxygen atoms of the sulfate ligands, which bind [Cu(SO 4 )(Hdmpz) 4 ] formula units along the b-axis direction. Bridging oxygen atoms of sulfate ligands are represented as red spheres, while all other atoms are depicted as wireframes. Hydrogen atoms are omitted for clarity.

Figure 4
Intramolecular hydrogen-bond network in the asymmetric unit of the title compound. Hydrogen bonds with the participation of oxygen atoms are indicated in red, blue for nitrogen atoms and yellow for sulfur atoms. Hydrogen donors are carbon atoms of methyl groups and nitrogen atoms of NH groups, while hydrogen acceptors are sulfur and oxygen atoms, and pyridine-like nitrogen atoms of the pyrazole ring.

Figure 5
Crystal packing of the title compound viewed along the (a) b-and (b) caxis directions: sulfate ligands are in a polyhedral representation with red spherical oxygen atoms, copper atoms are represented as orange spheres, while pyrazole rings atoms are depicted as wireframes. Hydrogen atoms are omitted for clarity.
dimensions can be explained because of the presence of four complex moieties in the asymmetric unit (Z 0 = 4, Z = 16). As a result of the sulfate ligand rotation, there is a pairwise alternation of the terminal oxygen atoms (which are not involved in coordinating the copper atom) of the SO 4 tetrahedra. Within one chain the intermetallic distance between two copper atoms, which are located at the edges of two neighboring asymmetric units, is 7.1625 (12) Å , while the interchalcogenic distance between the nearest sulfur atoms is 7.227 (2) Å . Polymeric chains, which are formed with the participation of bridging sulfate ligands, are stabilized by an extensive hydrogen-bond network. Neighboring chains are connected to each other by weak C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds. Geometric parameters for intermolecular hydrogen bonds are given in Table 2.

Hirshfeld surface analysis
The Hirshfeld surface analysis was performed and the associated two-dimensional fingerprint plots generated using Crystal Explorer 17.5 software (Spackman et al., 2021), with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed color scale of À0.5511 (red) to 1.8416 (blue) a.u. The red spots in Fig. 6. represent short contacts and negative d norm values on the surface corresponding to the interactions described above. The Hirshfeld surfaces mapped over d norm are shown for the HÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁC/ CÁ Á ÁH, CuÁ Á ÁO/OÁ Á ÁCu and HÁ Á ÁN/NÁ Á ÁH contacts, the overall two-dimensional fingerprint plot and the decomposed two-dimensional fingerprint plots are given in Fig. 7 (Spackman et al., 2021). A special filter 'by elements' was chosen during the calculation of the contributions of selected individual interactions to the total Hirshfeld surface. Quantitative physical properties of Hirshfeld surface for the title compound were also obtained, such as the molecular volume (650.80 Å 3 ), surface area (512.94 Å 2 ), globularity (0.708), as well as sphericity (0.034). These properties provide significant information on the shape of the molecules and may serve in the future to identify and establish correlations with other properties.   The overall two-dimensional fingerprint plot and those delineated into specified interactions. Hirshfeld surface representations with the function d norm plotted onto the surface for the different interactions. Symmetry codes: (i) x þ 1 2 ; Ày þ 1 2 ; z; (ii) Àx þ 1 2 ; y þ 1 2 ; z þ 1 2 ; (iii) Àx þ 1 2 ; y À 1 4-iodo-1H-pyrazole (Song et al., 2013) and XACTUR, a 1Hpyrazole-containing complex (Shen et al., 2004). These structures are similar to the title compound. Moreover there are 23 hits for the Cu(C 3 N 2 ) 2 SO 4 moiety, where C 3 N 2 is the backbone of the pyrazole ring. Most similar to the title compound are two catena-[( 2 -sulfato)bis(3,5-dimethyl-1H-pyrazole)aquacopper (

Synthesis and crystallization
The synthesis of [Cu(SO 4 )(Hdmpz) 4 ] n was conducted at room temperature by the oxidative dissolution method as a result of the addition of a copper powder (1.56 mmol, 0.1 g) and anhydrous copper(II) sulfate (3.1 mmol, 0.5 g) mixture to an acetonitrile (9 ml) solution of 3,5-dimethyl-1H-pyrazole (4.68 mmol, 0.45g). The mixture was stirred without heating for three h with free air access until dissolution of the copper powder and a gray-blue precipitate of the product was obtained (the precipitate weight was 0.86 g). The precipitate was filtered off and the obtained green-blue solution was analyzed. Clear, intense blue crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of the solvent at room temperature in an open vessel. The relative yield of the single-crystal portion of the product with respect to the ligand was approximately 7%. The obtained blue crystals were studied by elemental analysis (calculated for C 20 H 32 CuN 8 O 4 S: C 44.1%, H 5.9%, N 20.6%, found: C 44.5%, H 6.3%, N 21%). The elemental analysis data of the obtained grey-blue precipitate was: found C 36.8%, H 5.5%, N 17.2%. IR spectra of the starting 3,5-dimethyl-1H-pyrazole, grey-blue precipitate and clear, intense blue crystals of the title coordination polymer are given in the supporting information for this article.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Refinement of the N-H bond lengths was attempted, but this provided unrealistic values. Thus, hydrogens were placed at calculated positions and refined as riding with U iso (H) = 1.2U eq (N, C) or 1.5U eq (Cmethyl). The crystal studied was refined as a two-component inversion twin.

Funding information
This work was supported by the Ministry of Education and Science of Ukraine (grant No. 22BF037-09 at Taras Shevchenko National University of Kyiv).