Bis(propane-1,3-diaminium) hexafluoridoferrate(III) fluoride trihydrate

The asymmetric unit of the title iron hybrid fluoride, (C3H12N2)2[FeF6]F·3H2O, contains two propane-1,3-diaminium [(H2dap)2+] cations, an octahedral [FeF6]3− anion, an isolated F− anion and three water molecules of solvation. Each [FeF6]3− anion is surrounded by four separate hydrogen-bonded water molecules in the equatorial sites and by five separate aminium cation donor groups. The axial F atoms are only involved in N—H⋯F hydrogen bonds, resulting in a three-dimensional structure.

The asymmetric unit of the title iron hybrid fluoride, (C 3 H 12 N 2 ) 2 [FeF 6 ]FÁ3H 2 O, contains two propane-1,3-diaminium [(H 2 dap) 2+ ] cations, an octahedral [FeF 6 ] 3À anion, an isolated F À anion and three water molecules of solvation. Each [FeF 6 ] 3À anion is surrounded by four separate hydrogenbonded water molecules in the equatorial sites and by five separate aminium cation donor groups. The axial F atoms are only involved in N-HÁ Á ÁF hydrogen bonds, resulting in a three-dimensional structure.
Data collection: STADI4 (Stoe & Cie, 1998); cell refinement: STADI4; data reduction: X-RED (Stoe & Cie, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) within WinGX (Farrugia, 1999); molecular graphics: DIAMOND (Brandenburg & Putz, 2004) and ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: enCIFer (Allen et al., 2004).   In fluoride metallates, "free" fluoride ions, are always surrounded by amine groups and their coordination number varies from 3 to 6. Also F···N distances increase with the coordination number (Steiner, 1998). In the title compound, "free" F ions adopt a tetrahedral coordination with four hydrogen atoms from four H 2 dap cations ( Figure 4). The three hydrogen-bonded water molecules form trimer clusters, presenting various triangular environments with F acceptor atoms of the FeF 6 octahedra and H donor atoms of the cation aminium groups ( Figure 5). The infrared absorption spectrum of the title compound gives information on the organic moiety (C-C, C-N) and on the oxidation state of the iron atom, the presence of a vibrational band in the neighbourhood of 487 cm -1 being consistent with iron(III).

Experimental
The title compound was prepared from a starting mixture of FeF 3 (0.5 g) in 40% HF (3.0 ml) and ethanol (5 ml). 1,3diaminopropane (2.7 ml) was added and mild hydrothermal conditions (463 K) were applied in a Teflon lined autoclave (25 ml). The resulting product was washed with ethanol and dried in air giving colourless single crystals.

Refinement
All non-hydrogen atoms were refined with anisotropic displacement parameters. The H atoms of the water molecules were located using difference methods and their positional and isotropic displacement parameters were refined. Other H atoms including those on the aminium groups were included in the refinement at calculated positions and refined with a common isotropic thermal parameter. Fig. 1. An view the (H 2 dap) 2+ cation, the [FeF 6 ] 3and Fanions and the water molecules of solvation (I). Thermal displacement ellipsoids are shown at the 50% probability level. Fig. 2. The three-dimensional H bonding network in the structure of (I).

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.
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 > σ(F 2 ) is used only for calculating Rfactors(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.