Crystal structures of 9-[bis(benzylsulfanyl)methyl]anthracene and of cyclo-dodecakis(μ2-phenylmethanethiolato-κ2 S:S)hexapalladium(6 Pd—Pd)–anthracene-9,10-dione (1/1)

The dithioactal bis[(benzylthio)methyl]anthracene has been synthesized and reacted with [PdCl2(PhCN)2] to yield the cyclic cluster [Pd6(μ2-SCH2Ph)12].


Chemical context
Acyclic and cyclic thioacetals with the -S-C(R)(H)-S (R = H, alkyl, aryl) unit can either be synthesized by nucleophilic substitution of geminal dihalides X-C(R)(H)-X by thiolates RS À (Murray et al., 1981) or by reaction of aldehydes and ketones with thiols and dithiols (Shaterian et al., 2011). Because of their soft nature, organosulfur compounds preferentially interact with late transition metals in lower oxidation states. A variety of complexes as well as coordination polymers (CPs) of varying dimensionality, ranging from zero-dimensional (molecular) to three-dimensional, have been synthesized using these types of dithioether ligands and structurally characterized (Knaust & Keller, 2003;Awaleh et al., 2005Awaleh et al., , 2008. However, many factors including the structural characteristics of the organic ligands, temperature, solvent, molar ratio, etc., greatly influence the formation of the resulting materials. Over the last few years, we have been engaged in exploring the assembly of molecular cluster compounds and coordination polymers using thioether ligands RSCH 2 SR (Peindy et al., 2007;Knorr et al., 2014;Schlachter et al., 2020). Recently, we have also reported the synthesis of Cu I coordination complexes ligated with cyclic thioacetal ligands bearing various substituents (Raghuvanshi et al., 2017(Raghuvanshi et al., , 2019Schlachter et al., 2018;Knauer et al., 2020). Convenient synthetic protocols and interesting luminescent properties displayed by these complexes intrigued us to explore this field further.
Since the presence of an anthracene unit provides both rigidity as well as interesting luminescent properties to a given system, a large number of anthracene-based MOFs and CPs have been reported for various applications (for example : Hu et al., 2020;Mohanty et al., 2020;Quah et al., 2016;Wang et al., 2016). In most of these reports, either N-or O-donor substituents attached to the anthracene scaffold have been used as coordinating sites. In contrast, there are few reports where anthracene-based thioether ligands have been used for the construction of CPs. For example, a series of emissive molecular compounds and CPs have been assembled by reaction of 9,10-bis[(alkylthio)methyl]anthracenes with Ag I salts (Hu et al., 2006). The synthesis of anthracene-based thioacetals with different -SR substituents including L1 has been briefly reported (Goswami et al., 2008 andShaterian et al., 2011). However, no spectroscopic characterization data have been communicated. Furthermore, no examples of structurally characterized anthracene-based thioacetals could be found within the Cambridge Structural Database. These disparities make this field interesting for further investigations.
In this context, we synthesized the anthracene thioacetal L1 with the objective of using it as an S-donor ligand for the assembly of potentially luminescent coordination compounds. L1 was prepared straightforwardly by the reaction of benzyl mercaptan and 9-anthracenecarboxaldehyde in the presence of an excess conc. HCl at room temperature ( Fig. 1) and obtained in 80% yield as a yellow solid. Characteristic for its 1 H NMR spectrum are two doublets at 3.55 and 3.79 ppm for the diastereotopic methylene protons and a singlet at 5.94 ppm for the methine proton. The complete spectroscopic data are reported in the Synthesis and crystallization section.
Looking for a more rational manner to synthesize this tiaralike cluster, we attempted to prepare Pd6 independently by reacting [PdCl 2 (PhCN) 2 ] with 2.1 equivalents of benzyl mercaptan in CH 2 Cl 2 solution. However, the isolation of Pd6 was hampered by the co-crystallization of important amounts of the eight-membered cluster Pd8 [Pd 8 ( 2 -SCH 2 Ph) 16 ], having a structure similar to that of [Pd 8 ( 2 -SPr) 16 ] (Higgins et al., 1988). Details of this reaction will be reported elsewhere.

Figure 3
The molecular structure of Pd6ÁC 14 H 8 O 2 with the atom labelling and displacement ellipsoids drawn at the 50% probability level [symmetry codes: (i) Àx + 1, Ày + 1, Àz + 1; (ii) Àx + 1, Ày + 1, Àz + 2]. The H atoms are not shown for clarity. radii for Pd (3.26 Å ; Bondi, 1964). The mean separation of two symmetry-related opposite Pd nuclei is about 6.22 Å , the longest being that of 6.453 Å between Pd3 and Pd3 0 , justifying describing these compounds as nano-sized clusters. Each palladium atom is coordinated covalently to four 2 -sulfur atoms with an approximately square-planar geometry, and the average Pd-S bond length of 2.327 (5) Å is close to those of the other [Pd 6 ( 2 -SR) 12 ] analogues. The S-Pd-S bridge angles vary within the range 81.033 (16)-99.246 (16) . The twelve sulfur atoms form two S 6 hexagons parallel to the central Pd 6 ring from both sides, conferring finally a tiara-like shape to the Pd 6 S 12 scaffold. Note that the crystal structure of anthracene-9,10-dione (also named 9,10-anthraquinone) has already been the object of several crystallographic studies and is therefore not commented herein (Fu & Brock, 1998;Slouf, 2002).
A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) for the further investigation of close contacts and intermolecular interactions was performed for L1 using Crystal-Explorer17 (Turner et al., 2017). Figs. 6a and 7 illustrate the three-dimensional Hirshfeld surface mapped over d norm in the range from À1.11 to 1.36 (arbitrary units). The red spots on the surface indicate the close contacts to adjacent molecules. There are three areas of red spots which can be classified as C-HÁ Á Á interactions. The first and most important interaction is the C-HÁ Á Á contact of one of the phenylmethanethiolate substituents to the anthracene scaffold of a  A view along the b-axis direction of the crystal packing of L1.
neighboring molecule (C14-H14Á Á ÁC24). Furthermore, there are significant interactions of the anthracene unit to an adjacent anthracene unit (C21-H21Á Á ÁC16/17/29). Then, there is also a weak C-HÁ Á Á contact of two phenylmethanethiolate substituents (C1-H1BÁ Á ÁC9). The contributions of the different types of intermolecular interactions are shown in the two-dimensional fingerprint plots in Fig. 8. The weak van der Waals HÁ Á ÁH contacts appear as the largest region with a 51.0% contribution. The CÁ Á ÁH/HÁ Á ÁC contacts exhibit a significant contribution at 40.4% and constitute a major contribution to the packing arrangement within the crystal structure. Fig. 6b and 6c illustrate the Hirshfeld surface mapped over the shape-index and the curvedness. The shapeindex shows large red regions of concave curvature for the anthracene motif, whereas the C-H-donors shows opposite curvature.
Concerning the cluster Pd6, there are no particular directional intermolecular interactions in the packing warranting any discussion. The packing is shown in Fig. 9.
In contrast to mononuclear palladium complexes bearing terminal phenylmethanethiolate groups such as trans-     ized hit is the tetranuclear cluster [Pd 4 Se 4 ( 2 -SCH 2 Ph) 2 -(bis(diphenylphosphino)methane)Cl 2 ] (Cao et al. 1998;JIXRAJ). The aforementioned [Pd 6 ( 2 -SR) 12 ] clusters have found applications as precursors for the preparation of monodisperse PdS nanoparticles (Yang et al., 2007), for the self-assembly of palladiumthiolate bilayers (Thomas et al., 2001), as fluorescence materials  and as electrocatalysts for H and O evolution reactions (Gao & Chen, 2017). Also noteworthy is the observation that individual [Pd 6 ( 2 -SCH 2 CH 2 OH) 12 ] molecules are interconnected in the solid state by hydrogen bonds through the hydroxy groups of the thiolate ligands, thus generating an infinite three-dimensional supramolecular network (Mahmudov et al., 2013). Concerning the influence of hydrogen-bonding interactions on nuclearity and structure for other tiara-like palladium complexes, see: Martin et al. (2018). Recently, a structurally related Pt II thiolate complex [Pt 6 ( 2 -SC 12 H 23 ) 12 ] has been prepared and probed as a macrocyclic host to include an Ag I ion as guest (Shichibu et al., 2016).

Synthesis and crystallization
9-Anthracenecarboxaldehyde (206 mg, 1 mmol) and benzyl mercaptan (348 mg, 3 mmol) were suspended in conc. HCl (2 ml) and allowed to stir at room temperature. After 2 h, the reaction mixture was neutralized with aqueous NaHCO 3 solution and extracted with dichloromethane. The organic fraction was dried over Na 2 SO 4 , filtered and concentrated under reduced pressure. Purification by column chromatography using a hexane/dichloromethane solvent mixture as eluent gives a pale-yellow solid product in 80% yield (350 mg). Crystals suitable for single-crystal X-ray crystallography were grown by slow diffusion of hexane into a dichloromethane solution of L1, m.p. 438-440 K. 1  Reaction of L1 with PdCl 2 (PhCN) 2 : L1 (43 mg, 0.1 mmol) and PdCl 2 (PhCN) 2 (38 mg, 0.1 mmol) were dissolved in 5 ml of dichloromethane and allowed to stir at room temperature for 30 minutes. During the reaction, a red solution was obtained, which was kept in refrigerator overnight yielding yellow crystals of 9-anthraldehyde along with yellow-orange co-crystals of the [Pd 6 (SCH 2 Ph) 12 Áanthracene-9,10-dione]

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For both compounds, the H atoms were positioned geometrically (C-H = 0.95-1.00 Å ) and were refined using a riding model, with U iso (H) = 1.2U eq (C). Hydrogen atoms H1B, H14 and H21 for L1 were located in the difference-Fourier map and refined freely.

9-[Bis(benzylsulfanyl)methyl]anthracene (mo_b0159_0m)
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.

Hydrogen-bond geometry (Å, º)
Cg is the centroid of the C16/C17/C22-C24/C29 ring. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 1.20 e Å −3 Δρ min = −0.79 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.