Marsh David A, Goberna-Ferrón Sara, Baumeister Mary K, Zakharov Lev N, Nyman May, Johnson Darren W
Department of Chemistry & Biochemistry and Materials Science Institute, University of Oregon, Eugene, OR 97403-1253, USA.
Department of Chemistry, Oregon State University, 153A Gilbert Hall, 2100 SW Campus Way, Corvallis, OR 97331, USA.
Dalton Trans. 2017 Jan 17;46(3):947-955. doi: 10.1039/c6dt03733j.
Rare earth oxide materials, including thin film coatings, are critically important in magnetic, luminescent and microelectric devices, and few substitutes have been discovered with comparable performance. Thin film coatings from solution are almost unknown for rare earth oxides, likely due to their high activity towards hydrolysis which yields poor quality thin films. The hexamer [Ln(O)(OH)(HO)(NO)] is a rare example of a metal-oxo cluster isolated and stabilized without additional supporting organic ligands. Herein we report a new method for both the preparation and stabilization in non-aqueous media, which makes these clusters valuable precursors for solution-processed thin films. Solution characterization (NMR, small-angle X-ray scattering and Raman spectroscopy) in wet organic solvents indicated that the clusters evolve via a fragmentation and reaggregation process. This is especially true for hexamers of the smaller Ln-ions: the higher charge density yields higher hydration rates. This process produced an entirely new hexadecameric cluster formulated YO(OH)(NO)(OSMe)(OCMe)(HO). The new structure represents an intermediate hydrolysis product on the pathway from hexanuclear clusters to metal oxyhydroxide bulk solid. DMSO solvent ligands displace aqua ligands on the cluster and likely explain the additional stability observed for these clusters in organic solvents. The enhanced cluster stability in DMF and DMSO also enables solution-processing methods to create high quality thin films.
包括薄膜涂层在内的稀土氧化物材料在磁性、发光和微电子器件中至关重要，目前几乎未发现有性能相当的替代品。由于稀土氧化物对水解的高活性会导致薄膜质量不佳，因此几乎不存在由溶液制备的稀土氧化物薄膜涂层。六聚体[Ln(O)(OH)(HO)(NO)]是一种罕见的金属氧簇实例，它在没有额外支持性有机配体的情况下被分离并稳定下来。在此，我们报告了一种在非水介质中制备和稳定这些簇的新方法，这使得这些簇成为溶液处理薄膜的有价值的前体。在湿有机溶剂中的溶液表征（核磁共振、小角X射线散射和拉曼光谱）表明，这些簇通过碎片化和重新聚集过程演化。对于较小的Ln离子的六聚体尤其如此：较高的电荷密度产生较高的水合速率。这个过程产生了一种全新的十六聚体簇，其化学式为YO(OH)(NO)(OSMe)(OCMe)(HO)。这种新结构代表了从六核簇到金属羟基氧化物块状固体途径上的一种中间水解产物。二甲基亚砜溶剂配体取代了簇上的水配体，这可能解释了在有机溶剂中观察到的这些簇的额外稳定性。在二甲基甲酰胺和二甲基亚砜中增强的簇稳定性也使溶液处理方法能够制备高质量的薄膜。
