Electron spin resonance spectra of trimethylsilyl, trimethylgermyl and related free radicals in solution

Bennett, S. W.; Eaborn, Colin; Hudson, Andrew; Hussain, H. A.; Jackson, Richard A.

doi:10.1016/s0022-328x(00)81100-6

Cited by 37 publications

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“…Silyl radical formation in alkylsubstituted silicon-centered molecules was observed by many groups in the 1970s. Benett et al 11 and Krusic et al 12 reported trimethylsilyl radical formation on exposure to UV light. Benett et al 13 and Cooper et al 14 also presented the EPR spectra of dimethyl(trimethylsilyl)silyl radicals generated by UV light exposure.…”

Section: Introductionmentioning

confidence: 99%

Stability of Radicals in Aryl-Substituted Polysilanes with Linear and Planar Silicon Skeleton Structures

et al. 1998

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This paper discusses the stability of radicals produced under γ-irradiation for phenyl-substituted polysilanes with different backbone structures. Poly(methylphenylsilane) and structural defect-containing phenyl-substituted polysilanes were irradiated by 60Co γ-rays in the solid state. Temperature dependence of the EPR signal intensity from the radicals induced by radiolysis was measured. The radicals appeared to be more stable as the induced defect density in the backbone structure was increased, indicating that the structure defects on the polymer backbone may play a role in stabilizing silyl radicals. The migration of unpaired electrons was also observed from chain ends to chain center leading to stable radical species. The estimated-branched structures were less than 3.5% in the linear polysilane obtained by conventional Wurtz coupling condensation.

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Section: Introductionmentioning

confidence: 99%

Stability of Radicals in Aryl-Substituted Polysilanes with Linear and Planar Silicon Skeleton Structures

et al. 1998

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“…The first representative of this type of stable charged radicals of heavy group 14 elements, the potassium salt of the cyclotetrasilane anion-radical 11 − • • [K + (thf) 6 ], was recently synthesized by the reduction of dichloride 12 with potassium in THF (the doubly reduced cyclotetrasilane dianion was also isolated in the form of its dipotassium salt 13 2− • [K + (thf) 6 …”

Section: Cyclic Anion-radicalsmentioning

confidence: 99%

“…Cyclic delocalization of the unpaired electron over the cyclotetrasilane skeleton of 11 − • • [K + (thf) 6 ] was clearly seen in its EPR spectrum, which revealed a multiplet (g = 2.0025) of 15 lines (of total 17) with an hfcc of 0.35 mT because of the coupling of the unpaired electron with the eight equivalent 14 N nuclei (I = 1). Cyclic delocalization of the unpaired electron over the cyclotetrasilane skeleton of 11 − • • [K + (thf) 6 ] was clearly seen in its EPR spectrum, which revealed a multiplet (g = 2.0025) of 15 lines (of total 17) with an hfcc of 0.35 mT because of the coupling of the unpaired electron with the eight equivalent 14 N nuclei (I = 1).…”

Section: Scheme 217mentioning

confidence: 99%

“…All experimental (structural and spectral) data of 20 − • • [K(thf)6 ] + point to a formulation as a major contributor to the resonance structure in which each Sn atom bears a lone pair and the unpaired electron is accommodated over their 5p π -orbitals (Scheme 2.25). 119 Both Ar substituents at the Sn atoms are significantly trans-bent, whereas the Sn-Sn bond length of 2.8123(9)Å is quite normal for a Sn-Sn single bond.…”

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Heavy Analogs of Organic Free Radicals: Si‐, Ge‐, Sn‐ and Pb‐Centered Radicals

Lee

Sekiguchi

2010

Organometallic Compounds of Low‐Coordinate Si, Ge, Sn and Pb

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Heavy Analogs of Organic Free Radicals: Si-, Ge-, Sn-and Pb-Centered Radicals 49 region of 205-250 nm (absorption maximum at ca. 215 nm), indicative of its pyramidal structure. 41 The pyramidality of the F 3 Si • radical, generated by the glow discharge of the disilane F 3 Si-SiF 3 , was deduced from the analysis of its rotational spectrum recorded during a recent microwave spectroscopy study. 42 EPR and CIDNP Spectroscopy EPR SpectroscopyThe first EPR spectra of the transient radicals H 3 E • (E = Si, Ge, Sn) were recorded in inert gas matrices at low temperatures. 43 Accordingly, the following EPR parameters were reported at 4.2 K for the above-mentioned radical species [g-factor, hfcc for the central nuclei ( 29 Si, 73 Ge, 119 Sn) in mT, matrix inert gas]: H 3 Si • (2.0030, 19, Xe); H 3 Ge • (2.0073, 7.5, Xe); H 3 Sn • (2.0170, 38, Kr). 43 The large values of the hfcc suggest the pronounced pyramidality of the H 3 E • radicals, whose structural parameters were computationally estimated as follows (s-character of the bond orbital, bond angles in degrees): H 3 Si • (0.285, 113.5); H 3 Ge • (0.295, 115); and H 3 Sn • (0.310, 117). The pyramidal geometry of the heavy analogs H 3 E • is in sharp contrast to the planar environment of the prototypical methyl radical H 3 C • , which revealed a resonance at g = 2.0020 in Xe matrix and for which the s-character of the bond orbital of 0.333 and bond angles of 120 • were calculated. 43 The subsequent EPR reinvestigation of the H 3 Si • radical, generated by either γ -irradiation of H 4 Si adsorbed on a silica gel surface at 77 K 44 or by the reaction of H 4 Si with H atoms in a Kr matrix, 45 disclosed very similar values for the 29 Si hfcc of 18.2 mT 44 and 19.0 mT. 45 The large hyperfine splitting, implying a large s-fraction of its SOMO, is consistent with the pyramidal configuration of the H 3 Si • radical, in accordance with Pauling's hypothesis that the AX 3 • -type radical is expected to be nonplanar if X is more electronegative than A. 46 The EPR spectrum of the H 3 Ge • radical, generated in a matrix of nonmagnetic Xe isotopes, has also been reported. 47 On further increasing the electronegativity of substituents, one should expect a progressive increase in the degree of pyramidalization. Thus, the EPR spectra of perhalogenated silyl radicals F 3 Si • 48 and Cl 3 Si • , 49 generated by either radiolysis of F 3 SiH in an SF 6 matrix or irradiation of SiCl 4 , revealed very large 29 Si hfcc values of 49.8 mT (F 3 Si • ), 48 41.6 mT (Cl 3 Si • in Cl 3 SiCH 3 matrix) 49a and 44.0 mT (Cl 3 Si • in Cl 4 Si matrix), 49b thus pointing to a strong pyramidalization at the silicon radical centers because of the great difference in electronegativities of the Si and F atoms. The pyramidality of silyl radicals successively increased along the series (CH 3 ) 3 Si • < (CH 3 ) 2 ClSi • < (CH 3 )Cl 2 Si • < Cl 3 Si • , as was manifested by the increasing values of their hfcc (129 < 215 < 308 < 440). 49b Simple trialkylsilyl radicals were proved to be pyramidal; however, the ex...

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Application of Electron Spin Resonance Spectroscopy to Photochemistry

Wan

1974

Advances in Photochemistry

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Electron spin resonance spectra of trimethylsilyl, trimethylgermyl and related free radicals in solution

Cited by 37 publications

References 2 publications

Stability of Radicals in Aryl-Substituted Polysilanes with Linear and Planar Silicon Skeleton Structures

Stability of Radicals in Aryl-Substituted Polysilanes with Linear and Planar Silicon Skeleton Structures

Heavy Analogs of Organic Free Radicals: Si‐, Ge‐, Sn‐ and Pb‐Centered Radicals

Application of Electron Spin Resonance Spectroscopy to Photochemistry

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