I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[2871]
Abstract: A series of “light metal” metal–organic frameworks containing secondary building units (SBUs) based on Li+ and Na+ cations have been prepared using the silicon-centered linkers MexSi(p-C6H4CO2H)4-x (x = 2, 1, 0). The unipositive charge, small size, and oxophilic nature of the metal cations give rise to some unusual and unique SBUs, including a three-dimensional nodal structure built from sodium and oxygen ions when using the triacid linker (x = 1). The same linker with Li+ cations generated a chiral, helical SBU, formed from achiral starting materials. One-dimensional rod SBUs are observed for the diacid (x = 2) and tetra-acid (x = 0) linkers with both Li+ and Na+ cations, where the larger size of Na+ compared to Li+ leads to subtle differences in the constitution of the metal nodes.
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Nov 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[17308]
Abstract: Solid/gas Single–Crystal to Single–Crystal (SC–SC) hydrogenation of appropriate diene precursors forms the corresponding σ–alkane complexes [Rh(Cy2P(CH2)nPCy2)(L)][BArF4] (n = 3, 4) and [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(L)][BArF4] (n = 5, L = norbornane, NBA; cyclooctane, COA). Their struc-tures, as determined by single–crystal X-ray diffraction, have cations exhibiting Rh···H–C σ–interactions which are modulated by both the chelating ligand and the identity of the alkane, while all sit in an octahedral anion–microenvironment. These range from chelating η2,η2 Rh···H–C (e.g. [Rh(Cy2P(CH2)nPCy2)(η2η2–NBA)][BArF4], n = 3 and 4), through to more weakly bound η1 Rh··H–C in which C–H activation of the chelate backbone has also occurred (e.g. [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(η1–COA)][BArF4]) and ultimately to systems where the alkane is not ligated with the metal center, but sits encapsulated in the supporting anion microenvironment – [Rh(Cy2P(CH2)3PCy2)][COA⊂BArF4] – in which the metal center instead forms two intramolecular agostic η1 Rh···H–C interactions with the phosphine cyclohexyl groups. CH2Cl2 adducts formed by displacement of the η1–alkanes in solution (n = 5; L = NBA, COA), [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(η1–ClCH2Cl)][BArF4], are characterized crystallographically. Analyses via periodic DFT, QTAIM, NBO and NCI calculations, alongside variable temperature solid–state NMR spectroscopy, provide snapshots marking the onset of Rh σ-alkane interactions along a C···H activation trajectory. These are negligible in [Rh(Cy2P(CH2)3PCy2)][COA⊂BArF4]; in [RhH(Cy2P(CH2)2(CH)(CH2)2PCy2)(η1–COA)][BArF4] σC–H→Rh σ-donation is supported by Rh→σ*C-H ‘pregostic’ donation; and in [Rh(Cy2P(CH2)nPCy2)(η2η2-NBA)][BArF4] (n = 2-4) σ-donation dominates, supported by classical Rh(dπ)→σ*C-H π-back donation. Dispersive interactions with the [BArF4]- anions and Cy substituents further stabilize the alkanes within the binding pocket.
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Oct 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6916]
Abstract: The syntheses, characterization and experimental solid state X-ray structures of five low-spin paramagnetic 2-pyridyl-(1,2,3)-triazole-copper compounds, [Cu(Ln)2Cl2], are presented in this study, for the following five Ln ligands: L2 = 2-(1-(p-tolyl)-1H-1,2,3-triazol-4-yl)pyridine), L6 = 2-(1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)pyridine), L7 = 4-(4-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)benzonitril), L8 = 2-(1-phenyl-1H-1,2,3-triazol-4-yl)pyridine) and L9 = 2-(1-(4-(trifluoromethyl)phenyl)-1H-1,2,3-triazol-4-yl)pyridine). These five [Cu(Ln)2Cl2] complexes each contain two bidentate 2-pyridyl-(1,2,3)-triazole (Ln) and two chloride ions as ligands, with the Cu-N(pyridine) bonds, Cu-N(triazole) and Cu-Cl bonds trans to each other. All five [Cu(Ln)2Cl2] compounds display elongation Jahn-Teller distortion, either along opposite Cu-N(triazole) bonds, or along opposite Cu-Cl bonds, as indicated by their obtained solid state crystal structures. Quantum chemistry calculations, using density functional theory, indicated however that elongation Jahn-Teller distortion is in fact possible along any two opposite bonds in these octahedral compounds with the elongation distortion along the opposite Cu-N(triazole) bonds being the most stable structure.
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Sep 2018
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I19-Small Molecule Single Crystal Diffraction
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Sergio
Sanz
,
Helen M.
O'Connor
,
Priyanka
Comar
,
Amgalanbaatar
Baldansuren
,
Mateusz B.
Pitak
,
Simon J.
Coles
,
Høgni
Weihe
,
Nicholas F.
Chilton
,
Eric J. L.
Mcinnes
,
Paul J.
Lusby
,
Stergios
Piligkos
,
Euan K.
Brechin
Diamond Proposal Number(s):
[11238]
Abstract: The reaction of the simple metalloligand [FeIIIL3] [HL = 1-(4-pyridyl)butane-1,3-dione] with a variety of different MII salts results in the formation of a family of heterometallic cages of formulae [FeIII8PdII6L24]Cl12 (1), [FeIII8CuII6L24(H2O)4Br4]Br8 (2), [FeIII8CuII6L24(H2O)10](NO3)12 (3), [FeIII8NiII6L24(SCN)11Cl] (4), and [FeIII8CoII6L24(SCN)10(H2O)2]Cl2 (5). The metallic skeleton of each cage describes a cube in which the FeIII ions occupy the eight vertices and the MII ions lie at the center of the six faces. Direct-current magnetic susceptibility and magnetization measurements on 3–5 reveal the presence of weak antiferromagnetic exchange between the metal ions in all three cases. Computational techniques known in theoretical nuclear physics as statistical spectroscopy, which exploit the moments of the Hamiltonian to calculate relevant thermodynamic properties, determine JFe–Cu = 0.10 cm–1 for 3 and JFe–Ni = 0.025 cm–1 for 4. Q-band electron paramagnetic resonance spectra of 1 reveal a significantly wider spectral width in comparison to [FeL3], indicating that the magnitude of the FeIII zero-field splitting is larger in the heterometallic cage than in the monomer.
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Jan 2018
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I19-Small Molecule Single Crystal Diffraction
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Mireille H.
Smets
,
Mateusz B.
Pitak
,
Joseph
Cadden
,
Vincent R.
Kip
,
Gilles A.
De Wijs
,
Ernst R. H.
Van Eck
,
Paul
Tinnemans
,
Hugo
Meekes
,
Elias
Vlieg
,
Simon J.
Coles
,
Herma M.
Cuppen
Diamond Proposal Number(s):
[6916]
Open Access
Abstract: The rich landscape of enantiotropically related polymorphic forms and their solid-state phase transitions of DL-2-aminoheptanoic acid (DL-AHE) has been explored using a range of complementary characterisation techniques, and is largely exemplary of the polymorphic behaviour of linear aliphatic amino acids. As many as five new polymorphic forms were found, connected by four fully reversible solid-state phase transitions. Two low temperature forms were refined in a high Z' crystal structure, which is a new phenomenon for linear aliphatic amino acids. All five structures consist of 2D hydrogen-bonded bilayers interconnected by weak Van der Waals interactions. The single-crystal-to-single-crystal phase transitions involve shifts of bilayers and/or conformational changes in the aliphatic chain. Compared to two similar phase transitions of the related amino acid DL-norleucine, the enthalpies of transition and NMR chemical shift differences are notably smaller in DL-aminoheptanoic acid. This is explained to be a result of both the nature of the conformational changes, and the increased chain length, weakening the interactions between the bilayers.
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Nov 2017
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I19-Small Molecule Single Crystal Diffraction
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Abstract: Electrocrystallisations of the chiral donor molecule S,S-bis(2-hydroxylpropylthio)ethylenedithiotetrathiafulvalene have produced a series of 1[thin space (1/6-em)]:[thin space (1/6-em)]1 semiconducting radical-cation salts with anions bromide, chloride, perchlorate and hexafluorophosphate. The flexibility and hydrogen bonding ability of the donor's chiral side chains lead to three quite different packing arrangements of donor cation pairs. Conductivity is maintained despite significant separations of donor cation pairs in some cases.
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Aug 2017
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Abstract: Classic (dynamic exchange line-shape analysis) and novel (SSTD NMR) NMR techniques have been applied in order to obtain the kinetic and thermodynamic parameters of the three main processes occurring in the fluxional behavior of Pt-allene complexes with N-containing ligands, in four and five coordination mode, in solution. Our results show intramolecular helical and rotational movements closely related to each other, confirming η1-staggered structures as possible intermediates. The ligand exchange in these complexes seems to occur via a ligand-independent dissociative mechanism, where coordinating solvents might be involved in the stabilization of the intermediates. The differences observed in the interaction of allenes with other metals could be the basis to explain the divergent reactivity observed in platinum-catalyzed processes.
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Dec 2016
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8521]
Abstract: A new methodology for the synthesis of pyridine derivatives based on a triple cascade reaction catalyzed by chiral secondary amines. The resulting cyclohexenes (3 C-C bond were formed) were obtained in good yields, good diastereoselectivities and excellent enantioselectivity
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Nov 2016
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I19-Small Molecule Single Crystal Diffraction
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Georgios
Charalambidis
,
Evangelos
Georgilis
,
Manas K.
Panda
,
Christopher E.
Anson
,
Annie K.
Powell
,
Stephen
Doyle
,
David
Moss
,
Tobias
Jochum
,
Peter N.
Horton
,
Simon J.
Coles
,
Mathieu
Linares
,
David
Beljonne
,
Jean-Valère
Naubron
,
Jonas
Conradt
,
Heinz
Kalt
,
Anna
Mitraki
,
Athanassios G.
Coutsolelos
,
Teodor Silviu
Balaban
Diamond Proposal Number(s):
[8521]
Open Access
Abstract: Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. Here we describe a simple and robust FLFL-dipeptide construct to which a meso-tetraphenylporphyrin has been appended and which self-assembles to fibrils, platelets or nanospheres depending on the solvent composition. The fibrils, functioning as quenched antennas, give intense excitonic couplets in the electronic circular dichroism spectra which are mirror imaged if the unnatural FDFD-analogue is used. By slightly increasing the solvent polarity, these light-harvesting fibres disassemble to spherical structures with silent electronic circular dichroism spectra but which fluoresce. Upon further dilution with the nonpolar solvent, the intense Cotton effects are recovered, thus proving a reversible switching. A single crystal X-ray structure shows a head-to-head arrangement of porphyrins that explains both their excitonic coupling and quenched fluorescence.
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Sep 2016
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I19-Small Molecule Single Crystal Diffraction
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Gary
Conboy
,
Howard J.
Spencer
,
Enrico
Angioni
,
Alexander L.
Kanibolotsky
,
Neil J.
Findlay
,
Simon
Coles
,
Claire
Wilson
,
Mateusz B.
Pitak
,
Chad
Risko
,
Veaceslav
Coropceanu
,
Jean-Luc
Brédas
,
Peter J.
Skabara
Diamond Proposal Number(s):
[8521]
Open Access
Abstract: We consider the roles of heteroatoms (mainly nitrogen, the halogens and the chalcogens) in dictating the conformation of linear conjugated molecules and polymers through non-covalent intramolecular interactions. Whilst hydrogen bonding is a competitive and sometimes more influential interaction, we provide unambiguous evidence that heteroatoms are able to determine the conformation of such materials with reasonable predictability.
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Apr 2016
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