Properties of methyl radical trapped in amorphous SiO2 and in natural SiO2-clathrate Melanophlogite

Buscarino, Gianpiero; Agnello, S.; Gelardi, F. M.; Boscaino, R.

doi:10.1016/j.jnoncrysol.2012.10.034

Cited by 9 publications

(10 citation statements)

References 17 publications

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“…2 Thus, the structure and properties of the methyl radical have attracted much attention both theoretically and experimentally. [3][4][5] The methyl radical exhibits a planar structure with D 3h symmetry. 5 The carbon atom in the methyl radical is sp 2 -hybridized with one single electron held in a p orbital.…”

Section: Introductionmentioning

confidence: 99%

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

Guo

Yang

et al. 2014

Phys. Chem. Chem. Phys.

118

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A single-electron tetrel bond was predicted and characterized in FXH3···CH3 (X = C, Si, Ge, and Sn) complexes by performing quantum chemical calculations, where the methyl radical acts as the Lewis base and the σ-hole on the X atom in FXH3 as the Lewis acid. The interaction between the methyl radical and FXH3 is characterized by a red shift of F-X stretching frequency. The strength of the tetrel bond becomes stronger by not only increasing the atomic number of the central atom X (X = C, Si, Ge, and Sn) but also by enhancing the electron-withdrawing ability of substituents in the Lewis acid. The energy decomposition analysis highlights the importance of the electrostatic interaction in the formation of the tetrel bond, although the dispersion part is also non-negligible for the weak tetrel bond. There is a competition between the formation of single-electron tetrel bonds and hydrogen bonds for the complexes composed of the methyl radical and CNCH3 or NCCH3. Furthermore, the single-electron tetrel bond exhibits the cooperative effect not only with the hydrogen bond in the complex of NCH···NCCH3···CH3, but also with the conventional tetrel bond in NCCH3···NCCH3···CH3.

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Section: Introductionmentioning

confidence: 99%

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

Guo

Yang

et al. 2014

Phys. Chem. Chem. Phys.

118

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“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25] Notwithstanding, many fundamental aspects remain at the moment unclear and continue to motivate a strong research activity in this field. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] A large number of EPR studies have also been devoted to the methyl radical in less inert or invasive environments, as in liquid methane, 26 in aqueous solution, 27 in organic media, [28][29][30] in the interstitial position in bulk amorphous silica, [31][32][33] adsorbed on the surface of porous amorphous silica [34][35][36][37][38] or of aluminosilicate zeolite [39][40][41] and clathrate hydrate materials. 42 The CH 3 molecule involves an unpaired electron interacting with three nearly equivalent protons and consequently (in the coupled representation) it is described by two J = 1/2 (A states...…”

Section: Introductionmentioning

confidence: 99%

Isolation of the CH₃˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures

Buscarino

Alessi

Agnello

et al. 2014

Phys. Chem. Chem. Phys.

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Matrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecular radicals. However, the isolation matrices, usually composed of noble gases or small diamagnetic molecules, are stable only at very low temperatures, as they begin to desegregate even above a few tens of Kelvin. Here we report on the successful isolation of CH3˙ radicals in the cages of a nearly inert clathrate-SiO2 matrix. This host is found to exhibit a comparable inertness with respect to that of most conventional noble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to the covalent nature of the host material and gives the opportunity to study the confined radicals from a few degrees of Kelvin up to at least room temperature. Thanks to this advantage we were able to explore with continuity for the first time the CH3˙ rotor properties by electron paramagnetic resonance spectroscopy, starting from the quantum rotations which are observable only at the lowest temperatures (T ≈ 4 K), going through the gradual transition to the classical motion (4 K < T < 30 K), and ending with the properties of the fully classical rotor (T > 30 K). The method of isolation presented here is found to be very effective and promising, as it is expected to be applicable to a large variety of different molecular radicals.

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“…We state first the main reason for the unexpected stability of the CH 3 radical in the SiO 2 clathrate compared to the SG. It has to do with the minor probability of escape and recombination of the radicals, as can be derived from the conclusions in the work of Buscarino et al 1 describing the spatial limitation conditions of the CH 3 gas confined in the limited voids' space of the rather inert host. On the contrary, the SG do not contain stable voids with well-defined free space within a well organized crystalline structure, trapping instead the radicals at substitutional sites.…”

Section: Discussionmentioning

confidence: 99%

Methyl Radical in Clathrate Silica Voids. The Peculiar Physisorption Features of the Guest–Host Molecular Dynamics Interaction

2016

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EPR line shape simulations of CH3/SiO2 clathrates and comparison to CH3/N2O and CH3/SiO2 experiments reveal the motional conditions of the CH3 radical up to the unusual regime of its stability, the high-temperature diffusional regime, at 300 K. In the low-temperature region, the CH3 in clathrates is found to rotate around the in-plane axes even at as low temperatures as 3.8 K. However, nonrotating methyls performing only libration about the C2-axes as well as around the C3-axis are also found, proving the existence of special sites in the clathrate voids that begin to accumulate a significant fraction of methyl radicals at temperatures below approximately 7 K. A distinctive feature in the spectrum anisotropy and line width temperature profiles is found nearby 25 K, which is interpreted as the radical physisorption inside the voids that occurs with the sample temperature lowering. The unusual increase of the CH3/SiO2 clathrate EPR spectral width with temperature over approximately 120 K has its origin in repeated angular momentum vector alterations due to frequent collisions with the clathrate void walls between periodical free rotation periods. This relaxation mechanism resembles to spin-rotation interaction known only for small molecular species in nonviscous fluids but unknown earlier for methyl hosted in solids.

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Properties of methyl radical trapped in amorphous SiO2 and in natural SiO2-clathrate Melanophlogite

Cited by 9 publications

References 17 publications

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

Isolation of the CH₃˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures

Methyl Radical in Clathrate Silica Voids. The Peculiar Physisorption Features of the Guest–Host Molecular Dynamics Interaction

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Properties of methyl radical trapped in amorphous SiO2 and in natural SiO2-clathrate Melanophlogite

Cited by 9 publications

References 17 publications

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

Isolation of the CH3˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures

Methyl Radical in Clathrate Silica Voids. The Peculiar Physisorption Features of the Guest–Host Molecular Dynamics Interaction

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Isolation of the CH₃˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures