Tris(2-acetylcyclopentan-1-onato-κ2 O,O′)aluminium

In the title compound, [Al(C7H9O2)3], the AlIII cation is coordinated by six O atoms from three 2-acetylcyclopentanonate ligands in a slightly distorted octahedral environment, with Al—O bond lengths in the range 1.882 (2)–1.896 (2) Å. In the crystal, molecules are linked together via C—H⋯O interactions. One of the C atoms in one ring has a large thermal motion compared to the other atoms, indicating some possible disorder. However, the treatment of this C atom as disordered over two positions did not give a significant improvement.

In the title compound, [Al(C 7 H 9 O 2 ) 3 ], the Al III cation is coordinated by six O atoms from three 2-acetylcyclopentanonate ligands in a slightly distorted octahedral environment, with Al-O bond lengths in the range 1.882 (2)-1.896 (2) Å . In the crystal, molecules are linked together via C-HÁ Á ÁO interactions. One of the C atoms in one ring has a large thermal motion compared to the other atoms, indicating some possible disorder. However, the treatment of this C atom as disordered over two positions did not give a significant improvement.

Franc Perdih
Comment β-Diketonates have been proven to be versatile ligands for various metal ions. They can be easily derivatized, thus modifying the electronic and steric nature of these ligands to design suitable structure/function relationship (Bray et al., 2007;Garibay et al., 2009;Perdih, 2011). β-diketonate compounds of aluminium have received great attention due to the promise of the construction of cages (Vreshch et al., 2004;Wu & Wang, 2009). Besides that, the title compound is a close analogue of aluminium isomaltolato compound that was prepared for in vivo examinations of ion transport in order to shed some light on the mechanism of transport and the involvement of Al in neurological disorders (Lutz et al., 1989).

Experimental
To a clear solution of Al 2 (SO 4 ) 3 . 18H 2 O (1 mmol, 0.67 g) in water (15 ml) a solution of 2-acetylcyclopentanone (6 mmol, 0.76 g) in methanol (5 ml) was added while stirring. Afterwards the 1 M NaOH (6 ml) was slowly added and the resulting solution stirred at 70°C for 15 minutes. After cooling to the room temperature the light pink product was filtrated and washed with water (20 ml), and subsequently air-dried. Yield: 0.47 g, 58%. Crystals suitable for X-ray analysis were obtained by recrystallization from ethanol.

Refinement
All H atoms were initially located in a difference Fourier maps and were subsequently treated as riding atoms in geometrically idealized positions, with C-H = 0.97 (methylene) or 0.96 Å (methyl) and with U iso (H) = kU eq (C), where k = 1.5 for methyl groups, which were permitted to rotate but not to tilt, and 1.2 for all other H atoms. To improve the refinement results, one reflection with too high value of δ(F 2 )/e.s.d. and with F o 2 < F c 2 was deleted from the refinement.

Figure 1
The molecular structure of the title complex showing the numbering scheme and displacement ellipsoids drawn at the 30% probability level.  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 > 2σ(F 2 ) is used only for calculating R-factors(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.