Di-oxo and tri-oxo Re(VII)-oxosulfato complexes in the Re2O7-K2S2O7 molten system. Molecular structure, vibrational properties and temperature-dependent interconversion

Autor: Chrysanthi Andriopoulou, Ioannis Anastasiou, Soghomon Boghosian
Rok vydání: 2019
Předmět:
Zdroj: Vibrational Spectroscopy. 100:14-21
ISSN: 0924-2031
DOI: 10.1016/j.vibspec.2018.10.012
Popis: The reaction between Re2O7 and K2S2O7 in the molten phase is studied by Raman spectroscopy under static equilibrium oxidative conditions at temperatures of 260–470 °C and in the full composition range, X R e 2 O 7 0 = 0 − 1 . Raman band intensity correlations are adequate for inferring a 1:1 stoichiometry for the complex formation reaction. Depending on temperature and on composition of the mixture, two isomeric ReVII-oxosulfato complexes are formed: (a) ReO3SO4−, prevalent at low temperature (T 360 °C), with hexa-coordinated ReVII in di-oxo termination configuration. The characteristic symmetric and antisymmetric stretching modes ( ν s / ν a s ) of the Re(=O)3+ and Re(=O)23+ cores are found at 975/938 cm-1 and 989/944 cm-1 for the tri-oxo and di-oxo sites, respectively. A fully reversible temperature-dependent 2ReO3SO4−(l) ↔ (ReO2)2O2(SO4)22-(l) interconversion equilibrium is evidenced. Consistent molecular structural models are proposed for the ReO3SO4− and (ReO2)2O2(SO4)22- complexes as well as for their associated/polymeric counterparts, (ReO3SO4)nn- and ((ReO2)2O2(SO4)2)n2n-. Molten Re2O7 reacts with K2SO4 according to Re2O7(l) + 2SO42- → ReO4−(l) + S2O72-(l). The ReVII-oxosulfato complexes and their configurational, structural and vibrational properties are of interest as references for inferring corresponding properties for dispersed amorphous oxo-ReVII species in supported rhenia catalysts.
Databáze: OpenAIRE
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