Tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato-κ2 O,O′)molybdenum(III)

In the title compound, [Mo(C5HF6O2)3], the unit cell is built up by three independent MoIII atoms located on two different threefold axes. The three independent molecules are roughly identical and each MoIII atom is surrounded by three chelating hexafluoroacetonate ligands in a three-bladed propeller-like arrangement, as observed in related compounds with acetylacetonate-type ligands. The structure of the title compound is very similar to the trigonal form of the CrIII analogue. However, the latter crystallizes in a higher-symmetry space group, P c1. Both crystals are twinned by merohedry with the same twin law ( 0/010/00) in reciprocal space, but the symmetry of the Laue group in which it operates is different, to m for the title complex, and m to 6/mmm for the CrIII complex.

In the title compound, [Mo(C 5 HF 6 O 2 ) 3 ], the unit cell is built up by three independent Mo III atoms located on two different threefold axes. The three independent molecules are roughly identical and each Mo III atom is surrounded by three chelating hexafluoroacetonate ligands in a three-bladed propeller-like arrangement, as observed in related compounds with acetylacetonate-type ligands. The structure of the title compound is very similar to the trigonal form of the Cr III analogue. However, the latter crystallizes in a higher-symmetry space group, P3c1. Both crystals are twinned by merohedry with the same twin law (110/010/001) in reciprocal space, but the symmetry of the Laue group in which it operates is different, 3 to 3m for the title complex, and 3m to 6/mmm for the Cr III complex.

Comment
The title compound was of interest in our laboratory for potential application as reversible trapping agent of polymeric radical chains in controlled radical polymerization processes.
The stucture of the title compound, (I), is built up from three independent molybdenum centers located on two different three fold axes. As usually observed in such complexes (Raston & White, 1979;Jessop et al., 2002;Harada & Girolami, 2007) each molybdenum is surrounded by three chelating hexafluoroacetylacetonate ligands in a three-bladed propellor-like arrangement (Fig.1). The three molecules are roughly identical as can be seen from the molecular fitting views ( This compound appears to be isostructural with the related chromium complex (Harada & Girolami, 2007) although the space groups are different, P -3 for the title complex whereas it is reported as P -3c1 for the chromium complex. Both crystals are twinned by merohedry by the same twin law but the symmetry of the Laue group in which it operates is different: -3 to -3 m for the title complex whereas it is -3 m to 6/mmm for the Cr complex. The refinement of the title complex is much better than the one reported for the Cr complex (Harada & Girolami, 2007).

Experimental
The compound was prepared by refluxing Mo(CO) 6 in toluene in the presence of 3 equivalents of 1,1,1,5,5,5-hexafluoropentan-2,4-dione and a few drops of diglyme which is known to facilitate CO replacement reactions for the carbonyl molybdenum precursor. Single crystals of the product grew directly from the solution after cooling, concentration, filtration at room temperature, and further cooling to -20°C.

Refinement
The crystal is twinned by merohedry with the -1 -1 0 0 1 0 0 0 -1 twin law in the reciprocal space. A scale factor for the major twin domain is 0.8076 (9).
The three H atoms attached to the central C atoms were fixed geometrically and treated as riding with C-H = 0.95 Å with U iso (H) = 1.2U eq (C). Fig. 1. View of the three symmetry-independent molecules of (I) with atom labeling scheme. Dispalcement ellipsoids are shown at the 30% probability level. H atoms are represented as small spheres of arbitrary radii. (a) Molecule 1 [symmetry codes:

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Mo1