Alpha-Tris(2,4-pentanedionato-kappa2O,O')chromium(III) at 290 and 110 K: a new delta phase at 110 K.

The crystal structure of the title compound, [Cr(C(5)H(7)O(2))(3)], has been determined at 290 and 110 K to provide information on thermal vibrations and disorder. The alpha polymorph at room temperature has been reported [Morosin (1965). Acta Cryst. 19, 131-137]. The reinvestigation of this structure, presented here, indicates the presence of weak uninterpretable supercell reflections together with disorder streaks. The discussed structure can thus be considered as an average structure. After cooling to 110 K, a new delta polymorph was found, which is a superstructure of the alpha polymorph. The space group remains P2(1)/c and the phase transition can therefore be considered as klassengleich. The unit-cell volume increases by a factor of six, resulting in six independent molecules in the asymmetric unit.