Crystal Structure and Solution Species of Ce(III) and Ce(IV) Formates: From Mononuclear to Hexanuclear Complexes
详细信息 查看全文
- 作者：Christoph Hennig ; Atsushi Ikeda-Ohno ; Werner Kraus ; Stephan Weiss ; Philip Pattison ; Hermann Emerich ; Paula M. Abdala ; Andreas C. Scheinost
- 刊名：Inorganic Chemistry
- 出版年：2013
- 出版时间：October 21, 2013
- 年：2013
- 卷：52
- 期：20
- 页码：11734-11743
- 全文大小：457K
- 年卷期：v.52,no.20(October 21, 2013)
- ISSN：1520-510X
文摘
Cerium(III) and cerium(IV) both form formate complexes. However, their species in aqueous solution and the solid-state structures are surprisingly different. The species in aqueous solutions were investigated with Ce K-edge EXAFS spectroscopy. Ce(III) formate shows only mononuclear complexes, which is in agreement with the predicted mononuclear species of Ce(HCOO)2+ and Ce(HCOO)2+. In contrast, Ce(IV) formate forms in aqueous solution a stable hexanuclear complex of [Ce6(渭3-O)4(渭3-OH)4(HCOO)x(NO3)y]12鈥?i>x鈭?i>y. The structural differences reflect the different influence of hydrolysis, which is weak for Ce(III) and strong for Ce(IV). Hydrolysis of Ce(IV) ions causes initial polymerization while complexation through HCOO鈥?/sup> results in 12 chelate rings stabilizing the hexanuclear Ce(IV) complex. Crystals were grown from the above-mentioned solutions. Two crystal structures of Ce(IV) formate were determined. Both form a hexanuclear complex with a [Ce6(渭3-O)4(渭3-OH)4]12+ core in aqueous HNO3/HCOOH solution. The pH titration with NaOH resulted in a structure with the composition [Ce6(渭3-O)4(渭3-OH)4(HCOO)10(NO3)2(H2O)3]路(H2O)9.5, while the pH adjustment with NH3 resulted in [Ce6(渭3-O)4(渭3-OH)4(HCOO)10(NO3)4]路(NO3)3(NH4)5(H2O)5. Furthermore, the crystal structure of Ce(III) formate, Ce(HCOO)3, was determined. The coordination polyhedron is a tricapped trigonal prism which is formed exclusively by nine HCOO鈥?/sup> ligands. The hexanuclear Ce(IV) formate species from aqueous solution is widely preserved in the crystal structure, whereas the mononuclear solution species of Ce(III) formate undergoes a polymerization during the crystallization process.