Judith A. K. Howard

Durham University, Durham, England, United Kingdom

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Publications (770)2607.29 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Reactions of the vinylidene complexes [M([double bond, length as m-dash]C[double bond, length as m-dash]CH2)(PP)Cp']PF6 with NH3 readily afford the acyclic amino carbene complexes [M{C(Me)NH2}(PP)Cp']PF6 [M(PP)Cp' = Fe(dppe)Cp, Ru(dppe)Cp, Ru(PPh3)2Cp, Ru(dppe)Cp*]. Crystallographic, spectroscopic and computational data support a description of these complexes in terms of a M-{C(Me)[double bond, length as m-dash]N(+)H2} mesomeric form, and simple σ-coordination of the singlet acyclic amino carbene.
    Dalton Transactions 06/2015; 44(32). DOI:10.1039/C5DT01806D · 4.20 Impact Factor
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    ABSTRACT: A new styryl dye of the 2-benzothiazole series which contains three methoxy groups and an iodide anion was synthesized. Three triclinic crystal forms of this dye were investigated by single crystal X-ray diffraction. All the modifications were shown to contain centrosymmetrically related stacks of cations with the syn-“head-to-tail” mutual arrangement. Stacks of cations are arranged as dimeric pairs with short interatomic distances between the ethylene group carbon atoms, d1 = 3.54–3.75 Å and significantly longer analogous distances between the adjacent pairs, d2 = 4.61–4.68 Å. The main difference of the packing consists in various orientations of N-ethyl substituents with respect to the centre of the dimer. The solid phase [2+2] photocycloaddition (PCA) reaction resulting in rctt isomer of the cyclobutane derivative, only proceeds in pairs where N-substituents are oriented outward from the centre of the dimeric pair. PCA is accomplished as a “single crystal-to-single crystal” transformation.
    CrystEngComm 05/2015; 17(24). DOI:10.1039/C5CE00653H · 4.03 Impact Factor
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    ABSTRACT: In the title compound, C11H7Br3ClN, the quinoline ring system is approximately planar (r.m.s. = 0.011 Å). In the crystal, mol­ecules are linked by C—H⋯Br inter­actions forming chains along [10-1]. The chains are linked by C—H⋯π and π-π inter­actions involving inversion-related pyridine rings [inter­centroid distance = 3.608 (4) Å], forming sheets parallel to (10-1). Within the sheets, there are two significant short inter­actions involving a Br⋯Cl contact of 3.4904 (18) Å and a Br⋯N contact of 3.187 (6) Å, both of which are significantly shorter than the sum of their van der Waals radii.
    05/2015; 71(5):o354-o355. DOI:10.1107/S2056989015008002
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    ABSTRACT: This report deals with the synthesis, characterization, and crystal structure of a heteropentanuclear CuII3TlI2 compound [(CuIIL)3TlI2](NO3)2 (1), where H2L=N,N′-ethylenebis(3-ethoxysalicylaldimine). This compound crystallizes in the monoclinic crystal system within space group C2/c. Each of the two symmetry related thallium(I) centers is located between a terminal and a common, central [CuIIL] by forming bonds with four phenoxo and three ethoxy oxygens. The three [CuIIL] moieties are parallel and hence 1 is a triple-decker system. Neighboring triple-decker moieties are interlinked by π…π stacking interaction and weak hydrogen bonds to generate 3-D self-assembly in 1. Salient features in the composition and structure of the title compound are discussed; the title compound is the first example of a thallium(I) system in imino-phenolate Schiff base family.
    Journal of Coordination Chemistry 12/2014; 67(1). DOI:10.1080/00958972.2013.879122 · 2.01 Impact Factor
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    ABSTRACT: The synthesis of new styryl dyes derived from 4-pyridine and 4-quinoline and having an ammonioalkyl N-substituent and a benzocrown-ether moiety of different size and with different sets of heteroatoms was developed. Spontaneous "head-to-tail" dimerization of these dyes via the formation of numerous hydrogen bonds between the terminal NH3+ groups and crown-ether moieties was detected in MeCN solutions. The stability constants of the dimeric complexes having pseudocyclic structure were studied by 1H NMR titration. The most stable complexes (logKd up to 8.2) were found in the case of dyes with the (aza)-18-crown-6-ether moiety, which is most complementary for binding a primary ammonium group. Stacking interaction of the conjugated systems in the dimeric complexes contributes to their stability to a much lesser extent. In dimeric complexes, the ethylene bonds of the dyes are pre-organized for stereospecific [2+2] photocycloaddition (PCA) induced by visible light. The PCA yields only rctt isomers of bis-crown-containing cyclobutane derivatives. The dyes were studied by X-ray diffraction; it was found that the dimeric arrangement is also retained in the crystalline state. The possibility of topochemical PCA of the dyes in single crystals without their destruction was demonstrated. The possibility of retro-PCA of the obtained cyclobutane derivatives to give the starting dyes was shown. The elucidated regularities of PCA can be used to fabricate optical data recording systems based on ammonioalkyl derivatives of crown-ether styryl dyes.
    The Journal of Organic Chemistry 11/2014; 79(23). DOI:10.1021/jo5018074 · 4.72 Impact Factor
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    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 (3a–h) 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 Ru–Cl 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 3a–d,f–i 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 3a–i and 4–6 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 cm–1 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.
    Organometallics 09/2014; 33(18):4947-4963. DOI:10.1021/om500265s · 4.13 Impact Factor
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    ABSTRACT: A series of disubstituted urea, thiourea and dansyl amide calix[4]arene based anion receptors have been prepared and characterised by X-ray crystallography. The structures show a fine balance of intramolecular urea alpha-tape, and urea…calixarene phenolic oxygen atom hydrogen bonding patterns. Both motifs are in competition with the anion binding behaviour of the compounds in solution.
    CrystEngComm 07/2014; 16(36). DOI:10.1039/C4CE01240B · 4.03 Impact Factor
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    ABSTRACT: A family of styryl dyes of the 4-pyridine series, Et–Py+–CHCH–C6H3(OMe)2 X−, with different anions X−, was synthesized. Their ability to undergo [2 + 2] photocycloaddition (PCA) in the polycrystalline state with the formation of 1,2,3,4-tetrasubstituted rctt cyclobutanes under irradiation with visible light was investigated by 1H NMR spectroscopy. Crystal packing of the dyes and feasibility for the PCA reaction in single crystals were investigated by X-ray structural analysis. Small inorganic anions, such as ClO4−, BF4−, PF6− that do not form secondary interactions with the organic cation, aid the formation of cation stacking motifs of the “head-to-tail” type. In these stacks, any adjacent cations are arranged in an antiparallel fashion and approach one another at distances shorter than 4.2 Å, which corresponds to the Schmidt's rule for feasibility of PCA reaction in the solid state. As a result of PCA, rctt isomers of cyclobutane derivatives are formed. Success of the PCA reaction without single crystal degradation was only found for the dye containing BF4− anion. Upon irradiation with UV light of the cyclobutane product formed in the crystal, back phototransformation without single crystal degradation was observed. A number of weak interactions I−H–C in the dye with I− anion prevent significant atomic displacements that accompany the PCA transformation from being achieved. Occurrence of the bulky tosylate anion forming a set of hydrogen bonds with solvate acetonitrile and water molecules aids the formation of “head-to-head” type stacks, with a large separation between the adjacent ethylene bonds. In the dye containing bulky BPh4− anion, the main structure-forming role belongs to anions, which suppress the cation trend to form a stacking packing motif. The dye with picrate anion forms two types of crystals. Crystal packing of one of them excludes any PCA transformation, whereas, the other one permits it, but with single crystal degradation.
    CrystEngComm 06/2014; 16(24):5364-5378. DOI:10.1039/c4ce00266k · 4.03 Impact Factor
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    ABSTRACT: Pyrido[3,2-b][1,4]oxazine and pyrido[2,3-b][1,4]benzoxazine systems were synthesised by annelation reactions involving highly fluorinated pyridine derivatives and nitrogen and oxygen centred difunctional nucleophiles by sequential regioselective nucleophilic aromatic substitution processes.
    Journal of Fluorine Chemistry 05/2014; 46(15). DOI:10.1016/j.jfluchem.2014.05.003 · 1.95 Impact Factor
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    ABSTRACT: The bis(imido) complexes ((t)BuN[double bond, length as m-dash])2Mo(PMe3)(L) (L = PMe3, C2H4) react with up to three equivalents of silane PhSiH3 to give the imido-bridged disilyl silyl Mo(vi) complex ((t)BuN){μ-(t)BuN(SiHPh)2}Mo(H)(SiH2Ph)(PMe3)2 () studied by NMR, IR and X-ray diffraction. NMR data supported by DFT calculations show that complex is an unusual example of a silyl hydride of Mo(vi), without significant SiH interaction. Mechanistic NMR studies revealed that silane addition proceeds in a stepwise manner via a series of Si-HM agostic and silanimine complexes whose structures were further elucidated by DFT calculations.
    Dalton Transactions 04/2014; 43(22). DOI:10.1039/c4dt00154k · 4.20 Impact Factor
  • Rachael Lee · Judith A K Howard · Michael R Probert · Jonathan W Steed
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    ABSTRACT: This tutorial review looks at structural and supramolecular chemistry of molecular solids under extreme conditions, and introduces the instrumentation and facilities that enable single crystal diffraction studies on molecular crystals at both high pressure and low temperature. The equipment used for crystallography under extreme conditions is explored, particularly pressure cells such as the diamond anvil cell, and their mechanism of action, as well as the cryogenic apparatus which allows materials to be cooled to significantly low temperatures. The review also covers recent advances in the structural chemistry of molecular solids under extreme conditions with an emphasis on the use of single crystal crystallography in high pressure and low temperature environments to probe polymorphism and supramolecular interactions.
    Chemical Society Reviews 04/2014; 43(13). DOI:10.1039/c4cs00046c · 33.38 Impact Factor
  • Judith A K Howard · Michael R Probert
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    ABSTRACT: X-ray crystallography has become the leading technique for studying the structure of matter at the atomic and molecular level. Today it underpins all sciences and is widely applied in industry. It is essential in the development of new materials. The technique is very powerful, and the range of materials that can be studied expands as new technologies evolve and are applied in innovative ways to structure solution. It is now possible to record vast amounts of diffraction data in seconds electronically, whereas it took days and months by photographic methods 30 to 40 years ago. Single crystals can be created in various ways; they can be produced from compounds that are liquids or gases at room temperature, and complete molecular structures can be presented within minutes. This short review presents recent developments that are appropriate to the single-crystal x-ray studies of chemical and materials sciences.
    Science 03/2014; 343(6175):1098-102. DOI:10.1126/science.1247252 · 33.61 Impact Factor
  • Dmitry S. Yufit · Oleg V. Shishkin · Roman I. Zubatyuk · Judith A.K. Howard
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    ABSTRACT: The molecular complexes of tetrahydrofuran (THF) and diethyl ether (DEE) with chloroform (CF), dichlodromethane (DCM) and bromoform (BF) have been synthesised by in situ cryo-crystallization and their structures have been determined by single-crystal X-ray diffraction. CF forms 2:1 co-crystals with THF and DEE, where the components are linked in isolated 2:1 complexes by Cl3C-H center dot center dot center dot O interactions. Molecules of components in THF-BF complex form halogen-bonded chains, while the complexes DCM and BF with DEE contain two independent pairs of the components linked by C-H center dot center dot center dot O contacts. Supramolecular architecture of the molecular complexes is analysed using energy-based topology of intermolecular interactions.
    01/2014; 229(9). DOI:10.1515/zkri-2013-1718
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    ABSTRACT: Phosphinoalkynes P(C≡CC6H4Me-4)Ph2 (1) and P(C≡CC6H4C≡CC6H4Me-4)Ph2 (2) have been prepared from CuI catalysed reactions of the corresponding 1-alkyne and PClPh2. The trimethylamine-N-oxide promoted reaction of PPh3, 1 or 2 with [Fe2(μ-pdt)(CO)6] (pdt = propanedithiolate) affords derivatives [Fe2(μ-pdt)(CO)5{PRPh2}] [R=Ph (3), C≡CC6H4Me (5), C≡CC6H4C≡CC6H4Me (6)] or, at elevated temperatures, [Fe2(μ-pdt)(CO)4(PPh3)2] (4). The cyclic voltammograms of compounds 3 and 4 feature almost fully reversible one-electron oxidation processes and an irreversible reduction, whilst the electrochemical response of the alkynyl phosphine substituted complexes 5 and 6 is irreversible for both oxidation and reduction. IR spectroelectrochemical studies of 4 are consistent with an oxidation processes leading to a delocalized or (Class III) mixed valence [FeFe]3+ core in which the iron centers have an average oxidation state of 1.5. The molecular structures of the alkynyl phosphine substituted clusters 5 and 6 are also reported.
    Journal of Cluster Science 01/2014; 26(1). DOI:10.1007/s10876-014-0790-5 · 1.30 Impact Factor
  • Angshuman R. Choudhury · Dmitry S. Yufit · Judith A.K. Howard
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    ABSTRACT: "In situ crystallization" is a technique, which is used to crystallize the materials, which are liquid at ambient conditions, on the single crystal X-ray diffractometer. This technique has been utilized to study crystal structures of a number of liquids, gases and mixtures of liquids and gases in the past. In this manuscript, we describe the formation of cocrystals of a few cresols with aniline and fluoroanilines using this technique. Different pairs of cresol and aniline/fluoroaniline resulted into various cocrystals, which display different crystalline motifs involving strong O-H center dot center dot center dot N, N-H center dot center dot center dot O hydrogen bonds along with weak C-H center dot center dot center dot O and C-H center dot center dot center dot F hydrogen bonds. The observed differences in crystal packing indicate that the role of weak hydrogen bonds in these systems is significant and need to be considered.
    01/2014; 229(9). DOI:10.1515/zkri-2014-1729
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    ABSTRACT: The synthesis of three 9-diarylamino-substituted acridines is reported. The compounds of the donor-acceptor type - N,N-diphenylacridin-9-amine (1), 2,7-dimethyl-N,N-bis(4-methylphenyl)acridin-9-amine (2), and 2,7-bis(1-methyl-1-phenylethyl)-N,N-bis[4-(1-methyl-1-phenylethyl)phenyl]acridin-9-amine (3) were characterized by IR, 1H and 13C NMR, mass-spectral and elemental analysis. The crystal structures of compounds 1-3 and their protonated forms were determined by X-ray diffraction analysis. The absorption and fluorescence spectra were measured in various solvents. Solvatochromic shifts and dependence of the fluorescence quantum yields on the solvent polarity and protonation suggest the use of these compounds as chemical sensors. An example of a sensor material based on compound 2 is presented. Density functional theory calculations of the structures and time-dependent density functional theory calculations of the gas-phase excitation and emission energies of 1 were performed at the PBE0/SVP level of theory.
    Journal of Molecular Structure 12/2013; 1053:79-88. DOI:10.1016/j.molstruc.2013.09.001 · 1.60 Impact Factor
  • Jacqueline M. Cole · Paul G. Waddell · Chick C. Wilson · Judith A. K. Howard
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    ABSTRACT: The delicate balance between solid-state intermolecular interactions and electron-donating methyl-group influences in N-methylurea (NMU) is shown to distinguish its nonlinear optical properties, relative to those of urea, a standard reference material for second harmonic generation (SHG). The solid-state intermolecular interactions in NMU are identified using neutron diffraction data, showing that hydrogen bonding generates an extensive 3D supramolecular network of NMU molecules with secondary and tertiary nonbonded contacts helping to hold this network in a closely packed form. The undulating “urea tape” motif within this network renders an overall packing arrangement that is less SHG-favorable than that of urea, which exhibits a more head-to-tail molecular alignment. The primary, secondary, and tertiary nonbonded contacts are classified using graph-sets, Hirshfeld surfaces, and fingerprint plots. H···H contacts in NMU contribute to the overall Hirshfeld surface area much more than in urea, forming at the expense of O···H interactions. However, SHG-contributing electronic effects of the methyl group in NMU provide some compensation to these hydrogen-bonding influences. This methyl group is also shown to librate, which could augment SHG. Our experimental results offer a direct response to previous density functional theory calculations on NMU and urea,1 corroborating their predictions as well as enabling a better relationship between the molecular and bulk optical nonlinearity of NMU. To that end, crystal engineering options are discussed with a view to balancing these seemingly conflicting structural attributes, so that one can produce an SHG-active form of NMU that is superior to urea.
    The Journal of Physical Chemistry C 10/2013; 117(48):25669–25676. DOI:10.1021/jp4088699 · 4.77 Impact Factor
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Publication Stats

14k Citations
2,607.29 Total Impact Points


  • 1992–2014
    • Durham University
      • Department of Chemistry
      Durham, England, United Kingdom
    • Baylor University
      • Department of Chemistry and Biochemistry
      Waco, Texas, United States
  • 2002–2010
    • Georg-August-Universität Göttingen
      • Institute of Inorganic Chemistry
      Göttingen, Lower Saxony, Germany
  • 1979–2010
    • University of Glasgow
      • School of Chemistry
      Glasgow, Scotland, United Kingdom
  • 1974–2010
    • University of Bristol
      • School of Chemistry
      Bristol, England, United Kingdom
  • 2004–2006
    • Memorial University of Newfoundland
      • Department of Chemistry
      Saint John, New Brunswick, Canada
    • Argonne National Laboratory
      Lemont, Illinois, United States
    • Kiev Slavonic University
      Kievo, Kyiv City, Ukraine
  • 2005
    • Moscow State Forest University
      Mytishi, Moskovskaya, Russia
  • 1981–2002
    • Institut Laue-Langevin
      Grenoble, Rhône-Alpes, France
  • 1997
    • Università degli Studi di Torino
      Torino, Piedmont, Italy
    • Lomonosov Moscow State University
      • Division of Chemistry
      Moskva, Moscow, Russia
  • 1995
    • Odense Zoo
      Odense, South Denmark, Denmark
  • 1987–1995
    • University of Salford
      Salford, England, United Kingdom
  • 1994
    • University of Zaragoza
      Caesaraugusta, Aragon, Spain