Spin-echo Modulation Spectroscopy Research Articles

Solvation of exchangeable copper(2+) cations by primary alcohols in montmorillonite clay studied by electron spin resonance and electron spin echo modulation spectroscopies

A montmorillonite clay (STx-1), with Mg/sup 2 +/ as the major exchangeable cation and Cu/sup 2 +/ exchanged into 5% of the Mg/sup 2 +/ sites, is used to study the interaction between the exchangeable cations and adsorbed primary alcohols, methanol, ethanol, and 1-propanol, in the clay interlayer region. Electron spin resonance (ESR) shows that, on saturation of the clay with methanol, a freely rotating Cu/sup 2 +/ center is formed in the clay interlayer. Electron spin echo modulation (ESEM) spectroscopy indicates that the center is a four-coordinate Cu/sup 2 +/ solvate, in which the methanol ligands are in a square-planar configuration. On adsorption of ethanol into the interlayer region, a rotationally restricted Cu/sup 2 +/ center is detected. ESEM again indicates a four-coordinate, square-planar solvate, and ESR of oriented clay films reveals that the major symmetry axis of the ethanol-solvated Cu/sup 2 +/ center is perpendicular to the plane of the clay lattice. Similar ESP data are reported for 1-propanol-saturated montmorillonite, and a four-coordinate, square-planar Cu/sup 2 +/ solvate, similar to that described for ethanol, is proposed.

Aqueous coordination and location of exchangeable copper(2+) cations in montmorillonite clay studied by electron spin resonance and electron spin echo modulation

Electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies have been used to characterize the aqueous coordination and location of exchangeable Cu/sup 2 +/ cations in the interlayer regions of montmorillonite clay. Mg/sup 2 +/ montmorillonite, in which 5% of the exchangeable cations were replaced by Cu/sup 2 +/, was investigated. Under complete hydration, ESR indicates freely rotating Cu/sup 2 +/ ions in the interlayer region, and the corresponding ESEM indicates six directly bound water molecules. Under partial dehydration ESR shows Cu/sup 2 +/ in a second site with restricted rotation, and the corresponding ESEM indicates coordination to four water molecules. Following the collapse of the aqueous interlayer region on further dehydration, the Cu/sup 2 +/ enters a third site in a hexagonal cavity of the lattice structure, also with restricted rotation, in which it remains coordinated to only one water molecule. The natures and interconversions of these three sites are discussed.

Study of rhodium(II) species in CaA zeolite by electron spin resonance and electron spin echo modulation spectroscopies

Paramagnetic Rh(II) species generated in RhCa-A after activation and adsorption of various molecules were characterized by electron spin resonance (ESR) and electron modulation (ESEM) spectroscopies. (Rh(NH/sub 3/)/sub 5/Cl)Cl/sub 2/ was incorporated into the zeolite during synthesis. Activation of RhCa-A and RhNa-A at 400-500/sup 0/C either in flowing oxygen or under vacuum did not generate any substantial amount of Rh(II). However, exposure of activated RhCa-A to molecules such as O/sub 2/, CO, H/sub 2/O, NH/sub 3/, CH/sub 3/OH, H/sub 2/, and C/sub 2/H/sub 4/ at room temperature resulted in a considerable increase in the spin concentration which was assigned mainly by Rh(II) species. No such changes were observed in RhNa-A under similar conditions. The formation of the various paramagnetic Rh(II) species, their location within the zeolite structure, and their interaction with adsorbates in terms of the distance and number of interacting molecules as obtained from the ESEM data are discussed. The results are further compared with results previously obtained in Rh-exchanged X and Y zeolites.

Assessment of the spherical-averaging approximation for the interpretation of electron spin-echo modulation for cupric ion complexes

A comparison is made between three methods for the simulation of deuterated ligand modulation from cupric ion complexes as powders using electron spin-echo modulation (ESEM) spectroscopy: (a) the spherical-averaging approximation which assumes both isotropic g and a random distribution of deuterium nuclei about the paramagnetic center, (b) an average which is performed over specific orientations of the field H0 with respect to g∥ using analytical expressions for the spin-echo intensity for an axially symmetric g tensor, and (c) a similar approach to (b) but with full geometrical correlation between the deuterium nuclei. Approach (c) is found to be unnecessary because of the degree of freedom of the ligand molecules to rotate about the ligand axis before freezing locks them into a particular configuration. This, in effect, removes any strict correlation between the deuterium nuclei. Approaches (a) and (b) are found to be equivalent when (i) the electron–nuclear distance r is greater than 0.35 nm, (ii) r is less than 0.35 nm but the number of interacting nuclei, N, is 6 or greater, and (iii) r is less than 0.35 nm, N is less than 6, and the angle θI between g∥ and r is greater than 45°. In all cases microwave irradiation must be near g⊥. When the situation is none of the above, then parameters defined by the spherical-averaging approximation should be interpreted with caution.

Variation of alkymethylviologen radical cation-water interactions in micelles and vesicles from ESEM spectroscopy: effect of alkyl chain length

The variation in alkylmethylviologen radical cation-water interactions with the alkyl chain length in frozen sodium dodecyl sulfate (SDS) micelles and dihexadecyl phosphate (DHP) vesicles were investigated by electron spin echo modulation spectroscopy. In the DHP vesicle system, the measured deuterium modulation depth associated with deuteriated water indicated a significant decrease in the magnitude of these interactions with an increase in the alkyl chainlength of the viologen. However, a comparable trend was absent in the SDS micelle system. In addition, the strength of the dimethylviologen radical cation-water interactions in SDS micelles was much weaker than those measured for any of the viologen radicals in the vesicle system. These observations were found to be in qualitative agreement with currently proposed models of the binding characteristics of alkylmethylviologens to DHP vesicles and SDS micelles and may also reflect structural differences between these two types of assemblies.

Study of copper(2+)-doped zeolite NaH-ZSM-5 by electron spin resonance and electron spin echo modulation spectroscopies

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudy of copper(2+)-doped zeolite NaH-ZSM-5 by electron spin resonance and electron spin echo modulation spectroscopiesMichael W. Anderson and Larry. KevanCite this: J. Phys. Chem. 1987, 91, 15, 4174–4179Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://doi.org/10.1021/j100299a045RIGHTS & PERMISSIONSArticle Views263Altmetric-Citations99LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (713 KB) Get e-Alerts

Study of copper(2+)-doped zeolites Na-rho, K-rho, and Ca-rho by electron spin resonance and electron spin echo modulation spectroscopies

The location and adsorbate interaction of Cu/sup 2 +/ in Na-, K-, and Ca-rho zeolites doped with Cu/sup 2 +/ has been studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. It is found that the activation process varies very little with the type of countercation and the major hydrated species in zeolite rho is a square-coplanar or square-pyramidal Cu/sup 2 +/ bound to two water molecules. Adsorption of polar molecules, such as ammonia, methanol, and ethanol, results in complexing with the Cu/sub 2//sup +/ although in the case of methanol the number of ligands is less for Na-, K-, and Ca-rho than for H-rho studied previously. Nonpolar molecules, such as ethylene, are essentially excluded from the zeolite by the Na, K, and Ca cations which are located in the octagonal prisms blocking entrance to the zeolite interior.

An electron spin resonance and electron spin-echo modulation study of paramagnetic rhodium species generated in Ca-Y and Na-Y zeolites

Paramagnetic Rh species generated in RhNa-Y and RhCa-Y zeolites after various treatments were characterized by using electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies. Activation in flowing oxygen at 500/sup 0/C ..beta..-hydrogen a considerable amount of Rh(II) located in site I in the hexagonal prism of the zeolite structure for 3 wt % Rh in RhNa-Y zeolite. Samples of 1 wt % Rh in RhNa-Y and RhCa-Y did not show any paramagnetic signals. Adsorption of various adsorbates such as water, ammonia, methanol, carbon monoxide, and oxygen on activated samples induced a considerable increase in the ESR intensities. Adsorption of oxygen and carbon monoxide yields the corresponding adducts which are located in the ..cap alpha..-cage of the zeolite structure. Hydration generated a species which is coordinated to three water molecules. Adsorption of methanol on RhNa-Y generated a species H2 which is also formed after reduction of RhNa-Y with H/sub 2/, suggesting that the methanol molecule undergoes a reaction to generate products which further reduce Rh(III) species in the ..beta..-cage of the zeolite structure to Rh(II). No significant differences were observed between RhNa-Y and RhCa-Y except for the formation of different Rh(II) species after methanol adsorption in RhCa-Y and themore » generation of a larger amount of Rh(II) in site I in RhNa-Y. These results are compared to previously obtained data in RhNa-X and RhCa-X to account for the effect of the cocations and the Si/Al ratio on the generation of Rh(II) species in zeolites.« less

Studies of the interaction of palladium(3+) and palladium(1+) with organic adsorbates, water, and molecular oxygen in palladium-Ca-X zeolite by electron spin resonance and electron spin-echo modulation spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudies of the interaction of palladium(3+) and palladium(1+) with organic adsorbates, water, and molecular oxygen in palladium-Ca-X zeolite by electron spin resonance and electron spin-echo modulation spectroscopyJ. Michalik, M. Narayna, and Larry KevanCite this: J. Phys. Chem. 1985, 89, 21, 4553–4560Publication Date (Print):October 1, 1985Publication History Published online1 May 2002Published inissue 1 October 1985https://doi.org/10.1021/j100267a028RIGHTS & PERMISSIONSArticle Views124Altmetric-Citations44LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (967 KB) Get e-Alerts

Role of magnesium(2+) ion in modifying the environment of radiolytically produced silver atoms in A zeolites: electron spin resonance and electron spin echo modulation spectroscopy studies

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRole of magnesium(2+) ion in modifying the environment of radiolytically produced silver atoms in A zeolites: electron spin resonance and electron spin echo modulation spectroscopy studiesM. Narayana and Larry KevanCite this: J. Am. Chem. Soc. 1985, 107, 16, 4643–4647Publication Date (Print):August 1, 1985Publication History Published online1 May 2002Published inissue 1 August 1985https://doi.org/10.1021/ja00302a008RIGHTS & PERMISSIONSArticle Views43Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (606 KB) Get e-Alerts Get e-Alerts