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Muller C.,Institute For Chemie Und Biochemie
Journal of Computational Chemistry | Year: 2015

Combining classical force fields for the Hartree-Fock (HF) part and the method of increments for post-HF contributions, we calculate the cohesive energy of the ordered and randomly disordered nitrous oxide (N2O) solid. At 0 K, ordered N2O is most favorable with a cohesive energy of -27.7 kJ/mol. At temperatures above 60 K, more disordered structures become compatible and a phase transition to completely disordered N2O is predicted. Comparison with experiment in literature suggests that experimentally prepared N2O crystals are mainly disordered due to a prohibitively high activation energy of ordering processes. © 2015 Wiley Periodicals, Inc. This study demonstrates a statistical approach to the calculation of temperature-dependent cohesive energies of randomly disordered molecular crystals such as nitrous oxide (N2O) at sophisticated levels of post-Hartree-Fock theory. © 2015 Wiley Periodicals, Inc.

Sommer M.G.,University of Stuttgart | Schweinfurth D.,Institute For Chemie Und Biochemie | Weisser F.,Institute For Chemie Und Biochemie | Hohloch S.,Institute For Chemie Und Biochemie | Sarkar B.,Institute For Chemie Und Biochemie
Organometallics | Year: 2013

The ligand 2,5-bis[2-(methylthio)anilino]-1,4-benzoquinone (L) was used in its doubly deprotonated form to synthesize the complex [{Cl(η6- Cym)Os}2(μ-η2:η2-L-2H)] (1; Cym = p-cymene = 1-isopropyl-4-methylbenzene). Spectroscopic characterization and elemental analysis confirms the presence of the chloride ligands in 1, which indirectly shows that the bridging ligand L-2H acts in a bis-bidentate fashion in 1, with the thioether substituents on the bridge remaining uncoordinated. Abstraction of the chloride ligands in 1 by AgBF4 in CH3CN leads not only to the release of those chloride ligands but also to a simultaneous substituent-induced release of Cym with the bridging ligand changing its coordination mode to bis-tridentate. In the resulting complex [{(CH3CN)3Os}2(μ- η3:η3-L-2H)]2+ (2 2+), the thioether groups of L-2H are now coordinated to the osmium centers with the bridging ligand coordinating to the metal center in a bis-meridional form. The coordination mode of L-2H in 2 2+ was confirmed by single-crystal X-ray diffraction data. A structural analysis of 22+ reveals localization of double bonds within the "upper" and "lower" parts of the bridging ligand in comparison to bond distances in the free ligand. Additionally, the binding of the bridge to the osmium centers is seen to occur through O- and neutral imine-type N donors. The complexes 1 and 22+ were investigated by cyclic voltammetry and UV-vis-near-IR and EPR spectroelectrochemistry. This combined approach was used to unravel the redox-active nature of the ligand L-2H, to determine the sites of electron transfer (ligand radical versus mixed valency), and to compare the present systems with their ruthenium analogues 3 and 42+ (Schweinfurth, D.Inorg. Chem. 2011, 50, 1150). The effect of replacing ruthenium by its higher homologue osmium on the reactivity and the electrochemical and spectroscopic properties were explored, and the differences were deciphered by taking into account the intrinsic dissimilarities between the two homologues. The usefulness of incorporating additional donor substituents on potentially bridging quinonoid ligands was probed in this work. © 2013 American Chemical Society.

Sinha W.,National Institute of Science Education and Research NISER | Sommer M.G.,Institute For Chemie Und Biochemie | Van Der Meer M.,Institute For Chemie Und Biochemie | Plebst S.,University of Stuttgart | And 2 more authors.
Dalton Transactions | Year: 2016

Synthesis of two new AuIII corrole complexes with unsymmetrically substituted corrole ligands is presented here. The newly synthesized Au-compounds have been characterized by various spectroscopic techniques. The structural characterization of a representative AuIII corrole has also been possible. Electrochemical, UV-vis-NIR/EPR spectroelectrochemical and DFT studies have been used to decipher the electronic structures of various electro-generated species. These are the first UV-vis-NIR/EPR spectroelectrochemical investigations on AuIII corroles. Assignment of redox states of electro-generated AuIII corroles is supported by DFT analysis. In contrast to the metal centered reduction reported in AuIII porphyrins, one electron reduction in AuIII corroles has been assigned to corrole centered on the basis of experimental and theoretical studies. Thus, the AuIII corroles (not the analogous AuIII porphyrin derivatives!) bear a truly redox inactive AuIII center. Additionally, these Au-corrole complexes display NIR electrochromism, the origin of which is all on corrole-centered processes. © The Royal Society of Chemistry 2016.

Sinha W.,National Institute of Science Education and Research NISER | Deibel N.,University of Stuttgart | Garai A.,National Institute of Science Education and Research NISER | Schweinfurth D.,Institute For Chemie Und Biochemie | And 4 more authors.
Dyes and Pigments | Year: 2014

In-situ UV-visible and EPR Spectroelectrochemistry of a free base porphyrin, 5,10,15,20-tetrakis[3,4-(1,4-dioxan)phenyl]porphyrin, and its zinc derivative, 5,10,15,20-tetrakis[3,4-(1,4-dioxan)phenyl]porphyrinatozinc(II) were performed. On one-electron oxidation of the free base porphyrin in dichloromethane/0.1 M BuN4PF6 using an optically transparent thin layer cell, the initial Soret band retains its intensity and an equally intense new band appears at 453 nm. The initial Q bands disappear, and new bands appear at 516, 555 and 694 nm. At 295 K, it exhibits an isotropic EPR signal with a peak to peak separation of about 6 G and centered at g = 2.004. On one-electron oxidation of the zinc-porphyrin in similar conditions, the Soret band loses its intensity, and a new band appears at 466 nm. The in-situ generated one-electron oxidized species exhibits an isotropic EPR signal at 295 K which is centered at g = 2.0035. The formations of aggregates/self-assemblies of zinc-porphyrin were monitored by UV-vis spectroscopy, fluorescence imaging by confocal microscope, TEM, SEM and DLS measurements. A tentative mechanism has been also proposed for the generation of different aggregates, with varying size and shape, in water-DMF binary mixtures. © 2014 Elsevier Ltd. All rights reserved.

Lei S.,Institute For Chemie Und Biochemie | Paulus B.,Institute For Chemie Und Biochemie | Li S.,Institute For Mathematik | Schmidt B.,Institute For Mathematik
Journal of Computational Chemistry | Year: 2016

The curvature dependence of the physisorption properties of a water molecule inside and outside an armchair carbon nanotube (CNT) is investigated by an incremental density-fitting local coupled cluster treatment with single and double excitations and perturbative triples (DF-LCCSD(T)) study. Our results show that a water molecule outside and inside (n, n) CNTs (n=4, 5, 6, 7, 8, 10) is stabilized by electron correlation. The adsorption energy of water inside CNTs decreases quickly with the decrease of curvature (increase of radius) and the configuration with the oxygen pointing toward the CNT wall is the most stable one. However, when the water molecule is adsorbed outside the CNT, the adsorption energy varies only slightly with the curvature and the configuration with hydrogens pointing toward the CNT wall is the most stable one. We also use the DF-LCCSD(T) results to parameterize Lennard-Jones (LJ) force fields for the interaction of water both with the inner and outer sides of CNTs and with graphene representing the zero curvature limit. It is not possible to reproduce all DF-LCCSD(T) results for water inside and outside CNTs of different curvature by a single set of LJ parameters, but two sets have to be used instead. Each of the two resulting sets can reproduce three out of four minima of the effective potential curves reasonably well. These LJ models are then used to calculate the water adsorption energies of larger CNTs, approaching the graphene limit, thus bridging the gap between CNTs of increasing radius and flat graphene sheets. © 2016 Wiley Periodicals, Inc.

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