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Computational Study of 19 F NMR Spectra of Double Four Ring‐Containing Si/Ge‐Zeolites
Author(s) -
Pulido Angeles,
Sastre German,
Corma Avelino
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500634
Subject(s) - chemical shift , chemistry , atom (system on chip) , crystallography , covalent bond , ring (chemistry) , nmr spectra database , zeolite , ion , spectral line , physics , catalysis , biochemistry , organic chemistry , astronomy , computer science , embedded system
19 F NMR chemical shifts are calculated in order to study the F − environment in double four ring (D4R) containing Si/Ge‐zeolites. The calculations with the DFT/CSGT/B3PW91 methodology yielded an agreement within 2 ppm with respect to the experimental peaks corresponding to the D4R units containing 8Si0Ge, 7Si1Ge and 0Si8Ge of the octadecasil zeolite. The optimisation of the 7Si1Ge‐, 6Si2Ge‐, 5Si3Ge‐ and 4Si4Ge‐D4R units with DFT/B3LYP methodology shows that a covalent GeF bond is formed and therefore a Ge atom in the D4R is pentacoordinated. The displacement of the fluoride ion towards a Ge atom in the Ge‐containing D4R units locates four Si/Ge atoms in the close vicinity of the F − and this makes possible a rationalization of the 19 F NMR signals in groups according to the number of Si ( n ) and Ge ( m ) atoms in the nearest F − environment, F–Si n Ge m (where n+m=4). Thus, the calculated chemical shifts show that higher values are observed when the number of Ge atoms in the nearest F − environment increases.