Tetrakis(1,1,1-trifluoroacetylacetonato-κ2 O,O′)hafnium(IV) toluene disolvate

In the title compound, [Hf(C5H4F3O2)4]·2C7H8, the HfIV atom, lying on a twofold rotation axis, is coordinated by eight O atoms from four 1,1,1-trifluoroacetylacetonate ligands with an average Hf—O distance of 2.173 (1) Å and O—Hf—O bite angles of 75.69 (5) and 75.54 (5)°. The coordination polyhedron shows a slightly distorted Archimedean square antiprismatic geometry. The asymmetric unit contains a toluene solvent molecule. The crystal structure involves C—H⋯.F hydrogen bonds.

In the title compound, [Hf(C 5 H 4 F 3 O 2 ) 4 ]Á2C 7 H 8 , the Hf IV atom, lying on a twofold rotation axis, is coordinated by eight O atoms from four 1,1,1-trifluoroacetylacetonate ligands with an average Hf-O distance of 2.173 (1) Å and O-Hf-O bite angles of 75.69 (5) and 75.54 (5) . The coordination polyhedron shows a slightly distorted Archimedean square antiprismatic geometry. The asymmetric unit contains a toluene solvent molecule. The crystal structure involves C-HÁ Á Á.F hydrogen bonds.

Related literature
For the triclinic polymorph of the title compound, see: Zherikova et al. (2005). For related literature on hafnium -diketone complexes, see: Chattoraj et al. (1968). For the isomorphous zirconium complex, see: Steyn et al. (2008). For a description of the Cambridge Structural Database, see: Allen (2002).
The triclinic polymorph earlier reported by Zherikova et al. (2005) contains no solvent molecules and cannot be superimposed with the title compound due to differences in metal coordination modes. An isomorphous zirconium complex has been reported by Steyn et al. (2008). The Hf IV atom in the title compound is situated on a twofold rotation axis, with four βdiketonate ligands, 1,1,1-trifluoroacetylacetonate (tfaa), coordinating to the Hf IV atom adopting an Archimedean antiprism coordination geometry (Fig. 2). The Hf-O bond lengths vary from 2.1527 (13) Å to 2.1933 (13) (Table 1). This average bond distance is somewhat larger than the average of 2.156 Å obtained from the Cambridge Structural Database (Allen, 2002) (data extracted from 19 hits, yielding 45 observations ranging from 2.039 to 2.248 Å). Pairs of toluene molecules are π-stacked (interplanar distance = 3.65 (1) Å, centroid-centroid distance = 4.92 (1) Å) in channels formed by the metal complex moieties parallel to the b-axis (Fig. 3). The preferred CF 3 -group conformation is probably due to weak C-H···F interactions (Table 2).

Experimental
Chemicals were purchased from Sigma and Aldrich and used as received except for toluene, which was dried by passage over alumina. Syntheses were performed using modified Schlenk conditions. The ligand salt (Natfaa) was prepared by adding Htfaa (6.05 ml, 50 mmol) dropwise to NaOH (2.02 g, 50 mmol) over a period of 3 minutes. The resulting solids were washed with toluene and dried in vacuo. Natfaa (0.459 g, 2.6 mmol) was added to a suspension of HfCl 4 (0.207 g, 0.65 mmol) in toluene (10 ml). Dissolution gave a slightly yellow solution after 10 min. After refluxing for ca 20 h the crude product was filtered and washed with toluene. The filtrate was slowly recrystallized at 253 K at near quantitative yield. Spectroscopy data: 19 F {H} NMR (C 6 D 6 ; 564.77 MHz): -75.49 p.p.m.; IR (ATR): ν(CO) 1533 cm -1 .

Refinement
H atoms were positioned geometrically and refined as riding atoms, with C-H = 0.93 (aromatic) and 0.96 Å (methyl) and with U iso (H) = 1.2U eq (C) for aromatic and 1.5U eq (C) for methyl groups. Torsion angles for methyl H atoms were refined from electron density. The highest residual electron density lies within 1.0 Å from the Hf atom.

Special details
Experimental. The intensity data was collected on a Bruker X8 Apex II 4 K Kappa CCD diffractometer using an exposure time of 20 s/frame. A total of 1897 frames were collected with a frame width of 0.5° covering up to θ = 28.35° with 99.8% completeness accom-