Identifying Selective Host–Guest Interactions Based on Hydrogen Bond Donor–Acceptor Pattern in Functionalized Al-MIL-53 Metal–Organic Frameworks

We present a study analyzing the selectivity of host–guest interactions in a series of functionalized Al-MIL-53-X metal–organic frameworks with X = H, NH₂, and NHCHO using acetone, ethanol, and water as probe molecules. While the amino group introduces additional hydrogen bond donor centers the NHCHO anchors function as donor and acceptor. The guests were chosen due to their ability to act solely as an acceptor in the case of acetone, whereas ethanol and water provide acceptor and donor qualities with a gradual decrease of the acceptor strength toward ethanol. The characterization of the host–guest interactions includes a comprehensive solid-state NMR spectroscopic study based on a full assignment of ¹H and ¹³C high-resolution spectra using CRAMPS decoupling schemes to enhance ¹H resolution combined with advanced 2D HETCOR (¹H–¹³C, ¹H–²⁷Al, and ¹H–¹⁴N) spectra at high magnetic fields. In spite of a pronounced dynamical disorder of the guests, we could identify a preferred binding of the acetone via a NH···OC hydrogen bond for the NH₂ and the NHCHO anchor groups by analyzing trends in the ¹³C isotropic chemical shifts. At the same time ¹H–¹H through-space connectivities reveal a close vicinity of the acetone methyl groups to the benzene rings of the linkers. In contrast, for ethanol and water, the interaction with the anchor groups is too weak to compete with the thermal disorder at room temperature

Highly Efficient Supramolecular Nucleating Agents for Poly(3-hexylthiophene)

Controlling the solid-state morphology of semiconducting polymers is crucial for the function and performance of optoelectronic and photonic devices. Nucleation is a commonly used and straightforward approach to tailor the solid-state morphology of semi-crystalline polymers. However, efficient nucleating agents for semiconducting polymers are still rare. Here, we present a conceptual approach to tailor supramolecular nucleating agents for the semiconducting polymer, poly(3-hexylthiophene) (P3HT). Using this approach, we developed a class of supramolecular nucleating agents, which can achieve outstanding nucleation efficiencies of more than 95% at concentrations as low as 0.1 wt %. Such efficiencies can be achieved by combining an exceptionally high epitaxial match with highly regularly arranged donor-acceptor interactions between the nucleating agent and the polymer. Notably, the supramolecular agents do not induce trap states in thin films of P3HT and are beneficial for the film stability by controlling the solid-state morphology. We anticipate that this approach can be transferred to other semi-crystalline conjugated polymers, resulting in defined solid-state morphologies

Hydroxyl Defects and Oxide Vacancies within Ringwoodite-toward Understanding the Defect Chemistry of Spinel-Type Oxides

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Elucidating the formation of Al-NBO bonds, Al-O-Al linkages and clusters in alkaline-earth aluminosilicate glasses based on molecular dynamics simulations

Exploring the reasons for the initiation of Al-O-Al bond formation in alkali-earth alumino silicate glasses is a key topic in the glass-science community. Evidence for the formation of Al-O-Al and Al-NBO bonds in the glass composition 38.7CaO-9.7MgO-12.9Al(2)O(3)-38.7SiO(2) (CMAS, mol%) has been provided based on Molecular Dynamics (MD) simulations. Analyses in the short-range order confirm that silicon and the majority of aluminium cations form regular tetrahedra. Well-separated homonuclear (Si-O-Si) and heteronuclear (Si-O-Al) cluster regions have been identified. In addition, a channel region (C-Region), separated from the network region, enriched with both NBO and non-framework modifier cations, has also been identified. These findings are in support of the previously proposed extended modified random network (EMRN) model for aluminosilicate glasses. A detailed analysis of the structural distributions revealed that a majority of Al, 51.6%, is found in Si-O-Al links. Although the formation of Al-O-Al and Al-NBO bonds is energetically less favourable, a significant amount of Al is found in Al-O-Al links (33.5%), violating Lowenstein's rule, and the remainder is bonded with non-bridging oxygen (NBO) in the form of Al-NBO (Al-O-(Ca, Mg)). The conditions necessary for the formation of less favourable bonds are attributed to the presence of a high amount of modifier cations in current CMAS glass and their preferable coordination

Probing Interactions of N‑Donor Molecules with Open Metal Sites within Paramagnetic Cr-MIL-101: A Solid-State NMR Spectroscopic and Density Functional Theory 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

Identifying Selective Host-Guest Interactions Based on Hydrogen Bond Donor-Acceptor Pattern in Functionalized Al-MIL-53 Metal-Organic Frameworks

We present a study analyzing the selectivity of host guest interactions in a series of functionalized Al-MIL-53-X metal organic frameworks with X = H, NH2, and NHCHO using acetone; ethanol, and water as probe molecules. While the amino group introduces additional hydrogen bond donor centers the NHCHO anchors function as donor and acceptor. The guests were chosen due to their ability to act solely as an acceptor in the case of acetone, whereas ethanol and water provide acceptor and donor qualities with a gradual decrease of the acceptor strength toward ethanol. The characterization of the host guest interactions includes a comprehensive solid-state NMR spectroscopic study based on a full assignment of H-1 and C-13 high-resolution spectra using CRAMPS decoupling schemes to enhance H-1 resolution combined with advanced 2D HETCOR (H-1-C-13, H-1-Al-27, and H-1-N-14) spectra at high magnetic fields. In spite of a pronounced dynamical disorder of the guests, we could identify a preferred binding of the acetone via a NH center dot center dot center dot OC hydrogen bond for the NH2 and the NHCHO anchor groups by analyzing trends in the C-13 isotropic chemical shifts. At the same time H-1-H-1 through space connectivities reveal a close vicinity of the acetone methyl groups to the benzene rings of the linkers. In contrast, for ethanol and water, the interaction with the anchor groups is too weak to compete with the thermal disorder at room temperature