An acetonitrile solvatomorph of dichlorido(1,10-phenanthroline-5,6-dione)platinum(II)

In the title complex, [PtCl2(C12H6N2O2)]·CH3CN, the PtII atom lies in a slightly distorted square-planar arrangement defined by an N2Cl2 donor set. In the packed structure, columns of complex moieties are stacked such that the neighboring units are oriented at 180° and laterally displaced with respect to each other. This prevents any overlap of the phenanthroline rings and thus there is no possibility of any π–π interactions between aromatic rings.

In the title complex, [PtCl 2 (C 12 H 6 N 2 O 2 )]ÁCH 3 CN, the Pt II atom lies in a slightly distorted square-planar arrangement defined by an N 2 Cl 2 donor set. In the packed structure, columns of complex moieties are stacked such that the neighboring units are oriented at 180 and laterally displaced with respect to each other. This prevents any overlap of the phenanthroline rings and thus there is no possibility of anyinteractions between aromatic rings.
Three structural studies of dichloro(phendione)platinum(II) have been reported (Granger et al., 2005;Okamura et al., 2006;Roy et al., 2008). In all three studies, the complex was obtained as a DMSO solvate in the Cc space group. Two of these studies appear to be preliminary (Granger et al., 2005;Okamura et al., 2006) and the structural data were not submitted to the Cambridge Structural Database (CSD). The third study is thorough and its deposited data (CCDC 678530) are available for comparison (Roy et al., 2008). The structure reported here is an acetonitrile solvate belonging to a different monoclinic space group, P2 1 /c, resulting in a very different three dimensional packing arrangement compared to that in the reported study.
The title complex is essentially planar with three of the four bond angles about the Pt atom deviating slightly from the idealized square planar geometry. The N12-Pt1-N1 angle is significantly reduced to ~81° due to the constraints of the phendione ligand and two of the remaining bond angles are ~95° (Fig. 1). The unit cell contains four molecules each of the complex and the solvent, acetonitrile. Intermolecular interactions are responsible for the observed three dimensional array which may be described as consisting of zigzagging columns of stacked complex moieties, oriented 180° and laterally displaced with respect to each other. The separation between the stacked moieties alternates between 3.360 Å and 3.364 Å but due to the relative orientation of the stacked units, π-π stacking is not possible. The solvent molecules lie between the columns in the space created by the zigzagging (Fig. 2).
The three dimensional array of the title complex is clearly different from that of the reported structure (Roy et al., 2008). A major contributing factor to the different packing arrangements observed in the two studies is the relative orientation of the stacked complex moieties with respect to each other, 180° (current study) versus ~120° (reported (Roy et al., 2008)). The 120° orientation allows a partial overlap of the end rings of the stacked phendione ligands thereby increasing the potential for π-π interaction. Therefore, the structural study reported here is consistent with a solvate polymorph of [Pt(phendione)Cl 2 ] in which acetonitrile as the solvent leads to a different packing arrangement than in the DMSO solvate structure.

Synthesis and crystallization
The phendione ligand, K 2 PtCl 4 , and other reagents used in the syntheses were purchased from Sigma-Aldrich.
[Pt(DMSO) 2 Cl 2 ] was prepared from K 2 PtCl 4 and DMSO according to the literature (Romeo & Scolaro, 1998). The title complex was synthesized by adding the solid ligand in a 1:1 molar ratio to a stirred acetonitrile solution of [Pt(DMSO) 2 Cl 2 ] at maintained at 343 K. The pale yellow mixture was kept stirred at this temperature for ~2 hours while replenishing the solvent as necessary. During this time, as the color darkened, orange needles began to precipitate. The mixture was removed from heat and left covered at room temperature for slow crystallization. Good quality light orange needle-shaped crystals suitable for a crystal structure were obtained after ~6 hours. Yield: 40%.

Refinement
The H atoms were placed in idealized positions (aromatic C-H distances of 0.93 Å and methyl C-H distances of 0.96 Å) with displacement parameters U iso (H)set to 1.2U eq (C) for aromatic and 1.5U eq (C) for methyl protons.   Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.