102 research outputs found
Crystallography for university research: some basic case studies
An overview of commonly available, state-of-the-art diffraction techniques for university research is presented based on some chemical case studies. Examples from the Fribourg crystallography service are presented, aimed at scientists who would like to learn about the principal possibilities that X-ray powder and single-crystal diffraction can offer, how these methods can serve to determine the structure of a given material, and how they can help to identify polymorphs, surface coatings and enantiomers
The first phosphoÂramide-mercury(II) complex with a ClâHg-OP[N(C)(C)]â segment
Mercury(II) exhibits a strong preference for linear coordination which has been attributed to relativistic effects splitting the 6p orbitals and promoting sp hybridization. If the two ligands attached to the mercury(II) ion are weak donors, the metal ion can act as a good Lewis acid and expand its coordination number. Moreover, mercury has a special affinity for softer bases, such as S and N atoms, and has much less affinity for hard bases, such as those including an O atom. The asymmetric unit of diÂchloridoÂ[trisÂ(piperidin-1-yl)phosÂphane oxide- ÎO]mercury(II)-diÂchlorido mercury(II) (2/1), [HgClâ{(Câ
HââN)âPO}]â·[HgClâ], is composed of one HgClâ{(Câ
HââN)âPO} complex and one half of a discrete HgClâ entity located on an inversion centre. The coordination environment around the HgII centre in the complex component is a distorted T-shape. Bond- valence-sum calculations confirm the three-coordination mode of the HgII atom of the complex mol ecule. The noncovalent nature of the Hg...Cl and Hg...O interÂactions in the structure are discussed
Threading salen-type Cu- and Ni-complexes into one-dimensional coordination polymers: solution versus solid state and the size effect of the alkali metal ion
Compartmentalization of metal ions is crucial in biology as well as in materials science. For the synthesis of single source precursors, the preorganization of different metal ions is of particular interest for the low-temperature generation of mixed metal oxides. On the basis of a potentially Ω-shaped salen-type ligand providing an N2O2 as well as an O2O2 coordination site, mixed metal coordination compounds with Cu(II) or Ni(II) and alkali metal ions have been studied for their structural and optical properties. UVâvis and 1H NMR titrations show that the obtained compounds adopt partially different structures in solution compared to the solid state. In the latter case, the coordination geometry is mainly governed by the size of the alkali metal ion as well as the transition metal ion used
Model peptide studies of Ag+ binding sites from the silver resistance protein SilE
Using model peptides, each of the nine MX2H or HXnM (n = 1, 2) motifs of the silver resistance protein SilE has been shown to coordinate to one Ag+ ion by its histidine and methionine residues with Kd in the ÎŒM range. This suggests an Ag+ buffering role for SilE in the case of high Ag+ overload
Nanomaterials Meet Li-ion Batteries
Li-ion batteries are used in many applications in everyday life: cell phones, laser pointers, laptops, cordless drillers or saws, bikes and even cars. Yet, there is room for improvement in order to make the batteries smaller and last longer. The Fromm group contributes to this research
focusing mainly on nanoscale lithium ion cathode materials. This contribution gives an overview over our current activities in the field of batteries. After an introduction on the nano-materials of LiCoO2 and LiMnPO4, the studies of our cathode composition and preparation will be presented
A Thermoâ and mechanoresponsive cyanoâsubstituted oligo(pâphenylene vinylene) derivative with five emissive states
Multiresponsive materials that display predefined photoluminescence color changes upon exposure to different stimuli are attractive candidates for advanced sensing schemes. Herein, we report a cyano-substituted oligo(p-phenylene vinylene) (cyano-OPV) derivative that forms five different solvent-free solid-state molecular assemblies, luminescence properties of which change upon thermal and mechanical stimulation. Single-crystal X-ray structural analysis suggested that tolyl groups introduced at the termini of solubilizing side-chains of the cyano-OPV play a pivotal role in its solid-state arrangement. Viewed more broadly, this report shows that the introduction of competing intermolecular interactions into excimer-forming chromophores is a promising design strategy for multicolored thermo- and mechanoresponsive luminescent materials
Cis-Dioxido-molybdenum(VI) complexes of tridentate ONO hydrazone Schiff base: Synthesis, characterization, X-ray crystal structure, DFT calculation and catalytic activity
Two new cis-MoOâ [MoOâ(L)(EtOH)] (1), [MoOâ(L) (Py)] (2) [L: (3-methoxy-2oxidobenzylidene)benzohydrazidato], complexes have been synthesized and fully characterized on the basis of elemental analysis, FT-IR, molar conductivity, ÂčH NMR, ÂčÂłC NMR and electronic spectra. The structure of complexes has been accomplished by single crystal X-ray diffraction. All experimental results confirmed that both complexes have an octahedral geometry around the Mo(VI) central atom, which is coordinated by the donor atoms of the dianionic hydrazone ligand, two oxido groups and oxygen/nitrogen atoms of solvent molecules. Computational studies were also performed using DFT calculations at B3LYP/DGDZVP level of theory. Furthermore, their catalytic activities were investigated on the electrophilic reaction of indole with aldehydes in molten tetrabutyl ammonium bromide (TBAB) to obtain bis(indolyl)methane derivatives
Correlation of MLCTs of Group 7 fac-[M(CO)3]+ complexes (M = Mn, Re) with bipyridine, pyridinylpyrazine, azopyridine, and pyridin-2-ylmethanimine type ligands for rational photoCORM design
A mathematical correlation of the MLCT absorption maxima of structurally related facâ [M(CO)3L2Br] complexes (M = Mn, Re; L2 = bidentate ligand) is obtained by the comparison of a total of 50 species bearing bipyridine, pyridinylpyrazine, azopyridine and pyridinâ2âylmethanimine L2 type ligands. The empirical relationship is first derived by the initial comparison of the MLCT absorption maxima of 26 previously published complexes and subsequently used to predict the same absorption value of 24 other species. In order to check the validity of the prediction, several new complexes were prepared. These were spectroscopically characterized and, where possible, their Xâ ray solidâstate structure elucidated. The initial mathematical correlation allowed to predict MLCT absorption maxima of the unknown species with an average discrepancy of 12 nm. The relationship was subsequently refined to an average error of 6 nm with following derived formula CalcMnmLCT = (ObsReMLCT/0.88) â 15.1 (where CalcMnmLCT = predicted values of Mn complexes MLCT and ObsReMLCT = experimentally observed MLCT transitions of Re complexes). The correlation and the formula, the significance of which are discussed, may prove useful in the long run for the rational design of Mnâbased photoCORMs starting from known data of widely investigated facâ[Re(CO)3L2Br] complexes
Synthesis, X-ray structure and DFT calculation of oxido-vanadium(V) complex with a tridentate Schiff base ligand
Reaction of 4-bromo-2-(((5-chloro-2-hydroxyphenyl) imino)methyl)phenol (HâL) with VOSOâ·XHâO generates the oxido-vanadium(V) complex [VOL(OCHâ)(OHCHâ)], that characterized by FT-IR, UVâVis, and elemental analysis. The complex was also characterized by single crystal X-ray diffraction crystallography. A DFT calculation was carried out on the complex using the B3LYP/6-31+G(d,p) method. The agreement between the theoretical and experimental data is good. NBO data shows that the donation from donor atoms to the metal center is greater than back bonding
Heptacoordinate Coii complex: a new architecture for photochemical hydrogen production
The first heptacoordinate cobalt catalyst for light-driven hydrogen production in water has been synthesized and characterized. Photochemical experiments using [Ru(bpy)â]ÂČâș as photosensitizer gave a turnover number (TON) of 16300â
molâHââ(molâ cat.)â»Âč achieved in 2â
hours of irradiation with visible (475â
nm) light. This promising result provides a path forward in the development of new structures to improve the efficiency of the catalysis
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