The addition of Na+ cations to the starting gel prepared using NH4F significantly prolonged the crystallization time of beta zeolite. However, in the case of pure silica beta zeolite an addition of more NH4F reduced the crystallization time by one-half. From Si-29 MAS NMR measurements, the signal attributed to pentacoordinated silicon was found to be more pronounced for pure silica beta zeolite in the presence of Na+ cations even in the solid phase with low crystallinity, as compared to that in the absence of Na+ cations. Considering the results of theoretical calculation, because of more energetically stable state of Na+[SiO4/2F](-) species, it could be presumed that Na+[SiO4/2F](-) species might exist in pure silica beta zeolite. Furthermore, as confirmed by F-19 MAS NMR measurements tetraethyl ammonium fluoride (TEAF) species were enclathrated intact in solid phase during the initial crystallization stage. This suggests that TEAF species are required for the formation of beta zeolite framework, in other words, as "SDA" which conditions the formation of kinetically favored phase, i.e., beta zeolite. Moreover, since part of TEA(+) cations is replaced by sodium cations, forming Na+[SiO4/2F](-) species, the amount of TEA(+) [SiO4/2F](-) species involved in either nucleation or crystal growth decreases and thus the crystallization time becomes longer. (C) 2007 Elsevier B.V.. All rights reserved.