Crystal structure of bis[μ-N-(η2-prop-2-en-1-yl)piperidine-1-carbothioamide-κ2 S:S]bis[(thiocyanato-κN)copper(I)]

The crystal structure of the title compound consists of a dimeric CuI complex possessing a Cu2S2 core and contains thiocyanate anions and allylthiourea derivatives as chelating and bridging ligands. The dimeric CuI complexes are linked by N—H⋯S hydrogen bonds, forming a network extending in two dimensions parallel to (100).

The title crystalline compound, [Cu 2 (NCS) 2 (C 9 H 16 N 2 ) 2 ], was obtained from the reaction of copper(I) thiocyanate (CuSCN) with (N-prop-2-en-1-yl)piperidine-1-carbothioamide as a chelating and bridging thiourea ligand in chlorobenzene. The Cu 2 S 2 core of the dimeric molecule is situated on a crystallographic inversion centre. The copper atom is coordinated by a thiocyanate nitrogen atom, each sulfur atom of the two thiourea ligands, and the C C double bond of the ligand in a distorted tetrahedral geometry. The dimers are linked by N-HÁ Á ÁS hydrogen bonds, forming a network extending in two dimensions parallel to (100).

Chemical context
Thiourea and its derivatives, N-substituted thiourea and N, N 0disubstituted thiourea, are well-known ligands to copper ions, such as for their structural relatedness of proteins in bioinorganic chemistry and controlling redox potentials of copper ions in electrochemistry. Recently, copper-thiourea complexes [Cu(tu)s] have been investigated as electronic materials, for precursors of copper sulfide to be applied as semiconductors (Shamraiz et al., 2017;Sarma et al., 2019;Patel et al., 2019), photocatalysts (Tran et al., 2012;Pal et al., 2015), and sensors (Liu & Xue, 2011;Sabah et al., 2016;Sagade & Sharma, 2008). Cu(tu)s have also been used as a component of the precursor ink for forming CuIn(S, Se) as photo-absorbing layers in solar cells (Uhl et al., 2016). The solubility of Cu(tu)s in non-polar solvents is a potentially important property for their application as electronic materials. In order to synthesize a hydrophobic Cu(tu)s, we developed an allyl and a piperidinyl group bearing thiourea, (N-prop-2-en-1-yl)piperidine-1-carbothioamide, as a hydrophobic bidentate ligand and report here the crystal structure of the title non-ionic Cu I complex containing thiocyanates as coordinating anions. ISSN 2056-9890

Figure 2
A packing diagram of the title compound viewed along the a axis, i.e. a top view of the two-dimensional network. The N-HÁ Á ÁS hydrogen bonds are shown as green dashed lines. H atoms not involved in the interactions were omitted for clarity.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented by spheres of arbitrary radius. The hydrogen bonds are shown as green dashed lines. [Symmetry code: (i) Àx + 1, Ày + 1, Àz + 1].

Database survey
A search of the CSD (Version 5.41, update of August 2020; Groom et al., 2016) using ConQuest (Bruno et al., 2002) for compounds containing the 1-allylthiourea skeleton gave 892 hits, and for those containing the thiourea derivatives as ligands gave 945 hits of Cu complexes. The crystal structures of the ligand of the title compound, (N-prop-2-en-1-yl)piperidine-1-carbothioamide, itself and its metal complexes have not been reported. A survey for a Cu complex containing the 1-allylthiourea fragment as a S-coordination ligand reveals 53 examples, which includes six examples of 2 --coordination of an allyl group to Cu. All of these six examples are Cu I complexes, which comprise four coordination polymers of 4allyl-semicarbazide as ligands (Mel'nyk et al., 2001(Mel'nyk et al., , 2011Olijnik et al., 2011), one coordination polymer of 1,3-diallylthiourea as ligand (BOGNUH; Vakulka et al., 2007), and one discrete centrosymmetric dimer of 1-allylthiourea as ligand (RENNON; Filinchuk et al., 1996).

Synthesis and crystallization
To a chlorobenzene solution (2.5 mL) containing copper(I) thiocyanate (CuSCN, 122 mg, 1.0 mmol) and allyl isothiocyanate (298 mg, 3.0 mmol) in a 20 mL capped screw-tube bottle was slowly added piperidine (171 mg, 2.0 mmol) at 373 K under air and the mixture was stirred for 5 minutes. After that, it was left at room temperature. The pale-white precipitate formed in the bottle, and gradually changed to a pale-white solid containing single crystals. The mixture was filtered after 5 days to give a pale-white solid containing single crystals (267 mg, 0.87 mmol, 87%). Single crystals suitable for X-ray crystallographic analysis were selected in the product.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Atoms H14, H15A, and H15B were located in a difference-Fourier map and refined freely, considering the influence of the coordination of the ethenyl group to Cu I . H11A and H11B were also located in the difference-Fourier map and refined freely, because the distance between intramolecular H11B and H5 in the neighbouring molecule was abnormally short in the riding model. Other C-bound H atoms were placed in geometrically calculated positions (C-H = 0.99 Å ) and refined as part of a riding model with U iso (H) = 1.2U eq (C). The N-bound H5 atom was located in the difference-Fourier map but was refined with a distance restraint of N-H = 0.86AE0.01 Å , and with U iso (H) set to 1.2U eq (N).
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )