Crystal structure of di-μ-iodido-bis[(dimethyl sulfoxide-κO)(triphenylphosphane-κP)copper(I)]

The basic building unit of the title complex, CuI(DMSO)(PPh3), reproduced by a symmetry centre, leads to the rhomboid dimers in which the CuI atoms are in a tetrahedral geometry. The dimers are discrete molecules, but through weak intermolecular C—H⋯O interactions involving two adjacent DMSO ligands, a one-dimensional chain assembly is formed.

The centrosymmetric dinuclear title compound, [Cu 2 I 2 (C 2 H 6 OS) 2 (C 18 H 15 P) 2 ], represents the first example of a CuI complex ligated by an O-bound dimethyl sulfoxide ligand. In the crystal, the two tetrahedrally coordinated Cu I atoms are bridged by two 2 -iodido ligands in an almost symmetrical rhomboid geometry. The loose CuÁ Á ÁCu contact of 2.9874 (8) Å is longer than the sum of the van der Waals radii of two Cu atoms (2.8 Å ), excluding a significant cupriophilic interaction in the actual dimer. C-HÁ Á ÁO and C-HÁ Á ÁI hydrogen bonding interactions as well as C-HÁ Á Á(aryl) interactions stabilize the threedimensional supramolecular network.

Chemical context
There exists a large family of dinuclear Cu I Á Á ÁCu I -halidebridged complexes of the type [PPh 3 (L 0 )Cu( 2 -I) 2 Cu(L 0 )-PPh 3 ], with the ligands L commonly bearing the coordinating N and S atoms, in which cupriophilic interactions may play a crucial role in determining their photophysical properties (Lobana et al., 2012 and references therein;Engelhardt et al., 1989). The title compound, [PPh 3 (DMSO)Cu( 2 -I) 2 Cu-(DMSO)PPh 3 ] (1), belongs to this family of compounds for which an association of L = PPh 3 and L 0 = DMSO has never been mentioned before.

Database survey
The polar aprotic solvent (CH 3 ) 2 S=O (DMSO) is frequently used in organic chemistry for reactions involving salts such nucleophilic substitutions reactions, but it has also found widespread use as a ligating solvent in the coordination chemistry of transition metals, where it may act both as an Sdonor and an O-donor ligand towards a metal centre (Selbin et al., 1961). A survey of the Cambridge Structural Database (CSD; Groom & Allen, 2014) reveals a large number of structurally characterized Cu II halide complexes ligated by O-bound DMSO ligands. However, we found just one entry concerning a Cu I halide complex, namely the tetrametallic ISSN 1600-5368 chain complex [Cu 4 Br(-Br) 3 (-dpmppm) 2 (DMSO) 2 ] (dpmppm = bis[(diphenylphosphinomethyl)phenylphosphino]methane) reported by Takemura et al. (2009). Note that in the case of a soft Cu I ion (compared with a harder Cu II ion according the HSAB principle), DMSO could be a priori coordinating either via the sulfur or via the oxygen atom. Surprisingly, we found no Cu I I complex ligated by DMSO in the CSD.

Structural commentary
CuI is known to afford with DMSO in the presence of P 2 S 5 the 2D coordination polymer [(Me 2 S) 3 {Cu 4 (-I) 4 }] n , the production of SMe 2 being explained by the deoxygenation of Me 2 SO by P 2 S 5 (Zhou et al., 2006). In the context of our research on the coordination of thioethers R-S-R on CuX salts (Knorr et al., 2010;Lapprand et al., 2013), we reacted a CuI solution in hot DMSO with a stoichiometric amount of PPh 3 and succeeded in isolating in moderate yield X-ray-suitable crystals of (1). Structural analysis revealed that a centrosymmetric dinuclear complex is formed (Fig. 1), in which the two tetra-hedrally coordinated Cu I atoms are bridged by two 2 -iodido ligands in a slightly asymmetric rhomboid manner. Despite the soft character of CuI, the DMSO ligands are O-bound. The Cu-O bond length of 2.140 (2) Å is considerably longer than those of polymeric Cu II compounds [(DMSO) 2 CuBr 2 ] n [1.962 (9) Å ; Willett et al., 1977] and [(DMSO) 2 CuCl 2 ] n [1.955 (4) Å ; Willett & Chang, 1970], but is in the same range as found for [Cu 4 Br(-Br) 3 (-dpmppm) 2 (DMSO) 2 ] [2.200 (7) Å ]. The CuÁ Á ÁCu contact of 2.9874 (8) Å is longer than the sum of the van der Waals radii of two Cu atoms (2.8 Å ), excluding any cupriophilic interaction. This separation is in the same range as reported for [PPh 3 (pyridine)Cu( 2 -I) 2 Cu(pyridine)PPh 3 ] (2.97 Å ) (Bowmaker et al., 1994), and the P-Cu bond lengths are also quite similar in the two compounds [2.2295 (10) vs 2.24 Å ].

Supramolecular features
The assembly of the crystal structure seems to be first governed by C-HÁ Á ÁO-type hydrogen bonds (intermolecular ligand-to-ligand DMSO interactions), leading to a 1D chain The molecular structure of title compound built over a symmetry centre, with atom labels and 50% probability displacement ellipsoids for non-H atoms. Symmetry code for unlabelled atoms is (1 À x, Ày, Àz).

Synthesis and crystallization
Triphenylphosphane (262 mg, 1.0 mmol) was added to a solution of CuI (192 mg, 1.0 mmol) in 10 ml of DMSO. The reaction mixture was first stirred at room temperature for 30 min and then heated for further 30 min to 368 K. After allowing the mixture to reach ambient temperature, yellowish crystals were formed (36% yield).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were placed in calculated positions and treated in a riding-model approximation. C-H distances were set to 0.95 (aromatic) and 0.98 Å (methyl) with U iso (H) = xU eq (C), where x = 1.5 for methyl and 1.2 for aromatic H atoms.