Kirsten E. Christensen

Enhancement of anion recognition exhibited by a halogen-bonding rotaxane host system

We report the first use of solution-phase halogen bonding to control and facilitate the assembly of an interlocked structure through the bromide anion-templated formation of a rotaxane based upon an iodotriazolium axle. The incorporation of a halogen atom into the rotaxane host cavity dramatically improves the anion-recognition capabilities of the interlocked receptor, giving unusual iodide selectivity in a competitive aqueous medium.

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.

A Germanate Built from a 68126 Cavity Cotemplated by an (H2O)16 Cluster and 2‐Methylpiperazine

Totally tubular: A new tubular germanate is cotemplated by 2-methylpiperazine and an (H2O)16 cluster in a hydro(solvo)thermal synthesis. The germanate features a large, highly symmetric 68126 cavity (see picture; yellow sphere) built from 12 Ge7X19 (X=O, OH, F) clusters (GeX6 red, GeX5 yellow, GeX4 green).

An Open-Framework Silicogermanate with 26-Ring Channels Built from Seven-Coordinated (Ge,Si)10(O,OH)28 Clusters

We report a new open-framework silicogermanate SU-61 containing 26-ring channels with a low framework density. It can be seen as a crystalline analogue to the mesoporous silica MCM-41. The structure is built from the assembly of (Ge,Si)10(O,OH)28 clusters. It is the first time that silicon has been successfully introduced in the Ge10 cluster in significant amounts ( approximately 21% of the tetrahedral sites). Five- and six-coordinated Ge10 clusters have previously been observed in other germanate compounds leading to either dense or open structures. In SU-61, the seven-coordinated clusters fall onto yet another underlying net, the osf net. SU-61, along with other Ge10 based frameworks, shows the versatility of the germanate system to adopt defined topologies playing on the connectivity of the clusters following the principles of net decoration and scale chemistry.

Chalcogen Bonding Macrocycles and [2]Rotaxanes for Anion Recognition

Electron-deficient heavy chalcogen atoms contain Lewis acidic σ-holes which are able to form attractive supramolecular interactions, known as chalcogen bonding (ChB), with Lewis bases. However, their potential in solution-phase anion binding applications is only just beginning to be realized in simple acyclic systems. Herein, we explore the 5-(methylchalcogeno)-1,2,3-triazole (chalcogen = Se, Te) motif as a novel ChB donor for anion binding. Other than being chemically robust enough to be incorporated into macrocyclic structures, thereby significantly expanding the scope and complexity of ChB host systems, we also demonstrate, by 1H NMR and DFT calculations, that the chalcogen atoms oriented within the macrocycle cavity are able to chelate copper(I) endotopically. Exploiting this property, the first examples of mechanically interlocked [2]rotaxanes containing ChB-donor groups are prepared via an active metal template strategy. Solution-phase 1H NMR and molecular modeling studies provide compelling evidence for the dominant influence of ChB in anion binding by these interlocked host systems. In addition, unprecedented charge-assisted ChB-mediated anion binding was also studied in aqueous solvent mixtures, which revealed considerable differences in anion recognition behavior in comparison with chalcogen-free host analogues. Moreover, DFT calculations and molecular dynamics simulations in aqueous solvent mixtures indicate that the selectivity is determined by the different hydrophilic characters of the anions allied to the hydration of the binding units in the presence of the anions. Exploiting the NMR-active nuclei of the ChB-donor chalcogen atoms, heteronuclear 77Se and 125Te NMR were used to directly study how anion recognition influences the local electronic environment of the chalcogen atoms in the mechanically bonded rotaxane binding sites in organic and aqueous solvent mixtures.

Investigation of the GeO2-1,6-Diaminohexane-Water-Pyridine-HF Phase Diagram Leading to the Discovery of Two Novel Layered Germanates with Extra-Large Rings

The systematic exploration of the phase diagram of the GeO(2)-1,6-diaminohexane-water-pyridine-HF system has allowed the identification of specific roles of the HF, H(2)O contents, and HF/H(2)O ratio in the formation of Ge(7)X(19) (Ge(7)), Ge(9)X(25-26) (Ge(9)), and Ge(10)X(28) (Ge(10)) clusters (X = O, OH, F). This work has led to the discovery of two novel structures with extra-large 18-membered rings accommodating 1,6-diaminohexane (DAH): SU-63, |1.5H(2)DAH|[Ge(7)O(14)X(3)]·2H(2)O, a layered germanate constructed from Ge(7) clusters with the Kagomé topology, and SU-64, |11H(2)DAH|[Ge(9)O(18)X(4)][Ge(7)O(14)X(3)](6)·16H(2)O, a germanate built of two-dimensional slabs containing both Ge(7) and Ge(9) clusters (X = OH or F). We also put SU-64 in context with previously reported cluster germanate compounds with related topologies by means of a simple crystal deconstruction study.

Hydrogen Borrowing Catalysis with Secondary Alcohols: A New Route for the Generation of β-Branched Carbonyl Compounds

A hydrogen borrowing reaction employing secondary alcohols and Ph* (Me5C6) ketones to give β-branched carbonyl products is described (21 examples). This new C-C bond forming process requires low loadings of [Cp*IrCl2]2, relatively low temperatures, and up to 2.0 equiv of the secondary alcohol. Substrate-induced diastereoselectivity was observed, and this represents the first example of a diastereoselective enolate hydrogen borrowing alkylation. By utilizing the Ph* group, the β-branched products could be straightforwardly cleaved to the corresponding esters or amides using a retro-Friedel-Crafts reaction. Finally, this protocol was applied to the synthesis of fragrance compound (±)-3-methyl-5-phenylpentanol.

Two Open-Framework Germanates with Nickel Complexes Incorporated into the Framework

Two open-framework germanates, SUT-1 and SUT-2, have been synthesized under hydrothermal conditions using ethylenediamine (en, H(2)NCH(2)CH(2)NH(2)) as templates and Ni(NO(3))(2)·6H(2)O as the transition-metal source. Their frameworks are built with Ge(10) clusters and [Ni(en)(2)](2+) complexes. In both structures, Ge(10) clusters form square nets in the a-c plane, while the [Ni(en)(2)](2+) complexes bridge the square nets via Ni-O-Ge bonds to form 3D networks. They present the first examples to incorporate Ni(2+) complexes into the germanate frameworks. In SUT-2, additional linkages by Ge(2)O(7) clusters between the square nets generate a new type of topology.

Copper(I) O , O ′-dialkyldithiophosphate clusters: EXAFS, NMR and X-ray diffraction studies

Copper K-edge EXAFS data for six polycrystalline cubic cluster compounds, {Cu8[S2P(OR)2]6(μ8-S)} with R = Et, n Pr, i Pr, n Bu, i Bu and i Am, show that the architecture of their Cu8(S2P)2S cores is fairly rigid and independent of both length and branching of the alkyl chain, and that the structure of the cluster is maintained in acetone solution. Solid-state 31P CP-MAS and static 65Cu NMR data for {Cu8[S2P(O n Pr)2]6(μ8-S)} and {Cu8[S2P(OEt)2]6(μ8-S)} show similarities in the icosahedral O,O′-dialkyldithiophosphate shells and in the ‘cubic’ copper cores in these cluster compounds. The crystal structure of {Cu8[S2P(O n Pr)2]6(μ8-S)} was resolved using single-crystal X-ray diffraction.

Two novel Zn‐MOFs: structures and characterization

Two novel three-dimensional Zn-MOFs (zinc metal-organic frameworks), Zn(5)(μ(3)-OH)(BTC)(3)(Phen)(4)·5H(2)O (denoted as HUT-11) and Zn(4)(μ(4)-O)(BTC)(2)(Phen)(2)·4H(2)O (denoted as HUT-12), have been synthesized by metal-ligand-directed assembly under hydrothermal conditions. Here, BTC and Phen are denoted as 1,3,5-benzenetricarboxylate and phenanthroline. HUT-11 contains two kinds of secondary building units (SBUs), Zn(3)(μ(3)-OH)(COO)(5) clusters and Zn(2)(COO)(4) clusters. This material exhibits a new three-dimensional (3,4,5)-connected topology with the Schläfli symbol (4·6·8)(2)(4·8(2))(4·6(4)·8(5))(4(2)·6(2)·8(2)). Two perpendicular planes cross at five coordinated Zn1-Zn3-Zn5 nodes, giving a new three-dimensional network. HUT-12 is composed of Zn(4)(μ(4)-O)(COO)(6) clusters as the secondary building units and displays a two-dimensional (3,6)-connected TiS(2) related net topology with the Schläfli symbol (4(2)·6)(4(4)·6(2)·8(8)·10). Both MOFs show blue light emission and a high thermal stability above 673 K.