trans-Bis[bis(diphenylphosphanyl)methane-κ2 P,P′]dichloridoruthenium(II): a triclinic polymorph

The title compound crystallizes with two different inversion-symmetric molecules having a distorted octahedral {P4Cl2} coordination environment, and an average P—Ru—P bite angle of 71.1°.

The title compound, [RuCl 2 (C 25 H 22 P 2 ) 2 ] or [RuCl 2 (dppm) 2 ] (dppm = bis(diphenylphosphanyl)methane, C 25 H 22 P 2 ) crystallizes as two half-molecules (completed by inversion symmetry) in space group P1 (Z = 2), with the Ru II atoms occupying inversion centers at 0,0,0 and 1/2, 1/2, 1/2, respectively.The bidentate phosphane ligands occupy equatorial positions while the chlorido ligands complete the distorted octahedral coordination spheres at axial positions.The bite angles of the phosphane chelates are similar for the two molecules [(P-Ru-P) avg.= 71.1 � ], while there are significant differences in the twisting of the methylene backbone, with a distance of the methylene C atom from the RuP 4 plane of 0.659 (2) and 0.299 (3) A ˚, respectively, and also for the phenyl substituents for both molecules due to variations in weak C-H� � �Cl interactions.

Structure description
Ruthenium complexes have proven versatility in catalysis (Younus et al., 2015;Saha et al., 2022) and anti-cancer therapy (Levina et al., 2009).Hence, the quest for contributions towards advancing the exploration of ruthenium-based complexes in coordination chemistry is still on-going.Moreover, in the context of advancing sustainability with inexpensive materials, ruthenium(II) phosphane complexes are widely used as catalysts, e.g. in the hydrogenation of carbon dioxide to methanol (Wesselbaum et al., 2012), and formic acid (Tai et al., 2002), as well as for the homogeneous catalytic degradation of the latter (Treigerman & Sasson, 2017).
The asymmetric unit of the title compound comprises two half-molecules (Fig. 1), with the Ru II atoms situated at inversion centers (at 0,0,0 and 1/2, 1/2, 1/2).Bond lengths and angles of the Ru II coordination spheres (Table 1) are within the range of the monoclinic polymorph (Chakravarty et al., 1984) or the solvated triclinic solvates (Treigerman & Sasson, 2017;Figueira et al., 2006;Lynam et al., 2008).Fig. 2a shows the overlay of the two molecules present in the title compound; data reports

Figure 1
The molecular structures of the two molecules in the title compound.Displacement ellipsoids are drawn at the 50% probability level (H atoms were removed for clarity).Non-labelled atoms are generated by inversion symmetry (symmetry operations: À x, À y, À z for molecule Ru1; À x + 1, À y + 1, À z + 1 for molecule Ru2).   the root-mean-square deviation (r.m.s.d.) between the two molecules is 0.6828 A ˚.The non-solvated monoclinic polymorph and the title compound appear to be closely related as both have molecules situated at inversion centers, albeit there are two independent special positions for the title compound versus the one of the reported monoclinic polymorph.Further to this, a comparative overlay of the molecules in the two polymorphs, i.e. each of the two independent molecules of the title compound overlayed with that of the reported monoclinic polymorph (Fig. 2b,c), reveals differences in the orientations of some phenyl rings; r.m.s.d. are 0.3079 A ˚for overlays of molecule Ru1 of the title compound and that of the monoclinic polymorph, and 0.4154 A ˚for overlays of molecule Ru2 of the title compound and that of the monoclinic polymorph.
The inversion symmetry of all molecules in the triclinic title polymorph and the monoclinic polymorph causes a trans configuration of all ligands in the octahedral coordination environment, with the bis-phosphane ligands chelating in equatorial positions and the Cl ligands situated at axial positions.Most noticeable are the bite angles (P-Ru-P) avg. of 71.1 � in the title compound, causing a considerable distortion of the ideal octahedral environment.Interestingly, the methylene backbone is twisted out from the equatorial plane differently for the two molecules [distance of the C atom from the RuP 4 plane 0.659 (2) A ˚, dihedral angle between the P-C-P plane and the equatorial plane 31.31(10) � for molecule Ru1 and 0.299 (3) A ˚and 14.00 (10) � , respectively, for molecule Ru2].This may be due to the different intra-and intermolecular C-H� � �Cl interactions, which consolidate the crystal packing in the title compound (Table 2, Fig. 3).

Synthesis and crystallization
Bis(diphenylphosphanyl)methane (30 mg, 0.08 mmol, 2 eq.) was added to a solution of the dichlorido(� 6 -benzene)ruthenium(II) dimer (20 mg, 0.04 mmol, 1 eq.) in methanol at room temperature for 24 h with continuous stirring.Yellow crystals of the title compound were obtained by slow evaporation of the solvent.

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

Figure 2 (
Figure 2 (a) Overlay of the two molecules Ru1 (blue) and Ru2 (green) of the title compound; (b) overlay of molecule Ru1 of the title compound (blue) and that of the monoclinic polymorph (red); (c) overlay of molecule Ru2 of the title compound (green) and that of the monoclinic polymorph (red).

Table 3
Experimental details.
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