Incorporation of in situ generated 3,3′-(sulfanediyl)bis(1-methyl-1,3-imidazolidine-2-thione) into a one-dimensional CuI coordination polymer with sulfur-bridged {CuI 4S10} n central cores

The reaction of [Cu(CH3CN)4](BF4) with 1-methyl-1,3-imidazolidine-2-thione {SC3H4(NMe) NH} forms the one-dimensional coordination polymer [Cu4(κ5:L 1—N—S—N—L 1)2(κ1:L 1—NH)2(κ2: L 1—NH)2] n (BF4)4n {L 1 = SC3H4(NMe)NH} with sulfur-bridged {CuI 4S10} n central cores.


Chemical context
The coordination chemistry of the coinage metals (Cu-Au) with heterocyclic-2-thione ligands ( Fig. 1) is of considerable interest as these metals exhibit a wide range of coordination geometries, giving rise to coordination compounds of differing nuclearity, namely, mononuclear, homo-and hetero-bridged di-nuclear, clusters and coordination polymers (Lobana, 2021;Raper, 1994Raper, , 1996Raper, , 1997García-Vá zquez et al., 1999). It has been noted that coordination compounds of these metals have displayed promising bio-activity and, in addition, several copper-based reactions are involved in the activation of C S (thione) bonds (Lobana, 2021).
As part of out ongoing studies in this area, we now describe the synthesis and structure of the title coordination polymer, 1.
The construction of the polymer 1 is believed to occur as represented in Fig. 3. Here the basic repeat unit is A, which is shown in a simplified way as unit B (omitting the imidazolidine rings). Two such B units combine to form a tetranuclear unit C, a basic building block, to construct the polymer 1. The building block C exhibits all three patterns of ligand bonding as represented in Fig. 2. The crystals of the polymer are monoclinic in the space group P2 1 /c. Geometric parameters are given in Table 1 Fig. 4 shows the basic dinuclear unit, in which there are three bonding patterns: bridging bidentate sulfur ( 2 -L 1 -NH), monodentate sulfur ( 1 -L 1 -NH), and in situ generated pentadentate sulfur ligand ( 5 -L 1 -N-S-N-L 1 ) (Fig. 2). The combining of two dinuclear moieties gives Bonding pattern of 1-methyl-1,3-imidazodine-2-thione and its in situ generated bis(1-methyl-1,3-imidazolidinyl-2-thione)sulfide.

Figure 3
The basic repeating unit, A; the basic repeating unit with imidazolidine rings omitted, B; the tetranuclear unit, C; a part of the polymer, D.

Figure 5
The tetranuclear repeating unit. H atoms and BF 4 À anions are omitted for clarity.

Figure 4
The contents of the asymmetric unit. N-HÁ Á ÁF hydrogen bonds are shown as dashed lines. Atomic displacement parameters are drawn at the 30% probability level. rise to a tetranuclear moiety as shown in Figs. 2 and 5. The chains of the polymer are hydrogen bonded to BF 4 ions lying between the chains by multiple weak C-HÁ Á ÁF interactions as shown in Fig. 6 and listed in Table 2.
Cu1 is bonded to four sulfur donor atoms (S1-S4) (Table 1). Here the thione (C S) sulfur donor atoms are more strongly bonded relative to the sulfur atom of the -N-S-Nmoiety. The Cu2-S2 and Cu2-S3 bond distances are the longest, while the other two Cu2-S1 and Cu2-S5 distances are short, and comparable to the Cu1-sulfur (S1-S3) bond distances, as noted above. The CuÁ Á ÁCu separation of 2.9074 (8) Å , does not reveal any metal-metal interaction (the sum of the van der Waals radii of the Cu atoms is 2.80 Å ; Huheey et al., 1993). The C-S bond distances fall in the range 1.699 (4) to 1.723 (4) Å , and lie between a typical double-and single-bond distance (C S ' 1.68 Å ; C-S ' 1.81 Å ; Huheey et al., 1993). Finally, the geometry about Cu1 is significantly distorted from a regular tetrahedron, as revealed by the S-Cu1-S bond angles, which fall in the range 89.72 (4) to 131.86 (4) and this is illustrated by the 4 ' parameter of 0.725 (Okuniewski et al., 2015); in comparison, the geometry of Cu2 is less distorted, with S-Cu2-S bond angles in the range 100.47 (4)-122.65 (4) and a 4 ' parameter of 0.842.

Figure 6
Packing viewed along the b-axis direction. N-HÁ Á ÁF hydrogen bonds and C-HÁ Á ÁF interactions shown as dashed lines.

Supramolecular features
The BF 4 À anions lying between the chains are involved in interactions with various N-H and C-H hydrogen atoms of the thio-ligands (Figs. 4 and 6). Consider the dimeric unit shown in Fig. 4. Here the N11-H hydrogen atom interacts with the F12 and F12A fluorine atoms of one BF 4 À anion while the N51-H hydrogen atom interacts with the F23 fluorine atom of the second BF 4 À ion. Various other F atoms of both BF 4 À ions accept C-HÁ Á ÁF interactions from the imidazolidine ring and the N-methyl group. The distances and angles involving hydrogen-bond interactions are shown in Table 2. In summary, the distances and angles are given as follows: NÁ Á ÁF = 2.74 (2)-2.764 (11) Å , HÁ Á ÁF = 2.12-2.15 Å and N-HÁ Á ÁF = 124-129 ; CÁ Á ÁF = 2.93 (2)-3.57 (2)Å ; HÁ Á ÁF = 2.09-2.64 Å ; C-HÁ Á ÁF = 111-170 . The NÁ Á ÁF distances are less than the sum of van der Waals radii of N and F, namely, 3.05 to 3.15 Å , and likewise the CÁ Á ÁF distances are either less than or comparable to the sum of van der Waals radii of C and F, namely, 3.15 to 3.30 Å (Huheey et al., 1993).
In the literature, there are limited reports of complexes with ionic copper(I) salts, and the reported mono-, or di-nuclear ionic complexes have BF 4 À , ClO 4 À , PF 6 À etc., outside the metal coordination sphere (Lobana, 2021). The present study provides a basic background to develop a new class of polymers using copper(I) ionic salts with heterocyclic-2-thiones.
The resulting polymeric materials with a central metal atom linked only to sulfur donor atoms may have interesting conductivity properties.

Synthesis and crystallization
All solvents were of HPLC grade and were stored over molecular sieves. The precursor, tetrakis(acetonitrile)copper(I) tetrafluoroborate, [Cu(CH 3 CN) 4 ](BF 4 ), was prepared by the slow addition of HBF 4 acid (from boric acid H 3 BO 3 + HF acid in a plastic beaker) to a solution of Cu 2 O (0.200 g; 1.4 mmol) in dry acetonitrile (25 ml) in a round-bottom flask. The mixture slowly became colourless and a white salt settled in the flask. The mother liquor was removed and the salt was extracted with diethyl ether, followed by evaporation, which gave solid [Cu(CH 3 CN) 4 ](BF 4 ).
Synthesis of 1-methyl-1,3-imidazolidine-2-thione Carbon disulfide (4.1 ml, 76 mmol) was added to a cooled solution of 1-methyl-ethylenediamine (CH 3 -NH-CH 2 -CH 2 -NH 2 ) dissolved in ethanol (10 ml) followed by the addition of 10 ml of water (García-Vá zquez et al., 2005). A white precipitate formed, and the contents were heated at 333 K, followed by the further addition of CS 2 . The precipitate initially dissolved, but shortly thereafter, a large amount of precipitate was deposited. The reaction mixture was heated under reflux for 1h, followed by the addition of conc. HCl (0.5 mL). It was further refluxed for one h, and placed for cooling, and precipitate formed was filtered and washed with cold acetone. Colour: white. Yield: 1.15 g, 50%; m.p. 351-354 K.
Synthesis of 1 To a solution of [Cu(CH 3 CN) 4 ](BF 4 ) (0.050 g, 0.15 mmol) in methanol (10 mL) was added a solution of the thio-ligand, SC 3 H 4 (NMe)NH (0.036 g, 0.31 mmol) in methanol. The mixture was stirred for about half an hour, giving rise to the formation of a clear pale-yellow solution. It was kept undisturbed for evaporation at room temperature. The colour of the solution turned green and a colourless crystalline compound was formed at the bottom, which was separated and dried at room temperature. Yield: 0.025 g; 40%; m.p. 450-452 K. Analysis found: C 24.52; H 3.69; N 13.87; S 20.50; C 16 H 30 B 2 Cu 2 F 8 N 8 S 5 requires: C 24.14; H 3.77; N 14.08; S 20.11%.

bis(tetrafluoridoborate)]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.91 e Å −3 Δρ min = −1.29 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. Refined as a 2-component twin.