The structure of a diethyl ether (DEE) complex of fluorenyllithium, [Li(C 13 H 9 )(DEE) 2 ], was investigated by X-ray crystallography and quantum chemical calculations. In the crystal structure, the lithium cation interacts in an η 2 -arrangement with the fluorenyl anion at distances of 2.26 and 2.31 Å away from C9 and C10. In contrast to the uncomplexed ion pair where recent calculations revealed that Li + is situated over the five-membered ring, calculations at the B3LYP/6-31+G(d)//B3LYP/6-31G(d) level show that for the DEEcoordinated complex, the optimal structure resembles the X-ray structure. Since the η 2arrangement is the global minimum in both the solid state and gas phase, it was concluded that crystal packing is not the main factor that causes the lithium cation to change position when going from the uncomplexed to the DEE-complexed fluorenyllithium. A comparison with the smaller water-coordinated complex indicates that intramolecular steric interactions within the DEE-coordinated complex lead to an η 2 -arrangement instead.