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

The crystal structure of the title compound, [Hf(C₅ HF₆ O₂)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 CF 3 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.