Crystal structure of μ-fluorido-bis{(η4-cyclooctadiene)[hexafluoridoantimonato(V)]platinum(II)} hexafluoridoantimonate(V) hydrogen fluoride 0.75-solvate

In the cation of the title compound, [Pt2(COD)2F(SbF6)2]SbF6·0.75HF, a fluorine atom bridges two platinum atoms. Each platinum atom is furthermore surrounded by a COD ligand and one fluorine atom of the octahedral SbF6 anion.

In the complex cation of the binuclear solvated title salt, [Pt 2 F(SbF 6 ) 2 (C 8 H 12 ) 2 ]SbF 6 Á0.75HF, an F atom bridges the two platinum(II) atoms with a bond angle of 123.3 (2) . The corresponding Pt-F bond lengths are in the range of other fluorine-bridged binuclear platinum(II) complexes. Two of the three SbF 6 À anions each coordinate with one F atom to one platinum(II) atom. Including the 4 -bound cyclooctadiene (COD) ligands, the overall coordination sphere of each platinum(II) atom is square-planar. The third SbF 6 À anion is not bound to the complex. Hydrogen fluoride is present in the crystal structure as a solvent disordered over three positions, each with an occupancy of 0.25. FÁ Á ÁF distances of 2.5512 (7), 2.6076 (8) and 3.2215 (10) Å to surrounding SbF 6 À anions are indicative of F-HÁ Á ÁF hydrogen-bonding interactions although no H atoms could be localized for the disordered solvent molecules. The resulting hydrogen-bonded network is three-dimensional.

Chemical context
Platinum complexes of cyclic dienes, like cyclooctadiene (COD), are widely used in metal-organic chemistry to introduce new ligands by substitution of the diene. For instance, [Pt(CH 3 ) 2 (COD)] is a commercially available staring material for most of the dimethyl complexes of platinum(II). Methyl ligands in platinum complexes can be protonated in superacids and eliminated as methane quantitatively. With anhydrous hydrogen fluoride (aHF), one or both methyl groups are protonated and replaced by a fluoride ion, but the resulting products cannot be crystallized because the formed fluoride ion does not sufficiently stabilizes the platinum complexes. With larger counter-anions like BF 4 À , AsF 6 À or SbF 6 À , stable crystalline complexes can be formed and isolated (Friedemann & Seppelt, 2013).
One methyl group of [Pt(CH 3 ) 2 (COD)] reacts with aHF at low temperature under formation of methane; the second ISSN 2056-9890 methyl group can be eliminated by the addition of antimony pentafluoride. The resulting dissolved complex is stable at room temperature and can be crystallized by cooling to 200 K. The formed title compound [Pt 2 (COD) 2 F(SbF 6 ) 2 ]SbF 6 Á-0.75HF dissolves unreacted only in aHF or acetonitrile. With other organic solvents, a reaction takes place to form black undefined oils; with chlorinated solvents chlorido-platinum complexes are formed instead.

Structural commentary
Each of the two independent platinum(II) atoms is surrounded by one COD ligand in a double -coordination, one fluorine atom of a SbF 6 À anion and one bridging fluorine atom, resulting in a slightly distorted square-planar coordination sphere (Fig. 1). The fluorine atom F19 bridges the two platinum(II) atoms with a bond angle of 123.3 (2) . The corresponding Pt-F bond lengths [2.085 (4) Å and 2.065 (4) Å ] are in the range of other fluorine-bridged The structure of the molecular entities of the title compound, with displacement ellipsoids drawn at the 50% probability level. Hydrogen bridges are marked with dashed lines.

Supramolecular features
The [Pt 2 (COD) 2 F(SbF 6 ) 2 ] cations and SbF 6 anions are packed in such a way that voids are generated that are filled with disordered HF solvent molecules (F21, F221 and F222). The shortest distances of these atoms to fluorine atoms of the surrounding SbF 6 À anions [F221Á Á ÁF18 2.5512 (7), F222Á Á ÁF18 2.6076 (8) and F21Á Á ÁF5 3.2215 (10) Å ] are in the typical range of F-HÁ Á ÁF donor acceptor distances, marked in Fig. 1 with dashed lines. The packing of the molecular entities in the crystal structure is shown in Fig. 2.

Synthesis and crystallization
[Pt(CH 3 ) 2 (COD)] (40 mg, 0.12 mmol) and antimony(V) fluoride (80 mg, 0.36 mmol) were filled separated in a two chamber PFA tube. Anhydrous HF (0.5 ml) was condensed on it at 77 K. By heating to 200 K and mixing, a gas and a yellow solid were formed. The solid dissolved at room temperature under a second gas formation to a give clear yellow solution. The gas was removed and the sealed tube was slowly cooled to 200 K to form yellow single crystals of the title compound. NMR in aHF at room temperature:

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. H atom positions of the COD ligand were refined with calculated positions in a riding model with C-H = 0.97 and 0.98 Å and U iso (H) = 1.2U eq (C). Atoms F21, F221 and F222 that are associated with the hydrogen fluoride solvent are disordered and were refined isotropically. Their occupation factors were fixed to 0.25 for each of these atoms which showed the best results in terms of reliability factors and U iso values. Hydrogen atoms bound to the disordered solvent F atoms could not be detected and were consequently not considered in the final model. Some F atoms of the SbF 6 À anions exhibited somewhat elongated ellipsoids. Since consideration of a split atom model had a negative effect (parts of these atoms could then only be refined isotropically), all F atoms of the SbF 6 À anions were not refined as being disordered.