μ3-Chlorido-μ2-chlorido-(μ3-pyrrolidine-1-carbodithioato-κ4 S:S,S′:S′)tris[(triethylphosphane-κP)copper(I)]: crystal structure and Hirshfeld surface analysis

The dithiocarbamate ligand chelates one CuI atom and each S atom bridges a second CuI atom and thus, is tetracoordinate. The core of the molecule comprises Cu3Cl2S2 and defines seven corners of a distorted cube.


Chemical context
Recent studies have highlighted the potential of ternary coinage metal phosphane/dithiocarbamates as anti-microbial agents. Motivated by the quite significant activity exhibited by R 3 PAu(S 2 CNRR 0 ), R, R 0 = alkyl/aryl (Sim et al., 2014;, lower congeners, i.e. (Ph 3 P) 2 M(S 2 CNRR 0 ), M = Cu I and Ag I , were investigated and shown to be also potent in this context . A prominent lead compound, Et 3 PAu(S 2 CNEt 2 ), was shown to possess broad-range activity against Gram-positive and Gram-negative bacteria and, notably, was also bactericidal against methicillin-resistant Staphylococcus aureus (MRSA) . Given that Et 3 PAu(S 2 CNEt 2 ) exhibited the most exciting potential amongst the phosphanegold dithiocarbamates, it was thought of interest to extend the chemistry/biological investigations of (R 3 P) 2 M(S 2 CNRR'), M = Cu I and Ag I , to include trialkylphosphane species. It was during these studies that the title compound, (I), was isolated as an incomplete reaction product from the 1:2:1 reaction between CuCl, Et 3 P and NH 4 [S 2 CN(CH 2 ) 4 ]. Herein, the crystal and molecular structures of (I) are described along with a detailed analysis of the Hirshfeld surface. ISSN 2056-9890

Structural commentary
The molecular structure of (I), Fig. 1, represents a neutral, trinuclear Cu I complex comprising three monodentate phosphane ligands, two chlorido anions, one 3 -and the other 2bridging, and a dithiocarbamate ligand. The latter is tetracoordinating, chelating the Cu3 atom, and each sulfur atom also bridges another Cu I atom. As highlighted in Fig. 2, the Cu 3 Cl 2 S 2 atoms of the core occupy the corners of a distorted cube with the putative eighth position being occupied by the quaternary-carbon atom of the dithiocarbamate ligand. As listed in Table 1, there are systematic trends in the Cu-donoratom bond lengths. To a first approximation, the Cu-P bond lengths are about the same. As anticipated for the Cu1 and Cu2 atoms, the Cu-Cl bond lengths involving the 3 -chlorido ligand are systematically longer than those formed with the 2 -chlorido ligand. Despite being chelated by the dithio-carbamate ligand, the Cu3 atom forms longer Cu-S bond lengths than do the Cu1 and Cu2 atoms, an observation correlated with the presence of two electronegative chloride anions in the donor sets for the latter. The coordination geometries for the Cu1 and Cu2 atoms are based on Cl 2 PS donor sets while that of Cu3 is based on a ClPS 2 donor set, Table 1. While being based on tetrahedra, the coordination geometries exhibit wide ranges of angles subtended at the copper atoms, i.e. 30, 28 and 53 , respectively. The wider range of angles about the Cu3 atom can be traced, in part, to the acute angle subtended by the dithiocarbamate ligand. A measure of the geometry defined by a four-atom donor set is 4 (Yang et al., 2007). Based on this index, 4 values of 1 and 0 are computed for ideal tetrahedral and square-planar geometries, respectively. The 4 values calculated for the Cu1-Cu3 atoms in (I) are 0.84, 0.86 and 0.78, respectively, i.e. consistent with distortions from tetrahedral geometries.
Reflecting the near equivalence in the pairs of Cu-S1 and Cu-S2 bonds, the associated C-S bond lengths are equal within experimental error, The molecular core in (I) highlighting the 'incomplete cube'.

Figure 1
The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level.

Supramolecular features
The key feature of the molecular packing in (I) is the formation of linear supramolecular chains along the c axis, Fig. 3a and Table 2. The 2 -chlorido ligand accepts two phosphane-methylene-C-HÁ Á ÁCl type interactions to form a linear chain. Centrosymmetrically related chains are connected via pyrrolidine-methylene-C-HÁ Á Á(chelate) interactions where the chelate ring is defined by the Cu1,S1,S2,C1 atoms. Such C-HÁ Á Á(chelate) interactions are now well established in dithiocarbamate structural chemistry (Tiekink & Zukerman-Schpector, 2011) and are gaining greater recognition in coordination chemistry (Tiekink, 2017). The supramolecular chains pack in the crystal with no directional interactions between them, Fig. 3b.

Hirshfeld surface analysis
The Hirshfeld surface analysis of (I) was performed in accord with a recent study of a related dithiocarbamate complex (Jotani et al., 2016). The presence of tiny red spots near the Cl1 and methylene-H20B and H22B atoms on the Hirshfeld surfaces mapped over d norm in Fig. 4 is indicative of the double-acceptor (C-H) 2 Á Á ÁCl interaction. In the view of the Hirshfeld surface mapped over the calculated electrostatic potential in Fig. 5, the light-blue and pale-red regions around the electropositive and electronegative atoms result from the polarization of charges about the donors and acceptors, respectively, of the intermolecular interactions. The immediate environments about a reference molecule within the shape-index-mapped Hirshfeld surfaces in Fig. 6a Table 2 Hydrogen-bond geometry (Å , ).

Figure 3
The molecular packing in (I): (a) linear supramolecular chain mediated by methylene-C-HÁ Á ÁCl (orange dashed lines) and methylene-C-HÁ Á Á(chelate) (blue) interactions aligned along the c axis and (b) view of the unit-cell contents in projection down the c axis. One chain is highlighted in space-filling mode.

Figure 4
Two views of the Hirshfeld surface for (I) mapped over d norm over the range À0.016 to 1.529 au.
The two-dimensional fingerprint plots for (I), i.e. the overall, Fig. 7a, and those delineated into HÁ Á ÁH, ClÁ Á ÁH/ HÁ Á ÁCl and SÁ Á ÁH/HÁ Á ÁS contacts (McKinnon et al., 2007) in Fig. 7b-d, respectively, provide further information on the intermolecular interactions present in the crystal. It is evident from the fingerprint plot delineated into HÁ Á ÁH contacts, Fig. 7b, that the hydrogen atoms of the triethylphosphane and pyrrolidine ligands make the greatest contribution, i.e. 86.6%, to the Hirshfeld surface, but at distances greater than the sum of the van der Waals radii. The pair of tips at d e + d i $ 2.8 Å in the arrow-like distribution of points in the plot for ClÁ Á ÁH/ HÁ Á ÁCl contacts, Fig. 7c, represent the intermolecular C-HÁ Á ÁCl interactions. A pair of short spikes at d e + d i $ 3.0 Å in the SÁ Á ÁH/HÁ Á ÁS delineated plot, Fig. 7d, and the 5.8% contribution to Hirshfeld surfaces along with the small but significant contributions from CÁ Á ÁH/HÁ Á ÁC and CuÁ Á ÁH/ HÁ Á ÁCu contacts, Table 3, to the Hirshfeld surface are all indicative of the C-HÁ Á Á(chelate) interaction, Fig. 3a and Table 2. The small contributions from the other interatomic contacts, namely NÁ Á ÁH/HÁ Á ÁN and CÁ Á ÁN/NÁ Á ÁC, have little effect on the packing of the crystal.

Database survey
The isolated Cu 3 ( 3 -Cl)( 2 -Cl)S 2 core observed in (I) appears to be rare in the literature, being structurally observed only in one other structure with general formula, M 3 ( 3 -X)( 2 -X)S 2 , incidentally, a dithiocarbamate complex. Thus, in the Ru II species, Ru 3 (CO) 3 (S 2 CNEt 2 ) 4 Cl 2 , a discrete Ru 3 ( 3 -Cl)( 2 -Cl)S 2 core is found but where the 2 -S sulfur atoms are derived from four dithiocarbamate ligands and each Ru II atom is coordinated by two additional sulfur donor atoms leading to trans-RuCClS 4 octahedral coordination geometries (Raston & White, 1975). While other structures are known with the specified core, the core is embedded within higher nuclearity clusters or in coordination polymers.

Figure 5
A view of the Hirshfeld surface for (I) mapped over the calculated electrostatic potential in the range À0.071 to 0.030 au. The red and blue regions represent negative and positive electrostatic potentials, respectively.
From the foregoing, it is obvious there is considerable structural variability in these systems arising in part from the ability of the dithiocarbamate ligands to adopt quite diverse coordination modes.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4     included in the refinement in the riding model approximation, with U iso (H) set to 1.2-1.5U eq (C).

µ 3 -Chlorido-µ 2 -chlorido-(µ 3 -pyrrolidine-1-carbodithioato-κ 4 S:S,S′:S′)tris[(triethylphosphane-κP)copper(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.