Redetermination of the crystal structure of catena-poly[[[bis(ethylenediamine)platinum(II)]-μ-iodido-[bis(ethylenediamine)platinum(IV)]-μ-iodido] tetrakis(octane-1-sulfonate) dihydrate]

The redetermination of the structure of the title compound with the original measurement data revealed a centrosymmetric model in space group Pmcn, in contrast to the previous model in space group P21 cn.

The metal-halogen distances in crystals of MX-chain compounds characterize the physical properties based on the mixed-valence state. Compound (I) is one of the first examples of MX-chain structures including a long-chain alkyl group as an organic part. In a previous article (Matsushita & Taira, 1999), we have briefly reported the crystal data of (I), i.e. lattice parameter, space group, reliability indices, and have presented a view of the crystal packing; atomic coordinates and further structure data were not deposited at that time. The ISSN 2056-9890 reported structure was originally refined in the non-centrosymmetric space group P2 1 cn. However, close examination of the atomic coordinates strongly suggests that the crystal packing has an inversion center at (1/4, 1/2, 1/2). Therefore, the structure of (I) was redetermined in the centrosymmetric space group Pmcn and is reported here.

Structural comments
As shown in Fig. 1, the structure of (I) is built up of columns composed of square-planar [Pt(en) 2 ] 2+ and elongated octahedral trans-[PtI 2 (en) 2 ] 2+ cations stacked alternately, bridged by the I atoms, parallel to the c axis. The Pt and I sites lie on the same mirror plane, and form an infinite slight zigzag Á Á ÁI-Pt IV -IÁ Á ÁPt II Á Á Á chain. The I atoms are not located at the exact midpoint between adjacent Pt atoms and are equally disordered over two sites close to the midpoint. Thus, the Pt site is occupationally disordered by Pt II and Pt IV atoms. The valence ordering of the Pt site in (I) belongs to one of three different classes of the order-disorder problem pointed out by Keller (1982). The structure of (I) can be regarded as being of the one-dimensionally ordered structure type, with the other two directions being in a disordered state. The structural order-disorder situation of the Pt site in (I) has also been observed in a number of other MX-chain compounds (Beauchamp et al., 1982;Yamashita et al., 1985;Toriumi et al., 1993;Matsushita et al., 1992;Huckett et al., 1993;Matsushita, 2003Matsushita, , 2006. With respect to the two sites for the disordered I atoms, the shorter Pt-I distances are assigned to Pt IV -I and the longer ones to Pt II Á Á ÁI, as follows: I-Pt IV -I; Pt-I1 = 2.6888 (17), Pt-I2 = 2.7239 (17) Å , and I1-Pt IV -I2 = 179.1 (3) . IÁ Á ÁPt II Á Á ÁI; PtÁ Á ÁI1 = 3.2065 (17), PtÁ Á ÁI2 = 3.1732 (16) Å , and I1Á Á ÁPt II Á Á ÁI2 = 177.5 (2). Bond angles of the Pt-I chain are Pt-I1Á Á ÁPt = 178.3 (3) and Pt-I2Á Á ÁPt = 176.7 (2) . Other bond lengths and angles are given in Table 1.
bond linkages are a common structural characteristics of MXchain compounds. As a result of the intercolumnar hydrogen-bond linkages, as shown in Figs. 2 and 3, the columns form in layers parallel to the bc plane. The inorganic layer composed of the Pt-complex columns, -SO 3 À part of the octane-1-sulfonate ion and the water molecule of crystallization, are stacked alternately with organic layers composed of the long-chain alkyl groups along the direction of the a axis. The layer of the long-alkyl chain adopts an interdigitating structure.

Synthesis and crystallization
The title compound was prepared by a procedure previously reported (Matsushita & Taira, 1999). Metallic bronze plate-like crystals were obtained by recrystallization from an aqueous solution on slow evaporation.

Refinement
Although the refinement was performed on F in the previous report (Matsushita & Taira, 1999), the present refinement on basis of the original diffraction data was performed on F 2 . For better comparison with the previous model in space group P2 1 cn, the non-standard setting Pmcn of space group No. 62 (standard setting Pnma) was chosen. The present model converged with improved reliability factors, and the s.u. values for the bond lengths and angles also decreased.
The arrangements of both the Pt-complex cations and the anions with the long-alkyl chain suggest that the repeat unit is research communications The crystal packing of the title compound, viewed along the c axis. Blue dashed lines represent the hydrogen bonds. Orange solid lines indicate the unit cell.

Figure 3
The crystal packing of the title compound viewed along the b axis. Blue dashed lines represent the hydrogen bonds. Orange solid lines indicate the unit cell.
half of the c-axis dimension. However, the different orientations of the cations and the anions cause the repeat unit to be the c axis. Therefore, reflections with an index of l = odd are very weak. As the result, a rather low percentage of reflections with [I > 2(I)] are observed.
The H atoms were placed in geometrically calculated positions and refined as riding (C-H = 0.97 Å and N-H = 0.90 Å ), with the constraint U iso (H) = 1.5U eq (C, N). The H atoms of the water molecule were located from a Fourier map and restrained with a distance of O-H = 0.82 (2) Å and U iso (H) = 1.5U eq (O). The maximum and minimum electrondensity peaks lie within 0.75 Å of the Pt atom.

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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.