Erbium acetylacetonate is a coordination compound with the formula Er(C<sub>5</sub>H<sub>7</sub>O<sub>2</sub>)<sub>3</sub>. This anhydrous acetylacetonate complex is often discussed but unlikely to exist per se. The 8-coordinated dihydrate Er(C<sub>5</sub>H<sub>7</sub>O<sub>2</sub>)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub> is a more plausible formula based on the behavior of other lanthanide acetylacetonates. The dihydrate has been characterized by X-ray crystallography.
Upon heating under vacuum, the dihydrate converts to the oxo-cluster . This behavior, which is also observed for other lanthanide acetylacetonates, further illustrates the implausibility of six-coordinate Er(C<sub>5</sub>H<sub>7</sub>O<sub>2</sub>)<sub>3</sub>.