Dichloridobis(2-methoxydibenzo[c,e][1,2]oxaphosphorine-κP)platinum(II) trichloromethane solvate

The title compound, [PtCl2(C13H11O2P)2]·CHCl3, has a rare PtCl2 bridging of two dibenzooxaphosphorine ligands through the metal atom. The PtII ion is in a slightly distorted square-planar environment. The trichloromethane solvent molecule shows rotational disorder (major occupancy is 0.75) and is placed near to the inversion centre at (1/2, 1/2, 0) in channels parallel to the a axis. The solvent molecule is linked to the complex molecule via intermolecular bifurcated C—H⋯Cl and C—H⋯O hydrogen bonds. The crystal structure is further stabilized by π–π interactions involving the benzene rings, with a centroid–centroid distance of 3.658 (8) Å.


Related literature
For the synthesis of the title compound and related compounds, see: Keglevich et al. (2008) and references therein. For a related phosphonite structure, see: Claver et al. (2000). For a description of the Cambridge Structural Database, see: Allen (2002).

Experimental
Crystal data [PtCl 2 (C 13   Hydrogen-bond geometry (Å , ). TH thanks the HAS CRC for financial support and also a computer purchase administered through OTKA grant No. T-049712 kindly provided by Professor A. Ká lmá n. The authors are also grateful for partial funding from OTKA grants T-067679 (AK and GyK) and T-75869 (MC and TH). supporting information Acta Cryst. (2009) Keglevich et al. (2008).
The asymmetric unit of the title compound is shown in Fig. 1. The structure of the complex in the crystalline state is in agreement with that reported from theoretical modeling. A more stable cis form is prefered over the trans, with a synperiplanar disposition of O-P-Pt-P torsion angles (O1-P1-Pt1-P2 ca 13.7 (3)° and O3-P2-Pt1-P1 ca 49.8 (3)°). However, Pt-P and Pt--Cl distances appear to be 0.05-0.1 Å shorter in the crystal structure, compared to a theoretical model.
The shortest ring center···center distance of 3.658 (8) Å is observed between C14-C19 benzene rings of complex molecules at (x, y, z) and (1 -x, -y, 2 -z). The only other crystal structure in the CSD (Allen, 2002) having P-Pt-P bridging is MARJEU from the Orpen group (Claver et al., 2000). MARJEU entraps two kinds of solvents in differing stoichiometric ratios (1 for THF and 0.76 for dichloromethane) in its crystal. The title compound also shows disorder of the solvent placed near to inversion centres at (1/2, 1/2, 0) in channels parallel to the a axis. Partial fixation of the solvent occurs via bifurcated C-H ··· O and C-H ··· Cl close contacts from the trichloromethane H atom to an alkoxy O4 atom and to Cl1 (Table 2). Electronic influences of these interactions may also be reflected in the unequal bonding geometry around the metal center. Existence of this C-H···X interaction seems to be also corroborated by IR investigations that will be reported elsewhere together with the room-temperature X-ray study of this compound. It appears from these results that the trichloromethane guest disorder is partly of kinetical nature. The C and H atom positions are relatively well kept while chlorine atoms change their positions with respect to the C-H bond.

S2. Experimental
Synthesis of the parent compound and related ones is reported by Keglevich et al. (2008). Recrystallization of the title dibenzo-oxaphosphorine complex from chloroform yielded X-ray quality crystals, solvent content of which became apparent only after the X-ray study.

S3. Refinement
H atoms were placed in idealized positions (C-H = 0.95-0.98 Å) and refined using a riding model with U iso (H) = 1.2-1.5U eq (C). The Cl atoms of the trichloromethane solvent molecule were disordered over two sites. The site occupancies and displacement parameters of the disordered atoms were alternately refined and during the final cycles of refinement the occupancies were fixed at 0.75 and 0.25. The C-Cl and Cl···Cl distances involving the disordered atoms were restrained to be equal, and also their U ij parameters were restrained to an approximate isotropic behaviour. The free and restrained refinement models for the solvent resulted in small differences in occupancies of chlorine sites. The supporting information restraints virtually improved C-Cl and C···C distances but the maximum positive residual peak appeared close to a minor occupancy Cl site in contrast to the free disorder model, where both maximum and minimum residual densities appeared close to the metal atom.

Figure 1
The asymmetric unit of the title compound, with the atomic numbering. Displacement ellipsoids are drawn at the 50% probability level. Suffixes A and B indicate major and minor components of the disordered solvent molecule.    0.039 (7) 0.032 (6) 0.038 (7) −0.008 (5