Cerium oxygen bond distances

The projections of the crystal structure of bastnasite-(Ce) are given in fig. 7. The structure shows that the cerium atom is coordinated by three fluorine atoms and eight oxygen atoms of the carbonate ions, in which the Ce-Ol distance, 2.49 A, is shorter than the Ce-02 distance, 2.74 A. The Ce polyhedra share faces to form a sheet of cerium and fluorine, and share corners to form a three-dimensional structure. Donnay and Donnay (1953) have pointed out that the difference between the two kinds of Ce-O distances indicates the considerable strength of the shorter Ce-Ol bond accounting for the observed lack of (0001) cleavage in spite of the sheet structure. 

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