Synthesis, 45Sc NMR characterization, and interconversion of structurally diverse scandium chloride hydrates

Abstract

The dissolution of scandium metal (Sc°) in concentrated hydrochloric acid was found to generate a wide variety of products based on the reaction/processing conditions. The compounds [Sc(H2O)6]3[Cl] (1) and [ScCl2(H2O)4][Cl]·H2O (2) were isolated from the above reaction when an ice bath is used. If the reaction was allowed to warm uncontrolled during synthesis, [Sc(μ-OH)(H2O)5]24[Cl]·2H2O (termedOH) was produced. If 1 or 2 were heated (130 °C) in toluene or H2O, [ScCl2(H2O)4][ScCl4(H2O)2] (3) crystallized. Interconversion of the various hydrates and OH structure were studied via 45Sc NMR spectroscopy studies. Efforts to easily dehydrate 2 through the addition of a Lewis base led to the characterization of monohydrate solvates: [ScCl3(THF)2(H2O)]·THF (4·THF) or [ScCl3(κ2-DME)(H2O)] (5) where THF = tetrahydrofuran and DME = dimethoxyethane. In contrast, the use of pyridine formed [Sc(μ-OH)(Cl)2(py)2]2·py (6) where py = pyridine. The formation of the OH moiety is attributed to the higher reaction temperatures achieved using py as the solvent. These compounds were also characterized using 45Sc NMR spectroscopy and compared to commercial ScCl3 dissolved in the parent solvent.