Electron spin resonance spectra of the reaction products of copper(II) hydroxide suspensions in methanol with hydrogen peroxide and of polycrystalline copper(II) hydroxide and copper(II) peroxide

Vierke, Gerhard

doi:10.1039/f19736901523

Cited by 7 publications

(4 citation statements)

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“…This g value is the same as that reported for CuO. 37 Upon activating the zeolite to 500 °C for 3 h under a dynamic vacuum, the signal disappeared but reappeared after rehydration of the sample with water vapor. These observations indicate that the symmetric line should probably be attributed to a disordered surface species such as [Cu(OH)"]2-" or [Cu(H20)J2+ rather than to CuO.…”

Section: Discussionsupporting

confidence: 85%

Electron paramagnetic resonance parameters of copper(II) Y zeolites

Herman¹,

Flentge²

1978

J. Phys. Chem.

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The number of electron paramagnetic resonance (EPR) parameters for copper(II) ions held in lattice positions in dehydrated low exchanged sodium Y zeolites, as well as the relative intensity of each set of g values observed in the spectrum, was found to vary as a function of evacuation time at ambient temperature prior to activation. The usual procedure of evacuating the sample for 15-60 min before beginning the thermal treatment in hourly increments resulted in the following parameters for low Cu(II) exchanged Y zeolites: gj1 = 2.38(110), gLl = 2.06(20), gf = 2.30(175), g±2 = 2.03, and in some cases g||3 = 2.36(125), where the numbers in parentheses are the observed hyperfine splittings (in Gauss). Prolonged evacuation of the low Cu(II) ion exchanged Y zeolites yielded gj1 = 2.37(125), g^1 = 2.06(20), gf = 2.32(160), and g±2 = 2.03 following dehydration to 400-500 °C.Parameters similar to the latter values were obtained for highly ion exchanged Cu-Y zeolites following partial reduction with hydrogen or carbon monoxide, as well as upon partial reoxidation of the latter samples with oxygen or nitric oxide. The second set of EPR parameters is attributed to copper(II) ions located in sites in the small cages, while the g1 and g1 subsets of the first group are due to copper(II) ions localized in the zeolite supercages. Most, of these sites provide a distorted trigonal environment for the divalent copper ions. By correlating the zeolite treatments reported in the literature to the present results, the disparity among previously given EPR parameters for Cu(II)-Y zeolites can be explained in most cases.

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Section: Discussionsupporting

confidence: 85%

Electron paramagnetic resonance parameters of copper(II) Y zeolites

Herman¹,

Flentge²

1978

J. Phys. Chem.

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“…6 The failure to obtain an EPR signal for CuO was attributed to rapid relaxation,16 but Vierke recently obtained a broad symmetric line for this compound with g = 2.27 by using a high microwave power of 200 mW. 16 In the present study CuO was prepared by decomposing Cu(OH)2 under vacuum at 400°C. The latter was precipitated from a 0.1 M Cu(II) solution with NH4OH to a pH of 7.…”

Section: Discussionmentioning

confidence: 86%

Redox behavior of transition metal ions in zeolites. I. Reversibility of the hydrogen reduction of copper Y zeolites

Herman¹,

Lunsford²,

Beyer³

et al. 1975

J. Phys. Chem.

113

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Publication costs assisted by the National Science Foundation (USA) and the National Fonds voor Wetenschappelijk Onderzook (Belgium)The reduction of Cu(II) ions in CuNaY zeolites occurs via a two-step mechanism in which Cu(I) is first formed and then reduced to metallic copper. The first step in the reduction may be carried out by using relatively mild conditions, e.g., H2 at 200°C for 1 hr, and it is completely reversible. Reduction in H2 at 400°C results in the formation of copper crystallites, some of which grow to a size of 300 Á after 20 hr of reduction. The copper in these larger crystals may be reoxidized slowly to CuO. The smaller metal particles, which are postulated to reside within the zeolite cages, may be readily reoxidized to Cu(II), located at exchange sites within the zeolite. Approximately half of the metallic copper is in the form of the larger crystallites and half is present in small clusters. The reduction and reoxidation was followed by quantitatively observing the H2 or O2 consumption and H2O produced in the reaction, while the amount of Cu(II) was determined by EPR spectroscopy. The presence of Cu(I) was detected by the ir and EPR spectra of the Cu+-CO and Cu+-NO complexes, respectively.

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“…38 Here observed very weak and broad signals could be assigned to defects that occur during aging of the sample, in agreement with similar results found in the literature. 38,39 The spectrum of HKUST-1 is a superposition of two contributions; the first stronger contribution observed at a magnetic field of ≈330 mT corresponds to paramagnetic copper ions with spin S = 1 / 2 , and the second weaker contribution belongs to two coupled copper ions with total spin S = 1. 40 In accordance with the literature, this main resonance originates from the [Cu(OH 2 ) 6 ] 2+ complex, a defect formed during the synthesis, heterogeneously distributed over the HKUST-1 pores.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

In Situ Monitoring of the Mechanosynthesis of the Archetypal Metal–Organic Framework HKUST-1: Effect of Liquid Additives on the Milling Reactivity

et al. 2017

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We have applied in situ monitoring of mechanochemical reactions by high-energy synchrotron powder X-ray diffraction to study the role of liquid additives on the mechanochemical synthesis of the archetypal metal-organic framework (MOF) HKUST-1, which was one of the first and is still among the most widely investigated MOF materials to be synthesized by solvent-free procedures. It is shown here how the kinetics and mechanisms of the mechanochemical synthesis of HKUST-1 can be influenced by milling conditions and additives, yielding on occasion two new and previously undetected intermediate phases containing a mononuclear copper core, and that finally rearrange to form the HKUST-1 architecture. On the basis of in situ data, we were able to tune and direct the milling reactions toward the formation of these intermediates, which were isolated and characterized by spectroscopic and structural means and their magnetic properties compared to those of HKUST-1. The results have shown that despite the relatively large breadth of analysis available for such widely investigated materials as HKUST-1, in situ monitoring of milling reactions can help in the detection and isolation of new materials and to establish efficient reaction conditions for the mechanochemical synthesis of porous MOFs.

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Electron spin resonance spectra of the reaction products of copper(II) hydroxide suspensions in methanol with hydrogen peroxide and of polycrystalline copper(II) hydroxide and copper(II) peroxide

Cited by 7 publications

References 0 publications

Electron paramagnetic resonance parameters of copper(II) Y zeolites

Electron paramagnetic resonance parameters of copper(II) Y zeolites

Redox behavior of transition metal ions in zeolites. I. Reversibility of the hydrogen reduction of copper Y zeolites

In Situ Monitoring of the Mechanosynthesis of the Archetypal Metal–Organic Framework HKUST-1: Effect of Liquid Additives on the Milling Reactivity

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