Showing papers by "Thomas Bally published in 2009"
TL;DR: It is demonstrated, on a test set of 80 conformationally stable molecules of various kinds carrying different functional groups, that, in contrast to what is claimed in the literature, large basis sets are not needed to obtain rather accurate predictions of (1)H NMR chemical shifts by quantum chemical calculations.
Abstract: The purpose of this paper is to convince practitioners of 1H NMR spectroscopy to consider simple quantum chemical calculations as a viable option to aid them in the assignment of their spectra. To this end, it is demonstrated, on a test set of 80 conformationally stable molecules of various kinds carrying different functional groups, that, in contrast to what is claimed in the literature, large basis sets are not needed to obtain rather accurate predictions of 1H NMR chemical shifts by quantum chemical calculations. On the other hand, modeling the solvent by an SCRF-type calculation may improve certain predictions significantly. The best accuracy/cost ratio is provided by GIAO calculations in chloroform as a solvent with the specially parametrized WP04 functional of Cramer et al. using the cc-pVDZ or 6-31G** basis set, closely followed by similar calculations with the ubiquitious B3LYP functional (both predict 1H chemical shifts with an average deviation of ca. 0.12 ppm, if the results are scaled linearly...
251 citations
TL;DR: UV-visible/near-IR (NIR/mid-IR) solution, solid-state, and matrix-isolation electronic absorption spectra of the Fe(II)-Fe(III) mixed-valent homobimetallic compounds biferrocenyl triiodide and 1',1'''-diethylbiferrocenyltriiodide reveal the presence of a low-energy transition in the MIR region that has not been reported before.
Abstract: UV-visible/near-IR (NIR)/mid-IR (MIR) solution, solid-state, and matrix-isolation electronic absorption spectra of the Fe(II)-Fe(III) mixed-valent homobimetallic compounds biferrocenyl triiodide (1) and 1',1'''-diethylbiferrocenyltriiodide (2) reveal the presence of a low-energy transition in the MIR region that has not been reported before. The new absorption feature and the known NIR band are both assigned to intervalence charge-transfer (IVCT) transitions. To obtain insight into the electronic structures of 1 and 2, DFT calculations with the BP86 functionals and different basis sets have been performed. Based on the molecular orbital scheme of cation 1, one band corresponds to the transition between the highest occupied d(x(2)-y(2)) orbitals on the two iron centers, whereas the other one is assigned to a transition from a lower-lying d(z(2)) orbital to the d(x(2)-y(2)) orbital. For comparison, the doubly bridged bisfulvalenide diiron cation (3) has been investigated by optical absorption spectroscopy and DFT calculations. The experimental and theoretical results are discussed with respect to the degree of electron localization/delocalization in these systems.
27 citations
TL;DR: To elucidate the multifaceted but poorly understood chemistry of the pivotal polysulfur-nitrogen heterocycle, tetrasulfur tetranitride (S(4)N(4), 1), its photochemistry was studied in Ar matrices and three primary intermediates and a secondary one were detected.
Abstract: To elucidate the multifaceted but poorly understood chemistry of the pivotal polysulfur−nitrogen heterocycle, tetrasulfur tetranitride (S4N4, 1), its photochemistry was studied in Ar matrices. Thereby two primary intermediates and a secondary one (2−4) were detected, and their UV−vis and IR spectra were identified through specific interconversions of 1−4 that can be induced by selective irradiations. The structures associated with these spectra were assigned with the help of DFT calculations. From these assignments it follows that, under the conditions of the present experiments, the cage structure of 1 transforms into isomeric structures 2−4, one of which is a boat-shaped 8-membered cycle (2), and the two other are novel 6-membered S3N3 cycles carrying exocyclic (N)—S≡N (3) or (S)—N═S (4) groups, respectively, which have not been previously described. These three intermediates probably play a pivotal role in the formation of the diverse products that are observed in the reactions of S4N4 even under mild ...
21 citations
TL;DR: In this article, photoelectron (PE) spectra of dienes and polyenes were used to detect polyene radical cations by other methods, including the standard Huckel treatment.
Abstract: 1
Introduction
2
Photoelectron (PE) Spectroscopy
3
Excited States of Polyene Radical Cations by Other Methods
4
Acknowledgements
Keywords:
diene and polyene radical cation electronic structure;
photoelectron (PE) spectroscopy;
PE spectra of dienes and polyenes;
standard Huckel treatment;
deviations from planarity;
excited states of polyene radical cations by other methods;
Koopmans and non-Koopmans states;
linear conjugated polyenes
2 citations