Computational study of 19F NMR spectra of double four ring-containing Si/Ge-zeolites

F-19 NMR chemical shifts are calculated in order to study the 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 octodecasil zeolite. The optimisation of 7Si1Ge-, 6Si2Ge-, 5Si3Ge- and 4Si4Ge-D4R units with DFT/B3LYP methodology snows that a covalent Ge-F bond is formed and therefore a Ge atom in the D4R is pentaccardinated. The displacement of the flouride 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 F-19 NMR signals in groups according to the number of Si (n) and Ge (m) atoms in the nearest F- environment, F-SinGem (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.