Crystal structure of cis-[1,2-bis(diphenylphosphanyl)ethene-κ2 P,P′]dichloridoplatinum(II) chloroform disolvate: a new polymorph

A third monoclinic polymorph of the title compound is described. In the crystal, it exhibits C—H⋯Cl hydrogen bonds and face-on Cl⋯π interactions involving the chloroform disolvate molecules. Intermolecular weak offset π–π interactions are also present between the aromatic rings of the ligands.


Structural commentary
The molecular structures of the cis-dppe ligand and the title compound (I) are shown in Fig. 1. This Pt-ligand complex features a square-planar geometry around the Pt II metal center with bidentate coordination by the phosphorus atoms of the cis-dppe ligand. The metal coordination sphere is completed by two chloride anions.
As for the previously reported polymorphs of compound (I), structure HINCIQ (Oberhauser et al., 1998a) was solved in space group P2 1 /n without solvent in the unit cell, while structure ZOLYII (Oberhauser et al., 1995) was solved in the space group P2 1 /m as a chloroform and methylene chloride solvate. The latter complex molecule possesses mirror symmetry with the mirror bisecting the Pt atom and central C C bond of the cis-dppe ligand. Selected bond distances and bond angles for the title compound (I), and the two other monoclinic polymorphs are given in Table 1.
When comparing these two structures to the title compound, the bond lengths and angles around the Pt II center of all three structures are, unsurprisingly, quite similar. The Pt-P bond lengths range from 2.210 (2) to 2.219 (2) Å , while the Pt-Cl bond lengths range from 2.358 (2) to 2.366 (3) Å . The P-Pt-P bond angles range from 86.66 (11) to 87.08 (5) , while the Cl-Pt-Cl bond angles range from 90.33 (7) to 91.03 (5) . The 4 descriptor for fourfold coordination (where, for the extreme forms 4 = 0.00 for square-planar, 1.00 for tetrahedral and 0.85 for trigonal-pyramidal; Yang et al., 2007) of the Pt atoms range from 0.02 for compound (I), 0.05 for HINCIQ and 0.0 for ZOLYII, indicating perfect square-planar coordination spheres for each Pt atom.

Supramolecular features
In the crystal of (I), the metal-ligand complex is linked to the chloroform solvate molecules by C-HÁ Á ÁCl hydrogen bonds and ClÁ Á Á interactions. The hydrogen atoms of both chloroform molecules are engaged in weak hydrogen bonds with the metal-bound chlorine atoms ( Fig. 2 and Table 2). The DÁ Á ÁA distances range from 3.616 (9) to 3.789 (10) Å , while the D-HÁ Á ÁA bond angles range from 132 to 158 . Three face-on ClÁ Á Á interactions (Imai et al., 2008) are also present involving the chlorine atoms of the chloroform molecules and the

Figure 2
A view along the b axis of the title compound showing the C-HÁ Á ÁCl hydrogen bonds (blue dotted lines) and chlorineÁ Á Á interactions (red dashed lines) found in the crystal lattice [symmetry code: (i) x, Ày + 1 2 , z À 1 2 ].

Figure 1
A view of the molecular structure of the title compound, with the atom labeling. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms bonded to the ligand have been omitted for clarity. Table 2 Hydrogen-bond geometry (Å , ). aromatic rings of the cis-dppe ligand ( Fig. 2 and Table 3). The ClÁ Á Áring centroid distances for these interactions range from 3.242 (5) to 3.441 (7) Å , while the C-ClÁ Á Áring centroid angles range from 139.2 (5) to 160.3 (4) .

Database survey
The Cambridge Structural Database (CSD, version 5.39, February 2018; Groom et al., 2016) contains 21 structures in which the cis-dppe ligand is coordinated to a Pt II center. In addition to the two polymorphs described above, the most similar cis-dppe-Pt II coordination complexes include AFEXEO (Vaz et al., 2002) and FOQPUW (Lobana et al., 2000), where the Pt II center is bound by two thiolate ligands (-SPh and -SPy, respectively). Another structure related to the title compound is KADQEL (Oberhauser et al., 1998b) in which the Pt II center is coordinated by two acetonitrile molecules. Finally, structure ZOLYOO (Oberhauser et al., 1995) contains one Pt II center coordinated by two cis-dppe ligands with two outer sphere tetraphenylborate molecules as counter-anions. In each of these structures, the bond lengths and angles are similar to those described above for the title compound.

cis-[1,2-Bis(diphenylphosphanyl)ethene-κ 2 P,P′]dichloridoplatinum(II) chloroform disolvate
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.