Re-investigation and correct symmetry of Ca3CoAl4O10.

A re-investigation of the crystal structure of tricalcium cobalt(II) tetra-aluminate, Ca3CoAl4O10, using single-crystal X-ray diffraction data, revealed ortho-rhom-bic (Pbcm) symmetry. The present contribution corrects the results of a previous X-ray powder diffraction study [Vazquez et al. (2002 ▸). J. Solid State Chem. 166, 191-196] where this phase has been described in an unnecessarily low space-group symmetry (Pbc21). The compound belongs to the group of tetra-hedral framework structures. The distribution of the aluminium and cobalt ions among the centres of the four different tetra-hedra within the asymmetric unit has been studied in detail. Charge compensation is achieved by the incorporation of two symmetrically independent calcium ions located in voids of the tetra-hedral framework. Ca3CoAl4O10 is isotypic with Ca3MgAl4O10.