Mark Feyand

Automated Diffraction Tomography for the Structure Elucidation of Twinned, Sub‐micrometer Crystals of a Highly Porous, Catalytically Active Bismuth Metal–Organic Framework

The number of metal–organic framework (MOF) compounds has increased almost exponentially over the last decade as a consequence of their fascinating structures and potential applications. They are composed of inorganic building units, such as metal ions or clusters, which are connected through organic linker molecules to form a porous three-dimensional network. Most of the MOFs are based on rigid polycarboxylate linker molecules, but a large variety of metal ions, mainly transition-metal ions, have also been incorporated. The chemical and thermal stability of metal carboxylate based MOFs is crucial for potential applications and depends on the metal ions incorporated. In general, metal ions in higher oxidation states lead to more stable structures. While the use of divalent metal ions often results in the formation of single crystals, whose structures can be routinely determined by single-crystal X-ray diffraction, triand tetravalent metal carboxylates are mostly obtained as microcrystalline powders and the determination of their structures poses immense challenges. 4c,5] Direct methods have been successfully employed, but complicated structures with large unit cells necessitate the use of nonstandard approaches. Thus, computational assisted structure determination, namely, the AASBU approach (assembling of secondary building units), the ligand-replacement strategy, and DFT calculations have been applied. Recently automated diffraction tomography (ADT) has been introduced as a new method for collecting three-dimensional electron diffraction data from single nanosized crystals, thus allowing singlecrystal analysis even for porous and organic sub-microcrystalline samples. A trivalent metal that exhibits interesting catalytic properties is bismuth. It is nontoxic, noncarcinogenic, and for a rare metal relatively inexpensive, and thus bismuth compounds are used as green catalysts. Despite these characteristics, the number of bismuth-based MOFs is rather limited and only a few compounds with limited porosity have been described. This is in contrast to the many known bismuth-oxo clusters, which could possibly be used for the construction of new MOFs. Here, we present the synthesis of the first highly crystalline, porous, and catalytically active bismuth-based MOF Bi(BTB) (BTB = 1,3,5-benzenetrisbenzoate), whose structure was elucidated by a combination of electron diffraction, Rietveld refinement, and DFT calculations. Bi(BTB), denoted as CAU-7 (CAU = ChristianAlbrechts-Universit t) was synthesized by using conventional as well as microwave (MW) assisted heating. The reaction of Bi(NO3)3·5 H2O with H3BTB in methanol at 120 8C led to phase-pure CAU-7 (for a detailed synthesis procedure see the Supporting Information). The reaction time can be reduced from 12 h to 20 min by using MW-assisted instead of conventional heating, but this leads to the formation of 10–20 mm large agglomerates of strongly intergrown elongated crystals of about 100 nm (see Figures S2–S4 in the Supporting Information). The addition of DMF in the conventional synthesis results in the formation of larger rodlike crystals ranging from 200 to 300 nm in length. Transmission electron microscopy confirmed that isolated CAU-7 crystals have a typical rodlike shape with different length/diameter ratios (see Figure S5 in the Supporting Information). Such isolated rods were used to collect electron diffraction data by automated diffraction tomography (ATD). Single-crystal ADT electron diffraction datasets were collected using a cryo holder cooled to 120 K and mild illumination conditions. To prevent beam damage and improve the signal intensity, the diffraction data were acquired in the precession mode. The three-dimensional diffraction space reconstruction leads to lattice parameters a = 32 , b = 28 , c = 4 , a = b = g = 908, and extinction group Pb-a. The reconstructed reciprocal space is shown in Figure 1. [*] M. Feyand, T. Reimer, Prof. Dr. N. Stock Institut f r Anorganische Chemie Christian Albrechts Universit t zu Kiel Max-Eyth Strasse 2, 24118 Kiel (Germany) E-mail: stock@ac.uni-kiel.de

CAU-3: A new family of porous MOFs with a novel Al-based brick: [Al2(OCH3)4(O2C-X-CO2)] (X = aryl)

A new family of Al-based MOFs denoted as CAU-3 (CAU = Christian-Albrechts-Universität) was discovered in the solvothermal system Al(3+)/aryldicarboxylic acid/NaOH/methanol by applying high-throughput-methods. The three compounds reported in this article [Al(2)(OCH(3))(4)BDC], [Al(2)(OCH(3))(4)BDC-NH(2)] and[Al(2)(OCH(3))(4)NDC] (BDC = 1,4-benzenedicarboxylate; NDC = 2,6-naphtalenedicarboxylate) are all based on the same unprecedented inorganic building unit [Al(12)(OCH(3))(24)](12+), which is a dodecameric cyclic aluminium-methanolate-cluster. The material CAU-3-NDC was found to exhibit the highest surface area as well as the highest micropore volume of all Al-based MOFs reported until now.

Systematic and In Situ Energy Dispersive X-ray Diffraction Investigations on the Formation of Lanthanide Phosphonatobutanesulfonates: Ln(O3P-C4H8-SO3)(H2O) (Ln = La−Gd)

Using the flexible linker H(2)O(3)P-C(4)H(8)-SO(3)H (H(3)L) and rare earth ions Ln(3+) (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) we were able to synthesize the new isostructural inorganic organic hybrid compounds Ln(O(3)P-C(4)H(8)-SO(3))(H(2)O). High-throughput experiments were employed to study the influence of the molar ratios Ln:H(3)L and pH on the product formation. The crystal structure of the compounds Sm(O(3)P-C(4)H(8)-SO(3))(H(2)O) (1) and Pr(O(3)P-C(4)H(8)-SO(3))(H(2)O) (2) were determined by single crystal diffraction. The structures are built up from chains of edge-sharing LnO(8)-polyhedra that are connected by the phosphonate and sulfonate groups into layers. These layers are linked by the -(CH(2))(4)- group to form a three-dimensional framework. The synthesis of compound 1 was scaled up in a conventional oven as well as in a microwave reactor system. A modification of a microwave reactor system allowed its integration into the beamline F3 at HASYLAB, DESY, Hamburg. The crystallization was investigated in situ by means of energy dispersive X-ray diffraction using conventional as well as microwave heating methods applying temperatures varying from 110 to 150 °C. The formation of Sm(O(3)P-C(4)H(8)-SO(3))(H(2)O) takes place in two steps. In the first step a crystalline intermediate was observed, which transforms completely into compound 1. The method by Sharp and Hancock was used to determine the rate constants, reaction exponents, and the Arrhenius activation energy for both reaction steps. Comparing both heating methods, microwave heating leads to fully crystallized reaction product after shorter reaction times, but neither the temperature nor the heating method has significant influence on the induction time.

Unprecedented Topological Complexity in a Metal–Organic Framework Constructed from Simple Building Units

A bismuth-based metal-organic framework (MOF), [Bi(BTC)(H2O)]·2H2O·MeOH denoted CAU-17, was synthesized and found to have an exceptionally complicated structure with helical Bi-O rods cross-linked by 1,3,5-benzenetricarboxylate (BTC(3-)) ligands. Five crystallographically independent 1D channels including two hexagonal channels, two rectangular channels, and one triangular channel have accessible diameters of 9.6, 9.6, 3.6, 3.6, and 3.4 Å, respectively. The structure is further complicated by twinning. Rod-incorporated MOF structures typically have underlying nets with only one unique node and three or four unique edges. In contrast, topological analysis of CAU-17 revealed unprecedented complexity for a MOF structure with 54 unique nodes and 135 edges. The complexity originates from the rod packing and the rods themselves, which are related to aperiodic helices.

Bismuth Tri- and Tetraarylcarboxylates: Crystal Structures, In Situ X-ray Diffraction, Intermediates and Luminescence

A systematic investigation of the systems Bi(3+)/carboxylic acid/HNO3 for the tri- and tetracarboxylic acids pyromellitic acid (H4Pyr), trimellitic acid (H3Tri) and trimesic acid (H3BTC) acid led to the discovery of five new bismuth carboxylates. Structural characterisation allowed the influence of the linker geometry and the Bi(3+):linker molar ratio in the starting solution on the crystal structure to be determined. The crystallisation of three selected compounds was investigated by in situ energy-dispersive X-ray diffraction. Three new crystalline intermediates were observed within minutes, and two of them could be isolated by quenching of the reaction mixture. Their crystal structures were determined from laboratory and synchrotron X-ray powder diffraction data and allowed a possible reaction pathway to be established. In depth characterisation of the luminescence properties of the three bismuth pyromellate compounds was carried out. Fluorescence and phosphorescence could be assigned to (mainly) ligand- and metal-based transitions. The polymorphs of Bi(HPyr) exhibit different luminescence properties, although their structures are very similar. Surprisingly, doping of the three host structures with Eu(3+) and Tb(3+) ions was only successful for one of the polymorphs.

Crystallisation kinetics of metal organic frameworks from in situ time-resolved x-ray diffraction

A time-resolved powder diffraction study of the crystallisation of porous metal organic framework materials with the CPO-27 structure ([M2(dhtp)(H2O)2]·8H2O where, dhtp=2,5-dioxoterephthalate) using the energy dispersive X-ray diffraction method is described. Crystallisation under solvothermal conditions is performed between 70 - 110 °C from clear solutions of metal salts (M=Co2+ or Ni2+) and 2,5-dihydroxyterephthalic acid in a mixture of THF-water in sealed reaction vessels, using both conventional and microwave heating. Integration of Bragg peak areas with time provides accurate crystallisation curves, which are modelled using the method of Gualtieri to determine rate constants for nucleation and for growth and then, by Arrhenius analysis, activation energies. Crystallisation is determined to be one-dimensional, consistent with the elongated morphology of the crystals produced in these reactions. With conventional heating the Co-containing CPO-27 crystallises more rapidly than the isostructural Ni-containing analogue and analysis of the kinetic parameters would suggest a complex multi-step crystallisation process. The effect of microwave heating is upon activation energies: the values for both nucleation and for crystal growth are lowered compared to reactions using conventional heating.

Copper Phosphonatoethanesulfonates: Temperature Dependent in Situ Energy Dispersive X-ray Diffraction Study and Influence of the pH on the Crystal Structures

The system Cu(2+)/H2O3P-C2H4-SO3H/NaOH was investigated using in situ energy dispersive X-ray diffraction (EDXRD) to study the formation and temperature induced phase transformation of previously described copper phosphonosulfonates. Thus, the formation of [Cu2(O3P-C2H4-SO3)(OH)(H2O)]·3H2O (4) at 90 °C is shown to proceed via a previously unknown intermediate [Cu2(O3P-C2H4-SO3)(OH)(H2O)]·4H2O (6), which could be structurally characterized from high resolution powder diffraction data. Increase of the reaction temperature to 150 °C led to a rapid phase transformation to [Cu2(O3P-C2H4-SO3)(OH)(H2O)]·H2O (1), which was also studied by in situ EDXRD. The comparison of the structures of 1, 4, and 6 allowed us to establish a possible reaction mechanism. In addition to the in situ crystallization studies, microwave assisted heating for the synthesis of the copper phosphonosulfonates was employed, which allowed the growth of larger crystals of [NaCu(O3P-C2H4-SO3)(H2O)2] (5) suitable for single crystal X-ray diffraction. Through the combination of force field calculations and Rietveld refinement we were able to determine the crystal structure of [Cu1.5(O3P-C2H4-SO3)] 2H2O (3) and thus structurally characterize all compounds known up to now in this well investigated system. With the additional structural data we are now able to describe the influence of the pH on the structure formation.