Simon J. Teat

Hybrid organic–inorganic rotaxanes and molecular shuttles

The tetravalency of carbon and its ability to form covalent bonds with itself and other elements enables large organic molecules with complex structures, functions and dynamics to be constructed. The varied electronic configurations and bonding patterns of inorganic elements, on the other hand, can impart diverse electronic, magnetic, catalytic and other useful properties to molecular-level structures. Some hybrid organic–inorganic materials that combine features of both chemistries have been developed, most notably metal–organic frameworks, dense and extended organic–inorganic frameworks and coordination polymers. Metal ions have also been incorporated into molecules that contain interlocked subunits, such as rotaxanes and catenanes, and structures in which many inorganic clusters encircle polymer chains have been described. Here we report the synthesis of a series of discrete rotaxane molecules in which inorganic and organic structural units are linked together mechanically at the molecular level. Structural units (dialkyammonium groups) in dumb-bell-shaped organic molecules template the assembly of essentially inorganic ‘rings’ about ‘axles’ to form rotaxanes consisting of various numbers of rings and axles. One of the rotaxanes behaves as a ‘molecular shuttle’: the ring moves between two binding sites on the axle in a large-amplitude motion typical of some synthetic molecular machine systems. The architecture of the rotaxanes ensures that the electronic, magnetic and paramagnetic characteristics of the inorganic rings—properties that could make them suitable as qubits for quantum computers—can influence, and potentially be influenced by, the organic portion of the molecule.

Comprehensive study of carbon dioxide adsorption in the metal–organic frameworks M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn)

Analysis of the CO2 adsorption properties of a well-known series of metal–organic frameworks M2(dobdc) (dobdc4− = 2,5-dioxido-1,4-benzenedicarboxylate; M = Mg, Mn, Fe, Co, Ni, Cu, and Zn) is carried out in tandem with in situ structural studies to identify the host–guest interactions that lead to significant differences in isosteric heats of CO2 adsorption. Neutron and X-ray powder diffraction and single crystal X-ray diffraction experiments are used to unveil the site-specific binding properties of CO2 within many of these materials while systematically varying both the amount of CO2 and the temperature. Unlike previous studies, we show that CO2 adsorbed at the metal cations exhibits intramolecular angles with minimal deviations from 180°, a finding that indicates a strongly electrostatic and physisorptive interaction with the framework surface and sheds more light on the ongoing discussion regarding whether CO2 adsorbs in a linear or nonlinear geometry. This has important implications for proposals that have been made to utilize these materials for the activation and chemical conversion of CO2. For the weaker CO2 adsorbents, significant elongation of the metal–O(CO2) distances are observed and diffraction experiments additionally reveal that secondary CO2 adsorption sites, while likely stabilized by the population of the primary adsorption sites, significantly contribute to adsorption behavior at ambient temperature. Density functional theory calculations including van der Waals dispersion quantitatively corroborate and rationalize observations regarding intramolecular CO2 angles and trends in relative geometric properties and heats of adsorption in the M2(dobdc)–CO2 adducts.

Effective Detection of Mycotoxins by a Highly Luminescent Metal-Organic Framework.

We designed and synthesized a new luminescent metal-organic framework (LMOF). LMOF-241 is highly porous and emits strong blue light with high efficiency. We demonstrate for the first time that very fast and extremely sensitive optical detection can be achieved, making use of the fluorescence quenching of an LMOF material. The compound is responsive to Aflatoxin B1 at parts per billion level, which makes it the best performing luminescence-based chemical sensor to date. We studied the electronic properties of LMOF-241 and selected mycotoxins, as well as the extent of mycotoxin-LMOF interactions, employing theoretical methods. Possible electron and energy transfer mechanisms are discussed.

A new high-flux chemical and materials crystallography station at the SRS Daresbury. 1. Design, construction and test results

The scattering efficiencies of four test samples given in Table 1 of the original report [Cernik et al. (1997). J. Synchrotron Rad. 4, 279–286] were calculated incorrectly. Corrected values are provided; these are two to three orders of magnitude lower.

Solution Processable MOF Yellow Phosphor with Exceptionally High Quantum Efficiency

An important aspect in the research and development of white light-emitting diodes (WLEDs) is the discovery of highly efficient phosphors free of rare-earth (RE) elements. Herein we report the design and synthesis of a new type of RE-free, blue-excitable yellow phosphor, obtained by combining a strongly emissive molecular fluorophore with a bandgap modulating co-ligand, in a three-dimensional metal organic framework. [Zn6(btc)4(tppe)2(DMA)2] (btc = benzene-1,3,5-tricarboxylate, tppe = 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene, DMA = dimethylacetamide) crystallizes in a new structure type and emits bright yellow light when excited by a blue light source. It possesses the highest internal quantum yield among all RE-free, blue-excitable yellow phosphors reported to date, with a value as high as 90.7% (λex = 400 nm). In addition to its high internal quantum yield, the new yellow phosphor also demonstrates high external quantum yield, luminescent and moisture stability, solution processability, and color tunability, making it a promising material for use in phosphor conversion WLEDs.

Sequestering uranium from seawater: binding strength and modes of uranyl complexes with glutarimidedioxime

Glutarimidedioxime (H(2)A), a cyclic imide dioxime ligand that has implications in sequestering uranium from seawater, forms strong tridentate complexes with UO(2)(2+). The stability constants and the enthalpies of complexation for five U(VI) complexes were measured by potentiometry and microcalorimetry. The crystal structure of the 1 : 2 metal-ligand complex, UO(2)(HA)(2)·H(2)O, was determined. The re-arrangement of the protons of the oxime groups (-CH=N-OH) and the deprotonation of the imide group (-CH-NH-CH-) results in a conjugated system with delocalized electron density on the ligand (-O-N-C-N-C-N-O-) that coordinates to UO(2)(2+)via its equatorial plane.

Calix[4]arene-based single-molecule magnets

Calix[4]arene Based Single-Molecule Magnets** Georgios Karotsis, Simon J. Teat, Wolfgang Wernsdorfer, Stergios Piligkos, Scott J. Dalgarno* and Euan K. Brechin* Mr. G. Karotsis, Dr. E. K. Brechin, School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK. Fax: (+44)-131-650-6453 E-mail: ebrechin@staffmail.ed.ac.uk Dr. S. J. Dalgarno, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS. Fax: (+44)-131-451-3180 E-mail: S.J.Dalgarno@hw.ac.uk Prof. Dr. W. Wernsdorfer, Institut Neel, CNRS, Grenoble Cedex 9, France. Dr. S. Piligkos, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100, Denmark. Dr. S. J. Teat, Advanced Light Source, Berkeley Laboratory, 1 Cyclotron Road, MS6R2100, Berkeley, CA 94720, USA. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. Single-molecule magnets (SMMs) [1] have been the subject of much interest in recent years because their molecular nature and inherent physical properties allow the crossover between classical and quantum physics to be observed. [2] The macroscopic observation of quantum phenomena - tunneling between different spin states, [3] quantum interference between tunnel paths [4] - not only allows scientists to study quantum mechanical laws in great detail, but also provides model systems with which to investigate the possible implementation of spin- based solid state qubits [5] and molecular spintronics. [6] The isolation of small, simple SMMs is therefore an exciting prospect. To date almost all SMMs have been made via the self-assembly of 3d metal ions in the presence of bridging/chelating organic ligands. [7] However, very recently an exciting new class of SMMs, based on 3d metal clusters (or single lanthanide ions) housed within polyoxometalates, [8] has appeared. These types of molecule, in which the SMM is completely encapsulated within (or shrouded by) a “protective” organic or inorganic sheath have much potential for design and manipulation: for example, for the removal of unwanted dipolar interactions, the introduction of redox activity, or to simply aid functionalisation for surface grafting. [9] Calix[4]arenes are cyclic (typically bowl-shaped) polyphenols that have been used extensively in the formation of versatile self-assembled supramolecular structures. [10] Although many have been reported, p- t But-calix[4]arene and calix[4]arene (TBC4 and C4 respectively, Figure 1A) are frequently encountered due to a) synthetic accessibility, and b) vast potential for alteration at either the upper or lower rim of the macrocyclic framework. [11] Within the field of supramolecular chemistry, TBC4 is well known for interesting polymorphic behavior and phase transformations within anti-parallel bi-layer arrays, while C4 often forms self-included trimers. [12] The polyphenolic nature of calix[n]arenes (where n = 4 – 8) also suggests they should be excellent candidates as ligands for the isolation of molecular magnets, but to date their use in the isolation of paramagnetic cluster compounds is rather limited. [13] Herein we present the first Mn cluster and the first SMM to be isolated using any methylene bridged calix[n]arene - a ferromagnetically coupled mixed-valence [Mn III2 Mn II2 ] complex housed between either two TBC4s or two C4s. Reaction of MnBr 2 with TBC4 and NEt 3 in a solvent mixture of MeOH/DMF results in the formation of the complex [Mn III2 Mn II2 (OH) 2 (TBC4) 2 (DMF) 6 ] (1) which crystallises as purple blocks that are in the monoclinic space group P2 1 /c. The cluster (Figure 1B) comprises a planar diamond or butterfly-like [Mn III2 Mn II2 (OH) 2 ] core in which the wing tip Mn ions (Mn1) are in the 3+ oxidation state and the body Mn ions (Mn2) in the 2+ oxidation state. This is a common structural type in Mn SMM chemistry, [14] but the oxidation state distribution here is highly unusual, being “reversed” from the norm in which the body Mn ions are almost always 3+. Indeed the “reversed” core has been seen only once before, in the cluster [Mn III2 Mn II2 (teaH) 2 (acac) 4 (MeOH) 2 ] 2+ (2) (teaH 3 = triethanolamine) and its analogues. [15] The Mn 3+ ions are in distorted octahedral geometries with the Jahn-Teller axes defined by O5(DMF)-Mn1-O6(OH). The four equatorial sites are occupied by the oxygen atoms (O1-O4) of the TBC4, two of which bridge in a µ 2 -fashion to the central Mn 2+ ions (Mn1-O4-Mn2, 103.5°; Mn1-O1-Mn2, 105.4°). These are connected to each other (Mn2-O6-Mn2’, 94.7°) and to the Mn 3+ ions (Mn1-O6-Mn2, 100.4°; Mn1- O6-Mn2’, 98.8°) via two µ 3 -bridging OH - ions, with the two remaining equatorial sites (completing the distorted octahedral geometry on Mn2) filled by terminal DMF molecules. There are no inter-molecular H-bonds between symmetry equivalents of 1, with the closest

Impact of Regiochemistry and Isoelectronic Bridgehead Substitution on the Molecular Shape and Bulk Organization of Narrow Bandgap Chromophores

A comparison of two classes of small molecules relevant to the field of organic electronics is carried out at the molecular and supramolecular levels. First, two molecules that differ only in the position of a pyridyl N-atom within an acceptor fragment are compared and contrasted. X-ray investigation of single crystals reveals that positioning the pyridyl N-atoms proximal to the molecules center changes the molecular shape by bending the molecule into a banana shape. Second, we demonstrate that the banana shape of the molecule can be controlled by replacing a Si atom within the dithienosilole fragment with a C or Ge atom. Here, utilization of cyclopentadithiophene or dithienogermole as the internal electron-rich unit leads to a decrease or an increase in the bending of the conjugated backbone, respectively. Such molecular shape changes alter intermolecular packing and thus affect bulk properties, leading to large differences in the optical, thermal, and crystallization properties.

Effects of diphosphine structure on aurophilicity and luminescence in Au(I) complexes

The effects of diphosphine flexibility and bite angle on the structures and luminescence properties of Au(I) complexes have been investigated. A range of diphosphines based on heteroaromatic backbones [bis(2-diphenylphosphino)phenylether (dpephos), 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (xantphos), and 4,6-bis(diphenylphosphino)dibenzofuran (dbfphos)] has been used to prepare mono- and digold derivatives. A clear relationship between the presence of aurophilic contacts and the emission properties of dinuclear complexes has been observed, with one of the complexes studied, [Au(2)Cl(2)(micro-xantphos)], exhibiting luminescence thermochromism.

Alternative Donor−Acceptor Stacks from Crown Ethers and Naphthalene Diimide Derivatives: Rapid, Selective Formation from Solution and Solid State Grinding

The atypical 1:2 complexation between an electron-rich crown ether host and electron-deficient naphthalene diimide-based guests led to the formation of alternative donor-acceptor (ADA) stacks. The ADA stacks can be expediently obtained in high yield as polycrystalline aggregates from solution. More remarkably, the high degree of organization has also been realized in a simple solid-to-solid mechanical grinding process. The solid-state structures have been verified by solid-state NMR spectroscopy, single crystal, and powder X-ray diffraction analysis. The current findings not only provide convenient ways of obtaining novel donor-acceptor stacks involving a macrocyclic host but also represent an important step in transferring electroactive host-guest systems from solution to the solid state.