Comparing charge transfer tuning effects by chemical substitution and uniaxial pressure in the organic charge transfer complex tetramethoxypyrene-tetracyanoquinodimethane

In the search for novel organic charge transfer salts with variable charge transfer degree we study the effects of two modifications to the recently synthesized donor-acceptor Tetramethoxypyrene (TMP)-Tetracyanoquinodimethane (TCNQ). One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of TMP-F4TCNQ and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules alternately stacked (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP-TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our bandstructure calculations confirm the one-dimensional behavior of TMP-F4TCNQ with pro- nounced dispersion only along the stacking axis. Infrared measurements illustrating the CN vibration frequency shift in F4TCNQ suggest however no improvement on the degree of charge transfer in TMP-F4TCNQ with respect to TMP-TCNQ. In both complexes about 0.1 is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on designed TMP-TCNQ and TMP-F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP-TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer

Adsorption Behavior of Asymmetric Pd Pincer Complexes on a Cu(111) Surface

We address the adsorption of asymmetric Pd pincer complexes on a Cu(111) surface by scanning tunneling microscopy. The structural asymmetry is manifested in the observation of two chiral enantiomers. To enable an unambiguous identification of individual constituents, three closely related complexes with small modifications are investigated in parallel. Thereby, methyl substituents determine attractive molecule-molecule interaction. Depending on their distribution, dimerization and tetramerization can be observed

Influence of Ring Contraction on the Electronic Structure of Nickel Tetrapyrrole Complexes: Corrole vs Porphyrin

The influence of the contracted corrole macrocycle, in comparison to the larger porphyrin macrocycle, on the electronic structure of nickel was studied with X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Synthesis and in situ characterization of the Ni complexes of octaethylporphyrin (NiOEP) and hexaethyldimethylcorrole (NiHEDMC) were performed in ultra-high vacuum. XPS and NEXAFS spectra reveal a +2 oxidation state and a low-spin d8 electron configuration of Ni in both complexes, despite the formal trianionic nature of the corrole ligand. UPS, in combination with density functional theory (DFT) calculations, support the electronic structure of a Ni(II) corrole with a π-radical character of the ligand. The NEXAFS spectra also reveal differences in the valence electronic structure, which are attributed to the size mismatch between the small Ni(II) center and the larger central cavity of NiOEP. Analysis of the gas-phase structures shows that the Ni−N bonds in NiOEP are 4%–6% longer than those in NiHEDMC, even when NiOEP adopts a ruffled conformation. The individual interactions that constitute the Ni−ligand bond are altogether stronger in the corrole complex, according to bonding analysis within the energy decomposition analysis and the natural orbitals for chemical valence theory (EDA-NOCV)

An ontology-based framework for describing discoverable data services

Data-services are applications in charge of retrieving certain data when they are called. They are found in different communities such as the Internet Of Things, Cloud Computing, Big Data, etc. So, there is a real need to discover how can an application that requires some data automatically find a data-service which is providing it. To our knowledge, the problem of automatically discovering these data-services is still open. To make a step forward in this direction, we propose an ontology-based framework to address this problem. In our framework, input and output values of the request are mapped into concepts of the domain ontology. Then, data-services specify how to obtain the output from the input by stating the relationship between the mapped concepts of the ontology.Peer ReviewedPostprint (author's final draft

PorphyStruct – A Digital Tool for the Quantitative Assignment of Non‐Planar Distortion Modes in Four‐Membered Porphyrinoids

PorphyStruct, a new digital tool for the analysis of non‐planar distortion modes of different porphyrinoids, and its application to corrole structures is reported. The program makes use of the normal‐coordinate structure decomposition technique (NSD) and employs sets of normal modes equivalent to those established for porphyrins in order to describe the out‐of‐plane dislocation pattern of perimeter atoms from corroles, norcorroles, porphycenes and other porphyrinoids quantitatively and in analogy to the established terminology. A comparative study of 17 porphyrin structures shows very similar results to the original NSD analysis and no systematic error. Application to corroles is successful and reveals the necessity to implement an extended basis of normal modes for a large share of experimental structures. The results frequently show the concomitant occurence of several modes but remain interpretable. For group XI metal corroles the phenomenon of supersaddling was unravelled, allowing for more in‐depths discussions of structure‐function correlations

PorphyStruct: A Digital Tool for the Quantitative Assignment of Non-Planar Distortion Modes in Four-Membered Porphyrinoids

PorphyStruct, a new digital tool for the analysis of non-planar distortion modes of different porphyrinoids, and its application to corrole structures is reported. The program makes use of the normal-coordinate structure decomposition technique (NSD) and employs sets of normal modes equivalent to those established for porphyrins in order to describe the out-of-plane dislocation pattern of perimeter atoms from corroles, norcorroles, porphycenes and other porphyrinoids quantitatively and in analogy to the established terminology. A comparative study of 17 porphyrin structures shows very similar results to the original NSD analysis and no systematic error. Application to corroles is successful and reveals the necessity to implement an extended basis of normal modes for a large share of experimental structures. The results frequently show the concomitant occurence of several modes but remain interpretable. For group XI metal corroles the phenomenon of supersaddling was unravelled, allowing for more in-depths discussions of structure-function correlations

Palladiumkomplexe sterisch gehinderter 1,3-Bis(arylimino)isoindoline - Synthese, Struktur und Reaktivität

Es wurde eine Reihe neuer Liganden des BAI-Typs dargestellt, darunter unsymmetrische, sterisch stark belastete sowie erstmals chirale. Die eingehend untersuchte Komplexierung der Liganden durch Palladium(II)-Ionen (insbesondere Palladiumacetat) führt zur Ausbildung von Komplexen in verschiedenen zum Teil neuen Koordinationsmodi. Die erhaltenen Komplexe wurden eingehend sowohl strukturell und spektroskopisch als auch hinsichtlich ihrer Reaktivität untersucht. Insbesondere werden dabei intramolekulare CH-Aktivierungen beobachtet. Die daraus resultierenden Komplexe wurden ebenfalls strukturell und spektroskopisch charakterisiert. An einem Komplex wurden kinetische Messungen zur CH-Aktivierung durchgeführt und die Aktivierungsparameter der Reaktion bestimmt. Ausgehend von einem der dargestellten Komplexe (4-MeBTI)PdCl wurde eine Vielzahl von kationischen Komplexen der Art [(4-MeBTI)PdL]+ dargestellt. In einem strukturellen Vergleich dieser Komplexe mit den analogen Komplexen des Tripyrrinliganden [(TrPy)PdL]+ werden koordinationschemische Unterschiede und Gemeinsamkeiten beider Ligandentypen diskutiert. Einige der erhaltenen Palladiumkomplexe wurden als (Prä-)Katalysatoren in C=C-Hydrierungsreaktionen bzw. C–C-Kupplungsreaktionen eingesetzt. Dabei zeigt sich die prinzipielle Eignung dieser Komplexe als (Prä-)Katalysatoren, wenngleich deutliche Hinweise für nicht molekulare Katalysemechanismen erhalten wurden

Functional Dyes-Studien zu hybridisierbaren Tetrapyrrol-Farbstoffen

In der vorliegenden Arbeit wird die Synthese und Charakterisierung von unterschiedlichen tetrapyrrolischen Fluoreszenzfarbstoffen beschrieben. Diese Farbstoffe zeigen aufgrund ihrer molekularen Struktur Eigenschaften, die ursprünglich nur bei Farbstoffen in hohen Konzentrationen beobachtet werden konnten

Unexpected formation and structural characterisation of a novel rhodium B12 analogue

Dedicated to Prof. Dr. Dr. h.c. Helmut Werner for his contributions to inorganic chemistry.The metalation reactions of the 2,2′-bidipyrrin 4 with different rhodium(I) precursors yield the complexes 5 and 6 and the unusual corrinoid 7, depending only on the type of the ancillary ligand employed.This work was funded by the Deutsche Forschungsgemeinschaft (Emmy-Noether-Programm) and the Fonds der Chemischen Industrie.Peer reviewe