title: Water confinement in faujasite cages: a deuteron NMR investigation in a wide temperature range. 1. Low temperature spectra.
abstract: Deuteron NMR spectra were measured for D2O confined in NaX, NaY, and DY faujasites with various D2O loadings at temperatures ranging from T = 70 K to T = 200 K with the aim to study the molecular mobility of confined water as a function of Si/Al ratio and loading. The recorded spectra were fitted with linear combinations of representative spectral components. At low loading, with the number of water molecules per unit cell close to the abundance of sodium cations, a component related to π-jumps of water deuterons about the 2-fold symmetry axis dominated. For loadings at levels 3 times and 5 times higher than the initial loading level, Pake dublets due to rigid water deuterons dominated the recorded spectra. A set of the quadrupole coupling constant values of localized water deuterons was derived from the analysis of the Pake dublets. Their values were attributed to deuteron positions corresponding to the locations at oxygen atoms in the faujasite framework and locations within hydrogen-bonded water clusters inside faujasite cages. The contributions of the different spectral components were observed to change with increasing temperature according to the Arrhenius law with a characteristic dynamic crossover point at T = 165 K. Below T = 165 K a spectral component was observed whose contribution changed with temperature, yielding the activation energy of about 2 kJ/mol, characteristic for jumps between inversion-related water positions in clusters.
authors.affiliation: University of Agriculture , 31-120 Kraków, Poland.
authors.forename: A M
authors.initials: AM
authors.lastname: Szymocha
authors.forename: A
authors.initials: A
authors.lastname: Birczyński
authors.forename: Z T
authors.initials: ZT
authors.lastname: Lalowicz
authors.forename: G
authors.initials: G
authors.lastname: Stoch
authors.forename: M
authors.initials: M
authors.lastname: Krzystyniak
authors.forename: K
authors.initials: K
authors.lastname: Góra-Marek