Crystal structure of poly[[diaquatetra-μ2-cyanido-iron(II)platinum(II)] acetone disolvate]

In the title polymeric complex, the tetracyanoplatinate anions bridge the FeII cations to form infinite two-dimensional layers that propagate along the bc plane. Two guest molecules of acetone per FeII are located between the layers. These guest acetone molecules interact with the coordinated water molecules by O—H⋯O hydrogen bonds.

In the title polymeric complex, {[FePt(CN) 4 (H 2 O) 2 ]Á2C 3 H 6 O} n , the Fe II cation has an octahedral [FeN 4 O 2 ] geometry being coordinated by two water molecules and four cyanide anions. The Pt cation is located on an inversion centre and has a square-planar coordination environment formed by four cyanide groups. The tetracyanoplatinate anions bridge the Fe II cations to form infinite twodimensional layers that propagate in the bc plane. Two guest molecules of acetone per Fe II are located between the layers. These guest acetone molecules interact with the coordinated water molecules by O-HÁ Á ÁO hydrogen bonds.

Chemical context
Hofmann clathrates and their analogues form one the most famous families of compounds that are able to incorporate guest molecules. The first clathrate was obtained by Hofmann and Kü spert in 1897 (Hofmann & Kü spert, 1897) and was of composition [Ni(NH 3 ) 2 Ni(CN) 4 ]Á2C 6 H 6 . It was a 2D coordination compound formed by infinite cyanometallic layers that propagate along the ab plane. The 2D system was supported by ammine axial ligands, and guest molecules of benzene were trapped between the layers.
Additionally, the characteristics of spin transition in coordination compounds are known to be extremely sensitive to any changes in the chemical environment. As Hofmann clathrate analogues are very easy to modulate, numerous SCO complexes with very different temperatures, abruptnesses and hystereses of SCO were obtained. Moreover, the ability of Hofmann clathrate analogues to incorporate guest molecules provided SCO-based chemical sensors (Ohba et al., 2009

Structural commentary
The title compound crystallizes in the P4/mmm space group. The Fe II cation has a [FeN 4 O 2 ] coordination environment ( Fig. 1) comprising four CN À anions in the equatorial positions [Fe1-N1 = 2.158 (5) Å ] and two water molecules in the axial positions [Fe1-O1 = 2.130 (6) Å ]. The Fe-O bonds are slightly shorter than the Fe-N bonds, thus leading to a compressed octahedral geometry. Judging by the bond length, the Fe II cation is in a high-spin state at the experimental temperature (180 K). This is corroborated by the presence of H 2 O molecules in the coordination sphere of Fe II . The cyanide anions connect the Fe II and Pt II cations into infinite twodimensional layers. The Pt II cation is located at a fourfold rotation axis and possesses a square-planar geometry [Pt1-C1 = 1.993 (6) Å , C1-Pt-C1 = 90 ]. Thanks to the tetragonal symmetry of the crystalline compound, no deviation from an ideal octahedron is observed for Fe II , AE|90 -| = 0 , where is the N-Fe-N or O-Fe-N angles. Additionally, the compound incorporates two guest molecules of acetone per Fe II centers.

Supramolecular features
The crystalline structure is connected by bridging tetracyanoplatinate moieties, which form a two-dimensional grid that propagates along the ab plane (Fig. 2) A fragment of the molecular structure of the title compound showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level [symmetry codes: (i) x, Ày, 1 À z; (ii) Àx, Ày, z;

Figure 2
View of the crystal structure of the title compound in the bc plane showing the two-dimensional cyanometallic layers. Hydrogen bonds are shown as dashed lines. Acetone H atoms are omitted for clarity. symmetry, no deviation from linearity for the Fe-N-C-Pt linkages is observed [Fe-N-C = 180 , N-C-Pt = 180 , C-Pt-C = 180 ]. The distance between parallel cyanometallic layers is 7.973 (6) Å . The guest acetone molecules are located between the cyanometallic layers. Each oxygen atom of the coordinated water molecules interacts with acetone by O-HÁ Á ÁO hydrogen bonds (Fig. 3, Table 1), creating a threedimensional supramolecular framewor. The size of the available voids between the cyanometallic layers allows the acetone molecules to rotate freely, thus leading to disorder of the acetone molecules over four positions.

Synthesis and crystallization
Crystals of the title compound were obtained by slow diffusion (three layers) in a 3 ml tube. The first layer contained 19 mg (0.05 mmol) of K 2 [Pt(CN) 4 ] in 0.5 ml of water. The middle layer contained 1.5 ml of a water:acetone (1:1) solution. The third layer contained 25 mg (0.05 mmol) of Fe(OTs) 2 Á6H 2 O in 0.4 ml of acetone and 0.1 ml of water. The colourless crystals grew in the middle layer within three weeks and were kept in the mother solution prior to measurements.

Poly[[diaquatetra-µ 2 -cyanido-iron(II)platinum(II)] acetone disolvate]
Crystal data 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.