Crystal structure of (μ-1,4-dicarboxybutane-1,4-dicarboxylato)bis[bis(triphenylphosphane)silver(I)] dichloromethane trisolvate

The molecular structure of the distorted trigonal–planar-coordinated tetrakis(triphenylphosphanyl)disilver salt of butane-1,1,4,4-tetracarboxylic acid is reported, present as a dichloromethane trisolvate. The coordination complex exhibits an inversion centre through the CH2—CH2 bond and intermolecular T-shaped π–π interactions between the phenyl rings of the PPh3 substituents, forming a ladder-type superstructure parallel to the b axis.


Chemical context
Silver precursors [e.g. silver(I) carboxylates and silver(I) -diketonates] exhibit a wide range of applications, for instance the formation of thin, metallic layers by means of CVD (Chemical Vapour Deposition) or CCVD (Combustion Chemical Vapour Deposition) (Struppert et al., 2010;Jakob et al., 2006;Schmidt et al., 2005;Lang & Buschbeck, 2009;Lang, 2011;Lang & Dietrich, 2013;Chi & Lu, 2001), spin coating (Jakob et al., 2010) or inkjet printing (Jahn et al., 2010a,b;Gä bler et al., 2016). The respective silver layers show closed and homogeneous silver films and therefore possess a good conductivity. In addition, silver carboxylates such as [AgO 2 CR] n (n is the degree of aggregation) allow for the formation and stabilization of silver nanoparticles, which can, for example, be used for catalytic processes (Steffan et al., 2009). They are also used in biological studies (Fourie et al., 2012;Langner et al., 2012).
A further application of silver carboxylate precursors includes their use for joining of bulk copper to produce metallic interconnects, for example in microelectronic applications (Oestreicher et al., 2012(Oestreicher et al., , 2013. We anticipate that a metal oxide layer will need to be removed during such a silver-facilitated copper-joining process. Leaving some of the carboxyl groups of the silver precursor uncoordinated is expected to assist in this process. In the case of sparingly soluble silver carboxylates, the solubility in common organic solvents can be increased through addition of phosphanes, such as triphenyl phosphane. In this context, the title compound (I) was prepared by the reaction of the disilver salt of butane-1,1,4,4-tetracarboxyl acid (BTCA) with triphenylphosphane.
The anionic C 8 H 8 O 8 moiety contains an intramolecular hydrogen bond between the O3 atom of the HO 2 C-carboxy group and the O2 atom that is in interaction with Ag1 ( Fig. 1 The Ag1 atom exhibits a somewhat distorted trigonalplanar P 2 O coordination environment, whereby the two phosphanes enclose an increased P-Ag-P angle of 128.56 (2) , in contrast to the O1-Ag1-P angles of 117.69 (5) (P1) and 113.27 (5) (P2). The weak interaction to the O2 atom occurs below this AgP 2 plane with an interaction to the CO 2 group of 67.38 (17) with, however, two nearly equal C1-O1/O2 bond lengths of 1.251 (3) (O1) and 1.261 (3) Å (O2). Both phosphanes reveal an eclipsed conformation regarding the phenyl rings of 2.09 (10) .
One dichloromethane is stabilized by a non-classical hydrogen-bridge bond from C1S, as the hydrogen-bond donor, to the hydroxyl O3 atom (Table 1), which also acts as hydrogen-bridge bond donor in an intramolecular classical bridge bond (see Structural commentary).
Further intermolecular interactions involving hydrogen bonds or OÁ Á ÁAg interactions are not observed.

Database survey
In the CSD database (Groom & Allen, 2014; Version 5.36), only two acyclic silver tetracarboxylates with six-membered carbon backbones are reported. These are butane-1,2,3,4tetracarboxylato silver compounds containing further nitrogen and oxygen donor ligands, coordinating the silver ions either in a tetrahedral or a T-shaped trigonal fashion (Sun et al., 2010). Three aliphatic cyclohexane silver complexes with four to six carboxylate groups are also known. Within those, the silver ions are also coordinated by additional ligands such as ammonia and water and possess distorted tetrahedral coordination or Y-shaped coordination environments (Wang et al., 2006(Wang et al., , 2009. For six-membered unbranched acyclic silver dicarboxylates derived from adipic acid, more crystal structures are reported compared to the respective tetracarboxylato derivatives. Several coordination geometries for the silver atoms are reported such as T-shaped (Wu et al., 1995), tetra-hedral (Li et al., 2011) or trigonal-planar environments (Liu et al., 2009) containing nitrogen, oxygen or sulfur donor ligands. To the best of our knowledge, the title compound (I) is the only example of a silver tetracarboxylate consisting of a sixmembered carbon backbone and containing a silverphosphorus bond. In contrast to the title compound, which exists as a monomer presumably due to the steric shielding by triphenyl phosphane, all of the above-mentioned complexes exist as polymeric networks, formed by bridging through the different donor atoms of the ligands. For example, by using silver dicarboxylates frequently the formation of dimeric subunits can take place, which in turn results in the construction of polymeric systems (Wu et al., 1995). Structures containing water molecules coordinating to the Ag I ions result in the formation of a further polymeric hydrogen bridge-bond network, also including carboxylato moieties (Wang et al., 2006(Wang et al., , 2009

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bonded hydrogen atoms were placed in calculated positions and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C) and a C-H distance of 0.93 Å for aromatic (AFIX 43), 0.98 Å for methine (AFIX 13) and 0.97 Å for methylene H atoms (AFIX 23). The same applies for the O-bonded H atom; however, the torsion angle was derived from electron density (AFIX 147). The structure contains three molecules of dichloromethane as the solvent. Both crystallographically independent molecules consist of two moieties each. One molecule was refined as disordered over two positions (C1S; C1SB) with occupancies of 92.7 (2) and 7.3 (3)%, respectively. The less prevalent moiety of C1SB is located close to a crystallographic inversion centre and symmetry-related pairs are mutually exclusive. The second disordered molecule is located directly atop of another inversion centre with an occupancy of 0.5 (Fig. 1), with the inversion centre located near the C2S and Cl1B atoms. The less-occupied methylene chloride molecule was restrained to have a geometry similar to that of its major moiety counterpart by using the SAME command. U ij components of ADPs for C1S C1SB Cl1B and Cl2B were restrained to be similar if closer than 1.7 Å (SIMU restraint, McArdle, 1995;Sheldrick, 2008 (Farrugia, 2012) and SHELXTL (Sheldrick, 2008); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).  (2)  Ag1 0.02215 (9) 0.01473 (9) 0.01672 (9) 0.00874 (7) 0.00930 (6) 0.00856 (7)  O1 0.0280 (9) 0.0196 (9) 0.0237 (9) 0.0090 (7) 0.0139 (7) 0.0053 (7)