I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: The synthetic utility of europium complexes with three coordinated 4-bromopyridyl groups for chromophore elaboration has been assessed in palladium-catalysed Sonogashira coupling reactions, and in copper(I) mediated click reactions of the triazide derivative, generated in situ.
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Feb 2014
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6749]
Open Access
Abstract: The reaction of trans-RuCl(C≡CC6H4R1-4)(dppe)2 (2: R1 = Me (a), C5H11 (b), OMe (c), CO2Me (d), NO2 (e), C≡CSiMe3 (f), C≡CBut (g), NH2 (h)), prepared in situ from reactions of [RuCl(dppe)2]OTf ([1]OTf) with terminal alkynes in CH2Cl2 solutions containing 1,8-diazabicycloundec-7-ene (DBU) and TlBF4, provides a convenient and rapid route to bis(acetylide) complexes trans-Ru(C≡CC6H4R1-4)2(dppe)2 (3ah) and trans-Ru(C≡CC6H4R1-4)(C≡CC6H4R2-4)(dppe)2 (4, R1 = C≡CSiMe3, R2 = NH2; 5, R1 = CO2Me, R2 = NH2; 6, R1 = CO2Me, R2 = OMe). However, even in the absence of the chloride abstracting reagent, more strongly electron donating substituents (e.g., R1 = OMe (2c), NH2 (2h)) promote sufficient ionization of the RuCl bond in trans-RuCl(C≡CC6H4R1-4)(dppe)2 to lead to slow conversion to bis(alkynyl) complexes 3c,h in the presence of excess alkyne and DBU. Desilylation of 2f and 3f affords 2i and 3i (R1 = C≡CH), respectively. The molecular structures of 3ad,fi have been determined and are reported together with the structures of the monoalkynyl complexes 2f,g,i and compared with related compounds from the literature. Complexes 3ai and 46 undergo one reversible electrochemical oxidation process, which can be attributed to depopulation of an orbital with significant alkynyl ligand character. The one-electron-oxidation products [3f]+, [3h]+, [4]+, and [5]+, chosen to serve as representative examples of this family of complexes, each exhibit a series of NIR absorptions between 15000 and 5000 cm1 which on the basis of TDDFT calculations cannot be attributed to a single, static lowest energy molecular structure. Rather, the transitions that are responsible for the absorption band envelope have varying degrees of LMCT and inter-alkynyl ligand IVCT or MLCT character that depend not only on the nature of the Rn groups but also on the ensemble of thermally populated molecular conformers in solution with various relative orientations of the metal fragment and arylethynyl moieties.
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Jul 2014
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6749]
Abstract: Bipyridyl appended ruthenium alkynyl complexes have been used to prepare a range of binuclear homometallic ruthenium and heterometallic ruthenium–rhenium complexes. The two metal centers are only weakly coupled, as evinced by IR and UV–vis–near NIR spectroelectrochemical experiments and supported by quantum chemical calculations. The alkynyl complexes of the type [Ru(C≡Cbpy){Ln}] ({Ln} = {(PPh3)2Cp}, {(dppe)Cp*}, {Cl(dppm)2}) undergo reversible one-electron oxidations centered largely on the alkynyl ligands, as has been observed previously for closely related complexes. The homometallic binuclear complexes, exemplified by [Ru(C2bpy-κ2-N′N-RuClCp)(PPh3)2Cp] undergo two essentially reversible oxidations, the first centered on the (C2bpy-κ2-N′N-RuClCp) moiety and the second on the Ru(C≡Cbpy)(PPh3)2Cp fragment, leading to radical cations that can be described as Class II mixed-valence complexes. The heterometallic binuclear complexes [Ru(C2bpy-κ2-N′N-ReCl(CO)3){Ln}] display similar behavior, with initial oxidation on the ruthenium fragment giving rise to a new optical absorption band with Re → Ru(C≡Cbpy) charge transfer character. The heterometallic complexes also exhibit irreversible reductions associated with the Re hetereocycle moiety.
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Aug 2014
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6749]
Abstract: The Pd(PPh3)4/CuI-cocatalyzed reaction of
Ru(CñMCCñMCH)(PPh3)2Cp (2) with aryl iodides, Ar-I (3,
Ar = C6H4CN-4 (a); C6H4Me-4 (b); C6H4OMe-4 (c); 2,3-
dihydrobenzo[b]thiophene (d); C5H4N (e)) proceeds
smoothly in diisopropylamine and under an inert atmosphere
to give the substituted buta-1,3-diynyl complexes Ru(CñM
CCñMCAr)(PPh3)2Cp (4a-e) in moderate to good yield. The
procedure allows the rapid preparation of a range of metal
complexes of arylbuta-1,3-diynyl ligands without necessitating
the prior synthesis of the individual buta-1,3-diynes as ligand
precursors. Similar reaction of 2 with half an equivalent of 1,4-
diiodobenzene affords the bimetallic derivative {Ru-
(PPh3)2Cp}2(Ê-CñMCCñMC-1,4-C6H4−CñMCCñMC) (5). In
the presence of atmospheric oxygen, homocoupling of the diynyl reagent 2 takes place to provide the octa-1,3,5,7-tetrayndiyl
complex {Ru(PPh3)2Cp}2(Ê-CñMCCñMCCñMCCñMC) (6). Crystallographically determined molecular structures are reported
for five complexes (4a, 4b, 4d, 5, and 6). Quantum chemical calculations indicate that the HOMOs are mainly located on the
C4−C6H4−C4 and C8 bridges for 5 and 6, respectively, while spectroelectrochemical (UV−vis−NIR and IR) studies on 6
establish that oxidation takes place at the C8 bridge, likely followed by cyclodimerization reactions of the bridging ligand.
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Jun 2015
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6749]
Abstract: The synthesis and characterization of a series of cobalt compounds,
coordinated by the redox-active macrocyclic biquinazoline ligand, Mabiq [2−4:6−8-
bis(3,3,4,4-tetramethyldihydropyrrolo)-10−15-(2,2′-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-
1,3,7,9,11,14-N6], is presented. The series includes the monometallic Co(Mabiq)Cl2
(1), Co(Mabiq)Cl (2), and Co(Mabiq) (4), with formal metal oxidation states of 3+ →
1+. A binuclear cobaltous compound, Co2(Mabiq)Cl3 (3), also was obtained, providing
the first evidence for the ability of the Mabiq ligand to coordinate two metal ions. The
electronic structures of the paramagnetic 2 and 3 were examined by electron paramagnetic
resonance spectroscopy and magnetic susceptibility studies. The CoII ion that resides in
the N4-macrocylic cavity of 2 and 3 adopts a low-spin S = 1/2 configuration. The
bypirimidine functionality in 3 additionally coordinates a high-spin S = 3/2 cobaltous ion in
a tetrahedral environment. The two metal ions in 3 are weakly coupled by magnetometry.
The square-planar, low-valent 4 offers one of a limited number of examples of structurally
characterized N4-macrocyclic CoI compounds. Spectroscopic and density functional theory computational data suggest that a
CoII(Mabiq•) description may be a reasonable alternative to the CoI formalism for this compound.
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Jun 2015
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I19-Small Molecule Single Crystal Diffraction
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Oday A.
Al-owaedi
,
David C.
Milan
,
Marie-christine
Oerthel
,
Sören
Bock
,
Dmitry S.
Yufit
,
Judith A. K.
Howard
,
Simon J.
Higgins
,
Richard J.
Nichols
,
Colin J.
Lambert
,
Martin R.
Bryce
,
Paul J.
Low
Diamond Proposal Number(s):
[6749]
Open Access
Abstract: The single-molecule conductance of metal complexes of the general forms trans-Ru(C≡CArC≡CY)2(dppe)2 and trans-Pt(C≡CArC≡CY)2(PPh3)2 (Ar = 1,4-C6H2-2,5-(OC6H13)2; Y = 4-C5H4N, 4-C6H4SMe) have been determined using the STM I(s) technique. The complexes display high conductance (Y = 4-C5H4N, M = Ru (0.4 ± 0.18 nS), Pt (0.8 ± 0.5 nS); Y = 4-C6H5SMe, M = Ru (1.4 ± 0.4 nS), Pt (1.8 ± 0.6 nS)) for molecular structures of ca. 3 nm in length, which has been attributed to transport processes arising from tunneling through the tails of LUMO states.
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Sep 2016
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: The solution hydration behavior of a series of lactam-based kinetic clathrate hydrate inhibitors (KHIs) has been studied in order to determine mechanistic insight into their KHI performance. IR and 1H NMR spectroscopic titration data were compared across a series of mono- and bis(lactam) model compounds, and solid-phase hydration behavior was examined by Dynamic Vapour Sorption. The structures of several of the model compounds have been investigated by X-ray crystallography. The work reveals insight into the very low crystallinity and high hygroscopicity of these materials which is linked to their performance as KHIs. Analysis of water binding in sour gas systems, containing H2S and CO2, reveals no effect on the water affinity of the lactams suggesting that sour gas components do not inhibit KHI performance, but rather promote clathrate hydrate formation.
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Apr 2017
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: Lamellar supramolecular assemblies are a common feature of fibrous gels formed by molecules such as peptides and ureas. Competition between gelation and crystallization is highly solvent dependent and can be governed by the dynamics of nascent lamellae in solution. We hypothesize that gel fibrils are formed when the scrolling of lamellae outpaces multilayer stacking. Crystallographic data on model picolyl bis(urea)s were correlated with their gelation properties. Most structures are lamellar, and gels involving fibrous aggregates form concomitantly alongside crystalline solvates. A distinguishing feature of these solvate crystals is that the lamellae have unequal numbers of picolyl groups on opposite faces. Atomistic molecular dynamics simulations show that this asymmetry causes isolated lamellae to scroll spontaneously into fibrils, whereas symmetrical lamellae adopt flat, crumpled, or saddle-like morphologies. Scrolling represents a general mechanism for gel formation, affording networks of unbranched fibers with monodisperse diameters dictated by the equilibrium curvature of the folding lamellae.
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Oct 2017
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: This paper reports the characterization of the composition and morphology of mineral formation on glass and plastic (polymethylmethacrylate) substrates in a dishwasher environment and the identification of suitable phosphate-free mineral crystallization inhibitors as environmentally benign candidates to replace the currently used phosphate-containing inhibitor 1-hydroxyethane 1,1-diphosphoric acid (HEDP). Screening of the calcium carbonate crystallization inhibition performance of twenty-eight different compounds resulted in the identification of two phosphate-free, cyclic polycarboxylic acid inhibitors, which were found in combination to be effective replacements. Each inhibitor proved to be highly substrate specific with all-cis-cyclohexane-1,2,3,4,5,6-hexacarboxylic acid (CHHCA) preventing deposition on glass (where calcite is the dominant polymorph) and cis,cis,cis,cis-cyclopentane-1,2,3,4-tetracarboxylic acid (CPTCA) inhibiting aragonite deposition on polymethylmethacrylate (PMMA). When used in combination, these two species prevented all forms of calcium carbonate deposition on both substrate types. The underlying inhibition mechanism and structural requirements of an efficient calcium carbonate inhibitor are also discussed.
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Jan 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: We report the application of supramolecular gel and microemulsion droplet crystallisation methodologies to isoniazid crystallization. Tailored gelators have been designed with isoniazid mimetic functionality in an attempt to control crystal morphology and polymorphic behaviour. Microemulsion crystallisation was investigated to achieve thermodynamic control over drug crystallisation. Both techniques resulted in only a single form of isoniazid implying that it is genuinely monomorphic.
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Feb 2018
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