Evaluation of Volatility and Thermal Stability in Monomeric and Dimeric Lanthanide(III) Complexes Containing Enaminolate Ligands

Treatment of 3 equiv of the potassium salts derived from the β-amino ketones 1-(dimethylamino)-3,3-dimethylbutan-2-one (L1H), 3,3-dimethyl-1-(pyrrolidin-1-yl)­butan-2-one (L2H), and 3,3-dimethyl-1-(piperidin-1-yl)­butan-2-one (L3H) with anhydrous lanthanide­(III) chlorides afforded the complexes Ln­(L1)3(L1H) (Ln = Pr, Er, Y), Ln­(L1)3 (Ln = Pr, Er, Lu, Y), [Nd­(L1)3]2, [La­(L2)3]2, and Ln­(L3)3 (Ln = La, Pr, Nd, Er, Lu, Y) in 30–56% yields after crystallization from a solvent or sublimation. X-ray crystal structures of Ln­(L1)3(L1H), Lu­(L1)3, Er­(L3)3, and Lu­(L3)3 revealed monomeric molecular structures, whereas [Nd­(L1)3]2 and [La­(L2)3]2 exist as dimers bridged through the oxygen atoms of two L1 or L2 ligands. The L1, L1H, L2, and L3 ligands exist mostly with bidentate coordination modes through the oxygen and nitrogen atoms. The new complexes sublime between 95 and 160°C at 0.5 Torr. Thermogravimetric analysis traces of Ln­(L1)3(L1H) (Ln = Pr, Er, Y) showed two-step weight losses, with the first step entailing loss of L1H. The other complexes demonstrated single-step weight losses up to their decomposition temperatures. The complexes Ln­(L3)3 (Ln = La, Pr, Nd, Er, Lu, Y) show the highest thermal stabilities among the new complexes and are promising precursors for the growth of lanthanide-containing thin films by atomic layer deposition.