I19-Small Molecule Single Crystal Diffraction
|
Open Access
Abstract: The synthesis, spectroelectrochemical and structural characteristics of highly electron-accepting diketopyrrrolopyrrole (DPP) molecules with adjoining pyridinium rings is reported, along with an assessment of their toxicity, which is apparently low. The compounds show reversible electrochemistry and in one subfamily a massive increase in molar extinction coefficient upon electrochemical reduction.
|
Jan 2023
|
|
I19-Small Molecule Single Crystal Diffraction
|
Abstract: Reactivity of a series of related molecules under the 80 keV electron beam have been investigated and correlated with their structures and chemical composition. Hydrogenated and halogenated derivatives of hexaazatrinaphthylene, coronene, and phthalocyanine were prepared by sublimation in vacuum to form solventless crystals then deposited onto transmission electron microscopy (TEM) grids. The transformation of the molecules in the microcrystals were triggered by an 80 keV electron beam in the TEM and studied using correlated selected area electron diffraction, conventional bright field imaging, and energy dispersive X-ray spectroscopy. The critical fluence (ē nm-2) required to cause a disappearance of the diffraction pattern was recorded and used as a measure of the reactivity of the molecules. The same electron flux (102 ē nm-2 s-1) was used throughout. Fully halogenated molecules were found to be the most stable and did not change significantly under our experimental conditions, followed by fully hydrogenated molecules with critical fluences of 104 ē nm-2. Surprisingly, semi-halogenated molecules that contained an equal number of hydrogen and halogen atoms were found to be the least stable, with critical fluences an order of magnitude lower at 103 ē nm-2. This is attributed to elimination of H-X (where X = F or Cl), followed by polymerisation of aryne / aryl radicals within the crystal. The critical fluence for the semi-fluorinated hexaazatrinaphthylene is the lowest as the presence of water molecules in its crystal lattice significantly decreased the stability of the organic molecules under the electron beam. Semi-halogenation reduces the beam stability of organic molecules compared to the parent hydrogenated molecule, thus providing the chemical guidance for design of electron beam stable materials. Understanding of molecular reactivity in the electron beam is necessary for advancement of molecular imaging and analysis methods by the TEM, molecular materials processing, and electron beam-driven synthesis of novel materials.
|
Dec 2022
|
|
I19-Small Molecule Single Crystal Diffraction
|
Diamond Proposal Number(s):
[21755, 28766]
Open Access
Abstract: Previously inaccessible large S8-corona[n]arene macrocycles (n = 8-12) with alternating aryl and 1,4-C6F4 subunits are easily prepared on up to gram scales, without the need for chromatography (up to 45% yield, 10 different examples) through new high acceleration SNAr subsitution protocols (catalytic NR4F in pyridine, R = H, Me, Bu). Macrocycle size and functionality are tunable by precursor and catalyst selection. Equivalent simple NR4F catalysis allows facile late-stage SNAr difunctionalisation of the ring C6F4 units with thiols (8 derivatives, typically 95+% yields) providing two-step access to highly functionalised fluoromacrocycle libraries. Macrocycle host binding supports fluoroaryl catalytic activation through contact ion pair binding of NR4F and solvent inclusion. In the solid-state, solvent inclusion also intimately controls macrocycle conformation and fluorine-fluorine interactions leading to spontaneous self-assembly into infinite columns with honeycomb-like lattices.
|
Nov 2022
|
|
I19-Small Molecule Single Crystal Diffraction
|
Diamond Proposal Number(s):
[21755]
Open Access
Abstract: A mixed-addenda W/Mo hybrid polyoxometalate cluster – K6[P2W15Mo2O61(POC6H5)2] (1) was synthesised from the condensation of K10[P2W15Mo2O61] and PO3C6H7 under acidic conditions. Single-crystal X-ray diffraction confirmed the structure of the hybrid cluster and the presence of two Mo centres in the cap of the lacunary cluster. The electronic effects of metal substitution were studied by cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance spectroscopy and supported by density functional theory calculations. Comparing 1 to its tungsten-only analogue K6[P2W17O61(POC6H5)2] (2), a more positive potential for the first reduction process was induced by the substitution of W for Mo, consistent with a significant lowering of the cluster LUMO energy.
|
Apr 2022
|
|
I19-Small Molecule Single Crystal Diffraction
|
Nicholas
Pearce
,
Katherine E. A.
Reynolds
,
Surajit
Kayal
,
Xue Z.
Sun
,
E. Stephen
Davies
,
Ferdinando
Malagreca
,
Christian J.
Schürmann
,
Sho
Ito
,
Akihito
Yamano
,
Stephen P.
Argent
,
Michael W.
George
,
Neil R.
Champness
Diamond Proposal Number(s):
[21755]
Open Access
Abstract: The ability to control photoinduced charge transfer within molecules represents a major challenge requiring precise control of the relative positioning and orientation of donor and acceptor groups. Here we show that such photoinduced charge transfer processes within homo- and hetero-rotaxanes can be controlled through organisation of the components of the mechanically interlocked molecules, introducing alternative pathways for electron donation. Specifically, studies of two rotaxanes are described: a homo[3]rotaxane, built from a perylenediimide diimidazolium rod that threads two pillar[5]arene macrocycles, and a hetero[4]rotaxane in which an additional bis(1,5-naphtho)-38-crown-10 (BN38C10) macrocycle encircles the central perylenediimide. The two rotaxanes are characterised by a combination of techniques including electron diffraction crystallography in the case of the hetero[4]rotaxane. Cyclic voltammetry, spectroelectrochemistry, and EPR spectroscopy are employed to establish the behaviour of the redox states of both rotaxanes and these data are used to inform photophysical studies using time-resolved infra-red (TRIR) and transient absorption (TA) spectroscopies. The latter studies illustrate the formation of a symmetry-breaking charge-separated state in the case of the homo[3]rotaxane in which charge transfer between the pillar[5]arene and perylenediimide is observed involving only one of the two macrocyclic components. In the case of the hetero[4]rotaxane charge separation is observed involving only the BN38C10 macrocycle and the perylenediimide leaving the pillar[5]arene components unperturbed.
|
Jan 2022
|
|
I11-High Resolution Powder Diffraction
I19-Small Molecule Single Crystal Diffraction
|
Christopher
Marsh
,
Xue
Han
,
Jiangnan
Li
,
Zhenzhong
Lu
,
Stephen
Argent
,
Ivan
Da Silva
,
Yongqiang
Cheng
,
Luke L.
Daemen
,
Anibal J.
Ramirez-Cuesta
,
Stephen P.
Thompson
,
Alexander J.
Blake
,
Sihai
Yang
,
Martin
Schroeder
Diamond Proposal Number(s):
[23483, 11622]
Open Access
Abstract: We report the reversible adsorption of ammonia (NH3) up to 9.9 mmol g–1 in a robust Al-based metal–organic framework, MFM-303(Al), which is functionalized with free carboxylic acid and hydroxyl groups. The unique pore environment decorated with these acidic sites results in an exceptional packing density of NH3 at 293 K (0.801 g cm–3) comparable to that of solid NH3 at 193 K (0.817 g cm–3). In situ synchrotron X-ray diffraction and inelastic neutron scattering reveal the critical role of free −COOH and −OH groups in immobilizing NH3 molecules. Breakthrough experiments confirm the excellent performance of MFM-303(Al) for the capture of NH3 at low concentrations under both dry and wet conditions.
|
Apr 2021
|
|
I19-Small Molecule Single Crystal Diffraction
|
Diamond Proposal Number(s):
[15833]
Open Access
Abstract: The solid state supramolecular interactions of diketopyrrolopyrrole derivatives (DPPs) and their correlation with thin film optical properties are of particular interest because of the applications of these materials in organic electronics. In this study, we report the single crystal X-ray structures of several phenyl DPP derivatives, containing 4-methoxyphenyl, 4-hydroxyphenyl and 4-((tetrahydro-2H-pyran-2-yl)oxy)phenyl aryl units, and show how subtle changes in the substituent chains at side or end positions of the chromophore can lead to very different packing. They are compared to their phenyl counterpart to explore how the nature of both the alkyl chain and the aryl unit influence the optical properties that have been measured in solid and solution states. Importantly, for the three families of N-substituted compounds studied, the structures are changed by the conformation of the molecules and are apparently dominated by crystal packing effects where edge-to-face interactions are favoured rather than π stacking, with only one of the compounds showing a flat form, promoted by intermolecular contacts between the aromatic regions. It is therefore possible that the twist between DPP and phenyl units in crystals of DPPs results from edge-to-face interactions (rather than steric interactions between the N-substituent and the protons attached to the aromatic ring) that might be overcome in more extended structures. Hydrogen bonding dominates the packing to generate chains of DPP units for phenol derivatives. Remote bulky groups do affect the core conformation. The emission of the materials as thin films is dominated by local effects in the packing of the materials that are unique for each case as the structures are distinct from one another. Charge mobility (as calculated from the crystal structures) is not favoured because of twisted conformations and large displacement, but the sometimes high emission and large Stokes shift could make the materials interesting for other purposes, such as light emitters.
|
Feb 2021
|
|
I19-Small Molecule Single Crystal Diffraction
|
William J. F.
Trenholme
,
Daniil I.
Kolokolov
,
Michelle
Bound
,
Stephen P.
Argent
,
Jamie A.
Gould
,
Jiangnan
Li
,
Sarah A.
Barnett
,
Alexander J.
Blake
,
Alexander G.
Stepanov
,
Elena
Besley
,
Timothy L.
Easun
,
Sihai
Yang
,
Martin
Schroeder
Abstract: 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.
|
Feb 2021
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[21755, 8786]
Open Access
Abstract: We report four new A-site vacancy ordered thiocyanate double double perovskites,A1–x{Ni[Bi(SCN)6](1–x)/3}, A = K+, NH4+, CH3(NH3)+ (MeNH3+) and C(NH2)3+ (Gua+), includingthe first examples of thiocyanate perovskites containing organic A-site cations. We show, usinga combination of X-ray and neutron diffraction, that the structure of these frameworks dependson the A-site cation, and that these frameworks possess complex vacancy-ordering patterns andcooperative octahedral tilts distinctly different from atomic perovskites. Density functional theorycalculations uncover the energetic origin of these complex orders and allow us to propose asimple rule to predict favoured A-site cation orderings for a given tilt sequence. We use theseinsights, in combination with symmetry mode analyses, to show that these complex orders offera new route to non-centrosymmetric perovskites which render them as excellent candidates forpiezo- and ferroelectric applications.
|
Jan 2021
|
|
I11-High Resolution Powder Diffraction
I19-Small Molecule Single Crystal Diffraction
|
Stephen P.
Argent
,
Ivan
Da Silva
,
Alex
Greenaway
,
Mathew
Savage
,
Jack
Humby
,
Andrew J.
Davies
,
Harriott
Nowell
,
William
Lewis
,
Pascal
Manuel
,
Chiu C.
Tang
,
Alexander J.
Blake
,
Michael W.
George
,
Alexander V.
Markevich
,
Elena
Besley
,
Sihai
Yang
,
Neil R.
Champness
,
Martin
Schroeder
Diamond Proposal Number(s):
[861, 11622, 15833, 9443]
Open Access
Abstract: Designing porous materials which can selectively adsorb CO2 or CH4 is an important environmental and industrial goal which requires an understanding of the host–guest interactions involved at the atomic scale. Metal–organic polyhedra (MOPs) showing permanent porosity upon desolvation are rarely observed. We report a family of MOPs (Cu-1a, Cu-1b, Cu-2), which derive their permanent porosity from cavities between packed cages rather than from within the polyhedra. Thus, for Cu-1a, the void fraction outside the cages totals 56% with only 2% within. The relative stabilities of these MOP structures are rationalized by considering their weak nondirectional packing interactions using Hirshfeld surface analyses. The exceptional stability of Cu-1a enables a detailed structural investigation into the adsorption of CO2 and CH4 using in situ X-ray and neutron diffraction, coupled with DFT calculations. The primary binding sites for adsorbed CO2 and CH4 in Cu-1a are found to be the open metal sites and pockets defined by the faces of phenyl rings. More importantly, the structural analysis of a hydrated sample of Cu-1a reveals a strong hydrogen bond between the adsorbed CO2 molecule and the Cu(II)-bound water molecule, shedding light on previous empirical and theoretical observations that partial hydration of metal−organic framework (MOF) materials containing open metal sites increases their uptake of CO2. The results of the crystallographic study on MOP–gas binding have been rationalized using DFT calculations, yielding individual binding energies for the various pore environments of Cu-1a.
|
Oct 2020
|
|
