Selective Gas Uptake and Rotational Dynamics in a (3,24)-Connected Metal-Organic Framework Material.

The desolvated (3,24)-connected metal-organic framework (MOF) material, MFM-160a, [Cu3(L)(H2O)3] [H6L = 1,3,5-triazine-2,4,6-tris(aminophenyl-4-isophthalic acid)], exhibits excellent high-pressure uptake of CO2 (110 wt% at 20 bar, 298 K) and highly selective separation of C2 hydrocarbons from CH4 at 1 bar pressure. Henry's law selectivities of 79:1 for C2H2:CH4 and 70:1 for C2H4:CH4 at 298 K are observed, consistent with ideal adsorption solution theory (IAST) predictions. Significantly, MFM-160a shows a selectivity of 16:1 for C2H2:CO2. Solid-state 2H NMR spectroscopic studies on partially deuterated MFM-160-d12 confirm an ultra-low barrier (∼2 kJ mol-1) to rotation of the phenyl group in the activated MOF and a rotation rate 5 orders of magnitude slower than usually observed for solid-state materials (1.4 × 106 Hz cf. 1011-1013 Hz). Upon introduction of CO2 or C2H2 into desolvated MFM-160a, this rate of rotation was found to increase with increasing gas pressure, a phenomenon attributed to the weakening of an intramolecular hydrogen bond in the triazine-containing linker upon gas binding. DFT calculations of binding energies and interactions of CO2 and C2H2 around the triazine core are entirely consistent with the 2H NMR spectroscopic observations.

Self-Assembly of Angiotensin-Converting Enzyme Inhibitors Captopril and Lisinopril and Their Crystal Structures.

The peptide angiotensin-converting enzyme inhibitors captopril and lisinopril are unexpectedly shown to exhibit critical aggregation concentration (CAC) behavior through measurements of surface tension, electrical conductivity, and dye probe fluorescence. These three measurements provide similar values for the CAC, and there is also evidence from circular dichroism spectroscopy for a possible conformational change in the peptides at the same concentration. Cryogenic transmission electron microscopy indicates the formation of micelle-like aggregates above the CAC, which can thus be considered a critical micelle concentration, and the formation of aggregates with a hydrodynamic radius of ∼6-7 nm is also evidenced by dynamic light scattering. We also used synchrotron radiation X-ray diffraction to determine the single-crystal structure of captopril and lisinopril. Our results improve the accuracy of previous data reported in the literature, obtained using conventional X-ray sources. We also studied the structure of aqueous solutions containing captopril or lisinopril at high concentrations. The aggregation may be driven by intermolecular interactions between the proline moiety of captopril molecules or between the phenylalanine moiety of lisinopril molecules.

One Guest or Two? A Crystallographic and Solution Study of Guest Binding in a Cubic Coordination Cage.

A crystallographic investigation of a series of host-guest complexes in which small-molecule organic guests occupy the central cavity of an approximately cubic M8 L12 coordination cage has revealed some unexpected behaviour. Whilst some guests form 1:1 H⋅G complexes as we have seen before, an extensive family of bicyclic guests-including some substituted coumarins and various saturated analogues-form 1:2 H⋅G2 complexes in the solid state, despite the fact that solution titrations are consistent with 1:1 complex formation, and the combined volume of the pair of guests significantly exceeds the Rebek 55±9 % packing for optimal guest binding, with packing coefficients of up to 87 %. Re-examination of solution titration data for guest binding in two cases showed that, although conventional fluorescence titrations are consistent with 1:1 binding model, alternative forms of analysis-Job plot and an NMR titration-at higher concentrations do provide evidence for 1:2 H⋅G2 complex formation. The observation of guests binding in pairs in some cases opens new possibilities for altered reactivity of bound guests, and also highlights the recently articulated difficulties associated with determining stoichiometry of supramolecular complexes in solution.

One Guest or Two? A Crystallographic and Solution Study of Guest Binding in a Cubic Coordination Cage.

Invited for the cover of this issue is the group of Michael D. Ward at the University of Warwick. The image depicts structures of the host cage containing one guest or two guests. Read the full text of the article at 10.1002/chem.201905499.

Single-Crystal-to-Single-Crystal Postsynthetic Modification of a Metal-Organic Framework via Ozonolysis.

We describe solid-gas phase, single-crystal-to-single-crystal, postsynthetic modifications of a metal-organic framework (MOF). Using ozone, we quantitatively transformed the olefin groups of a UiO-66-type MOF into 1,2,4-trioxolane rings, which we then selectively converted into either aldehydes or carboxylic acids.

A novel bismuth-based metal-organic framework for high volumetric methane and carbon dioxide adsorption.

Solvothermal reaction of H4L (L = biphenyl-3,3',5,5'-tetracarboxylate) and Bi(NO3)3⋅(H2O)5 in a mixture of DMF/MeCN/H2O in the presence of piperazine and nitric acid at 100 °C for 10 h affords the solvated metal-organic polymer [Bi2(L)1.5(H2O)2]⋅(DMF)3.5⋅(H2O)3 (NOTT-220-solv). A single crystal X-ray structure determination confirms that it crystallises in space group P2/c and has a neutral and non-interpenetrated structure comprising binuclear {Bi2} centres bridged by tetracarboxylate ligands. NOTT-220-solv shows a 3,6-connected network having a framework topology with a {4⋅6(2)}2{4(2)⋅6(5)⋅8(8)}{6(2)⋅8} point symbol. The desolvated material NOTT-220a shows exceptionally high adsorption uptakes for CH4 and CO2 on a volumetric basis at moderate pressures and temperatures with a CO2 uptake of 553 g L(-1) (20 bar, 293 K) with a saturation uptake of 688 g L(-1) (1 bar, 195 K). The corresponding CH4 uptake was measured as 165 V(STP)/V (20 bar, 293 K) and 189 V(STP/V) (35 bar, 293 K) with a maximum CH4 uptake for NOTT-220a recorded at 20 bar and 195 K to be 287 V(STP)/V, while H2 uptake of NOTT-220a at 20 bar, 77 K is 42 g L(-1). These gas uptakes have been modelled by grand canonical Monte Carlo (GCMC) and density functional theory (DFT) calculations, which confirm the experimental data and give insights into the nature of the binding sites of CH4 and CO2 in this porous hybrid material.

A Frustrated Antipolar Phase Analogous to Classical Spin Liquids.

The study of magnetic frustration in classical spin systems is motivated by the prediction and discovery of classical spin liquid states. These uncommon magnetic phases are characterized by a massive degeneracy of their ground state implying a finite magnetic entropy at zero temperature. While the classical spin liquid state is originally predicted in the Ising triangular lattice antiferromagnet in 1950, this state has never been experimentally observed in any triangular magnets. The discovery of an electric analogue of classical spin liquids on a triangular lattice of uniaxial electric dipoles in EuAl12O19 is reported here. This new type of frustrated antipolar phase is characterized by a highly-degenerate state at low temperature implying an absence of long-range antiferroelectric order, despite short-range antipolar correlations. Its dynamics are governed by a thermally activated process, slowing down upon cooling toward a complete freezing at zero temperature.

DetOx: a program for determining anomalous scattering factors of mixed-oxidation-state species.

Overlapping absorption edges will occur when an element is present in multiple oxidation states within a material. DetOx is a program for partitioning overlapping X-ray absorption spectra into contributions from individual atomic species and computing the dependence of the anomalous scattering factors on X-ray energy. It is demonstrated how these results can be used in combination with X-ray diffraction data to determine the oxidation state of ions at specific sites in a mixed-valance material, GaCl(2).

I19, the small-molecule single-crystal diffraction beamline at Diamond Light Source.

The dedicated small-molecule single-crystal X-ray diffraction beamline (I19) at Diamond Light Source has been operational and supporting users for over three years. I19 is a high-flux tunable-wavelength beamline and its key details are described in this article. Much of the work performed on the beamline involves structure determination from small and weakly diffracting crystals. Other experiments that have been supported to date include structural studies at high pressure, studies of metastable species, variable-temperature crystallography, studies involving gas exchange in porous materials and structural characterizations that require analysis of the diffuse scattering between Bragg reflections. A range of sample environments to facilitate crystallographic studies under non-ambient conditions are available as well as a number of options for automation. An indication of the scope of the science carried out on the beamline is provided by the range of highlights selected for this paper.

Coordination polymers utilizing N-oxide functionalized host ligands.

Pyridyl functionalized host molecules are oxidized to their N-oxide analogues and form a series of coordination polymers and discrete complexes with transition metal cations. Complex {[Ag(3)(NMP)(6)(L1)(2)]·3(ClO(4))}(∞) where L1 = tris(isonicotinoyl-N-oxide)cyclotriguaiacylene, NMP = N-methylpyrrolidone, is a three-dimensional (3-D) 3,6-connected coordination polymer of pyrite-like (pyr) topology and features ligand unsupported argentophilic interactions, while two-dimensional (2-D) 3,6-connected coordination polymers with the rarely reported kagome dual (kgd) topology are found for [M(L1)(2)](2+) where M = Zn, Cd, Cu. Ligand L2 = tris(nicotinoyl-N-oxide)cyclotriguaiacylene forms a 2-D coordination polymer with 4(4) (sql) grid topology in complexes {[M(L2)(2)(DMF)(2)]·2ClO(4)·8(DMF)}(∞) M = Cd or Cu, DMF = N,N'-dimethylformamide, and a double-linked chain structure in {[Co(L2)(2)(DMF)(2)]·2NO(3)·4(DMF)·H(2)O}(∞), and both types of structure feature hand-shake self-inclusion motifs either within or between the polymers. 2-D coordination networks with 6(3) (hcb) topologies are found in complexes {[M(L3)(NO(3))(2)]·2(DMF)}(∞) (M = Cd, Zn) and {[Cu(5)(L3)(2)Cl(10)(NMP)(4)]}(∞) where L3 = tris(2-pyridylmethyl)cyclotriguaiacylene, while [Ag(2)(L3)(2)(NMP)(4)]·2(BF(4))·2(NMP) has a discrete dimeric structure which again shows hand-shake host-guest interactions supported by π-π stacking.

Modifying cage structures in metal-organic polyhedral frameworks for H2 storage.

Three isostructural metal-organic polyhedral cage based frameworks (denoted NOTT-113, NOTT-114 and NOTT-115) with (3,24)-connected topology have been synthesised by combining hexacarboxylate isophthalate linkers with {Cu(2)(RCOO)(4)} paddlewheels. All three frameworks have the same cuboctahedral cage structure constructed from 24 isophthalates from the ligands and 12 {Cu(2)(RCOO)(4)} paddlewheel moieties. The frameworks differ only in the functionality of the central core of the hexacarboxylate ligands with trimethylphenyl, phenylamine and triphenylamine moieties in NOTT-113, NOTT-114 and NOTT-115, respectively. Exchange of pore solvent with acetone followed by heating affords the corresponding desolvated framework materials, which show high BET surface areas of 2970, 3424 and 3394 m(2) g(-1) for NOTT-113, NOTT-114 and NOTT-115, respectively. Desolvated NOTT-113 and NOTT-114 show high total H(2) adsorption capacities of 6.7 and 6.8 wt%, respectively, at 77 K and 60 bar. Desolvated NOTT-115 has a significantly higher total H(2) uptake of 7.5 wt% under the same conditions. Analysis of the heats of adsorption (Q(st)) for H(2) reveals that with a triphenylamine moiety in the cage wall, desolvated NOTT-115 shows the highest value of Q(st) for these three materials, indicating that functionalisation of the cage walls with more aromatic rings can enhance the H(2)/framework interactions. In contrast, measurement of Q(st) reveals that the amine-substituted trisalkynylbenzene core used in NOTT-114 gives a notably lower H(2)/framework binding energy.

An electric field cell for performing in situ single-crystal synchrotron X-ray diffraction.

With the recent increase in research into ferroelectric, anti-ferroelectric and piezoelectric materials, studying the solid-state properties in situ under applied electric fields is vital in understanding the underlying processes. Where this behaviour is the result of atomic displacements, crystallographic insight has an important role. This work presents a sample environment designed to apply an electric field to single-crystal samples in situ on the small-molecule single-crystal diffraction beamline I19, Diamond Light Source (UK). The configuration and operation of the cell is described as well as its application to studies of a proton-transfer colour-change material.

Metal-organic polyhedral frameworks: high h(2) adsorption capacities and neutron powder diffraction studies.

Neutron powder diffraction experiments on D(2)-loaded NOTT-112 reveal that the axial sites of exposed Cu(II) ions in the smallest cuboctahedral cages are the first, strongest binding sites for D(2) leading to an overall discrimination between the two types of exposed Cu(II) sites at the paddlewheel nodes. Thus, the Cu(II) centers within the cuboctahedral cage are the first sites of D(2) binding with a Cu-D(2) distance of 2.23(1) A.

Structures and H2 adsorption properties of porous scandium metal-organic frameworks.

Two new three-dimensional Sc(III) metal-organic frameworks {[Sc(3)O(L(1))(3)(H(2)O)(3)]·Cl(0.5)(OH)(0.5)(DMF)(4)(H(2)O)(3)}(∞) (1) (H(2)L(1)=1,4-benzene-dicarboxylic acid) and {[Sc(3)O(L(2))(2)(H(2)O)(3)](OH)(H(2)O)(5)(DMF)}(∞) (2) (H(3)L(2)=1,3,5-tris(4-carboxyphenyl)benzene) have been synthesised and characterised. The structures of both 1 and 2 incorporate the trinuclear trigonal planar [Sc(3)(O)(O(2)CR)(6)] building block featuring three Sc(III) centres joined by a central µ(3)-O(2-) donor. Each Sc(III) centre is further bound by four oxygen donors from four different bridging carboxylate anions, and a molecule of water located trans to the µ(3)-O(2-) donor completes the six coordination at the metal centre. Frameworks 1 and 2 show high thermal stability with retention of crystallinity up to 350 °C. The desolvated materials 1a and 2a, in which the solvent has been removed from the pores but with water or hydroxide remaining coordinated to Sc(III), show BET surface areas based upon N(2) uptake of 634 and 1233 m(2) g(-1), respectively, and pore volumes calculated from the maximum N(2) adsorption of 0.25 cm(3) g(-1) and 0.62 cm(3) g(-1), respectively. At 20 bar and 78 K, the H(2) isotherms for desolvated 1a and 2a confirm 2.48 and 1.99 wt% total H(2) uptake, respectively. The isosteric heats of adsorption were estimated to be 5.25 and 2.59 kJ mol(-1) at zero surface coverage for 1a and 2a, respectively. Treatment of 2 with acetone followed by thermal desolvation in vacuo generated free metal coordination sites in a new material 2b. Framework 2b shows an enhanced BET surface area of 1511 m(2) g(-1) and a pore volume of 0.76 cm(3) g(-1), with improved H(2) uptake capacity and a higher heat of H(2) adsorption. At 20 bar, H(2) capacity increases from 1.99 wt% in 2a to 2.64 wt% for 2b, and the H(2) adsorption enthalpy rises markedly from 2.59 to 6.90 kJ mol(-1).

Facilities for small-molecule crystallography at synchrotron sources.

Although macromolecular crystallography is a widely supported technique at synchrotron radiation facilities throughout the world, there are, in comparison, only very few beamlines dedicated to small-molecule crystallography. This limited provision is despite the increasing demand for beamtime from the chemical crystallography community and the ever greater overlap between systems that can be classed as either small macromolecules or large small molecules. In this article, a very brief overview of beamlines that support small-molecule single-crystal diffraction techniques will be given along with a more detailed description of beamline I19, a dedicated facility for small-molecule crystallography at Diamond Light Source.

Structural isomerism in CuSCN coordination polymers.

CuSCN reacts with the angular ligand 2,4-bis(4-pyridyl)-1,3,5-triazine (dpt) to afford rare examples of coordination polymer structural isomers including a non-centrosymmetric three-dimensional framework with Cd(SO4) topology constructed from tetrahedral metal cations.

Femtolitre chemistry assisted by microfluidic pen lithography.

Chemical reactions at ultrasmall volumes are becoming increasingly necessary to study biological processes, to synthesize homogenous nanostructures and to perform high-throughput assays and combinatorial screening. Here we show that a femtolitre reaction can be realized on a surface by handling and mixing femtolitre volumes of reagents using a microfluidic stylus. This method, named microfluidic pen lithography, allows mixing reagents in isolated femtolitre droplets that can be used as reactors to conduct independent reactions and crystallization processes. This strategy overcomes the high-throughput limitations of vesicles and micelles and obviates the usually costly step of fabricating microdevices and wells. We anticipate that this process enables performing distinct reactions (acid-base, enzymatic recognition and metal-organic framework synthesis), creating multiplexed nanoscale metal-organic framework arrays, and screening combinatorial reactions to evaluate the crystallization of novel peptide-based materials.

A mesoporous metal-organic framework constructed from a nanosized C3-symmetric linker and [Cu24(isophthalate)24] cuboctahedra.

The mesoporous framework [Cu(3)(L)(H(2)O)(3)]·(DMF)(35)·(H(2)O)(35) (NOTT-119) shows on desolvation a BET surface area of 4118(200) m(2) g(-1), a pore volume of 2.35 cm(3) g(-1), a total H(2) uptake of 101 mg g(-1) at 60 bar, 77 K and a total CH(4) uptake of 327 mg g(-1) at 80 bar, 298 K.

Aerosol assisted chemical vapor deposition of In2O3 films from Me3In and donor functionalized alcohols.

The reaction of Me3In and ROH (R = CH2CH2NMe2, CH(CH3)CH2NMe2, C(CH3)2CH2OMe, CH2CH2OMe) in toluene under aerosol assisted chemical vapor deposition (AACVD) conditions leads to the production of indium oxide thin films on glass. The indium oxide films were deposited at 550 degrees C and analyzed by scanning electron microscopy (SEM), X-ray powder diffraction, wavelength dispersive analysis of X-rays (WDX), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. This CVD technique offers a rapid, convenient route to In2O3, which presumably involves the in situ formation of dimethylindium alkoxides, of the type [Me2InOR]2. In order to identify compounds present in the aerosol mist, the solution-phase reaction between Me3In and ROH (R = CH2CH2NMe2, C(CH3)2CH2OMe, CH(CH3)CH2NMe2, CH(CH2NMe2)2) at room temperature in toluene was carried out. Dimeric indium alkoxides, of the type [Me2In(OR)]2, were isolated, and their structures were determined by X-ray crystallography.

5-Fluorouracil and thymine form a crystalline solid solution.

The crystal structure of a 5-fluorouracil-thymine [5-fluoropyrimidine-2,4(1H,3H)-dione-5-methylpyrimidine-2,4(1H,3H)-dione, C(4)H(3)FN(2)O(2)xC(5)H(6)N(2)O(2)] solid solution has been determined. Both of the crystallographically independent sites can accommodate either 5-fluorouracil or thymine molecules, leading to occupational disorder [C(5-x)H(6-3x)F(x)N(2)O(2)xC(5-y)H(6-3x)F(y)N(2)O(2), with x = 0.52 and y = 0.7 for determination (I), x = 0.55 and y = 0.69 for (II), and x = 0.67 and y = 0.76 for (III)]. The 5-fluorouracil-thymine ratio in the crystal structure is influenced by the 5-fluorouracil-thymine ratio in the crystallization solution, though it does not exactly mirror it. The crystal structure comprises interpenetrating hydrogen-bonded nets, containing four independent hydrogen bonds.