Gary S Nichol

The University of Edinburgh, Edinburgh, Scotland, United Kingdom

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Publications (154)443.19 Total impact

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    ABSTRACT: A series of 22 tridentate unsaturated mono-anionic ligands having the atom-sequence Y-C=C-N=CH-C=C-Z-1, with Y = N, O, or S and Z = O or S, has been studied to establish whether this backbone could be used to develop strong solvent extractants for nickel(II) which will preferably also show a high selectivity over iron(III) in the pH-dependent process: 2LHorg + NiSO4 ⇌ [(L)2Ni]org + H2SO4. All are capable of forming octahedral [(L)2Ni] complexes with a mer-arrangement of the YNZ-1 donor set. X-ray crystal structures of three salicylaldimine proligands derived from 3-bromo-5-t-butyl-2-hydroxybenzaldehyde show these to have pre-organised donor sets in which the three donors are held in an approximately orthogonal arrangement by intramolecular hydrogen bonds. The tautomers observed are dependent on the nature of the Y atom and the extent to which it is favourable for this to form a bonding interaction with the acidic hydrogen atom on the salicylaldimine unit. X-ray crystal structure determinations of seven of the [(L)2Ni] complexes show these to have significantly distorted octahedral coordination geometries which partly account for the proligands proving to be fairly weak Ni-extractants. DFT calculations show that extractant strength is dependent on a combination of the binding strength of the YNZ-1 donor set to the nickel ion and on the ease of deprotonation of the extractant. On this basis 3-nitro-4-t-octyl-6-(quinolin-8-imino)phenol is predicted, and is found, to be the strongest Ni-extractant. The extractants have low hydrolytic stability, reverting to their aldehyde precursors when solutions in water-immiscible solvents are contacted with aqueous acid, making them poor candidates for development as reagents for nickel recovery based on pH-swing processes of the type shown above.
    No preview · Article · Jan 2016 · Dalton Transactions
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    ABSTRACT: The asymmetric hydrocyanation of vinylarenes was investigated using hydrogen cyanide (HCN) in the presence of 5 mol% of a catalyst prepared from a phenol-derived chiral phosphine-phosphite ligand and bis(cyclooctadiene)nickel [Ni(cod)2]. The reactions were performed in tetrahydrofuran (THF) at room temperature to give exclusively the branched nitriles with superior enantioselectivities of 88–99% ee for vinylarenes and 74–94% ee for vinylheteroarenes, respectively. Using styrene as a model substrate it was shown that the catalyst loading could be decreased to 0.42 mol% without any loss of selectivity (88% ee). The structure of the pre-catalyst, i.e., a tetrahedral Ni(0)(P,P-chelate)(cod) complex, was proven by X-ray and NMR analysis. Additional insight into the reaction course was gained by monitoring the hydrocyanation of styrene-d8 by means of 2D NMR spectroscopy.
    No preview · Article · Oct 2015 · Advanced Synthesis & Catalysis
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    ABSTRACT: A family of Mn(III) dimers of general formula [Mn(R-sao)2(dpa)2](ClO4)2 () has been synthesised using derivatised phenolic oximes (R-saoH2, where R = H, Me, Et, Ph) in combination with di-(2-picolyl)-amine (dpa). Their structures reveal a double-oxime bridged [Mn(III)(NO)]2 magnetic core in which the Jahn-Teller axes lie perpendicular to the bridging plane, in contrast to two previously reported family members (, ). The switch in the orientation of the Jahn-Teller axes is enforced through the use of the chelating ligand which is present in and absent in . Dc magnetic susceptibility measurements reveal that the exchange interactions between the Mn(III) metal centres in are antiferromagnetic in contrast to that observed for and which are ferromagnetic. DFT calculations performed on complexes reproduce both the sign and strength of the J values found experimentally. Molecular orbital analysis unlocks a common mechanism of magnetic coupling based upon the orientation of the Jahn-Teller axis, with the magneto-structural correlation also dependent upon the Mn-N-O-Mn angles - with ferromagnetic interactions at smaller dihedral angles.
    No preview · Article · Oct 2015 · Dalton Transactions
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    ABSTRACT: High anion selectivity for PtCl6(2-) over Cl(-) is shown by a series of amidoamines, R(1)R(2)NCOCH2CH2NR(3)R(4) (L1 with R(1) = R(4) = benzyl and R(2) = R(3) = phenyl and L3 with R(1) = H, R(2) = 2-ethylhexyl, R(3) = phenyl and R(4) = methyl), and amidoethers, R(1)R(2)NCOCH2CH2OR(3) (L5 with R(1) = H, R(2) = 2-ethylhexyl and R(3) = phenyl), which provide receptor sites which extract PtCl6(2-) preferentially over Cl(-) in extractions from 6 M HCl solutions. The amidoether receptor L5 was found to be a much weaker extractant for PtCl6(2-) than its amidoamine analogues. Density functional theory calculations indicate that this is due to the difficulty in protonating the amidoether to generate a cationic receptor, LH(+), rather than the latter showing weaker binding to PtCl6(2-). The most stable forms of the receptors, LH(+), contain a tautomer in which the added proton forms an intramolecular hydrogen bond to the amide oxygen atom to give a six-membered proton chelate. Dispersion-corrected DFT calculations appear to suggest a switch in ligand conformation for the amidoamine ligands to an open tautomer state in the complex, such that the cationic N-H or O-H groups are also readily available to form hydrogen bonds to the PtCl6(2-) ion, in addition to the array of polarized C-H bonds. The predicted difference in energies between the proton chelate and nonchelated tautomer states for L1 is small, however, and the former is found in the X-ray crystal structure of the assembly [(L1H)2PtCl6]. The DFT calculations and the X-ray structure indicate that all LH(+) receptors present an array of polarized C-H groups to the large, charge diffuse PtCl6(2-) anion resulting in high selectivity of extraction of PtCl6(2-) over the large excess of chloride.
    No preview · Article · Aug 2015 · Inorganic Chemistry
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    ABSTRACT: Abstract The synthesis and characterization of a series of compounds of the type Re(diimine)(CO)2(L)Cl (where L = P(OEt)3, PMe3) is reported. The non-photochemical ligand substitution (non-PLS) utilizes the trans-labilizing effect of phosphorus ligands to facilitate carbonyl replacement. The non-PLS pathway leads to good yields (> 60%) of single isomer products, comparing favorably to the lower yield, mixed isomer products of analogous PLS pathways. The substitution of a carbonyl group by a phosphine/phosphite ligands shifts absorption further into the visible region without diminishing molar absorptivity. The synthesis presented provides a general facile ligand substitution pathway for related light-sensitive neutral rhenium/manganese carbonyl halide compounds.
    No preview · Article · Jul 2015 · Inorganic Chemistry Communications
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    ABSTRACT: Metacetamol is a structural isomer of the widely used drug paracetamol and is being considered as a promising alternative to the latter because of its lower toxicity. Due to the importance of the well-known polymorphism of paracetamol, an investigation of the polymorphism of metacetamol was successfully undertaken. A new polymorph of metacetamol has been discovered and extensively characterised using a variety of analytical techniques (IR- and Raman spectroscopy, UV-visible optical spectroscopy, X-ray powder and single-crystal diffraction, TGA and DSC). A procedure for the reliable and reproducible preparation of the new polymorph is described. Its properties and crystal structure are compared with those of the previously known polymorph, as well as with those of paracetamol.
    Full-text · Article · Jul 2015 · CrystEngComm
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    ABSTRACT: The reaction of the pro-ligand H4L, which combines the complementary phenolic oxime and diethanolamine moieties within the same organic framework, with Zn(NO3)2•6H2O and Ln(NO3)3•6H2O in a basic methanolic solution generates a family of isostructural heterometallic coordination compounds of general formula [Ln6Zn2(CO3)5(OH)(H2L)4(H3L)2(H4L)]NO3 [Ln = Gd (1), Dy (2), Sm (3), Eu (4), Tb (5)]. The octametallic skeleton of the cage describes a heavily distorted [GdIII6] octahedron capped on two faces by ZnII ions. The metal core is stabilised by a series of µ3- and µ4-CO32- ions, originating from the serendipitous fixation of atmospheric CO2. The magnetic properties of all family members were examined via SQUID magnetometry, with the χMT product and VTVB data of the Gd analogue (1) being independently fitted by numerical diagonalisation to afford the same best-fit parameter JGd-Gd = -0.004 cm-1. The MCE of complex 1 was elucidated from specific heat data, with the magnetic entropy change reaching a value of 22.6 J kg-1 K-1 at T = 1.7 K, close to the maximum entropy value per mole expected from six GdIII spins (SGd = 7/2), 23.7 J kg-1 K-1.
    Full-text · Article · May 2015 · Dalton Transactions
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    ABSTRACT: [CrIII8MII6]12+ (MII=Cu, Co) coordination cubes were constructed from a simple [CrIIIL3] metalloligand and a “naked” MII salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Computational techniques (known in theoretical nuclear physics as statistical spectroscopy) in tandem with EPR spectroscopy are used to interpret the magnetic behavior.
    No preview · Article · Apr 2015 · Angewandte Chemie
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    ABSTRACT: [CrIII8MII6]12+ (MII=Cu, Co) coordination cubes were constructed from a simple [CrIIIL3] metalloligand and a “naked” MII salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Computational techniques (known in theoretical nuclear physics as statistical spectroscopy) in tandem with EPR spectroscopy are used to interpret the magnetic behavior.
    Full-text · Article · Apr 2015 · Angewandte Chemie International Edition in English
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    ABSTRACT: [CrIII8MII6]12+ (MII=Cu, Co) coordination cubes were constructed from a simple [CrIIIL3] metalloligand and a “naked” MII salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Computational techniques (known in theoretical nuclear physics as statistical spectroscopy) in tandem with EPR spectroscopy are used to interpret the magnetic behavior. All about cubes: [CrIII8MII6]12+ (M=Cu, Co) cubes were constructed from a simple [CrIIIL3] metalloligand and a “naked” MII salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Statistical and EPR spectroscopy were used to interpret the magnetic behavior.
    Full-text · Article · Apr 2015 · Angewandte Chemie International Edition
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    ABSTRACT: While the phenolic oximes (R-saoH2) are well known for producing monometallic complexes of the type [MII(R-saoH)2] with CuII ions in near quantitative yield, their derivatisation opens the door to much more varied and interesting coordination chemistry. Here we show that combining the complimentary diethanolamine and phenolic oxime moieties into one organic framework (H4L1 and H4L2) allows for the preparation and isolation of an unusual family of [CuII]n wheels, including saddle-shaped, single-stranded [CuII8] wheels of general formula [Cu8(HL1)4(X)4]n[Y] (when n = 0, X = Cl−, NO3−, AcO−, N3−; when n = 2+ X = (OAc)2/(2,2’-bpy)2 and Y = [BF4]2) and [Cu8(HL2)4(X)4] (X = Cl−, Br−), a rectangular [Cu6(HL1)4] wheel, and a heterometallic [Cu4Na2(HL1)2(H2L1)2] hexagon. Magnetic studies show very strong antiferromagnetic exchange between neighbouring metal ions, leading to diamagnetic ground states in all cases. DFT studies reveal that the magnitude of the exchange constants are correlated to the Cu-N-O-Cu dihedral angles, which in turn are correlated to the planarity/puckering of the [CuII]n rings.
    Full-text · Article · Apr 2015 · Dalton Transactions
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    ABSTRACT: Uranyl complexes of a large, compartmental N8-macrocycle adopt a rigid, "Pacman" geometry that stabilizes the U(V) oxidation state and promotes chemistry at a single uranyl oxo-group. We present here new and straightforward routes to singly reduced and oxo-silylated uranyl Pacman complexes and propose mechanisms that account for the product formation, and the byproduct distributions that are formed using alternative reagents. Uranyl(VI) Pacman complexes in which one oxo-group is functionalized by a single metal cation are activated toward single-electron reduction. As such, the addition of a second equivalent of a Lewis acidic metal complex such as MgN″2 (N″ = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg functionalized as a result of Mg-N bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(N″)Cl] favor the formation of weaker U-O-Zn dative interactions, leading to reductive silylation of the uranyl oxo-group in preference to metalation. Spectroscopic, crystallographic, and computational analysis of these reactions and of oxo-metalated products isolated by other routes have allowed us to propose mechanisms that account for pathways to metalation or silylation of the exo-oxo-group.
    No preview · Article · Mar 2015 · Inorganic Chemistry
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    ABSTRACT: The conversion of carbon dioxide into liq. fuels is a postulated route to the utilization of the overabundance of carbon dioxide in the atm.; which has the potential to be recycled into a source of energy. We are proposing the use of rhenium and manganese- based organometallic complexes with diaminophenyl ligands to perform as electrocatalysts in the conversion of CO2 to CO. These coordination complexes are of the form M(DL) (CO) 3X (where M = rhenium or manganese; DL = diaminophenyl ligands; and X = Cl or Br) with the focus being on the manganese complexes because of their relative abundance, and subsequent lower price, than rhenium counterparts. Synthesis and characterization by NMR, IR, X- ray crystallog. and cyclic voltammetry will be presented. While a proton source is required for catalysis to occur in all cases, catalytic icat/ip values are in excess of 35 (in the presence of 10̂ MeOH) .
    No preview · Conference Paper · Mar 2015
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    Markus Zegke · Gary S Nichol · Polly L Arnold · Jason B Love
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    ABSTRACT: Reactions between the uranyl(vi) Pacman complex [(UO2)(py)(H2L)] of the Schiff-base polypyrrolic macrocycle L and Tebbe's reagent or DIBAL result in the first selective reductive functionalisation of the uranyl oxo by Al to form [(py)(R2AlOUO)(py)(H2L)] (R = Me or (i)Bu). The clean displacement of the oxo-coordinated Al(iii) by Group 1 cations has enabled the development of a one-pot, DIBAL-catalysed reduction of the U(vi) uranyl complexes to a series of new, mono-oxo alkali-metal-functionalised uranyl(v) complexes [(py)3(MOUO)(py)(H2L)] (M = Li, Na, K).
    Preview · Article · Mar 2015 · Chemical Communications
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    ABSTRACT: Three new complexes of the type Mn(NN)(CO)3Br have been synthesized, where NN = 5-substituted-1,10-phenanthroline. The novel compounds have been characterized by 1H NMR, FTIR, CV, HRMS, and UV/Vis, as well as X-ray crystallography in one case. The known NN = phenanthroline compound, and four analogous Re(I) compounds are also presented; their photophysical and electrochemical properties are discussed. A correlation is apparent between the MLCT absorbance bands and the electrochemical reduction of both the Re and Mn series of compounds.
    No preview · Article · Mar 2015 · Inorganica Chimica Acta
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    Gary S Nichol · Jamie M Frost · Sergio Sanz · Euan K Brechin
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    ABSTRACT: The structure of the title hydrated mol­ecular salt, C14H23N2O4 +·C2H3O2 −·H2O, was determined as part of a wider study on the use of the mol­ecule as a polydentate ligand in the synthesis of MnIII clusters with magnetic properties. The cation features intra­molecular O—H⋯N and N—H⋯O hydrogen-bond inter­actions. The crystal structure features a range of inter­molecular hydrogen-bonding inter­actions, principally O—H⋯O inter­actions between all three species in the asymmetric unit. An R 2 4(8) graph-set hydrogen-bonding motif between the anion and water mol­ecules serves as a unit which links to the cation via the di­ethano­lamine group. Each O atom of the acetate anion accepts two hydrogen bonds.
    Full-text · Article · Feb 2015 · Acta Crystallographica Section E Structure Reports Online
  • DA Kurtz · B Dhakal · BD Cox · GS Nichol · Greg A. N. Felton
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    ABSTRACT: Eight novel manganese complexes of the type [Mn(bpy-tBu)(CO)3L]+ have been prepared and characterized, where the L ligand is various phosphorous containing ligands. From a known compound Mn(bpy-tBu)(CO)3Br, the halide is removed by precipitation. Substitution of labile intermediate (OTf- bound species) by L is then achieved at very mild conditions. All complexes are characterized by 1H NMR, FT-IR, UV/vis, Cyclic Voltammetry and HRMS. There is evidence for interesting pi-stacking interactions when L is an aryl phosphine ligand.
    No preview · Conference Paper · Nov 2014
  • Jamie McKinven · Gary S. Nichol · Polly L. Arnold
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    ABSTRACT: Bulky terphenolate ligands allow the synthesis of rare heteroleptic thorium chloride, and borohydride complexes; in the absence of donor solvents, the terphenolate ligands protect the metal ions through neutral Th–η6-arene interactions in a thorium bis(arene) sandwich motif.
    No preview · Article · Oct 2014 · Dalton Transactions
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    ABSTRACT: Cobalt(III) tetrahedral capsules have been prepared using an assembly-followed-by-oxidation protocol from a Cobalt(II) precursor and a readily derivatizable pyridyl-triazole ligand system. Experiments designed to probe the constitutional dynamics show that these architectures are in a non-equilibrium state. A preliminary investigation into the host-guest chemistry of a water-soluble derivative shows it can bind and differentiate a range of different neutral organic molecules. The stability of this ensemble also permits the study of guest-binding at high salt concentrations.
    Preview · Article · Oct 2014 · Chemical Science
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    ABSTRACT: Tricyanofuran (TCF) derivatives attached to both anthracene and pyrene moieties were synthesised and characterised by optical, electrochemical and computational techniques. Both compounds exhibited similar absorption profile as well as electrochemical behaviour, however the pyrene derivative showed 20-fold higher non-linear optical activity measured by the EFISH technique. This huge difference has been assigned to i) a lower molar absorption and ii) a higher torsion angle for the anthracene derivative, confirmed by both experimental X-Ray diffraction and DFT calculations. Furthermore, we note that the μβ1.907 value of –1700 x 10-48 esu recorded for the pyrene derivative in CHCl3/pyridine is remarkable for a NLO chromophore lacking a classical push-pull structure.
    No preview · Article · Sep 2014 · Physical Chemistry Chemical Physics

Publication Stats

1k Citations
443.19 Total Impact Points

Institutions

  • 2012-2015
    • The University of Edinburgh
      • School of Chemistry
      Edinburgh, Scotland, United Kingdom
  • 2006-2013
    • The University of Arizona
      • • Department of Chemistry and Biochemistry (College of Science)
      • • Department of Materials Sciences and Engineering
      Tucson, Arizona, United States
  • 2004-2010
    • Newcastle University
      • School of Chemistry
      Newcastle upon Tyne, ENG, United Kingdom
  • 2009
    • University of Northern Iowa
      • Department of Chemistry and Biochemistry
      سدار فالز، آیووا, Iowa, United States