Comment

The structure of the title compound, (I), a mixed-ligand MOCVD precursor, has been analysed. The hafnium coordination polyhedron is a distorted square antiprism, with each ligand spanning the opposite edges of the two square faces of the antiprism. The nitrate ligand has a very small bite [2.110 (7) Å] and hence this square face is highly distorted, but it is more planar than the other square face of the antiprism. The angle between the mean planes fitted to the two square faces is 1.3 (1)° (Nardelli, 1995), close to the ideal value of zero. The bite distances for the three acetylacetonate ligands are 2.608 (7), 2.638 (6) and 2.611 (6) Å. In a zirconium complex with similar ligands, the coordination polyhedron was found to be a distorted dodecahedron, with the distortion arising due to the small bite of the nitrate ligand (Muller et al., 1976).

The tertiary butyl groups have high displacement parameters, and four of these groups have positional disorder, with each of the three methyl C atoms having two positions with partial occupancies for each group. This makes these groups very labile, a favourable feature for chemical vapour deposition.

Figure 1 View of the title compound with the disordered tert-butyl groups. Displacement ellipsoids are drawn at the 30% probability level. H atoms are omitted for clarity, and disordered C atoms labelled with the suffix `a' have higher occupancy.

Experimental

The title complex was synthesized by dissolving 2,2,6,6-tetramethyl-3,5-heptadione (15 mmol, 2.76 g) and potassium hydroxide (15 mmol, 1.68 g) in 25 ml of 30% ethanol. This was followed by the addition of hafnium nitrate (5 mmol, 2.13 g), dissolved in 20 ml of distilled water. The mixture was stirred at room temperature for 3 h and the resulting yellow precipitate was filtered, dried and recrystallized from n-hexane.