Chemists of all fields currently publish about 50 000 crystal structures per year, the vast majority of which are X‐ray structures. We determined two molecular structures by employing electron rather ...than X‐ray diffraction. For this purpose, an EIGER hybrid pixel detector was fitted to a transmission electron microscope, yielding an electron diffractometer. The structure of a new methylene blue derivative was determined at 0.9 Å resolution from a crystal smaller than 1×2 μm2. Several thousand active pharmaceutical ingredients (APIs) are only available as submicrocrystalline powders. To illustrate the potential of electron crystallography for the pharmaceutical industry, we also determined the structure of an API from its pill. We demonstrate that electron crystallography complements X‐ray crystallography and is the technique of choice for all unsolved cases in which submicrometer‐sized crystals were the limiting factor.
Electrons instead of X‐rays: An electron diffractometer was tailored and employed for de novo structure determination from submicrometer‐sized crystals. A new methylene blue derivative was analysed together with a microcrystalline extract of an active pharmaceutical ingredient from a pill. The results obtained on submicrometer‐sized samples complement X‐ray crystallography.
Two-dimensional (2D) materials are a key target for many applications in the modern day. Self-assembly is one approach that can bring us closer to this goal, which usually relies upon strong, ...directional interactions instead of covalent bonds. Control over less directional forces is more challenging and usually does not result in as well-defined materials. Explicitly incorporating topography into the design as a guiding effect to enhance the interacting forces can help to form highly ordered structures. Herein, we show the process of shape-assisted self-assembly to be consistent across a range of derivatives that highlights the restriction of rotational motion and is verified using a diverse combination of solid state analyses. A molecular curvature governed angle distribution nurtures monomers into loose columns that then arrange to form 2D structures with long-range order observed in both crystalline and soft materials. These features strengthen the idea that shape becomes an important design principle leading towards precise molecular self-assembly and the inception of new materials.
Lewis superacidity? In analogy to Brønsted superacids, Lewis superacids can be defined as Lewis acids that are stronger than the strongest conventional and commercially employed Lewis acid SbF5. The ...fluorobenzene complex PhF→Al(ORF)3 (RF=C(CF3)3) qualifies as an easily accessible, non‐oxidizing and stable Lewis acid that conforms with our Lewis superacidity criterion.
Electron diffraction (known also as ED, 3D ED or microED) is gaining momentum in science and industry. The application of electron diffraction in performing nano-crystallography on crystals smaller ...than 1 µm is a disruptive technology that is opening up fascinating new perspectives for a wide variety of compounds required in the fields of chemical, pharmaceutical and advanced materials research. Electron diffraction enables the characterization of solid compounds complementary to neutron, powder X-ray and single-crystal X-ray diffraction, as it has the unique capability to measure nanometre-sized crystals. The recent introduction of dedicated instrumentation to perform ED experiments is a key aspect of the continued growth and success of this technology. In addition to the ultra-high-speed hybrid-pixel detectors enabling ED data collection in continuous rotation mode, a high-precision goniometer and horizontal layout have been determined as essential features of an electron diffractometer, both of which are embodied in the Eldico ED-1. Four examples of data collected on an Eldico ED-1 are showcased to demonstrate the potential and advantages of a dedicated electron diffractometer, covering selected applications and challenges of electron diffraction: (i) multiple reciprocal lattices, (ii) absolute structure of a chiral compound, and (iii)
-values achieved by kinematic refinement comparable to X-ray data.
The absolute structure of the 3D MOF anhydrous zinc (II) tartrate with space group I222 has been determined for both Zn(L-TAR) and Zn(D-TAR) by electron diffraction using crystals of sub-micron ...dimensions. Dynamical refinement gives a strong difference in R factors for the correct and inverted structures. These anhydrous MOFs may be prepared phase pure from mild hydrothermal conditions. Powder X-ray diffraction indicates that isostructural or pseudo-isostructural phases can be similarly prepared for several other M2+ = Mg, Mn, Co, Ni and Cu. I222 is a relatively uncommon space group since it involves intersecting two-fold axes that place constraints on molecular crystals. However, in the case of MOFs the packing is dominated by satisfying the octahedral coordination centers. These MOFs are dense 3D networks with chiral octahedral metal centers that may be classed as Δ (for L-TAR) or Λ (for D-TAR).
The coordination chemistry of the ligand 3-(2-pyridyl)-1,2,4triazolo4,3-apyridine (L¹⁰) has been investigated and iron(II), cobalt(II), nickel(II) and copper(II) complexes featuring diverse ...structural motifs have been prepared. In the 2 : 1-type complexes Co(II)(L¹⁰)₂(MeOH)₂(ClO₄)₂ (20), Ni(II)(L¹⁰)₂(MeOH)₂(ClO₄)₂ (21), Cu(II)(L¹⁰)₂(MeOH)₂(ClO₄)₂ (22), Co(II)(L¹⁰)₂(H₂O)₂(ClO₄)₂ (23) and Cu(II)(L¹⁰)₂(ClO₄)₂ (24) the metal centres are N₄O₂ octahedrally coordinated with two N²,N(pyr) bidentate ligands L¹⁰ in the equatorial positions. In the N₆ octahedral 4 : 1-type complex Co(II)(L¹⁰)₄(ClO₄)₂·H₂O (25) both axially coordinating N¹ unidentate and equatorially bound N²,N(pyr) bidentate ligands L¹⁰ are observed. The N₆ octahedral 3 : 1-type complex Fe(II)(L¹⁰)₃(OTf)₂·1.5MeCN·0.13H₂O·0.87MeO(t)Bu (27) features three N²,N(pyr) bidentate ligands L¹⁰ in the mer configuration. The two closely related N₆ octahedral complexes Fe(II)(L¹⁰)₂(NCS)₂ (29) and Fe(II)(L¹⁰)₂(dca)₂ (30) have fundamentally different structures. While complex 29 features two equatorially bound N²,N(pyr) bidentate ligands L¹⁰ and axial NCS⁻ co-ligands, complex 30 is a one-dimensional doubly μ1,5-dicyanamido-bridged polymer with N¹ unidentate ligands L¹⁰ in the axial positions. Temperature-dependent magnetic susceptibility measurements of the iron(II) complexes 28 and 29 have shown the 3 : 1-type complex Fe(II)(L¹⁰)₃(ClO₄)₂·H₂O (28) to be in the low-spin state over the range 300-2 K and the 2 : 1-type complex 29 to be a spin crossover compound with T(1/2) = 269 K whereas the dicyanamido-bridged complex 30 remains in the high-spin state even down to 113 K, according to X-ray diffraction data. A single end-to-end bridging NCS⁻ co-ligand is found in the N₄S square-pyramidal complex Cu(II)(L¹⁰)(NCS)₂ (31) which shows Curie-Weiss behaviour over the range 300-2 K. A brief review of the coordination chemistry of triazolopyridines is given.
The S3Zn−SR coordination of thiolate-alkylating enzymes such as the Ada DNA repair protein was reproduced in tris(thioimidazolyl)borate-zinc-thiolate complexes TtiRZn−SR‘. Four different TtiR ligands ...and nine different thiolates were employed, yielding a total of 12 new complexes. In addition, one TtiRZn−SH complex and two thiolate-bridged TtiR-SEt-TtiR+ complexes were obtained. A selection of six thiolate complexes was converted with methyl iodide to the corresponding methyl thioethers and TtiRZn−I. According to a kinetic analysis these reactions are second-order processes, which implies that the alkylations are likely to occur at the zinc-bound thiolates. They are much faster than the alkylations of zinc thiolates with N3 or N2S tripod ligands. The most reactive thiolate, TtiXylZn−SEt, reacts slowly with trimethyl phosphate in a nonpolar medium at room temperature, yielding methyl-ethyl-thioether and TtiXylZn−OPO(OMe)2 which can be converted back to the thiolate complex with NaSEt. This is the closest reproduction of the Ada repair process so far.
A series of new dicobalt complexes of the permethylated macrocyclic hexaamine dithiophenolate ligand H2LMe have been prepared and investigated in the context of ligand binding and oxidation state ...changes. The octadentate ligand is an effective dinucleating ligand that supports the formation of bioctahedral complexes with a central N3Co(μ-SR)2(μ-X)CoN3 core structure, leaving a free bridging position X for the coordination of the substrates. The acetato- and cinnamato-bridged complexes (LMe)CoII 2(μ-O2CMe)+ (2) and (LMe)CoII 2(μ-O2CCHCHPh)+ (5) were prepared by reaction of the μ-Cl complex (LMe)CoII 2(μ-Cl)+ (1) with the corresponding sodium carboxylates in methanol. The electrochemical properties of these and of the methyl carbonate complex (LMe)CoII 2(μ-O2COMe)+ (8) were also investigated. All complexes undergo two stepwise oxidations at ca. E 1 1/2 = +0.22 and at E 2 1/2 = ca. +0.60 V vs SCE, affording the mixed-valent complexes (LMe)CoIICoIII(μ-O2CR)2+ (3, 6, 9) and the fully oxidized CoIIICoIII forms (LMe)CoIII 2(μ-O2CR)3+ (4, 7, 10), respectively. Compounds 3, 6, 9 and 4, 7, 10 refer to acetato-, cinnamato-, and methylcarbonato species, respectively. The CoIICoIII compounds were prepared by comproportionation of the respective CoII 2 and CoIII 2 compounds. The CoIIICoIII species were prepared by bromine oxidation of the CoIICoII forms. The crystal structures of complexes 2·BPh4·MeCN, 3·(I3)2, 5·BPh4·2MeCN, 6·(ClO4)2·EtOH, 7·(ClO4)3·MeCN·(H2O)3, and 9·(ClO4)2·(MeOH)2·H2O were determined by single-crystal X-ray crystallography at 210 K. The oxidations occur without gross structural changes of the parent complexes. The CoIICoIII complexes are composed of high-spin CoII (d7) and low-spin CoIII (d6) ions. The CoIIICoIII complexes are diamagnetic. The oxidation reactions affect the binding mode of the substrates. In the CoII 2 and CoIICoIII forms the carboxylates bridge the two Co2+ ions in a symmetric μ-1,3 fashion with uniform C−O bond distances, whereas asymmetric bridging modes, with one short CO and one long C−O distance, are adopted in the fully oxidized species. This is consistent with the observed shifts in vibrational frequencies for νas(C−O) and νs(C−O) across the series.
On the design of a dedicated electron diffractometer Hovestreydt, Eric; Santiso-Quinones, Gustavo; Steinfeld, Gunther
Acta crystallographica. Section A, Foundations and advances,
08/2019, Volume:
75, Issue:
a2
Journal Article
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