Chlorido(dimethyl sulfoxide-κS)[2-(2-pyridyl)phenyl-κ2 N,C 1]platinum(II)

In the title compound, [Pt(C11H8N)Cl(C2H6OS)], the S atom of dimethyl sulfoxide is trans to the pyridyl N atom [Pt—S = 2.2181 (11) Å] and the chlorido ligand is trans to the carbon donor of 2-(2-pyridyl)phenyl [Pt—Cl = 2.4202 (10) Å]. The [2-(2-pyridyl)phenyl]platinum(II) unit forms a one-dimensional stack along the c axis with two independent interplanar separations of 3.44 (9) and 3.50 (2) Å.


Comment
Interests over many years have concentrated on the molecular catalysis of Pt II complexes in photochemical hydrogen production from water (Sakai et al., 1993;Ozawa et al., 2006;Ozawa, Yokoyama et al., 2007). The results obtained so far suggest that destabilization of the HOMO, which generally corresponds to the filled Pt II d z 2 orbital, gives rise to the higher H 2 -evolving activity of the complexes . It has also been ascertained that the mononuclear Pt II complexes possessing a cis-PtCl 2 unit, such as cis-PtCl 2 (NH 3 ) 2 , PtCl 2 (4,4'-dicarboxy-2,2'-bipyridine), and PtCl 2 (2,2'-bipyrimidine), exhibit considerably higher H 2 -evolving activity in comparison with those only having the amine or pyridyl type of neutral ligands, such as [Pt(NH 3 ) 4 ] 2+ and [Pt(bpy) 2 ] 2+ (Ozawa, Yokoyama et al., 2007). In this context, the 2-phenylpyridinate (ppy) ligand was selected because of the well known strong σ-donating character of the C(ppy) donor, expecting the higher energy level of the HOMO for the Pt II (ppy) complexes. As a result, the first water-soluble salt of [Pt(ppy)Cl 2 ] -, that is, [K(18-crown-6)][Pt(ppy)Cl 2 ] . 0.5H 2 O (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) [abbreviated as compound (II)], was recently prepared in our group and its catalytic activity in photochemical hydrogen production from water was examined in detail (Kobayashi et al., in submission). The title compound, Pt(ppy)Cl(DMOS-S) (DMSO = dimethyl sulfoxide) [abbreviated as compound (I)], was first prepared from recrystallization of (II) from DMSO, but an improved synthetic route is reported in this work (see Experimental Section). It has been ascertained that the H 2evolving activity of (I) is much lower than that of (II), the reason for which remains ambiguous at the moment.
The donor atoms, except for the sulfur atom S1, comprise a planar geometry and the Pt atom (Pt1) does not deviate from this plane at all. The four-atom r.m.s. deviation, given in the best-plane calculation for the plane defined by atoms N1, C11, Cl1, and Pt1, was negligible (0.0003). Hereafter, this plane is defined as the Pt coordination plane. The sulfur atom (S1) and the oxygen atom (O1) of DMSO are only slightly shifted out of this plane by 0.067 (5) and 0.045 (8) Å, respectively. The torsion angles given by C11-Pt1-S1-O1 = 2.4 (2) and Cl1-Pt1-S1-O1 = -177.83 (17)° also reveal that the oxygen atom of DMSO is not largely shifted out of the coordination plane. Thus, it can be considered that (I) adopts a pseudo mirror symmetry. The benzene ring consisting of atoms C6-C11 is nearly coplanar with the coordination plane, where the dihedral angle between the benzene and the coordination planes is calculated as 0.7 (2)°. The pyridyl plane defined by atoms N1 and C1-C5 is slightly declined with respect to the coordination plane by 2.8 (2)°. The dihedral angle between the two aromatic rings is 2.5 (2)°.
On the other hand, compound (I) forms a one-dimensional stack along the c axis based on the π-π stacking interactions between the phenylpyridinatoplatinum(II) units (see Fig. 2). The separation between the two adjacent planes is estimated as 3.44 (9) Å for the stack shown in Fig. 4 and 3.50 (2) Å for that in Fig. 5. In the former (Fig. 4), atoms C1 i , C5 i , N1 i , and Pt1 i have an interaction to the phenylpyridinate moiety originally located and therefore shifts of these atoms from the best plane defined by atoms N1 and C1-C11 are used to calculate the separation of the two stacked planes at this geometry. In the latter (Fig. 5), atoms N1 ii , C1 ii , C ii 2, C5 ii , C6 ii , C10 ii , C11 ii , and Pt1 ii are involved in the π-stacking association and their shifts from the best plane defined by atoms N1 and C1-C11 are similarly used to calculate the separation at this geometry.
In these geometries, strong d-π interactions also contribute to the stabilization of stacking associations [Pt1-C4 i = 3.525 (4) and Pt1-C4 ii = 3.523 (4) Å; symmetry codes: . A good quality single-crystal was prepared by diffusion of methanol into a DMSO solution of (I).

Refinement
All H atoms were placed in idealized positions (methyl C-H = 0.98 Å and aromatic C-H = 0.95 Å), and included in the refinement in a riding-model approximation, with U iso (H) = 1.5U eq (methyl C) and U iso (H) = 1.2U eq (aromatic C). In the final difference Fourier map, the highest peak was located 0.83 Å from atom Pt1. The deepest hole was located 1.07 Å from atom H9. Fig. 1. The molecular structure of (I) showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.

Special details
Experimental. The first 50 frames were rescanned at the end of data collection to evaluate any possible decay phenomenon. Since it was judged to be negligible, no decay correction was applied to the data.   (2)