The Si-Ge substitutional series in the chiral STW zeolite structure typeElectronic supplementary information (ESI) available: Gef in zeolites as a function of Gef in the gel, calculation of the energy of the configurations, synthesis results, cell parameters vs. Gef computed with effective Hamiltonians, some of the energy-minimised D4R configurations, infrared spectra, FE-SEM images, thermograms, direct irradiation 29Si MAS NMR, difference between calculated and experimental 19F chemical shifts,

• Main Authors: Rigo, Reus T, Balestra, Salvador R. G, Hamad, Said, Bueno-Perez, Rocio, Ruiz-Salvador, A. Rabdel, Calero, Sofía, Camblor, Miguel A
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c8ta03879a

The whole compositional range (Ge f = Ge/(Ge + Si) = 0 to 1) of zeolite STW has been synthesized and studied by a comprehensive combined experimental-theoretical approach. The yield of the zeolite goes through a maximum and then drops at the GeO 2 side of the series, following the inverse of the calculated free energy curve. The unit cell generally expands, roughly linearly, as the Ge f increases, but a notable resilience to expansion is observed at the high silica side. This can be attributed to the more rigid character of SiO 2 and the ability of Ge units to deform. Density functional theory calculations provide a new assignment of the previously controversial 19 F MAS NMR resonances for occluded fluoride, which is based not only on the number of Ge atoms in the double-4-ring units but also on the way they are associated (namely, no Ge, isolated Ge, Ge pairs or closed Ge clusters). While we found an overall good agreement between the experimental and theoretical trends in preferential occupation of different crystallographic sites by Ge, the theoretical models show more sharp and abrupt tendencies, likely due both to limitations of the approach and to kinetic factors that allow metastable configurations to actually exist. Ge substitution for Si in zeolites containing double-four-membered rings is far more complex than thought.