I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[30280]
Open Access
Abstract: A new teaching resource comprised of raw X-ray diffraction data sets from crystallography experiments has been compiled. The aim of this resource is to provide a tool with which to plug the teaching gap between crystals and chemical structures present at various levels of education, as well as providing examples for early stage researchers and institutions without the requisite instrumentation to use for training. The data sets mirror the contents of the highly successful CSD Teaching Subset and include examples that demonstrate the effects of wavelength, crystal quality, and collection temperature. As crystallography underpins our understanding of chemical structure, exposure to the technique will be beneficial to students in terms of providing understanding of where the structures in the CSD Teaching Subset originate as well as insights into many overlapping fields such as scattering theory and symmetry. The resource will be available through the CCDC Web site and will provide links to the software required for data processing and documentation describing its use. It is hoped that this resource will expand with contributions from users in terms of both data and teaching exercises.
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Sep 2024
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Open Access
Abstract: The benzyl-substituted phosphine–boranes PhCH2P(BH3)R2 [R = iPr (1H), Ph (2H), Cy (3H)] are accessible through either the reaction between R2PCl and PhCH2MgBr, followed by treatment with BH3·SMe2 or the reaction between R2P(BH)3Li and PhCH2Br. Treatment of 1H, 2H, or 3H with nBuLi, PhCH2Na, or PhCH2K gave the corresponding alkali metal complexes [{iPr2P(BH3)CHPh}Li(THF)]2 (1Li), [{Ph2P(BH3)CHPh}Li(OEt2)2] (2Li), [{Cy2P(BH3)CHPh}Li(TMEDA)] (3Li), [iPr2P(BH3)CHPh]Na (1Na), [{Ph2P(BH3)CHPh}Na(THF)2]2 (2Na), [Cy2P(BH3)CHPh]Na(THF)0.5 (3Na), [{iPr2P(BH3)CHPh}K]∞ (1K), [{Ph2P(BH3)CHPh}K(THF)]∞ (2K), and [{Cy2P(BH3)CHPh}K.0.5PhMe]∞ (3K). X-ray crystallography revealed that, while 2Li and 3Li crystallize as monomers, 1Li and 2Na crystallize as borane-bridged dimers. The potassium complexes 1K, 2K, and 3K all crystallize with polymeric structures, in which the monomer units are linked to each other through a range of both bridging BH3 groups and multihapto interactions between the potassium cations and the aromatic rings. The reactions between two equivalents of either 1Li or 3Li and Cp2Sn gave the corresponding dialkylstannylenes [{R2P(BH3)CHPh}2Sn] [R = iPr (1Sn), Cy (3Sn)]. These compounds were isolated as mixtures of the rac and meso diastereomers. X-ray crystallography reveals that rac-1Sn and rac-3Sn crystallize as discrete monomers each exhibiting two agostic-type B–H···Sn contacts.
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Jan 2024
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[16117]
Open Access
Abstract: Zˈ is a parameter used to denote the number of symmetry-independent molecules in the asymmetric unit of a crystal structure. High Zˈ (>1) crystal structures are relatively uncommon and are thought to arise through competition between intermolecular interactions of similar strength. As such high Zˈ crystal structures are challenging to predict and new examples are valuable in improving understanding in the field. Herein, we report the X-ray crystal structures of a series of shikimate esters, the asymmetric units of which exhibit high Zˈ values. Of special interest is the crystal structure of methyl shikimate, the asymmetric unit of which comprises 12 independent molecules; Zˈ = 12. This uncommonly large Zˈ value arises through a combination of factors, including the intrinsic homochirality of the molecule, the conformational inflexibility of the cyclohexene ring, the presence of multiple hydrogen bonding motifs, and both the cis- and trans-conformers of the ester moiety. Comparison of the X-ray crystal structures of shikimic acid, methyl shikimate, ethyl shikimate, and iso-propyl shikimate suggests that instances of high Zˈ in this series correlate with specific hydrogen bonding motifs influenced by the steric bulk of the ester. The results of this study provide important insights into factors that influence the formation of organic crystal structures where the value of Zˈ is greater than 1.
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Jan 2024
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I19-Small Molecule Single Crystal Diffraction
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Eman A. A.
Alkhudhayr
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Dumitru
Sirbu
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Miriam
Fsadni
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Benjamin
Vella
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Bening T.
Muhammad
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Paul G.
Waddell
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Michael R.
Probert
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Thomas J.
Penfold
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Toby
Hallam
,
Elizabeth
Gibson
,
Pablo
Docampo
Diamond Proposal Number(s):
[302080]
Open Access
Abstract: Organic–inorganic hybrid halide perovskite solar cells (PSCs) have attracted substantial attention from the photovoltaic research community, with the power conversion efficiency (PCE) already exceeding 26%. Current state-of-the-art devices rely on Spiro-OMeTAD as the hole-transporting material (HTM); however, Spiro-OMeTAD is costly due to its complicated synthesis and expensive product purification, while its low conductivity ultimately limits the achievable device efficiency. In this work, we build upon our recently introduced family of low-cost amide-based small molecules and introduce a molecule (termed TPABT) that results in high conductivity values (∼10–5 S cm–1 upon addition of standard ionic additives), outperforming our previous amide-based material (EDOT-Amide-TPA, ∼10–6 S cm–1) while only costing an estimated $5/g. We ascribe the increased optoelectronic properties to favorable molecular packing, as shown by single-crystal X-ray diffraction, which results in close spacing between the triphenylamine blocks. This, in turn, results in a short hole-hopping distance between molecules and therefore good mobility and conductivity. In addition, TPABT exhibits a higher bandgap and is as a result more transparent in the visible range of the solar spectrum, leading to lower parasitic absorption losses than Spiro-OMeTAD, and has increased moisture stability. We applied the molecule in perovskite solar cells and obtained good efficiency values in the ∼15% range. Our approach shows that engineering better molecular packing may be the key to developing high-efficiency, low-cost HTMs for perovskite solar cells.
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Nov 2023
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I19-Small Molecule Single Crystal Diffraction
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Hannes
Michaels
,
Matthias Johannes
Golomb
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Byeong
Kim
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Tomas
Edvinsson
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Fabio
Cucinotta
,
Paul G.
Waddell
,
Michael R.
Probert
,
Steven J.
Konezny
,
Gerrit
Boschloo
,
Aron
Walsh
,
Marina
Freitag
Diamond Proposal Number(s):
[22240]
Open Access
Abstract: Emerging technologies in solar energy will be critical in enabling worldwide society in overcoming the present energy challenges and reaching carbon net zero. Inefficient and unstable charge transport materials limit current emerging energy conversion and storage technologies. Low-dimensional coordination polymers represent an alternative, unprecedented class of charge transport materials, comprised of molecular building blocks. Here, we provide a comprehensive study of mixed-valence coordination polymers from an analysis of the charge transport mechanism to their implementation as hole conducting layers. CuII dithiocarbamate complexes afford morphology control of 1D polymer chains linked by (CuI2X2) copper halide rhombi. Concerted theoretical and experimental efforts identified the charge transport mechanism at the transition to band-like transport with an modeled effective hole mass of 6 me. The iodide-bridged coordination polymer showed an excellent conductivity of 1 mS cm-1 and a hole mobility of 5.8 10-4 cm2(Vs)-1 at room temperature. Nanosecond selective hole injection into coordination polymer thin films was captured by nanosecond photoluminescenceof halide perovskite films. The coordination polymers constitute a sustainable, tunable alternative to the current standard of heavily doped organic hole conductors.
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Mar 2022
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Abstract: Conventional redox mediators based on metal coordination complexes undergo electron transfer through the change in oxidation state of the metal center. However, electron transfer kinetics are offset toward preferred oxidation states when preorganized ligands constrain the reorganization of the coordination sphere. In contrast, we report here on dimeric copper(II/I) redox couples, wherein the extent of oxidation/reduction of two metal centers dictates the dynamic formation of dimer and monomer complexes: the dimeric (Cu(I))2 transitions to monomers of Cu(II). The bis(thiazole/pyrrole)-bipyridine tetradentate ligands stabilize both oxidation states of the unique redox systems. The dynamic dimer redox mediators offer a viable two-electron redox mechanism to develop efficient hybrid solar cells through inhibited recombination and rapid charge transport. Density functional theory calculations reveal inner reorganization energies for single-electron transfer as low as 0.27 eV, marking the dimeric complexes superior redox systems over single complexes as liquid and potentially solid-state electrolytes.
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Nov 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: Herein we present a rearomative diastereoselective etherification/amination reaction of 2,3,9,9a-tetrahydro-
1H-carbazoles, themselves accessible via the Diels-Alder reaction of N-protected 3-vinyl-1H-indoles. We
have developed a one-pot rearomative bromination/nucleophilic substitution reaction sequence employing both
O- and N-centred nucleophiles, inverting the typical reactivity of 2,3,9,9a-tetrahydro-1H-carbazoles at the
4-position. Alcohols or secondary amines can be incorporated allowing access to the corresponding 4-substituted-
2,3,4,9-tetrahydro-1H-carbazoles, the diastereoselectivity of the reaction being controlled by the nature of
the nucleophile and the reaction conditions.
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Apr 2021
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I19-Small Molecule Single Crystal Diffraction
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Jonathan
Bould
,
Kamil
Lang
,
Kaplan
Kirakci
,
Luis
Cerdán
,
Daniel
Roca-Sanjuán
,
Antonio
Francés-Monerris
,
William
Clegg
,
Paul G.
Waddell
,
Marcel
Fuciman
,
Tomáš
Polívka
,
Michael G. S.
Londesborough
Diamond Proposal Number(s):
[22240]
Abstract: We present the first examples of alkylated derivatives of the macropolyhedral boron hydride, anti-B18H22, which is the gain medium in the first borane laser. This new series of ten highly stable and colorless organic–inorganic hybrid clusters are capable of the conversion of UVA irradiation to blue light with fluorescence quantum yields of unity. This study gives a comprehensive description of their synthesis, isolation, and structural characterization together with a delineation of their photophysical properties using a combined theoretical and experimental approach. Treatment of anti-B18H221 with RI (where R = Me or Et) in the presence of AlCl3 gives a series of alkylated derivatives, Rx-anti-B18H22–x (where x = 2 to 6), compounds 2–6, in which the 18-vertex octadecaborane cluster architectures are preserved and yet undergo a linear “polyhedral swelling”, depending on the number of cluster alkyl substituents. The use of dichloromethane solvent in the synthetic procedure leads to dichlorination of the borane cluster and increased alkylation to give Me11-anti-B18H9Cl211, Me12-anti-B18H8Cl212, and Me13-anti-B18H7Cl213. All new alkyl derivatives are highly stable, extremely efficient (ΦF = 0.76–1.0) blue fluorophores (λems = 423–427 nm) and are soluble in a wide range of organic solvents and also a polystyrene matrix. The Et4-anti-B18H18 derivative 4b crystallizes from pentane solution in two phases with consequent multiabsorption and multiemission photophysical properties. An ultrafast transient UV–vis absorption spectroscopic study of compounds 4a and 4b reveals that an efficient excited-state absorption at the emission wavelength inhibits the laser performance of these otherwise remarkable luminescent molecules. All these new compounds add to the growing portfolio of octadecaborane-based luminescent species, and in an effort to broaden the perspective on their highly emissive photophysical properties, we highlight emerging patterns that successive substitutions have on the molecular size of the 18-vertex borane cluster structure and the distribution of the electron density within.
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Nov 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Open Access
Abstract: A new class of light-activated ruthenium(II) complex was designed as a potential blocker of biological functioning, especially for targeting redox reactions within mitochondria under light activation. Based on our concepts the complex [Ru(bipy)2(1-hydroxyanthra-9,10 quinone)]Cl (RU1) was prepared and studied to understand the preliminary reaction mechanisms and its excited state behaviour through a series of stability tests, electrochemistry, UV–Visible kinetics and femtosecond transient absorption spectroscopy experiments. Under white light in the presence of H2O2 two different reactions (fast and slow) appear to take place. The complex loses the quinone-based ligand and a resulting Ru(III) or Ru(V) species is produced. The complex RU1 shows potential to consume H2O2 from the one carbon metabolism in mitochondria, and hence may cut the energy cycle pathway of tumor cells.
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Aug 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Open Access
Abstract: Single-crystal X-ray diffraction analysis (SCXRD) constitutes a universal approach for the elucidation of molecular structure and the study of crystalline forms. However, the discovery of viable crystallization conditions remains both experimentally challenging and resource intensive in both time and the quantity of analyte(s). We report a robot-assisted, high-throughput method for the crystallization of organic-soluble small molecules in which we employ only micrograms of analyte per experiment. This allows hundreds of crystallization conditions to be screened in parallel with minimal overall sample requirements. Crystals suitable for SCXRD are grown from nanoliter droplets of a solution of analyte in organic solvent(s), each of which is encapsulated within an inert oil to control the rate of solvent loss. This encapsulated nanodroplet crystallization methodology can also be used to search for new crystal forms, as exemplified through both our discovery of a new (13th) polymorph of the olanzapine precursor ROY and SCXRD analysis of the “uncrystallizable” agrochemical dithianon.
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May 2020
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