Infrared Spectra and Quantum-Chemical Studies of Disilylmethanes

McKean, D.C.

doi:10.1021/jp030178i

Cited by 16 publications

(22 citation statements)

References 39 publications

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“…These two A 2 vibrations are calculated to have the weakest infrared intensities among the fundamentals for the four molecules and thus were difficult to assign without the DFT calculations. Several other studies – have employed DFT calculations to predict vibrational frequencies and to compare them with previous experimental results for some noncyclic silicon-containing molecules including dimethylsilane, , trimethylsilane, , disilylmethane, , and ethylsilane . These studies utilized the calculated frequencies to reinvestigate some of the uncertain aspects of the vibrational spectra recorded many years earlier, but none of these studies noted why such a discrepancy between the experimental and calculated frequencies for these CH 2 out-of-phase modes should occur. – Nevertheless, one conclusion drawn from all these studies as well as our own is that the presence of a silicon atom in the structure of a molecule does not adversely affect the accuracy of the vibrational frequencies calculated by the DFT method.…”

Section: Vibrational Assignmentsmentioning

confidence: 99%

“…Several other studies – have employed DFT calculations to predict vibrational frequencies and to compare them with previous experimental results for some noncyclic silicon-containing molecules including dimethylsilane, , trimethylsilane, , disilylmethane, , and ethylsilane . These studies utilized the calculated frequencies to reinvestigate some of the uncertain aspects of the vibrational spectra recorded many years earlier, but none of these studies noted why such a discrepancy between the experimental and calculated frequencies for these CH 2 out-of-phase modes should occur. – Nevertheless, one conclusion drawn from all these studies as well as our own is that the presence of a silicon atom in the structure of a molecule does not adversely affect the accuracy of the vibrational frequencies calculated by the DFT method. Moreover, for disilylmethane (CH 3 SiH 2 CH 3 ), the CH 2 twisting vibration was previously predicted with the B3LYP/6-311G(d,p) level of theory to be at 1043 cm −1 , which is at a somewhat lower value than had been assigned before (1101 cm −1 ).…”

Section: Vibrational Assignmentsmentioning

confidence: 99%

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Structure, Vibrational Spectra, and DFT and ab Initio Calculations of Silacyclobutanes

Al‐Saadi

Laane

2008

Organometallics

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Ab initio calculations have been carried out for silacyclobutane (SCB) and its 1,1-difluoro and 1,1-dichloro derivatives in order to compute the structures and dihedral angles of puckering for these molecules. For SCB the calculated dihedral angle of 35° agrees nicely with the 36° value obtained from far-infrared work. The calculated angles of 29° and 31° for the fluoro and chloro derivatives, respectively, can be compared to electron diffraction results of 25° and 26°. The zero-point-corrected barriers calculated using the MP2/cc-pVTZ level of theory were 523 (as compared to 440 cm−1 experimental), 186, and 433 cm−1 for SCB and its fluoro and chloro derivatives, respectively. Calculated structural changes in the dihalo derivatives can be ascribed to the high electronegativity of the halogen atoms. High-level DFT computations were also carried out in order to calculate the infrared and Raman spectra of these three molecules as well as the SCB 1,1-d 2 isotopomer. The agreement between experimental and calculated spectra is remarkably good for all four molecules. The predicted frequencies and intensities were utilized to reassign several of the weaker spectral bands and also to characterize the 1130 cm−1 signature band present in the infrared spectra of all silacyclobutanes. This arises from the α-CH2 in-phase wagging vibration, which is very much affected by the neighboring silicon atom. The DFT calculations also demonstrated that two of the wagging and twisting motions of the CH2 group next to the silicon atom have frequencies much lower than in typical organic molecules. This work also provides frequency ranges that can be expected for the six vibrations of SiX2 groups (X = H, D, F, Cl) in organosilanes.

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Section: Vibrational Assignmentsmentioning

confidence: 99%

Section: Vibrational Assignmentsmentioning

confidence: 99%

Structure, Vibrational Spectra, and DFT and ab Initio Calculations of Silacyclobutanes

Al‐Saadi

Laane

2008

Organometallics

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“…14 The sample was purified several times and the identity and the purity of the compound were confirmed by 1 H, 13 C and 19 F NMR and by infrared spectroscopy. The chloro derivative was prepared by the reaction of trichlorosilane with trichlorovinylsilane.…”

Section: Sample Preparationmentioning

confidence: 99%

“…However, for DSB the discrepancies from the observed values were considerable. 19 A normal coordinate analysis based on harmonic force constants derived from the DFT calculations was carried out as described below. Applying the much larger cc-pVQZ basis sets, however, the wavenumbers 1295 and 1298 cm 1 were obtained for 14 .…”

Section: Normal Coordinate Calculationsmentioning

confidence: 99%

Infrared and Raman Spectra, conformations, ab initio calculations and spectral assignments of 1,3‐disilabutane (SiH₃CH₂SiH₂CH₃)

Guirgis

Mazzone

Pasko

et al. 2007

J Raman Spectroscopy

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Raman spectra of 1,3-disilabutane (SiH 3 CH 2 SiH 2 CH 3 ) as a liquid were recorded at 293 K and as a solid at 78 K. In the Raman cryostat at 78 K an amorphous phase was first formed, giving a spectrum similar to that of the liquid. After annealing to 120 K, the sample crystallized and large changes occurred in the spectra since more than 20 bands present in the amorphous solid phase vanished. These spectral changes made it possible to assign Raman bands to the anti or gauche conformers with confidence. Additional Raman spectra were recorded of the liquid at 14 temperatures between 293 and 137 K. Some Raman bands changed their peak heights with temperature but were countered by changes in linewidths, and from three band pairs assigned to the anti and gauche conformers, the conformational enthalpy difference 1 conf H.gauche-anti/ was found to be 0 ± 0.3 kJ mol −1 in the liquid. Infrared spectra were obtained in the vapor and in the liquid phases at ambient temperature and in the solid phases at 78 K in the range 4000-400 cm −1 . The sample crystallized immediately when deposited on the CsI window at 78 K, and many bands present in the vapor and liquid disappeared. Additional infrared spectra in argon matrixes at 5 K were recorded before and after annealing to temperatures 20-34 K. Quantum chemical calculations were carried out at the HF, MP2 and B3LYP levels with a variety of basis sets. The HF and DFT calculations suggested the anti conformer as the more stable one by ca 1 kJ mol −1 , while the MP2 results favored gauche by up to 0.4 kJ mol −1 . The Complete Basis Set method CBS-QB3 gave an energy difference of 0.1 kJ mol −1 , with anti as the more stable one. Scaled force fields from B3LYP/cc-pVQZ calculations gave vibrational wavenumbers and band intensities for the two conformers. Ł 965 m 960 m" 961 s, sh 968 m 958 m" 961 m,sh 956 m, sh, P? 959 vs 958 vs 17 A 0 954 m 948 s, sh 952 vs Ł 18 950 vs 954 m 951 m" 947 vvs 945 s, D 950 vs 947 vs 18 A 00

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“…Several such studies have been reported for silyl compounds using density functional theory in the B3LYP approach with the basis set 6-311G**. 4,5…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Studies of the Structures and Vibrations of Trisilylmethane and Tetrasilylmethane

McKean

2004

J. Phys. Chem. A

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Quantum chemical studies of trisilylmethane, (SiH3)3CH, (TSM) and tetrasilylmethane, (SiH3)4C, (TTSM) have been made by the HF, MP2, and B3LYP methods. The silyl groups in each compound are twisted through 12−20° from the completely staggered configurations, yielding the point groups C 3 (TSM) and T (TTSM), respectively, in fair agreement with electron diffraction results. Structures have also been calculated for the higher energy, fully staggered configurations. These exhibit H···H distances between neighboring silyl groups, which are significantly less than those in the staggered, equilibrium structures calculated for disilylmethane (DSM). In a survey of QC-based torsional frequencies in molecules containing silyl groups, TSM, TTSM, and DSM are exceptional in exhibiting marked variations in their calculated in-phase torsional frequencies according to the computational method employed. In TSM and TTSM, MP2 values are much larger than B3LYP ones, reflecting similar differences in internal rotation barrier. This may be due to the longer bond lengths and nonbonded H···H distances yielded by the DFT method. QC-based vibration frequencies and overall intensities of SiH and CH stretching bands in TSM and TTSM are scaled using earlier experimental data from related compounds such as DSM. Agreement with the sparse infrared data currently available for condensed phases is only fair. Electrical properties of the Si−H and C−H bonds are compared with those of related silyl compounds. Infrared intensities of CH and SiH stretching bands show the expected behavior due to inductive effects on the charges on the H atoms involved.

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Infrared Spectra and Quantum-Chemical Studies of Disilylmethanes

Cited by 16 publications

References 39 publications

Structure, Vibrational Spectra, and DFT and ab Initio Calculations of Silacyclobutanes

Structure, Vibrational Spectra, and DFT and ab Initio Calculations of Silacyclobutanes

Infrared and Raman Spectra, conformations, ab initio calculations and spectral assignments of 1,3‐disilabutane (SiH₃CH₂SiH₂CH₃)

Quantum Chemical Studies of the Structures and Vibrations of Trisilylmethane and Tetrasilylmethane

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Infrared Spectra and Quantum-Chemical Studies of Disilylmethanes

Cited by 16 publications

References 39 publications

Structure, Vibrational Spectra, and DFT and ab Initio Calculations of Silacyclobutanes

Structure, Vibrational Spectra, and DFT and ab Initio Calculations of Silacyclobutanes

Infrared and Raman Spectra, conformations, ab initio calculations and spectral assignments of 1,3‐disilabutane (SiH3CH2SiH2CH3)

Quantum Chemical Studies of the Structures and Vibrations of Trisilylmethane and Tetrasilylmethane

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Infrared and Raman Spectra, conformations, ab initio calculations and spectral assignments of 1,3‐disilabutane (SiH₃CH₂SiH₂CH₃)