[μ2-Bis(diphenylphosphanyl)hexane]bis[undecacarbonyl-triangulo-triruthenium(3 Ru—Ru)] hexane monosolvate: crystal structure and Hirshfeld surface analysis

The title crystal features two Ru3(CO)11 fragments linked by a Ph2P(CH2)6PPh2 bridge, the latter with an all-trans conformation. The molecular packing features C—H⋯O, as well as C≡O⋯π(arene) interactions.

In the title cluster complex hexane solvate, [Ru 6 (C 30 H 32 P 2 )(CO) 22 ]ÁC 6 H 14 , two Ru 3 (CO) 11 fragments are linked by a Ph 2 P(CH 2 ) 6 PPh 2 bridge with the P atoms equatorially disposed with respect to the Ru 3 triangle in each case; the hexane solvent molecule is statistically disordered. The RuÁ Á ÁRu distances span a relatively narrow range, i.e. 2.8378 (4) to 2.8644 (4) Å . The hexyl chain within the bridge has an all-trans conformation. In the molecular packing, C-HÁ Á ÁO interactions between cluster molecules, and between cluster and hexane solvent molecules lead to a three-dimensional architecture. In addition, there are a large number of C OÁ Á Á(arene) interactions in the crystal. The importance of the carbonyl groups in establishing the packing is emphasized by the contribution of 53.4% to the Hirshfeld surface by OÁ Á ÁH/HÁ Á ÁO contacts.

Chemical context
In the realm of cluster chemistry, diphosphane ligands are known to maintain the integrity of the metal core during chemical reactions (Kabir & Hogarth, 2009). In the solid state, diphosphane ligands are known to adopt a variety of bonding modes towards triruthenium clusters, including monodentate, chelating, edge-bridging and linking two clusters (Bruce et al., 1982;Lozano Diz et al., 2001;Shawkataly et al., 2012). The motivation for studying triruthenium cluster complexes containing diphosphane ligands arises primarily due to these complexes making attractive starting materials for further reactivity studies (Kabir & Hogarth, 2009;Rajbangshi et al., 2015, Shawkataly et al., 2016. Despite this, only relatively few compounds with diphosphane ligands connecting two triruthenium clusters have been structurally characterized (Bruce et al., 1982;Van Calcar et al., 1998;O'Connor et al., 2003;Kakizawa et al., 2015). Our interest in synthesizing the title [Ru 3 (CO) 11 ] 2 [Ph 2 P(CH 2 ) 6 PPh 2 ] cluster is to enable a comparison of the structural variations that arise from lengthening of the organic backbone in the diphosphane ligand. Furthermore, the joining of smaller cluster units with such spacer ligands is a useful method for the construction of larger aggregates (Bruce et al., 1985;Kakizawa et al., 2015). In the present study, two triruthenium cluster units were successfully connected through a bidentate bridging Ph 2 P(CH 2 ) 6 PPh 2 ligand in the compound [Ru 3 (CO) 11 ] 2 [Ph 2 P-(CH 2 ) 6 PPh 2 ], which was isolated as a 1:1 n-hexane solvate, (I). Herein, the crystal and molecular structures of (I) are ISSN 2056-9890 described, as well as an analysis of the calculated Hirshfeld surface.

Structural commentary
The molecular structure of the cluster molecule in (I) is shown in Fig. 1. The asymmetric unit comprises two Ru 3 (CO) 11 cluster molecules linked by a Ph 2 P(CH 2 ) 6 PPh 2 bridge and a hexane molecule which is statistically disordered over two sets of sites. The phosphane P atom occupies a position effectively coplanar with the Ru 3 core in each case, i.e. an equatorial site. The two Ru 3 cluster residues are each constructed about a triangular Ru 3 core, and the Ru-Ru edges span a relatively narrow range of distances, i.e. 2.8378 (4) Å for Ru2Á Á ÁRu3 to 2.8644 (4) Å , for Ru1Á Á ÁRu3. Each of the carbonyl ligands occupies a terminal position, with the Ru-C O angles ranging from 169.7 (4) for Ru-C10 O10 to 179.4 (4) for Ru5-C18 O18. The hexyl chain in the diphosphane ligand has an all-trans conformation, with the P1/P2-C-C-C torsion angles being À177.8 (3) and 175.5 (2) , respectively, and the C-C-C-C torsion angles ranging from 173.7 (3) for C33-C34-C35-C36 to À177.4 (3) for C32-C33-C34-C35. The consequence of this is that the pairs of Pbound phenyl rings lie to either side of the chain.

Supramolecular features
The molecular packing of (I) comprises a complex network of C-HÁ Á ÁO and C OÁ Á Á interactions. The C-H donors for the C-HÁ Á ÁO interactions are either methylene-or phenyl-H, Table 1, and by themselves define a three-dimensional architecture, Fig. 2. Additional stability to the crystal is provided by a number of C OÁ Á Á(arene) interactions, either with end-on or side-on approaches. Further discussion and details of the identified C OÁ Á Á(arene) interactions are found below in Analysis of the Hirshfeld surface (x4). The closest interactions between the cluster molecule and the solvent hexane molecule are of the type solvent-methylene-C-HÁ Á ÁO(carbonyl), Table 1. The solvent molecules reside in cavities defined by the cluster molecules.

Analysis of the Hirshfeld surface
The Hirshfeld surface calculations of (I) were performed in accord with a recent publication on a related heavy-atom complex and its dioxane solvate (Jotani et al., 2017). The presence of the carbonyl groups in (I) lead to their participation in C-HÁ Á ÁO, C OÁ Á Á and CÁ Á ÁO/OÁ Á ÁC interactions, Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the Ru 6 cluster molecule in (I), showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.

Figure 2
A view of the unit-cell contents shown in projection down the b axis. The C-HÁ Á ÁO interactions are shown as blue dashed lines. and the Hirshfeld surfaces mapped over d norm , Fig. 3, indicate the influence of these in the crystal. Of the C-HÁ Á ÁO interactions summarized in Table 1, the donors and acceptors of more influential contacts are viewed as bright-red spots near the phenyl-H52 and C55, diphosphane-hexyl-H32B and C82X, and carbonyl-O4, O8, O14 and O19 atoms, whereas the comparatively weak C-HÁ Á ÁO contacts are viewed as faintred spots near the phenyl-C42, hexane-C81X and C82X, and carbonyl-O7, O11 and O17 atoms in Fig. 3. In addition, the presence of bright-red spots near the O2, O13, O21 and C21 atoms and the diminutive-red spots near the O1, O4, O19 and C15 atoms in Fig. 3, are also indicative of short inter-atomic OÁ Á ÁO and CÁ Á ÁO/OÁ Á ÁC contacts effective in the crystal. The donors and acceptors of intermolecular interactions can also be viewed as blue and red regions, respectively, on the Hirshfeld surface mapped over electrostatic potential for the cluster molecule in Fig. 4a, and for the hexane molecule in Fig. 4b. Two intramolecular C-OÁ Á Á contacts, i.e. one between carbonyl-O9 and the phenyl C51-C56 ring, and the other between carbonyl-O21 and the phenyl C71-C76 ring are also illustrated through black, dotted lines in Fig. 4a. The cavity occupied by the hexane molecule, showing the relevant C-HÁ Á ÁO contacts, Table 1, is highlighted in Fig. 5. The overall two-dimensional fingerprint plots for the cluster molecule alone and for (I) are shown in Fig. 6a and clearly indicate the significance of the solvent molecule on the packing. This is also evident from the percentage contribution from the different surface contacts summarized in Table 2     two specific types of interactions leading to two distinct distributions of points in the delineated fingerprint plot of Fig. 6c. The pair of sharp spikes having green aligned points within the plot and with tips at d e + d i $ 2.5 Å are the result of C-HÁ Á ÁO interactions involving cluster-bound atoms as donors and acceptors; the points corresponding to short interatomic weak C-HÁ Á ÁO contacts (Table 1) and OÁ Á ÁH/ HÁ Á ÁO contacts (Table 3) are merged within the plot. On the other hand, the exterior portion with broad tips at d e + d i $ 2.6 Å are due to C-HÁ Á ÁO interactions involving hexanebound atoms as donors and carbonyl-oxygen atoms as acceptors. The comparison of OÁ Á ÁH/HÁ Á ÁO delineated fingerprint plots for in Fig. 6c confirm this observation. The involvement of hexane-H83A and H83B atoms in the short interatomic CÁ Á ÁH/HÁ Á ÁC contacts (Table 3) results in forceps-like peaks at d e + d i $ 2.9 Å in the delineated fingerprint, Fig. 6d. The 7.8% contribution from CÁ Á ÁO/OÁ Á ÁC contacts to the Hirshfeld surface of (I) is due to the involve-ment of all carbonyl-O atoms (except O5) either in short interatomic CÁ Á ÁO/OÁ Á ÁC contacts, Table 3, or in end-on or side-on C OÁ Á Á interactions, summarized in  Table 3 Summary of short inter-atomic (Å ) in (I).

Figure 5
A view of Hirshfeld surface mapped over d norm about a hexane molecule within a cavity defined by Ru 6 -cluster molecules and showing intermolecular C-HÁ Á ÁO contacts as black dashed lines.  impact of end-on metal-C OÁ Á Á(arene) interactions upon supramolecular aggregation patterns has been addressed in the recent literature (Zukerman-Schpector et al., 2011, 2012 Fig. 6f, has a distribution of points within the rocket-shape with the tip at d e + d i $ 2.9 Å , extending up to 3.0 Å , and is the result of significant short OÁ Á ÁO contacts summarized in Table 3. The small contribution from CÁ Á ÁC contacts on the Hirshfeld surfaces of (I) has a negligible effect on the packing.

Database survey
The most closely related structure in the literature is that of the dppe (Ph 2 PCH 2 CH 2 PPh 2 ) analogue, i.e. Ru 3 (CO) 11 (dppe)Ru 3 (CO) 11 (Van Calcar et al., 1998). The centrosymmetric molecule presents the same key features as described above for the cluster molecule in (I). There are only a handful of structures whereby two triangular clusters are bridged by a Ph 2 P(CH 2 ) 6 PPh 2 ligand as in (I). The most closely related of these to the present report is formulated as Fe 3 (CO) 11 (Ph 2 P(CH 2 ) 6 PPh 2 )Fe 3 (CO) 11 (Ferguson et al., 1991). The difference in this centrosymmetric molecule, cf. (I), is that there are two 2 -bridging carbonyls connecting the Fe atom bonded to P to one of the other Fe atoms of the triangle; the remaining Fe atom is bound to four terminal carbonyl ligands as in (I).

Synthesis and crystallization
The reagents Ru 3 (CO) 12 (200.0 mg, 0.0003 mol) and Ph 2 P(CH 2 ) 6 PPh 2 (70.0 mg, 0.0002 mol) were mixed in distilled tetrahydrofuran (25 ml). The reaction mixture was treated dropwise with sodium diphenylketyl solution until the colour of the mixture turned from orange to dark-red followed by stirring for 30 min. The reaction was monitored by thin-layer chromatography (TLC). The solvent was removed under reduced pressure and the product was separated by preparative TLC (2:3 dichloromethane:n-hexane) to afford three bands. The second band was characterized as [Ru 3 (CO) 11 ] 2 (Ph 2 P(CH 2 ) 6 PPh 2 ). Orange laths were grown by solvent/solvent diffusion of CH 2 Cl 2 /n-hexane at 283 K.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. The carbon-bound H atoms were placed in calculated positions (C-H = 0.95-0.99 Å ) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2-1.5U eq (C). The hexane molecule was statistically disordered over two sites and the atomic positions of each were refined independently but, the C-C bond lengths for each component were refined with the distance restraint C-C = 1.50AE0.005 Å . The anisotropic displacement parameters were restrained to be almost isotropic and those for matching atoms to be similar. Owing to poor agreement, one reflection, i.e. 254, was omitted from the final cycles of refinement. The maximum and minimum residual electron density peaks of 2.43 and 1.32 e Å À3 , respectively, were located 1.34 and 0.50 Å from the C22 and Ru6 atoms, respectively.  Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

[µ 2 -Bis(diphenylphosphanyl)hexane]bis[undecacarbonyl-triangulo-triruthenium(3 Ru-Ru)] hexane monosolvate
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.