Crystal structure of the unusual coordination polymer catena-poly[[gold(I)-μ-1,2-bis(diphenylphosphinothioyl)ethane-κ2 S:S′] dibromidoaurate(I)]

In the title compound, the gold(I) centres of the cation are coordinated by the P=S groups of the disulfide ligands to form a chain polymer parallel to the c axis. Both independent gold atoms lie on the same twofold axis, and the midpoint of the H2C—CH2 bond lies on an inversion centre. The anions flank the polymeric chain; they are connected to it by short aurophilic interactions and C—H⋯Br contacts, and to each other by Br⋯Br contacts.

In the title compound, {[Au(C 26 H 24 P 2 S 2 )][AuBr 2 ]} n , the gold(I) centres of the cation are coordinated by the P S groups of the disulfide ligands to form a chain polymer parallel to the c axis. Both independent gold atoms lie on the same twofold axis, and the midpoint of the H 2 C-CH 2 bond lies on an inversion centre. The anions flank the polymeric chain; they are connected to it by short aurophilic interactions and C-HÁ Á ÁBr contacts, and to each other by BrÁ Á ÁBr contacts.

Chemical context
Although phosphane sulfides are known to act as ligands towards gold(I) centres, not many complexes have been structurally characterized in which two such ligands coordinate to gold(I). A search of the Cambridge Database (2019 Version, ConQuest 2.0.5) revealed only three structures involving the cation [(Ph 3 P S) 2 Au] + ; the PO 2 F 2 À salt (LeBlank et al., 1997), the nitrate (Jones & Geissler, 2016a) and a bis(methylsulfonyl)amide salt (Jones & Geissler, 2016b). Cationic 1:1 complexes of gold(I) with diphosphane disulfides can only be achieved if the ligand geometry allows for linear coordination at the gold atom, which is not generally the case unless suitable spacers, such as ferrocene units or other metal centres, are present (Gimeno et al., 2000, and references therein;Parkanyi & Besenyei, 2017;Wang & Fackler, 1990).
In the course of our studies of phosphane chalcogenide complexes of gold (Upmann et al., 2019, and references therein) we planned to study complexes of the diphosphane disulfides 1,2-bis(diphenylphosphinothioyl)ethane [previously known as 1,2-bis(diphenylphosphino)ethane disulfide; dppeS 2 ] and bis(diphenylthiophosphinoyl)methane [previously known as bis(diphenylphosphino)methane disulfide; dppmS 2 ] with gold(I) halide fragments AuBr and AuCl, with particular attention to the mononuclear complexes. This succeeded to some extent; we were able to isolate and determine the structure of dppmS 2 AuCl, the isotypic dppmS 2 AuBr and its oxidation product with bromine [(dppmS 2 )AuBr 2 ] + [AuBr 4 ] À (Jones et al., 2020a,b,c, respectively), but yields were ISSN 2056-9890 poor and it was clear that scrambling reactions were a problem. With dppeS 2 even less was achieved, but a few thin needles, isolated from the attempted synthesis of dppeS 2 AuBr, proved to be an unusual coordination polymer [(dppeS 2 )Au] n n+ Án[AuBr 2 ] À , the structure of which we report here.

Structural commentary
The title compound is shown in Fig. 1. The cation has the stoichiometry [dppeS 2 Au] + , and forms a chain polymer (Á Á ÁAu-S PCH 2 CH 2 P SÁ Á Á) n parallel to the c axis; the anion is [AuBr 2 ] À . Both gold atoms lie on twofold axes 1 2 , y, 1 4 and show the linear coordination geometry expected for Au I ; the midpoint of the central H 2 C-CH 2 bond lies on the inversion centre 1 2 , 1 2 , 1 2 . Bond lengths and angles may be considered normal; for a selection, see Table 1. Coordination polymers are scarce for diphosphane disulfide ligands (see below).

Supramolecular features
The gold atoms of the cation and anion are connected via a short aurophilic contact of 2.9622 (3) Å , and the anions thus flank the cation polymer (Fig. 2). Neighbouring anions are connected by short BrÁ Á ÁBr contacts of 3.7424 (8) Å (operator 1 À x, 2 À y, 1 À z), and also provide links to adjacent polymers (not shown in Fig. 2). We have previously noted an example of short contacts between dibromoaurate(I) anions (Dö ring & Jones, 2013); for a further example, see Beno et al. (1990). We have also described BrÁ Á ÁBr and ClÁ Á ÁCl contacts in a series of tetrabromidoaurate(III) and tetrachloridoaurate(III) salts (Dö ring & Jones, 2016).
Two C-HÁ Á ÁBr contacts between cation and anions are sufficiently short and linear to be considered 'weak' hydrogen bonds (Table 2), and thus to contribute further cohesion to the structure, but are omitted from Fig. 2 for clarity.

Database survey
A database search (CSD 2019 Version, ConQuest 2.0.5) found 11 hits for systems involving two P S units bonded to Au I . The P S bond lengths range from 1.985-2.039, av. 2.018 Å , and the S-Au bond lengths from 2.275-2.317, av. 2.296 Å . The only other coordination polymer found for a diphosphane disulfide was [(CuCN) 2 (dppeS 2 )] n (Zhou et al., 2006), a twodimensional polymer involving four-coordinate Cu centres.

Synthesis and crystallization
The compound arose from an attempt to synthesize dppe-S 2 AuBr. A solution of thtAuBr (tht = tetrahydrothiophene; 0.775 g, 2.12 mmol) in CH 2 Cl 2 (50 ml) was added to dppeS 2 (0.981 g, 2.12 mmol) dissolved in CH 2 Cl 2 (50 ml). After stirring for 1 h, the solvent was removed, and the solid thus obtained was dried under vacuum and recrystallized from dichloromethane/n-pentane. The elemental analysis was approximately correct for the expected stoichiometry: calculated, C 42.23%, H 3.27%, S 8.67%; found, C 43.22%, H 3.87%, S 8.19%. However, attempts to obtain crystals suitable for X-ray structure analysis (by evaporation from a solution in CH 2 Cl 2 ) led only to a few very thin needles of the title compound, with overall stoichiometry dppeS 2 (AuBr) 2 .

Figure 1
Structure of the title complex in the crystal; the asymmetric unit is numbered. The aurophilic contact and the S-Au connections to the next gold atoms in the polymer are indicated by filled and open dashed bonds, respectively.

Refinement
Crystal data, data collection and structure refinement details are summarized in

catena-Poly[[gold(I)-µ-1,2-bis(diphenylphosphinothioyl)ethane-κ 2 S:S′] dibromidoaurate(I)]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.42 e Å −3 Δρ min = −0.99 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.