A one-dimensional iodido-bridged PtII/PtIV mixed-valence complex cation with a hydrogen sulfate counter-anion

Straight ⋯I—PtIV—I⋯PtII⋯ chains are observed in the mixed-valent title salt. Extensive hydrogen bonding involving the amino groups, hydrogen sulfate counter-anions and water molecules of crystallization stabilizes the crystal packing.

The metal-halogen distances in crystals of MX-chains characterize their physical properties based on the mixedvalence electronic state. The X-ray structure determination of (I) was performed to gain structural information for MXchains and to compare (I) with chlorido-and bromido-bridged Pt II /Pt IV mixed-valence complexes with a hydrogen sulfate counter-anion, i.e. [Pt II (en) 2 ][Pt IV X 2 (en) 2 ](HSO 4 ) 4 (X = Cl, Br) (Matsushita et al., 1992;Matsushita, 2003). ISSN 2056-9890

Structural commentary
The structures of the molecular components of (I) are displayed in Fig. 1. The asymmetric unit of (I) comprises half of a Pt-complex moiety, [Pt II (en) 2 ] 2+ or [Pt IV I 2 (en) 2 ] 2+ , one HSO 4 À anion, and a half-molecule of water. The Pt and I atoms of the Pt-complex moiety and the O atom of the water molecule are located on twofold rotation axes. The hydrogen sulfate anion lies on a general position. As shown in Fig. 2, the structure of (I) is built up of columns extending parallel to the b axis, composed of square-planar [Pt(en) 2 ] 2+ cations and elongated octahedral trans-[PtI 2 (en) 2 ] 2+ cations stacked alternately and bridged by the I ligands. The Pt and I atoms form an infinite straight Á Á ÁI-Pt IV -IÁ Á ÁPt II Á Á Á chain. The same straight chains are also observed in [Pt II (en) 2 ]-[Pt IV X 2 (en) 2 ](HSO 4 ) 4 (X = Cl, Br) (Matsushita et al., 1992;Matsushita, 2003). The title salt (I) is, however, not isotypic with these hydrogen sulfates of the chlorido-and bromidobridged complexes whereas the latter structures show isotypism with each other.
The I sites in (I) are not located at the exact midpoint between adjacent Pt sites and thus are equally disordered over two sites close to the midpoint. Consequently, the Pt site is occupationally disordered over the 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 a one-dimensionally ordered structure type, with the other two directions being in a disordered state. The structural orderdisorder situation of the Pt site in (I) has also been observed in the structures of a number of other MX-chains (Endres et al., 1980;Beauchamp et al., 1982;Cannas et al., 1983;Yamashita et al., 1985;Matsushita et al., 1992Matsushita et al., , 2017Toriumi et al., 1993;Huckett et al., 1993;Matsushita, 2003Matsushita, , 2005aMatsushita, ,b, 2015Matsushita & Taira, 2015).
As a result of the intercolumnar hydrogen-bond linkages, N1-H1AÁ Á ÁO1Á Á ÁH2B-N2 between the Pt-complex columns and hydrogen sulfate ions, and N2-H2AÁ Á Á O5Á Á ÁH2A-N2 between the Pt-complex columns and the water molecule of crystallization, represented by light-blue dashed lines in Fig. 3, the columns are organized in layers parallel to the ab plane.

Figure 3
The crystal packing of compound (I), projected on the ac plane. Magenta dashed lines represent hydrogen bonds between the hydrogen sulfate ions. Light-blue dashed lines represent the other hydrogen bonds. Solid orange lines indicate the unit cell.  (Matsushita et al., 1992;Matsushita, 2003). In these hydrogen sulfates, however, the hydrogen atoms of the hydrogen sulfate anions, which also hydrogen-bond to neighbouring hydrogen sulfate anions, are not disordered. The lengths of the S-O(H) bond and the S-O bond for the acceptor O atom are 1.494 (10) and 1.420 (8) Å , respectively, for the chlorido-bridged complex and 1.45 (2) and 1.35 (3) Å for the bromido-bridged complex. These longer and shorter lengths for the S-O bonds indicate that the hydrogen atoms of the hydrogen sulfate ions are not disordered.
The intracolumnar, intercolumnar and interlayer hydrogenbonds, as discussed above, stabilize the crystal packing in (I).

Synthesis and crystallization
A preparation procedure for the title salt was previously reported (Matsushita et al., 1989). In the literature, the obtained salt was originally reported as a tetrahydrate. The present X-ray crystallographic study, however, reveals the salt to be a dihydrate. Probably, the amount of water molecules of the salt was overestimated at that time due to the hygroscopic nature of the polycrystalline sample because the salt was obtained from a concentrated sulfuric acid solution. The powder X-ray diffraction pattern simulated on the basis of the present single-crystal data is in good agreement with the experimental data reported previously for the powder sample.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Atoms I1, I2 and H2 and H4 are each disordered over two positions and were modelled with an occupancy factor of 0.5. Hydrogen atoms were placed in geometrically calculated positions and refined as riding, with C-H = 0.97 Å , N-H = 0.89 Å , and O-H = 0.82 Å , and with U iso (H) = 1.2U eq (C,N) and 1.5U eq (O). Hydrogen atoms bonded to O atoms were calculated by the HFIX 147 command of SHELXL (Sheldrick, 2015b). Evaluation of the S-O2 bond length for atom H2, the S-O4 bond length for atom H4, and the O3Á Á ÁO5 and O1Á Á ÁO5 hydrogen bonds together with other hydrogen-bonding interactions showed the expected behaviour, and therefore the localization of these H atoms was considered to be correct. The maximum and minimum electron density peaks are located 0.67 and 0.17 Å , respectively, from atom Pt.

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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )