Notizen:Spektroskopische Untersuchungen an Komplexverbindungen XIV

Keller, H. J.; Laubereau, P.; Nöthe, D.

doi:10.1515/znb-1969-0226

Cited by 27 publications

(11 citation statements)

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“…Magnetic susceptibility measurements of solid V(CO) 6 have shown that this molecule has one unpaired electron and that for temperatures lower than 66 K a weak antiferromagnetic coupling ( J = −50 cm -1 ) exists . As the 2 T 2g ground state of a d 5 system is three-fold degenerate, a distorted octahedral geometry should be present, in accordance with the Jahn−Teller theorem. − To clarify this question and to characterize its molecular properties, V(CO) 6 has been studied in different aggregation states with different techniques: IR − UV−vis ,, , ESR, − MCD, and PE spectroscopy as well as electron and X-ray diffraction . These investigations show that V(CO) 6 is subject to a dynamical Jahn−Teller effect and has nearly octahedral geometry at room temperature.…”

Section: Introductionmentioning

confidence: 99%

D₃_d Ground-State Structure of V(CO)₆: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

et al. 2003

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Structures, relative energies, vibrational spectra, and ESR parameters of the 17emolecule V(CO) 6 in O h , D 3d , D 4h , and D 2h symmetry have been computed with density functional and high-level ab initio methods. At all theoretical levels applied, the same energetic order is obtained, D 3d < D 2h < D 4h < O h , with the D 2h structure as a transition state connecting equivalent D 3d species. At the RCCSD(T)/AE2 level using UBP86/ AE2 geometries, the energies of the D 2h , D 4h and O h species relative to that of D 3d minimum are predicted to be 210, 535, and 731 cm -1 , respectively. According to molecular dynamics simulations on the UBP86/AE1 potential energy surface, the D 3d minimum is preserved at very low temperatures (around 16 K), whereas at 300 K the molecule is highly fluxional with an averaged structure indistinguishable from that of [V(CO) 6 ]with its O h symmetric ground state. Nearly complete IR and Raman spectra of V(CO) 6 and V( 13 CO) 6 have been recorded at 300 K for the first time in the gas phase, in solution, and at cryogenic temperatures in Ne and Ar matrices. The spectra show a pronounced temperature dependence, especially for the Jahn-Teller active modes, E g and T 2g . The observed infrared matrix spectra generally agree well with the calculated spectrum (BP86/AE2 level) for the D 3d structure and much less with that of the D 4h isomer. The A 1g modes in the Raman spectra are reasonably well reproduced computationally in the harmonic approximation, whereas this approximation breaks down for the E g and T 2g bands, as expected. Further evidence for the D 3d symmetry of V(CO) 6 is obtained from a reanalysis of the experimental ESR spectrum that is reported in the literature. The observed ordering of the hyperfine coupling constants A | and A ⊥ is reproduced theoretically only when distortion to D 3d symmetry is assumed. In addition, the bonding properties of V(CO) 6 are compared to those of [V(CO) 6 ]and Cr(CO) 6 .

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Section: Introductionmentioning

confidence: 99%

D₃_d Ground-State Structure of V(CO)₆: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

et al. 2003

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“…There is a large body of literature on transition-metal carbonyls, and that interest, particularly along theoretical lines, continues to this day. , V(CO) 6 has been studied in a variety of experiments, − including ESR, − but the results are not consistent. Electronic spectra of V(N 2 ) 6 and V(CO) 6 have been compared and discussed via crystal-field and charge-transfer effects. , Our ESR studies here of the hexa-carbonyls of niobium and tantalum are also new; although Ta(CO) 6 has been observed earlier in the optical and infrared regions, and some dinitrogen complexes of Nb have been observed in the infrared …”

Section: Introductionmentioning

confidence: 99%

“…1,2 There is a large body of literature on transition-metal carbonyls, and that interest, particularly along theoretical lines, continues to this day. 3,4 V(CO) 6 has been studied in a variety of experiments, [5][6][7][8][9][10][11][12][13][14] including ESR, [11][12][13][14] but the results are not consistent. Electronic spectra of V(N 2 ) 6 and V(CO) 6 have been compared and discussed via crystal-field and charge-transfer effects.…”

Section: Introductionmentioning

confidence: 99%

Vanadium and Niobium Hexadinitrogen and Hexacarbonyl Complexes: Electron-Spin-Resonance Spectra at 4 K

1999

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Electron-spin-resonance (ESR) spectroscopy has been applied to vanadium, niobium (and tantalum) complexes with N2 and CO in the corresponding pure solid matrixes at 4 K. Except for V(CO)6, none has previously been studied by ESR. For these d, S = 1/2, radicals, g values and hyperfine parameters (51V, 93Nb nuclei) are obtained and interpreted in terms of axial molecules, distorted from octahedral symmetry by Jahn−Teller effects. There are significant differences with previous work, and the new metal hyperfine data in the two types of complexes are informative.

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“…Review of prior literature has shown that the V′ ) 0 f 1 transition for the V(CO) 6 radical occurs at 1973 cm -1 in dichloromethane. 17 An anharmonicity of 21 cm -1 between vibrational levels then places the V′ ) 1 f 2 and V′ ) 2 f 3 transitions at 1952 and 1931 cm -1 , respectively. Pump/probe measurements were performed at each of these frequencies using pump wavelengths of 800, 700, 620, and 555 nm.…”

Section: Methodsmentioning

confidence: 99%

Ultrafast Electron Transfer in the [Co(Cp)₂|V(CO)₆] Radical Pair

2002

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We have reexamined our earlier report of electron transfer in the [Co(Cp) 2 |V(CO) 6 ] radical pair using ultrafast infrared transient absorption spectroscopy. The radical pair is created from the [Co(Cp) 2 + |V(CO) 6 -] ion pair by ultrafast visible charge-transfer excitation. Transient absorption experiments with <75 fs resolution reveal two major direct electron-transfer (ET) components with ∼700 fs and ∼5 ps time constants. A small ET component with a ∼75 ps time constant is due to some separation and re-formation of the radical pairs. Transient absorption experiments monitoring the recovery of the ion-pair state show that both fast components are due to ET rather than some other vibrational relaxation (VR) process in the radical state. By modeling the visible charge-transfer band, the two fast ET decay times are assigned to two ion-pair contact geometries with absorption origins different by about 1250 ( 350 cm -1 . The ∼700 fs ET lifetime depends on the vibrational quantum state of the nontotally symmetric CO stretch in the V(CO) 6 radical, where the lifetime decreases by ∼10% for the first vibrational quantum and ∼45% for the second quantum. There is no quantum effect for the second ion-pair geometry with a 5 ps ET lifetime. Standard ET rate models cannot explain the rate dependence upon vibrational quantum state for a nontotally symmetric vibration, and it may arise from a breakdown of the Condon approximation. We also find that the intramolecular vibrational redistribution (IVR) time to transfer vibrational energy from the totally symmetric CO stretch to the nontotally symmetric stretch is less than 75 fs for a 1-quantum IVR process. This is unusually fast for metal carbonyls and may be assisted by the Jahn-Teller geometry change of the radical. The 2-quantum IVR time is ∼200 fs for 800 and 700 nm charge-transfer excitation wavelengths. At excitation wavelengths of 620 and 555 nm all quantum levels show a 200 fs rise time, which is unexpected for the zero quantum level. We assign this effect to the onset of sufficient internal vibrational energy in low-frequency vibrations to cause geometric interconversion between energetically similar Jahn-Teller geometries in the V(CO) 6 radical. The 200 fs rise time is the time for the V(CO) 6 radical species to assume a stable geometry, which requires VR of low-frequency vibrations to the solvent. These results demonstrate that earlier measurements from our group on the same molecule had insufficient time resolution to observe the ultrafast ET component and thereby inferred a vibrational quantum effect in a single ET rate of longer duration.

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Notizen:Spektroskopische Untersuchungen an Komplexverbindungen XIV

Cited by 27 publications

References 0 publications

D₃_d Ground-State Structure of V(CO)₆: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

D₃_d Ground-State Structure of V(CO)₆: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

Vanadium and Niobium Hexadinitrogen and Hexacarbonyl Complexes: Electron-Spin-Resonance Spectra at 4 K

Ultrafast Electron Transfer in the [Co(Cp)₂|V(CO)₆] Radical Pair

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Notizen:Spektroskopische Untersuchungen an Komplexverbindungen XIV

Cited by 27 publications

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D3d Ground-State Structure of V(CO)6: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

D3d Ground-State Structure of V(CO)6: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

Vanadium and Niobium Hexadinitrogen and Hexacarbonyl Complexes: Electron-Spin-Resonance Spectra at 4 K

Ultrafast Electron Transfer in the [Co(Cp)2|V(CO)6] Radical Pair

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D₃_d Ground-State Structure of V(CO)₆: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

D₃_d Ground-State Structure of V(CO)₆: A Combined Matrix Isolation and ab Initio Study of the Jahn−Teller Effect

Ultrafast Electron Transfer in the [Co(Cp)₂|V(CO)₆] Radical Pair