Syntheses and crystal structures of two copper(I)–halide π,σ-coordination compounds based on 2-[(prop-2-en-1-yl)sulfanyl]pyridine

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Chemical context
Cu-containing complexes have been found very promising regarding their catalytic activities in organic syntheses, nonlinear optical properties and fluorescent activity (Wang et al., 2005;Yoshikai & Nakamura, 2012;Slyvka et al., 2018a;Fedorchuk et al., 2020). Copper complexes also exhibit considerable biochemical activities, ranging from antibacterial and anti-inflammatory properties to cytostatic and enzyme inhibitory (Iakovidis et al., 2011;Tisato et al., 2010). Some of these compounds have been tested in vitro as potential anticancer drugs and found to be effective against A549 adenocarcinoma cells that are resistant to the widely used anticancer drug cisplatin (Marzano et al., 2006). It is worth noting that copper is an essential trace element with vital roles in many metalloenzymes participating in intracellular processes under normal and pathological conditions (Iakovidis et al., 2011).
Over the last two decades, increased interest has also been devoted to the crystal engineering of copper(I)-olefin complexes with allyl derivatives of heterocyclic compounds (Goreshnik et al., 2011;Slyvka et al., 2013;Hordiichuk et al., 2019). The presence of a C C olefin bond in a substituent attached to the heterocyclic ring may serve as a key feature for the selective coordination of transition-metal ions due to metal-olefin -bonding (Rourke, 2006;Slyvka et al., 2013;Kowalska et al., 2021). Allyl derivatives of some heterocyclic compounds were found to be suitable for the preparation ofcoordination compounds with Cu I salts that are unknown (or less stable) in the free state. For instance, the first examples of ISSN 2056-9890 Cu(C 6 H 5 SO 3 ), Cu(p-CH 3 C 6 H 4 SO 3 ) or CuHSO 4 -complexes as well as the direct Cu I Á Á ÁF(SiF 6 2-) interaction have been observed in copper(I) -compounds with allyl derivatives of triazole and thiadiazole (Goreshnik et al., 2016;Ardan et al., 2017;Slyvka et al., 2018b;Fedorchuk et al., 2020). N-Allyl derivatives of pyridine were found to be suitable ligands for the crystal engineering of Cu I coordination compounds with inorganic fragments of different complexibility and related to the pK a values of the initial pyridine bases (Goreshnik et al., 2003;Pavlyuk et al., 2005). Taking into account the fact that allylsulfanyl derivatives of pyridine have not been investigated for their coordination behavior regarding copper(I), in this work we present the synthesis and structural characterization of two novel copper(I) halide -coordination compounds [Cu 2 Cl 2 (Psup) 2 ] (I) & [Cu 2 Br 2 (Psup) 2 ] (II) with 2-[(prop-2en-1-yl)sulfanyl]pyridine (Psup), C 8 H 9 NS.

Structural commentary
The title compounds are isostructural and crystallize in the centrosymmetric space group P2 1 /c with one Psup organic molecule, one copper(I) ion and one halide ion in the asym-metric unit. As shown in Figs. 1 and 2, these structures are constructed from centrosymmetric [Cu 2 Hal 2 (Psup) 2 ] [Hal = Cl (I) or Br (II)] dimers, which are formed due to the chelating behavior of the organic ligand. A close to trigonal-pyramidal coordination environment of the Cu I cation includes the 2 allylic C C bond, the pyridine N atom and a Hal1 ion in the basal plane (Tables 1 and 2). The apical position of the Cu I polyhedron is occupied by the Hal1 i [symmetry code: (i) Àx + 1, Ày + 1, Àz + 1) ion at 2.6186 (9) Å in I and at 2.7113 (6) Å in II. The corresponding four-coordinate geometry indices 4 (Yang et al., 2007) are 0.81 (I) and 0.83 (II). For comparison, in the structures of previously studied CuCl and CuBr ,complexes with allylacetoneoxime, the Cu-Hal ap distances are slightly higher at 2.719 (5) and 2.778 (4) Å (Filinchuk et al., 1998).
interactions. The hydrogen atom H6 of the pyridine ring participates in an intramolecular C-HÁ Á ÁHal bond with the Hal ion of the inorganic subunit. The other hydrogen atom H6 of the pyridine ring and the methylene hydrogen atom H7B of the allylsulfanyl substituent are involved in intermolecular C-HÁ Á ÁHal bonding, linking the dimeric moieties into a three-dimensional network. The pyridine rings of adjacent dimers are also involved in face-to-facestacking interactions with a centroid-centroid separation of 3.680 (4) Å in I and 3.693 (4) Å in II. The unit-cell packing for (I) is shown in Fig. 4.

Synthesis and crystallization
Crystals of the title compounds were obtained under conditions of alternating-current electrochemical synthesis (Slyvka et al., 2018a) starting from an ethanolic solution of 2-[(prop-2en-1-yl)sulfanyl]pyridine (Psup) and the copper(II) halide. For this, a solution of Psup (1.5 mmol, 0.227 g) in 2.0 ml of 96% ethanol was added to a solution of CuCl 2 Á2H 2 O (1.6 mmol, 0.273 g) or CuBr 2 (1.6 mmol, 0.357 g) in 3.0 ml of 96% ethanol. The mixture was carefully stirred and then was placed into a small 5.5 ml test tube. A copper wire was wrapped into a spiral of 1 cm diameter. A straight copper wire was placed inside the spiral. These copper electrodes were inserted in a cork and immersed in the aforementioned mixture. The mixture was subjected to alternating current reduction (frequency 50 Hz, voltage 0.45 V) and after 3-4 days, good-quality slightly yellowish crystals of the title compounds appeared on the copper wire electrodes.  Table 3 Hydrogen-bond geometry (Å , ) for I. Symmetry codes: (ii) x þ 1; y; z; (iii) Àx þ 1; y þ 1 2 ; Àz þ 1 2 .

Figure 4
A view along the a-axis direction of the crystal packing of I.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. All H atoms were positioned geometrically with C-H = 0.95-0.99 Å and refined as riding atoms. The constraint U iso (H) = 1.2U eq (C) was applied in all cases.

Funding information
This work was supported by the Ministry of Education and Science of Ukraine (Grant Nos. 0120U101622 and 0120U102028) and the Slovenian Research Agency (ARRS) within the research program P1-0045 Inorganic Chemistry and Technology.

Di-µ-chlorido-bis({2-[(η-2,3)-(prop-2-en-1-yl)sulfanyl]pyridine-κN}copper(I)) (I)
Crystal data 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.