Juergen Senker

A new Al-MOF based on a unique column-shaped inorganic building unit exhibiting strongly hydrophilic sorption behaviour

The new Al-based metal-organic framework [Al(13)(OH)(27)(H(2)O)(6)(BDC-NH(2))(3)Cl(6)(C(3)H(7)OH)(6)] denoted CAU-6 (CAU = Christian-Albrechts-Universität) was solvothermally synthesized in 2-propanol and was thoroughly characterized. The framework structure exhibits a unique column-shaped inorganic building unit, which is based on stacked, corner-sharing Al(13)-clusters. The compound exhibits unprecedented hydrophilicity for metal-organic frameworks.

Probing Interactions of N-Donor Molecules with Open Metal Sites within Paramagnetic Cr-MIL-101 – A Solid-State NMR Spectroscopic and DFT Study

Understanding host-guest interactions is one of the key requirements for adjusting properties in metal-organic frameworks (MOFs). In particular, systems with coordinatively unsaturated Lewis acidic metal sites feature highly selective adsorption processes. This is attributed to strong interactions with Lewis basic guest molecules. Here we show that a combination of 13C MAS NMR spectroscopy with state-of-the-art density functional theory (DFT) calculations allows one to unravel the interactions of water, 2-aminopyridine, 3-aminopyridine, and diethylamine with the open metal sites in Cr-MIL-101. The 13C MAS NMR spectra, obtained with ultrafast magic-angle spinning, are well resolved, with resonances distributed over 1000 ppm. They present a clear signature for each guest at the open metal sites. Based on competition experiments this leads to the following binding preference: water < diethylamine ≈ 2-aminopyridine < 3-aminopyridine. Assignments were done by exploiting distance sum relations derived from spin-lattice relaxation data and 13C{1H} REDOR spectral editing. The experimental data were used to validate NMR shifts computed for the Cr-MIL-101 derivatives, which contain Cr3O clusters with magnetically coupled metal centers. While both approaches provide an unequivocal assignment and the arrangement of the guests at the open metal sites, the NMR data offer additional information about the guest and framework dynamics. We expect that our strategy has the potential for probing the binding situation of adsorbate mixtures at the open metal sites of MOFs in general and thus accesses the microscopic interaction mechanisms for this important material class, which is essential for deriving structure-property relationships.

Anhydrous proton conduction in porous organic networks

Solid electrolyte separators within fuel cells enable efficient charge transport and prevent a mass bypass between the two half cells. Hydrated systems, like Nafion, reach unprecedented proton conductivities at ambient temperatures, but the demanding humidity management prevents their use beyond 80 °C, hence limiting the efficiency of current polymer-based systems. As such, water free and chemically inert, solid materials with excellent conductivities between 100 °C and 200 °C, are of high interest. A promising approach is the incorporation of heavier amphoteric molecules into micro- and mesoporous frameworks. Stronger host–guest interactions allow for higher temperatures, while still maintaining sufficient mobility and efficient transport pathways. Here, we present a systematic study investigating the influence of porosity, framework topology and dimensionality as well as framework functionality and charge carrier uptake on the proton conductivity for six porous organic networks (PONs) loaded with imidazole via gas phase adsorption. The resulting materials were thoroughly characterized by multinuclear NMR and IR spectroscopy and physisorption as well as powder X-ray diffraction and DSC experiments, revealing homogeneous distribution of the amphoteric guests within the pore structure. Electrochemical impedance spectroscopy up to 130 °C revealed remarkable conductivities of up to 10−3 S cm−1 under anhydrous conditions. We found 3D networks to favour high imidazole loading leading to high proton conductivities based on the Grotthuss mechanism. In contrast, 2D networks showed a lower guest molecule uptake and thus lower proton conductivities, which were governed by vehicle transport. Additional acid/base functionalities within the frameworks seem to have a negative effect on the proton conduction.

Structure, disorder and function of supramolecular polymer additives

Juergen Senker1, Christoph Zehe1, Marko Schmidt1, Joshua Hill1, Renée Siegel1, Venita Daebel2, Klaus Kreger3, Andrew Goodwin4, Hans-Werner Schmidt3 1Inorganic Chemistry III, Bayreuth, Germany, 2Bruker Biospin, Karlsruhe, Germany, 3Macromolecular Chemistry I, University of Bayreuth, Bayreuth, Germany, 4Inorganic Chemistry, University of Oxford, Oxford, United Kingdom E-mail: juergen.senker@uni-bayreuth.de

Structural Investigation of a Layered Carbon Nitride Polymer by Electron Diffraction

Graphitic carbon nitride has attracted continuous interest because of its potential use as a precursor for ultrahard materials [1]. Down to present days, the synthesis of truly binary carbon nitride C3N4 has always been spoiled by the presence of additional salts or hydrogen. Inclusion of the latter ‘defects’ likely results in incomplete condensation of the network forming molecules triazine (C3N3) and heptazine (C6N7), which is typically accompanied by amorphisation and denitrification. For the characterisation of the nanocrystalline and disordered character of the resulting light-element materials, electron microscopy is particularly well suited, be it with respect to synthesis optimisation or structure analysis.