A zero-valent palladium cluster-organic framework

Acquiring spatial control of nanoscopic metal clusters is central to their function as efficient multi-electron catalysts. However, dispersing metal clusters on surfaces or in porous hosts is accompanied by an intrinsic heterogeneity that hampers detailed understanding of the chemical structure and its relation to reactivities. Tethering pre-assembled molecular metal clusters into polymeric, crystalline 2D or 3D networks constitutes an unproven approach to realizing ordered arrays of chemically well-defined metal clusters. Herein, we report the facile synthesis of a {Pd3} cluster-based organometallic framework from a molecular triangulo-Pd3(CNXyl)6 (Xyl = xylyl; Pd3) cluster under chemically mild conditions. The formally zero-valent Pd3 cluster readily engages in a complete ligand exchange when exposed to a similar, ditopic isocyanide ligand, resulting in polymerization into a 2D coordination network (Pd3-MOF). The structure of Pd3-MOF could be unambiguously determined by continuous rotation 3D electron diffraction (3D-ED) experiments to a resolution of ~1.0 Å (>99% completeness), showcasing the applicability of 3D-ED to nanocrystalline, organometallic polymers. Pd3-MOF displays Pd03 cluster nodes, which possess significant thermal and aerobic stability, and activity towards hydrogenation catalysis. Importantly, the realization of Pd3-MOF paves the way for the exploitation of metal clusters as building blocks for rigidly interlocked metal nanoparticles at the molecular limit.

The Elusive Structure of Levocetirizine Dihydrochloride Determined by Electron Diffraction

Levocetirizine is an orally administrated, second-generation antihistaminic active pharmaceutical ingredient that has been used to treat allergy symptoms and long-term hives for over 25 years. Despite the wide use of this compound, its crystal structure has remained unknown. Here we report the application of 3D electron diffraction (3D ED)/microelectron diffraction (MicroED) to determine the crystal structure of Levocetirizine dihydrochloride directly from crystalline powders extracted from commercially available tablets containing the compound. We also showcased the utility of dynamical refinement to unambiguously assign absolute configuration. The results highlight the immense potential of 3D ED/MicroED) for structure elucidation of components of microcrystalline mixtures that obviates the need to grow large-size single crystals and the use of complementary analytical techniques, which could be important for identification as well as for primary structural characterization.

Chiral Lanthanum Metal-Organic Framework with Gated CO2 Sorption and Concerted Framework Flexibility

A metal–organic framework (MOF) CTH-17 based on lanthanum(III) and the conformationally chiral linker 1,2,3,4,5,6-hexakis(4-carboxyphenyl)benzene, cpb^6–: [La₂(cpb)]·1.5dmf was prepared by the solvothermal method in dimethylformamide (dmf) and characterized by variable-temperature X-ray powder diffraction (VTPXRD), variable-temperature X-ray single-crystal diffraction (SCXRD), and thermogravimetric analysis (TGA). CTH-17 is a rod-MOF with new topology och. It has high-temperature stability with Sohncke space groups P6₁22/P6₅22 at 90 K and P622 at 300 and 500 K, all phases characterized with SCXRD and at 293 K also with three-dimensional (3D) electron diffraction. VTPXRD indicates a third phase appearing after 620 K and stable up to 770 K. Gas sorption isotherms with N₂ indicate a modest surface area of 231 m² g^–1 for CTH-17, roughly in agreement with the crystal structure. Carbon dioxide sorption reveals a gate-opening effect of CTH-17 where the structure opens up when the loading of CO₂ reaches approximately ∼0.45 mmol g^–1 or 1 molecule per unit cell. Based on the SCXRD data, this is interpreted as flexibility based on the concerted movements of the propeller-like hexatopic cpb linkers, the movement intramolecularly transmitted by the π–π stacking of the cpb linkers and helped by the fluidity of the LaO₆ coordination sphere. This was corroborated by density functional theory (DFT) calculations yielding the chiral phase (P622) as the energy minimum and a completely racemic phase (P6/mmm), with symmetric cpb linkers representing a saddle point in a racemization process.

Hexagonal Layer Manganese Metal-Organic Framework for Photocatalytic CO2 Cycloaddition Reaction

A novel manganese metal-organic framework (Mn-MOF) termed UAEU-50 assembled from a benzenedicarboxylate linker (BDC) and trinuclear manganese clusters was synthesized and fully characterized using different spectroscopic and analytic techniques (e.g., X-ray powder diffraction, UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy). UAEU-50 adopted a hexagonal layer structure and exhibited superior thermal stability and robust chemical stability. Photocatalytic activities of UAEU-50 were investigated using the cycloaddition of CO₂ to different epoxides, forming cyclic carbonates. Impressively, UAEU-50 can transform up to 90% photocatalytic CO₂ conversion to cyclic carbonates in the visible-light region at ambient conditions.

Teaching a large-scale crystallography school with Zoom Webinar

In order to address the loss of crystallographic training opportunities resulting from the cancelation of conventional schools around the world due to the COVID-19 pandemic, we have started an online crystallography school with live lectures and live Q&A using Zoom Webinar. Since we were trying to reach a large audience in a relatively short period, we have limited the school to ten 1 h lectures covering practical aspects of small molecule crystallography including data collection, data processing, and structure solution. In the school, we also covered some advanced topics that students commonly see in their work: absolute structure determination, twinning, and disorder. To round out the education, we provided lectures on macromolecular crystallography and powder diffraction. For students to practice on their own, we used freely available data reduction and structure solution software, as well as datasets with which to practice. To give students credit for course completion, we provided an online exam and an electronic certificate of completion. In this editorial, we will provide some insight into the issues of holding lectures with up to 750 students of very diverse backgrounds and review the efficacy of the school in teaching crystallography for the two cohorts of students.

MeSi(CH2 SnRO)3 (R=Ph, Me3 SiCH2 ): Building Blocks for Triangular-Shaped Diorganotin Oxide Macrocycles

The syntheses of the novel silicon-bridged tris(tetraorganotin) compounds MeSi(CH2 SnPh2 R)3 (2, R=Ph; 5, R=Me3 SiCH2 ) and their halogen-substituted derivatives MeSi(CH2 SnPh(3-n) In )3 (3, n=1; 4, n=2) and MeSi(CH2 SnI2 R)3 (6, R=Me3 SiCH2 ) are reported. The reaction of compound 4 with di-t-butyltin oxide (t-Bu2 SnO)3 gives the oktokaideka-nuclear (18-nuclear) molecular diorganotin oxide [MeSi(CH2 SnPhO)3 ]6 (7) while the reaction of 6 with sodium hydroxide, NaOH, provides the trikonta-nuclear (30-nuclear) molecular diorganotin oxide [MeSi(CH2 SnRO)3 ]10 (8, R=Me3 SiCH2 ). Both 7 and 8 show belt-like ladder-type macrocyclic structures and are by far the biggest molecular diorganotin oxides reported to date. The compounds have been characterized by elemental analyses, electrospray mass spectrometry (ESI-MS), NMR spectroscopy, 1 H DOSY NMR spectroscopy (7), IR spectroscopy (7, 8), and single-crystal X-ray diffraction analysis (2, 7, 8).

Supramolecular Metallacycles and Their Binding of Fullerenes

The synthesis of a new triaminoguanidinium-based ligand with three tris-chelating [NNO]-binding pockets and C3 symmetry is described. The reaction of tris-(2-pyridinylene-N-oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C60 can be observed by NMR spectroscopy and single-crystal X-ray diffraction and is verified using computation.