Crystal structure of bis(acetylacetonato-κ2 O,O′)(tetrahydrofuran-κO)(trifluoromethanesulfonato-κO)iron(III)

The mononuclear complex [Fe(acac)2(OTf)(THF)] (acac = acetylacetonate; OTf = trifluoromethanesulfonate) consists of a mononuclear six-coordinate Fe3+ center in a slightly distorted octahedral environment and is only the second crystal structure reported of a mononuclear bis(acetylacetonato)iron(III) complex.


Supramolecular features
There are no significant supramolecular features to discuss in the extended structure of (I). There are weak C-HÁ Á ÁO and C-HÁ Á ÁF intermolecular hydrogen-bonding interactions resulting in the formation of two-dimensional layers parallel to the (100) plane (Fig. 2a,b). A series of C methyl -HÁ Á ÁO acac , C methyl -HÁ Á ÁO triflate , C methyl -HÁ Á ÁF triflate , C THF -HÁ Á ÁO triflate , and C THF -HÁ Á ÁF triflate interactions make up the layers, the details of these interactions are presented in Table 2. Each molecule connects to six neighboring molecules through various combinations of these interactions, Fig. 2c,d.

Database survey
Only one other mononuclear bis(acetylacetonato)iron(III) complex has been characterized crystallographically, [Fe(acac) 2 Cl] (Lindley & Smith, 1970). This complex comprises a five-coordinate iron(III) atom in a square-pyramidal geometry. The Fe-O distance reported is 1.95 (1) Å , which is comparable to the average Fe-O acac distance in (I) of 1.9668 Å . A search of the Cambridge Structural Database (Groom & Allen, 2014) reveals twelve bis(acetylacetonato)iron(III) complexes with a Fe-O acac range of 1.945-2.062 Å .

Synthesis and crystallization
Triflic acid (251 mL, 0.24 g, 1 equiv) was added to a solution of [Fe(acac) 3 ] (1 g, 2.83 mmol, 1 equiv) in dry THF (5 mL). The resulting purple-red solution was stirred at room temperature for 1 h. The reaction mixture was then concentrated under vacuum to a volume of approximately 2 mL, and 20 mL of pentane was added. A dark purple-red microcrystalline solid precipitated. The mixture was filtered through a glass-frit and the microcrystalline solid was dried under vacuum (1.25 g, 2.63 mmol, 93%). Crystals suitable for X-ray diffraction were grown by slow diffusion of pentane into a THF solution of the purple-red solid. CH analysis calculated for C 15   Hydrogen-bond geometry (Å , ).

Figure 1
A molecule plot showing the atom numbering, with 35% probability ellipsoids for non-H atoms and spheres of arbitrary size for H atoms. Only the major component of the disordered triflate ligand is shown.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. A structural model consisting of the target molecule was developed. The triflate ion is disordered over two positions, with refined site-occupancies of 0.622 (16) and 0.378 (16). The equivalent Fe-O, O-S, S-C, and C-F distances were restrained to be similar (s.u. = 0.01 Å ). The disordered atoms were restrained to behave relatively isotropically. Similar displacement amplitudes were imposed on disordered sites overlapping by less than the sum of van der Waals radii. Methyl H atom positions were opti-mized by rotation about R-C bonds with idealized C-H, RÁ Á ÁH and HÁ Á ÁH distances and included as riding idealized contributors [C-H methyl = 0.98 Å with U iso = 1.5U eq (C)].

Special details
Experimental. One distinct cell was identified using APEX2 (Bruker, 2013). Six frame series were integrated and filtered for statistical outliers using SAINT (Bruker, 2013) then corrected for absorption by integration using SAINT/SADABS (Bruker, 2013) to sort, merge, and scale the combined data. No decay correction was applied. 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. Structure was phased by direct methods (Sheldrick, 2008). Systematic conditions suggested the unambiguous space group. The space group choice was confirmed by successful convergence of the full-matrix leastsquares refinement on F 2 . The final map had no significant features. A final analysis of variance between observed and calculated structure factors showed little dependence on amplitude or resolution.