sentences:  Coordination numbers of 8 to 12 are commonly observed for "f"-block elements.For example, with bidentate nitrate ions as ligands, CeIV and ThIV form the 12-coordinate ions [Ce(NO3)6]2− (ceric ammonium nitrate) and [Th(NO3)6]2−.When the surrounding ligands are much smaller than the central atom, even higher coordination numbers may be possible.