Crystal structure of tetra-kis-(1,1,1,5,5,5-hexa-fluoro-acetyl-acetonato)hafnium(IV).

W Franklin Schwandt,Gregory S Girolami,Toby J Woods

doi:10.1107/s2056989018010514

W Franklin Schwandt, Gregory S Girolami + Show 1 more

Open Access

https://doi.org/10.1107/s2056989018010514

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Abstract

The crystal structure of the title compound, [Hf(C5HF6O2)4], has been determined. The asymmetric unit contains two Hf(hfac)4 mol-ecules (hfac = 1,1,1,5,5,5-hexa-fluoro-acetyl-acetonate); both are located on general positions and have identical structures apart from the disorder involving three CF3 groups in one of the two mol-ecules. The mol-ecules of Hf(hfac)4 are arranged in layers that are parallel to the ab plane, and the coordination geometry of each hafnium(IV) center is a distorted square anti-prism. An inter-esting aspect of the structure is that the hfac ligands are arranged so that the Hf(hfac)4 mol-ecules have idealized 2 point symmetry, in which two of the hfac groups bridge between the two squares. Although all other M(β-diketonate)4 compounds of Hf (and Zr) also have square-anti-prismatic geometries; in almost all of them the ligands are arranged so that the mol-ecules have 222 point symmetry (in which none of the hfac ligands bridges between the two squares). The factors that favor one structure over another are not clear.

Highlights

The crystal structure of the title compound, [Hf(C5HF6O2)4], has been determined
The molecules of Hf(hfac)4 are arranged in layers that are parallel to the ab plane, and the coordination geometry of each hafnium(IV) center is a distorted square antiprism
An interesting aspect of the structure is that the hfac ligands are arranged so that the Hf(hfac)4 molecules have idealized 2 point symmetry, in which two of the hfac groups bridge between the two squares

Summary

Chemical context

The molecule tetrakis(1,1,1,5,5,5-hexafluoroacetylacetonato)hafnium(IV), Hf(hfac), has a relatively high vapor pressure for a hafnium compound, and in part for this reason it has been identified as a potential chemical vapor deposition (CVD) precursor for thin films of hafnium dioxide (Balog et al, 1977; Morozova et al, 2008; Wilk et al, 2001; Zherikova & Morozova, 2012; Zherikova et al, 2008). One intermolecular FÁ Á ÁF interaction (again ignoring the minor site F atoms) is shorter than 2.8 A , the sum of van der Waals radii for two F atoms attached to a primary alkyl, that involving F2Á Á ÁF22 (2.76 A ). All these intermolecular contacts must be weak, given that the

Structural commentary

Database survey

Synthesis and crystallization

Refinement