α‐Tris(2,4‐pentanedionato‐κ2O,O′)chromium(III) at 290 and 110 K: a new δ phase at 110 K

The crystal structure of the title compound, Cr(C₅H₇O₂)₃], has been determined at 290 and 110 K to provide information on thermal vibrations and disorder. The α 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 δ polymorph was found, which is a superstructure of the α polymorph. The space group remains P2₁/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.