Cation vibrations

This technique offers possibilities of direct probing of the cation on their different sites in the intracrystalline channels and cavities of zeolites. In a simple approach Coulomb interaction between the cation and the rigid framework has been assumed giving rise to the frequency relation [49] 

FIR results have to be considered as preliminary. Until now it is impossible to interpret a number of results free of any contradiction, e.g. there is no guarantee for a safe assignment of FIR bands to distinct cation vibrations. Furthermore, there is some doubt especially about cations on sites SI, SF and SIl in faujasites. The concept of uncoupled vibrations should be 

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All physical properties of pyrylium salts (unsubstituted or substituted with alkyl and/or aryl groups) prove the aromaticity of these cations vibrational spectra [66], mass-spectral fragmentations [67], magnetic properties [68-70], and electronic absorption spectra [71]. It should be mentioned that there is a close similarity between the electronic absorption bands of pyrylium salts and those of benzene, easily recognized by the marked bathochromic effect of substituents in y-position of pyrylium salts on one of these bands. Two-photon absorption spectra of 2,4,6-triarylpyrylium cations [72] may be used in optical data storage, lasing, and photodynamic therapy. 

Introduction of aluminium into a zeolite lattice broadens the lattice modes, but also introduces additional bands in the Raman spectra at low frequencies due to cation vibrations, completely analogous to the far infrared bands described in section 3.3. Figure 18 shows, for example, Raman spectra taken from the work of Bremard and Le Maire [53] of zeolite Y exchanged with different alkali metal cations. The arrows indicate bands assigned to translational modes of the cations these move to lower frequency as the mass of the cations increases, just as in the far infared spectra. 

The earliest studies on the IR spectra of crown ethers and their complexes were carried out by Pederson (B-78MI52101). Since then IR spectroscopy has been applied a number of times to solve structural problems in crown ether chemistry including ion pair interactions and conformational analysis (B-79MI52103). A low frequency vibration of the cation within the macrocycle has been identified which is dependent on the cation but not on the solvent (214 cm for Na -dibenzo[18]crown-6 in both DMSO and pyridine). This is in contrast to the frequency of cation vibration within a solvent cage, which for Na is 202 cm in... 

Fielicke A, von Helden G, Meijer G, Pederson D, Simard B, Rayner D (2005) Gold cluster carbonyls Saturated adsorption of CO on gold cluster cations, vibrational spectroscopy, and implications for their structures. J Am Chem Soc 127 8416... 

N.m.r. relaxation studies by Alexandre and Rigny117 have yielded information on the difference in chemical shifts between the non-equivalent fluorines and the rate of exchange between them. New 1 1 adducts of C10F3 with a number of pentafluorides MF5 (M = P, V, Ta, Nb, or Bi) have been obtained and characterized by X-ray powder diffraction measurements.118 The essentially ionic nature of these compounds was confirmed by means of their vibrational spectra. Solution studies in liquid HF allowed a more confident assignment of some of the cation vibrations. 

The jump frequency, F, in a thermally activated process and is related to the cation vibrational frequency. If the free energy barrier for migration is AG = A// - TAS, then F can be written as... 

Of the remaining cations in K -A, there are 0.3 K+ ions per pseudo unit cell in site H and 0.1. K+ ions per pseudo cell in site G. The vibrational frequency of Na+(H) cations would translate to a K+(H) cation vibration at 49 cm l. It appears from the spectrum that a weak band at about 117 cm i is best ascribed to K+(G), with K+(H)... 

The far-IR spectra of hydrated and dehydrated SrA are displayed in Figure 10. The form of the spectra aside from red shifts are remarkably similar to those of the Ca-A described above. This is not surprising as the siting and populations of Sr2+ ions are identical to Ca2+ in Ca -A (19b). The Sr2+ ions are located in the six-rings, with 4.5 ions per pseudo-cell in site B, and 1.2 ions per pseudo-cell in site C. Together the Ca2+ and Sr2+ zeolites yield a consistent picture of the divalent cation far-IR vibrational frequencies, and are useful models for the investigation of the transition metal (2+) -A systems. Strontium cation vibrations anticipated to occur at 175 cm-l (site B) and at 145 cm (site C) compare quite well with the observed bands at 182 and 142 cm l respectively. 

The IR reported spectra ) forl2Sb2Ffi and ijTaFg include only lines of SbFs and SbFj as well as TaFj and TaFg, but no cationic vibrations were observed, which is as expected of a symmetric diatomic species, to have only a Raman active Une, and no IR active one. 

In 1965 Edgell and co-workers reported an infrared band, from solutions of alkali metal salts of Co CO) dissolved in tetrahydrofuran (THF), which was assigned to the cation vibrating in a solvent cage. Subsequently a detailed report about the nature of the vibration of these monatomic ions in several non-aqueous solvents was given. The bands are broad and of medium intensity. Thus their properties are... 

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