Cerium-Based Coordination Network Formation: An In Situ X-ray Absorption Spectroscopy and Powder X-ray Diffraction Study

High Resolution Image Download MS PowerPoint Slide The Ce(NO 3 ) 3 ·6H 2 O/H 2 TDC/CH 3 COOH/CH 3 CN (H 2 TDC = 2,5-thiophenedicarboxylic acid) chemical system was studied under solvothermal reaction conditions. Four different phases that successively crystallized as a function of time were observed. Three coordination networks, [Ce IV (TDC)(CH 3 COO) 2 ] ( 1 ), [Ce III 4 (TDC) 3 (CH 3 COO) 6 ] ( 2a ), and [Ce III (TDC)(CH 3 COO)] ( 3 ), could be isolated as orange, beige, and white phase pure products, respectively, and their crystal structures were resolved from powder X-ray diffraction data. Another crystalline compound ( 2b ) was observed in situ, which seems to be structurally related to compound 2a . Compound 2a is a metal–organic framework (MOF) with a pore size of ∼3 Å. The use of Ce III (NO 3 ) 3 as the starting material, the different colors of the products, and the crystal structures indicated a peculiar redox behavior with a Ce(III)–Ce(IV)–Ce(III) redox transformation during product formation of 1, 2a, and 3 . The oxidation states of 1 and 3 were confirmed by ex situ X-ray absorption near-edge structure (XANES) measurements, and the crystallization process was followed using quasi-simultaneous in situ powder X-ray diffraction (PXRD) and X-ray absorption spectroscopy (XAS) measurements. During the reaction, the consecutive crystallization in the order 1 – 2b – 3 was clearly observed. Linear combination fitting (LCF) of the in situ XAS data also affirmed the formation of the title compounds.