X‐Ray Diffraction as a Local Probe Tool

For the structural characterization of nanoscale objects, X‐ray diffraction is widely used as a technique complementing local probe analysis methods such as scanning electron microscopy and transmission electron microscopy. Details on strain distributions, chemical composition, or size and shape of nanostructures are addressed. X‐ray diffraction traditionally obtains very good statistically averaged properties over large ensembles—provided this averaging is meaningful for ensembles with sufficiently small dispersion of properties. In many cases, however, it is desirable to combine different analysis techniques on exactly the same nano‐object, for example, to gain a more detailed insight into the interdependence of properties. X‐ray beams focused to diameters in the sub‐micron range, which are available at third‐generation synchrotron sources, allow for such X‐ray diffraction studies of individual nano‐objects.     

ChemInform Abstract: Structural Characterization of Moganite‐Type AlPO4 by NMR and Powder X‐Ray Diffraction.

A new high‐pressure AlPO₄ phase obtained at 5 GPa and 1500 °C is characterized by synchrotron powder XRD and MAS NMR spectroscopy.     

Differential Adsorption of l‐ and d‐Lysine on Achiral MFI Zeolites as Determined by Synchrotron X‐Ray Powder Diffraction and Thermogravimetric Analysis

Reported here is the first crystallographic observation of stereospecific bindings of l ‐ and d ‐lysine (Lys) in achiral MFI zeolites. The MFI structure offers inherent geometric and internal confinement effects for the enantiomeric difference in l ‐ and d ‐Lys adsorption. Notable differences have been observed by circular dichroism (CD) spectroscopy and thermogravimetric analysis (TGA). Distinct l ‐ and d ‐Lys adsorption behaviours on the H‐ZSM‐5 framework have been revealed by the Rietveld refinement of high‐resolution synchrotron X‐ray powder diffraction (SXRD) data and the density‐functional theory (DFT) calculations. Despite demonstrating the approach for l ‐ and d ‐Lys over MFI zeolites at an atomistic resolution, the differential adsorption study sheds light on the rational engineering of molecular interaction(s) with achiral microporous materials for chiral separation purposes.     

Isolation and Structural X‐ray Investigation of Perfluoroalkyl Derivatives of Six Cage Isomers of C84

Perfluoroalkylation of a higher fullerene mixture with CF₃I or C₂F₅I, followed by HPLC separation of CF₃ and C₂F₅ derivatives, resulted in the isolation of several C₈₄(R^F)_n (n=12, 16) compounds. Single‐crystal X‐ray crystallography with the use of synchrotron radiation allowed structure elucidation of eight C₈₄(R^F)_n compounds containing six different C₈₄ cages (the number of the C₈₄ isomer is given in parentheses): C₈₄ (23)(C₂F₅)₁₂ ( I ), C₈₄ (22)(CF₃)₁₆ ( II ), C₈₄ (22)(C₂F₅)₁₂ ( III ), C₈₄ (11)(C₂F₅)₁₂ ( IV ), C₈₄ (16)(C₂F₅)₁₂ ( V ), C₈₄ (4)(CF₃)₁₂ ( VI with toluene and VII with hexane as solvate molecules), and C₈₄ (18)(C₂F₅)₁₂ ( VIII ). Whereas some connectivity patterns of C₈₄ isomers (22, 23, 11) had previously been unambiguously confirmed by different methods, derivatives of C₈₄ isomers numbers 4, 16, and 18 have been investigated crystallographically for the first time, thus providing direct proof of the connectivity patterns of rare C₈₄ isomers. General aspects of the addition of R^F groups to C₈₄ cages are discussed in terms of the preferred positions in the pentagons under the formation of chains, pairs, and isolated R^F groups.     

Screening the Thermodynamics of Trimethylaluminum‐Hydrolysis Products and Their Co‐Catalytic Performance in Olefin‐Polymerization Catalysis

Herein, we introduce an approach for the computational screening of stoichiometric reactions between trimethylaluminum (TMA) and water. The thermodynamic products of these reactions are methylaluminoxanes (MAOs) with different compositions, which have the general formula (AlOMe)_n(AlMe₃)_m, in which n describes the degree of oligomerization and m is the number of associated TMA molecules. These reaction products were thoroughly explored up to n=4, thus demonstrating the thermodynamically preferable association of up to four AlMe₃ molecules, that is, TMA molecules in their monomeric form. The relative Lewis acidities of the Al sites in these MAOs were systematically explored and we found that the associated TMA molecules were a key ingredient for co‐catalytic activity in olefin‐polymerization catalysis. This conclusion was supported by computational studies on catalyst activation, which revealed an exergonic insertion of ethene into the metallocene/MAO complex.     

Solution NMR and X‐Ray Structural Studies on Phthalocyaninatoiron Complexes

The addition of primary amines as solubilizing reagents for phthalocyaninatoiron complexes is shown to afford six‐coordinate bis(amine)phthalocyaninato complexes, i.e., [Fe(amine)₂(pc)] 2 (amine = decan‐1‐amine) and 3 (amine = benzylamine), with the two new N‐donors occupying the trans‐axial positions. The new complexes were characterized by extensive NMR measurements in THF solution. For complex 3 with the benzylamine ligand, the solid‐state structure was determined by X‐ray diffraction methods. Complex 2 is sufficiently labile in THF solution to exchange one amine ligand against CO (gas) affording an equilibrium mixture containing [Fe(amine)(CO)(pc)] 4 .     

Structural Characterization of a High-Nuclearity Niobium(V) Carboxylate Cluster Based on Pivalic Acid

We report a novel Nb(V)−carboxylate cluster obtained from reaction of niobium(V) ethoxide and pivalic (trimethylacetic) acid. Single crystal X-ray diffraction data reveal a structure composed of 16 Nb(V) ions featuring oxo-, ethoxy- and pivalate moieties. The new cluster exhibits the highest nuclearity among structurally characterized niobium carboxylates reported to date.     

Structural Tracking of a Bimolecular Reaction in Solution by Time‐Resolved X‐Ray Scattering

Molecular movies : Time‐resolved X‐ray scattering provides direct structural information on an electronically excited complex while it is formed in the bimolecular reaction between excited octahydrogen[tetrakis‐μ‐diphosphito‐1κP:2κP′‐diplatinate](4‐) (PtPOP*) and thallium ions. In the exciplex one thallium(I) and two platinum(II) ions are found to be collinear.

     

Anion‐Controlled Switching of an X Ligand into a Z Ligand: Coordination Non‐innocence of a Stiboranyl Ligand

The tetravalent platinum stiboranyl complex [(o‐(Ph₂P)C₆H₄)₂(o‐C₆Cl₄O₂)Sb]PtCl₂Ph ( 2 ) has been synthesized by reaction of [(o‐(Ph₂P)C₆H₄)₂SbClPh]PtCl ( 1 ) with o‐chloranil. In the presence of fluoride anions, the stiboranyl moiety of 2 displays non‐innocent behavior and is readily converted into a fluorostiborane unit. This transformation, which is accompanied by elimination of a chloride ligand from the Pt center, results in the formation of [(o‐(Ph₂P)C₆H₄)₂(o‐C₆Cl₄O₂)SbF]PtClPh ( 3 ). Structural, spectroscopic, and computational studies show that the conversion of 2 into 3 is accompanied by a cleavage of the covalent Pt? Sb bond present in 2 and formation of a longer and weaker Pt→Sb interaction in 3 . These results show that this new Pt–Sb platform supports the fluoride‐induced metamorphosis of a stiboranyl X ligand into a stiborane Z ligand.     

X‐ray Crystallography in Open‐Framework Materials

Open‐framework materials, such as metal–organic frameworks (MOFs) and coordination polymers have been widely investigated for their gas adsorption and separation properties. However, recent studies have demonstrated that their highly crystalline structures can be used to periodically organize guest molecules and non‐structural metal compounds either within their pore voids or by anchoring to their framework architecture. Accordingly, the open framework can act as a matrix for isolating and elucidating the structures of these moieties by X‐ray diffraction. This concept has broad scope for development as an analytical tool where obtaining single crystals of a target molecule presents a significant challenge and it additionally offers potential for obtaining insights into chemically reactive species that can be stabilized within the pore network. However, the technique does have limitations and as yet a general experimental method has not been realized. Herein we focus on recent examples in which framework materials have been utilized as a scaffold for ordering molecules for analysis by diffraction methods and canvass areas for future exploration.     

Synthesis of a Stable Selenoaldehyde by Self‐Catalyzed Thermal Dehydration of a Primary‐Alkyl‐Substituted Selenenic Acid

The unprecedented dehydration of a selenenic acid (RCH₂SeOH) to a selenoaldehyde (RCH?Se) has been demonstrated. A primary‐alkyl‐substituted selenenic acid was synthesized for the first time by taking advantage of a bulky cavity‐shaped substituent. Upon heating in solution, the selenenic acid underwent thermal dehydration to produce a stable selenoaldehyde, which was isolated as stable crystals and crystallographically characterized. Investigation of the reaction mechanism revealed that this β dehydration reaction involves two processes, both of which reflect the characteristics of a selenenic acid: 1) dehydrative condensation of two molecules of selenenic acid to generate a selenoseleninate intermediate [RCH₂SeSe(O)CH₂R], an isomer of a selenenic anhydride, and 2) subsequent β elimination of the selenenic acid from this intermediate to form a C?Se double bond, which establishes the self‐catalyzed β dehydration of the selenenic acid.     

ChemInform Abstract: Magnesium Perchlorate Anhydrate,Mg(ClO4)2, from Laboratory X‐Ray Powder Data.

The title compound is prepared by dehydration of Mg(ClO₄)₂·6H₂O (silica tube, continuous vacuum, 523 K, 2 h) and characterized by powder XRD.     

Alkali‐Metal ortho‐Hydroxyphenolates: Syntheses and Crystal Structures from Powder X‐Ray Diffraction

Colorless and highly air‐ and moisture‐sensitive powders of M[o‐C₆H₄O(OH)] with M = K, Rb, or Cs have been synthesized from reaction mixtures of the appropriate alkali metal and catechol in thf. All compounds were structurally characterized by means of powder X‐ray diffraction using the Rietveld profile refinement technique including restraints for the C—C/C—O bond distances and the C—C—C angles. The atomic arrangements of M[o‐C₆H₄O(OH)] (K: monoclinic P2₁/c; Rb/Cs: orthorhombic Pbcm) are characterized by polymeric chains of [M₁^[4]O₂^[2]η⁶] units connected by hydrogen bonds, thereby making up layered structures similar to the one of catechol. The coordinatively unsaturated alkali metals are forming edge‐sharing MO₄ pyramids and exhibit asymmetrical η⁶‐interactions with the phenylene rings. The symmetry of the unit cells increases with increasing size of the cation, and this results in a decrease of the monoclinic angle from 118.5° (catechol) to 93.7° (K compound), eventually leading to orthorhombic cells for the Rb and Cs compounds.     

Adding a Structural Context to the Deprotometalation and Trans‐Metal Trapping Chemistry of Phenyl‐Substituted Benzotriazole

Organometallic bases are becoming increasingly complex, because mixing components can lead to bases superior to single‐component bases. To better understand this superiority, it is useful to study metalated intermediate structures prior to quenching. This study is on 1‐phenyl‐1H‐benzotriazole, which was previously deprotonated by an in situ ZnCl₂ ? TMEDA/LiTMP (TMEDA=N,N,N′,N′‐tetramethylethylenediamine; TMP=2,2,6,6‐tetramethylpiperidide) mixture and then iodinated. Herein, reaction with LiTMP exposes the deficiency of the single‐component base as the crystalline product obtained was [{4‐R‐1‐(2‐lithiophenyl)‐1H‐benzotriazole ? 3THF}₂], [R=2‐C₆H₄(Ph)NLi], in which ring opening of benzotriazole and N₂ extrusion had occurred. Supporting lithiation by adding iBu₂Al(TMP) induces trans‐metal trapping, in which C?Li bonds transform into C?Al bonds to stabilise the metalated intermediate. X‐ray diffraction studies revealed homodimeric [(4‐R′‐1‐phenyl‐1H‐benzotriazole)₂], [R′=(iBu)₂Al(μ‐TMP)Li], and its heterodimeric isomer [(4‐R′‐1‐phenyl‐1H‐benzotriazole){2‐R′‐1‐phenyl‐1H‐benzotriazole}], whose structure and slow conformational dynamics were probed by solution NMR spectroscopy.