The structures of the precursor Hf(OnBu)4 and its modification in solution: EXAFS-investigation in combination with XANES- and IR-spectroscopy
作者:Matthias Bauer、Sonja Müller、Guido Kickelbick、Helmut Bertagnolli
DOI:10.1039/b707079a
日期:——
The solution structure of hafnium-n-butoxide Hf(OnBu)4, an important precursor for the sol–gel preparation of hafnium oxide containing materials, was studied in solution in pure toluene, and in presence of acetylacetone, iso-propanol and tetrahydrofuran by EXAFS-, XANES- and IR-spectroscopy. The combination of these three methods and the additional measurements and discussions of well known solid state references allow us to identify structural motives and to gain a detailed picture of the structures formed in solution without any a priori knowledge about these structures. The dimeric structure of crystalline Hf(OnBu)4 is not preserved in solution and a trimeric cyclic structure is formed. While the addition of HOiPr and THF does not induce any change of the formed complexes, one equivalent of Hacac reduces the degree of aggregation by the partial formation of dimers. In the presence of two and three equivalents of Hacac, solely monomeric species are formed. The obtained structural parameters are used to establish for the first time an empirical correlation of a spectral feature in the XANES region with the average oxygen coordination number.
溶胶凝胶法制备含氧化铪材料的重要前驱体--正丁氧化铪 Hf(OnBu)4 的溶液结构在纯甲苯溶液中以及在乙酰丙酮、异丙醇和四氢呋喃存在下通过 EXAFS、XANES 和红外光谱进行了研究。通过这三种方法的结合以及对已知固态参考文献的额外测量和讨论,我们可以确定结构动机,并在对溶液中形成的结构没有任何先验知识的情况下详细了解这些结构。晶体 Hf(OnBu)4 的二聚体结构在溶液中没有得到保留,而是形成了三聚环状结构。虽然加入 HOiPr 和 THF 不会导致所形成的复合物发生任何变化,但一当量的 Hacac 会通过部分形成二聚体而降低聚集程度。在含有两个和三个当量的 Hacac 时,形成的只是单体。利用所获得的结构参数,首次建立了 XANES 区域光谱特征与平均氧配位数之间的经验相关性。