Standard molar enthalpies of formation of eight lanthanide(III) 2,2,6,6-tetramethyl-3, 5-heptanedione chelates in the crystalline and gaseous states: mean Ln–O bond dissociation enthalpies

Giera, Edward

doi:10.1006/jcht.2000.0660

Cited by 15 publications

(2 citation statements)

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“…The experimental observations described above for Eu(thd) 3 are similar to those reported for the nanosecond pulsed-laser photoionization of Co(acetylacetonate) 3 , where Co + was the only metal-containing fragment detected . Indeed, metal−ligand bonds are generally weak and a common gas-phase photoionization mechanism involves metal−ligand dissociation followed by ionization. − The metal ion is usually the largest peak in the mass spectrum, and observation of the parent ion is rare. , …”

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confidence: 71%

Wavelength Dependent Photofragmentation Patterns of Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)Ln (III) (Ln = Eu, Tb, Gd) in a Molecular Beam

Berry

May

et al. 2006

J. Phys. Chem. A

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Laser photoionization and ligand photodissociation in Ln(thd)(3) (Ln = Eu, Tb, Gd; thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) are studied in a molecular beam via time-of-flight mass spectrometry. The fragmentation patterns are strongly wavelength dependent. With 355 nm excitation, the mass spectrum is dominated by Ln(2+), Ln(+), and LnO(+) fragments. The bare Ln ions are believed to arise from photoionization of neutral Ln atoms. The Ln atoms, in turn, are produced from the Ln(thd)(3) complex in a sequence of Ln reductions (through ligand-to-metal charge-transfer transitions), with each reduction being accompanied by the dissociation of a neutral ligand radical. In contrast, under visible-light (410-450 nm) excitation, a significant Ln(thd)(n)(+) signal is observed (where n = 2,3 for Ln = Tb,Gd and n = 1-3 for Ln = Eu). Thus, with visible excitation, photoionization of Ln(thd)(n) competes effectively with the Ln-reduction/ligand-dissociation sequence that leads to the dominant bare Ln-ion signal seen with 355 nm excitation. The fact that monoligated Ln(thd)(+) is observed only for Ln = Eu is interpreted in terms of the relative accessibility of an excited ligand-to-metal charge-transfer state from the ground electronic state of neutral Ln(thd).

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confidence: 71%

Wavelength Dependent Photofragmentation Patterns of Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)Ln (III) (Ln = Eu, Tb, Gd) in a Molecular Beam

Berry

May

et al. 2006

J. Phys. Chem. A

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“…1), there are two peaks at 1.179 and 5.729 ppm, which can be assigned, respectively, to the tertiary butyl groups protons (R 1 : C(CH 3 ) 3 ), the proton bonded to the carbon between the two carbonyl groups (R 2 : CH) in DPM [17]. The most important feature of b-diketonate compounds is the tautomeric equilibrium of the keto and enol forms because of the presence of b-carbonyl groups with at least one proton on the intermediate carbon atom [18], and based on this, the peak at 16.153 ppm can be assigned to the hydroxyl group in the enol form (R 3 : HO-R 4 ¼CR 5 ). This phenomenon has not been observed in the similar characterization in previous papers [16,19], which may be the result from solvent effect or the definition of device instruments.…”

Section: Elemental Analyses and Nmr Spectroscopymentioning

confidence: 99%