α-Tris(2,4-pentanedionato-κ2O,O')cobalt(III) at 240, 210, 180, 150 and 110 K

The crystal structure of the title compound, [Co(C5H7O2)3], has been investigated by a multi-temperature measurement. In contrast to the isomorphous Al compound, the title compound exists in the studied temperature range as its monoclinic α polymorph (space group P21/c) and does not undergo a phase transition. Rigid-body TLS analyses have been performed and the anisotropic thermal expansion tensor αij has been determined. The cell axes show a linear expansion behavior with respect to the temperature, but the slope is significantly different. A possible explanation are the different strengths of different intermolecular C-H...O contacts, which run in different crystallographic directions.