Structure of dichloroaluminium acetylacetonate in the solid state and in methylene chloride solution

Abstract

The structure of dichloroaluminium acetylacetonate in a CH 2Cl 2 solution and in the crystalline state has been determined. On the basis of variable-temperature 1H, 13C and 27Al NMR as well as of IR studies it has been found that the monomer Cl 2Alacac occurs in equilibrium with a trimeric complex. The equilibrium depends on temperature and the dichloroaluminium acetylacetonate concentration in the solution. For a higher concentration and a lower temperature the trimeric complex is predominant. An X-ray structure determination revealed that in the solid state dichloroaluminium acetylacetonate occurs exclusively as the trimeric complex and its molecular structure comprises the [Al 2Cl 2(acac) 3] + cation and the [AlCl 4] − anion. The cation consists of two five-coordinated Al atoms interconnected by a double bridge of two oxygen atoms of two acac ligands. The third acac ligand is symmetrically bonded to one of the aluminium atoms. The two chlorine atoms bonded to each aluminium atom lie on the same side with respect to the plane of the Al(O 2)Al bridges. Crystals of the trimer are monoclinic with space group C2/ c and cell constants a=18.81(1), b=11.30(2), c=27.70(1) Å, β=106.53(4)° and Z=8. The structure was refined to a final R=0.067 with 1925 observed reflections.