High-yield synthesis of heavy rare earth(III) anhydrous solvates: known, new, and unexpected products

Ten anhydrous rare-earth (RE) chloride solvates were prepared by dehydration of RECl₃·6H₂O with triethylorthoformate (teof) in O-donor solvents as an accessible and general synthetic route. Reactions are quick, safe, mild, easily reproducible, and cost-effective. They run at room temperature or under reflux to give high-yield, pure crystalline products that are either new, such as [Gd₂Cl₄(μ-Cl)₂(PrⁱOH)₆] (1) and [{GdCl(μ-Cl)₂(thf)₂}_∞] (2), or obtained for the first time from teof, such as [GdCl₃(thf)₄] (3), trans-[MCl₂(thf)₅]trans-[MCl₄(thf)₂], M = Gd (4), Dy (6), and Y (7), [YbCl₃(thf)₃] (8), and [MCl₃(dme)₂], M = Gd (5), Dy (9), and Er (10). Structural and spectroscopic characterization is presented for all products, and variable-temperature magnetic susceptibility data are discussed for the Dy³⁺ complexes 6 and 9. The latter behaves as a field-induced single-ion magnet for which theoretical (ab initio) and experimental data allowed a non-trivial assignment of overlapping high- (Orbach, U_eff 139 cm^-1) and low-temperature (Raman, w_eff 46.8(2) cm^-1) magnetic relaxation mechanisms (1 kOe field). Besides the main products, unanticipated Lewis and redox reactivity led to serendipitous 11, [({Gd₃Cl₄(μ-Cl)₄(μ-H₃CCOO)(C₃H₈O₂)(PrⁱOH)₄}·PrⁱOH)_∞], and 12, [{(thf)₂Cl₂Gd(μ-Cl)₂(μ₃-O₂)Gd(thf)₃}₂]·3thf, whose formation is discussed. The final RE³⁺ anhydrous complexes serve as valuable starting materials for numerous substitution reactions in coordination and organometallic chemistry.