Crystal structure of bis(μ₂-diethyldithiocarbamato-κ³S,S′:S′)-bis(tricyclohexylphosphane-κP)dicopper(I), C₄₆H₈₆Cu₂N₂P₂S₄

Source of materials

The title complex was prepared from the in situ reaction of CuCl, Cy₃P and Na[S₂CNEt₂] in a 1:1:1 ratio. Cy₃P (Sigma–Aldrich; 1.0 mmol, 0.283 g) dissolved in hexane (10 mL) was added to a hexane solution (10 mL) of CuCl (Sigma–Aldrich; 1.0 mmol, 0.100 g). The temperature of reaction was maintained at below 4 °C. Then, Na[S₂CNEt₂] (BDH, 1.0 mmol, 0.250 g) in hexane (10 mL) was added to the reaction mixture, followed by stirring for 4 h. The resulting mixture was filtered and left for evaporation at room temperature to yield bright-yellow crystals. Yield: 0.239 (68.7%). M.p.: 418–420 K. IR (cm⁻¹): 2909 (s), 2843 (s) ν(C—H); 1474 (s) ν(C—N); 1072 (m), 995 (m) ν(C–S).

Experimental details

The C-bound H atoms were geometrically placed (C–H = 0.98–1.00 Å) and refined as riding with U_iso(H) = 1.2–1.5 U_eq(C).

Comment

The initial interest in complexes related to the title compound, i.e. of general formula [R₃PCu(S₂CNRR′)]₂, R, R′ = alkyl or aryl, arose as a result of the desire to generate more efficacious synthetic precursors for copper sulfide nanomaterials [5]. Thus, the addition of base, in this case triorganophosphanes with relatively small R substituents, disrupted the polymeric structure of [Cu(S₂CNRR′)]_n to provide soluble materials that were more suitable for decomposition studies. However, it was in recognition of the biological potential of metal dithiocarbamates [6] that prompted more recent investigations into these types of ternary compounds. Specifically, a recent report [7] highlighted the species-specific anti-microbial activity of certain (Ph₃P)₂Cu(S₂CNRR′) derivatives and it was this observation that prompted the synthesis of the title compound, [Cy₃PCu(S₂CNEt₂)]₂.

As seen from the Figure (70% displacement ellipsoids; the C4 atom is obscured), the title compound is binuclear and indeed, disposed about a centre of inversion; unlabelled atoms are related by the symmetry operation: −x, 1 − y, 1 − z. The diethyldithiocarbamate ligand is μ₂-bridging, chelating one copper(I) centre, while simultaneously binding to a second via one of the sulfur atoms only. The bridging Cu—S1 bond length of 2.5169(3) Å is systematically longer than the chelating Cu—S1ⁱ, S2ⁱ bond lengths of 2.3480(3) and 2.3905(3) Å; the internal Cu⋯Cuⁱ separation is 2.8034(3) Å. These variations are reflected in the associated C—S bond lengths with the bond formed by the bridging-S1 atom being systematically longer than the bond involving the chelating-S2 atom, i.e. 1.7356(13) cf. 1.7087(13) Å. The pattern in Cu—S bond lengths implies the central Cu₂S₂ core is rectangular. The overall Cu₂S₄ arrangement resembles a partial step-ladder as the edge-shared CuS₂ triangles lie above and below the plane through the central core. The four-coordinate geometry of the copper(I) atom is completed by a phosphane-P atom and the resultant PS₃ donor set approximates a tetrahedron but, with significant distortions. Thus, the smallest angle subtended at copper(I) of 73.827(11)° corresponds to the chelate angle and the widest angle of 123.178(12)° corresponds to S1—Cu—P1, i.e. involving the bridging-S1 and sterically crowded phosphorous atoms.

There are two direct literature precedents for the structure of the title compound, namely [R₃PCu(S₂CNEt₂)]₂ for R = Me and Et [5]. These adopt the same structural motif and they are both located around a inversion centre.