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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.

Hermann G.,Institute For Chemie Und Biochemie | Pohl V.,Institute For Chemie Und Biochemie | Tremblay J.C.,Institute For Chemie Und Biochemie | Paulus B.,Institute For Chemie Und Biochemie | Schild A.,Max Planck Institute For Mikrostrukturphysikweinberg 2Halle06120 Germany
Journal of Computational Chemistry | Year: 2016

ORBKIT is a toolbox for postprocessing electronic structure calculations based on a highly modular and portable Python architecture. The program allows computing a multitude of electronic properties of molecular systems on arbitrary spatial grids from the basis set representation of its electronic wavefunction, as well as several grid-independent properties. The required data can be extracted directly from the standard output of a large number of quantum chemistry programs. ORBKIT can be used as a standalone program to determine standard quantities, for example, the electron density, molecular orbitals, and derivatives thereof. The cornerstone of ORBKIT is its modular structure. The existing basic functions can be arranged in an individual way and can be easily extended by user-written modules to determine any other derived quantity. ORBKIT offers multiple output formats that can be processed by common visualization tools (VMD, Molden, etc.). Additionally, ORBKIT possesses routines to order molecular orbitals computed at different nuclear configurations according to their electronic character and to interpolate the wavefunction between these configurations. The program is open-source under GNU-LGPLv3 license and freely available at https://github.com/orbkit/orbkit/. This article provides an overview of ORBKIT with particular focus on its capabilities and applicability, and includes several example calculations. © 2016 Wiley Periodicals, Inc.

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.

Schweinfurth D.,Institute For Chemie Und Biochemie | Rechkemmer Y.,University of Stuttgart | Hohloch S.,Institute For Chemie Und Biochemie | Deibel N.,University of Stuttgart | And 6 more authors.
Chemistry - A European Journal | Year: 2014

The complexes [{(tmpa)CoII}2(μ-L1) 2-]2+ (12+) and [{(tmpa)CoII} 2(μ-L2)2-]2+ (22+), with tmpa=tris(2-pyridylmethyl)amine, H2L1=2,5-di-[2- (methoxy)-anilino]-1,4-benzoquinone, and H2L2=2,5-di-[2- (trifluoromethyl)-anilino]-1,4-benzoquinone, were synthesized and characterized. Structural analysis of 22+ revealed a distorted octahedral coordination around the cobalt centers, and cobalt-ligand bond lengths that match with high-spin CoII centers. Superconducting quantum interference device (SQUID) magnetometric studies on 12+ and 2 2+ are consistent with the presence of two weakly exchange-coupled high-spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 12+ and ferromagnetic for 22+. Both complexes exhibit several one-electron redox steps, and these were investigated with cyclic voltammetry and UV/Vis/near-IR spectroelectrochemistry. For 12+, it was possible to chemically isolate the pure forms of both the one-electron oxidized mixed-valent 13+ and the two-electron oxidized isovalent 14+ forms, and characterize them structurally as well as magnetically. This series thus provided an opportunity to investigate the effect of reversible electron transfers on the total spin-state of the molecule. In contrast to 22+, for 14+ the metal-ligand distances and the distances within the quinonoid ligand point to the existence of two low-spin CoIII centers, thus showing the innocence of the quintessential non-innocent ligands L. Magnetic data corroborate these observations by showing the decrease of the magnetic moment by roughly half (neglecting spin exchange effects) on oxidizing the molecules with one electron, and the disappearance of a paramagnetic response upon two-electron oxidation, which confirms the change in spin state associated with the electron-transfer steps. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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 | Deibel N.,Institute For Chemie Und Biochemie | Deibel N.,University of Stuttgart | And 3 more authors.
Chemistry - A European Journal | Year: 2014

Macrocycles such as porphyrins and corroles have important functions in chemistry and biology, including light absorption for photosynthesis. Generation of near-IR (NIR)- absorbing dyes based on metal complexes of these macrocycles for mimicking natural photosynthesis still remains a challenging task. Herein, the syntheses of four new AgIII corrolato complexes with differently substituted corrolato ligands are presented. A combination of structural, electrochemical, UV/Vis/NIR-EPR spectroelectrochemical, and DFT studies was used to decipher the geometric and electronic properties of these complexes in their various redox states. This combined approach established the neutral compounds as stable AgIII complexes, and the one-electron reduced species of all the compounds as unusual, stable AgII complexes. The one-electron oxidized forms of two of the complexes display absorptions in the NIR region, and thus they are rare examples of mononuclear complexes of corroles that absorb in the NIR region. The appearance of this NIR band, which has mixed intraligand charge transfer/intraligand character, is strongly dependent on the substituents of the corrole rings. Hence, the present work revolves round the design principles for the generation of corrole-based NIR-absorbing dyes and shows the potential of corroles for stabilizing unusual metal oxidation states. These findings thus further contribute to the generation of functional metal complexes based on such macrocyclic ligands. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Schweinfurth D.,Institute For Chemie Und Biochemie | Demeshko S.,University of Gottingen | Hohloch S.,Institute For Chemie Und Biochemie | Steinmetz M.,University of Bonn | And 5 more authors.
Inorganic Chemistry | Year: 2014

The complexes [Fe(tbta)2](BF4)2· 2EtOH (1), [Fe(tbta)2](BF4)2·2CH 3CN (2), [Fe(tbta)2](BF4)2· 2CHCl3 (3), and [Fe(tbta)2](BF4)2 (4) were synthesized from the respective metal salts and the click-derived tripodal ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (tbta). Structural characterization of these complexes (at 100 or 133 K) revealed Fe-N bond lengths for the solvent containing compounds 1-3 that are typical of a high spin (HS) Fe(II) complex. In contrast, the solvent-free compound 4 show Fe-N bond lengths that are characteristic of a low spin (LS) Fe(II) state. The Fe center in all complexes is bound to two triazole and one amine N atom from each tbta ligand, with the third triazole arm remaining uncoordinated. The benzyl substituents of the uncoordinated triazole arms and the triazole rings engage in strong intermolecular and intramolecular noncovalent interactions. These interactions are missing in the solvent containing molecules 1, 2, and 3, where the solvent molecules occupy positions that hinder these noncovalent interactions. The solvent-free complex (4) displays spin crossover (SCO) with a spin transition temperature T1/2 near room temperature, as revealed by superconducting quantum interference device (SQUID) magnetometric and Mössbauer spectroscopic measurements. The complexes 1, 2, and 3 remain HS throughout the investigated temperature range. Different torsion angles at the metal centers, which are influenced by the noncovalent interactions, are likely responsible for the differences in the magnetic behavior of these complexes. The corresponding solvent-free Co(II) complex (6) is also LS at lower temperatures and displays SCO with a temperature T1/2 near room temperature. Theoretical calculations at molecular and periodic DFT-D3 levels for 1-4 qualitatively reproduce the experimental findings, and corroborate the importance of intermolecular and intramolecular noncovalent interactions for the magnetic properties of these complexes. The present work thus represents rare examples of SCO complexes where the use of identical ligand sets produces SCO in Fe(II) as well as Co(II) complexes. © 2014 American Chemical Society.

PubMed | Institute For Chemie Und Biochemie, University of Stuttgart and University of Gottingen
Type: Journal Article | Journal: Inorganic chemistry | Year: 2016

The azide anion is widely used as a ligand in coordination chemistry. Despite its ubiquitous presence, controlled synthesis of azido complexes remains a challenging task. Making use of click-derived tripodal ligands, we present here various coordination motifs of the azido ligands, the formation of which appears to be controlled by the peripheral substituents on the tripodal ligands with otherwise identical structure of the coordination moieties. Thus, the flexible benzyl substituents on the tripodal ligand TBTA led to the formation of the first example of an unsupported and solely

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