Finally, it is worth noting that when analyzing different zeolite structures, an
attempt was also made to identify characteristic RO vibrations (fully symmetric) of
larger structural elements than SBUs—i.e., chambers (CBUs), confirming previous
evidence [36], that this type of vibrations was not identified for either CAN
structure (cancrinite chamber), LTA (a and b chambers) or FAU (b chamber). The
only identified vibration of this type concerns a hypothetical structure of the SOD
type, for which discussed vibration is active in Raman spectrum. The probable
cause here is the relatively high symmetry and atomic density of the discussed
structural fragment.
10.7 Influence of Extra-Framework Ions on Vibrational
Spectra
As already mentioned, introducing into zeolite framework extra ions (cations or
anions) causes specific structural changes that can be observed in spectrum
envelope changes, both in the mid-infrared (MIR) and in the far-infrared
(FIR) ranges. In the case of the mid-infrared, these changes mainly concern the
pseudolattice range of the spectrum and changes in the position or intensity of the
bands associated with characteristic vibrations. In the far-infrared range, changes in
the spectrum envelope are related to the interaction of individual ions with the
framework and therefore most often with the change in the nature of Me–O bonds
(vibrations of the cation sublattice), as well as the presence of bands associated with
lattice vibrations.
10.7.1 Ion Exchange Versus Spectrum
Analyzing the pseudolattice range of zeolite spectra, changes were found due to the
exchange of extra-framework cations [36, 56, 68]. This observation can help in
understanding one of the most important properties of zeolites, namely the ability to
exchange and retain foreign ions in their structure. The essence of this type of
research was to determine whether and what changes will be observed in the spectra
of selected structures under the influence of the exchange of extra-framework
elements. In the case of theoretical analysis of the influence of the presence of
extra-framework ions on the zeolite spectra, the calculations for which the SBU
models were used are inadequate. In order to thoroughly investigate the effect of
such ions on the structural properties and the shape of vibrational spectra, one
should take into account the influence of the presence of long-range order and the
position of particular cations/anions relative to coordinating them oxygen atoms.
The presence of extra-framework ions has a significant impact on charge distribution between Si, Al, and O atoms, Si–O and Al–O force constants, as well as the
10 Vibrational Spectroscopy of Zeolites …
319
attempt was also made to identify characteristic RO vibrations (fully symmetric) of
larger structural elements than SBUs—i.e., chambers (CBUs), confirming previous
evidence [36], that this type of vibrations was not identified for either CAN
structure (cancrinite chamber), LTA (a and b chambers) or FAU (b chamber). The
only identified vibration of this type concerns a hypothetical structure of the SOD
type, for which discussed vibration is active in Raman spectrum. The probable
cause here is the relatively high symmetry and atomic density of the discussed
structural fragment.
10.7 Influence of Extra-Framework Ions on Vibrational
Spectra
As already mentioned, introducing into zeolite framework extra ions (cations or
anions) causes specific structural changes that can be observed in spectrum
envelope changes, both in the mid-infrared (MIR) and in the far-infrared
(FIR) ranges. In the case of the mid-infrared, these changes mainly concern the
pseudolattice range of the spectrum and changes in the position or intensity of the
bands associated with characteristic vibrations. In the far-infrared range, changes in
the spectrum envelope are related to the interaction of individual ions with the
framework and therefore most often with the change in the nature of Me–O bonds
(vibrations of the cation sublattice), as well as the presence of bands associated with
lattice vibrations.
10.7.1 Ion Exchange Versus Spectrum
Analyzing the pseudolattice range of zeolite spectra, changes were found due to the
exchange of extra-framework cations [36, 56, 68]. This observation can help in
understanding one of the most important properties of zeolites, namely the ability to
exchange and retain foreign ions in their structure. The essence of this type of
research was to determine whether and what changes will be observed in the spectra
of selected structures under the influence of the exchange of extra-framework
elements. In the case of theoretical analysis of the influence of the presence of
extra-framework ions on the zeolite spectra, the calculations for which the SBU
models were used are inadequate. In order to thoroughly investigate the effect of
such ions on the structural properties and the shape of vibrational spectra, one
should take into account the influence of the presence of long-range order and the
position of particular cations/anions relative to coordinating them oxygen atoms.
The presence of extra-framework ions has a significant impact on charge distribution between Si, Al, and O atoms, Si–O and Al–O force constants, as well as the
10 Vibrational Spectroscopy of Zeolites …
319