135 results for Boyd, Peter, Journal article

  • Spin–spin interactions in polynuclear nickel(II) complexes: susceptibility and low-temperature magnetisation studies of tris[bis(pentane-2,4-dionato)nickel(II)]

    Boyd, Peter; MARTIN, RL (1979)

    Journal article
    The University of Auckland Library

    The magnetic susceptibility and magnetisation of the trinuclear complex [Ni3(pd)6](pd = pentane-2,4-dionate) have been reinvestigated in the range 1.8–300 K. Detailed magnetisation studies have been performed to low temperatures to evaluate the properties of the septet (S= 3) ground state of the molecule. The results have been analysed in terms of the Heisenberg–Dirac–Van Vleck isotropic exchange Hamiltonian including contributions from single-ion zero-field splittings. Ferromagnetic coupling between adjacent ions is confirmed, although the magnitude of both this interaction and the antiferromagnetic interaction between the terminal ions is found to be half that previously reported. This diminution is due to the effect of zero-field splitting on the low-temperature magnetic properties, the ground-state septet (S= 3) having a splitting of –1.3 cm–1.

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  • Molten salt mixtures. XI. Integral and partial molar volumes in the molten salt systems PbCl2 + NaCl, PbCl2 + RbCl, PbCl2 + CsCl, CdCl2 + RbCl, and CdCl2 + CsCl

    Bloom, H; Boyd, Peter; Laver, JL; Wong, J (1966)

    Journal article
    The University of Auckland Library

    The densities of molten PbCl2, CsCl, and RbCl and of the molten salt systems PbCl2 + NaCl, PbCl2 + RbCl, PbCl2 + CsCl, CdCl2 + RbCl, and CdCl, + CsCl have been measured to an accuracy of ±0.1% by an Archimedean method over a considerable temperature range. Integral and partial molar volume isotherms have been constructed for the above binary systems and are interpreted to show that complex ions are formed in all but the PbCl2+NaCl system.

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  • SCALED HARTREE-FOCK FORCE-FIELD CALCULATIONS FOR ORGANOTHALLIUM COMPOUNDS - NORMAL-MODE ANALYSIS FOR TLCH3, TL(CH3)2+, TL(CH3)3, TL(CH3)2BR, AND TL(CH3)4-

    SCHWERDTFEGER, P; Bowmaker, Graham; Boyd, Peter; Ware, David; Brothers, Penelope; NIELSON, A (1990-02)

    Journal article
    The University of Auckland Library

    In a recent paper we presented Hartree-Fock (HF) calculations for aliphatic organothallium compounds. The diagonal HF force constants obtained from a Fletcher-Powell geometry optimization are now used for a normal-mode analysis of TlCH,, Tl(CH,),+, T1(CH3),, T1(CHJ2Br, and Tl(CH3)c. In order to calculate frequencies comparable to experimental values, the HF force field has been scaled by using scaling factors obtained from experimental infrared and Raman measurements on T1(CH3)2+ and TlBr. The vibrational spectra of Tl(CH3)2+ were remeasured (infrared and Raman) in order to obtain an accurate force field. Predictions are made for the vibrational spectrum of the as yet undetected TlCH, molecule. Experimental infrared and Raman results for T1(CH3), compare reasonably well with our calculated frequencies (ex- perimental v,,(Tl-C) = 450 cm-', v,,(Tl-C) = 465 cm-l, v,,(C-H) = 2917 cm-l, v,,(C-H) = 3020 cm-l; scaled HF u,,(Tl-C) = 488 cm-', v,,(Tl-C) = 514 cm-', vSp(C-H) = 2892 cm-l, Y, (C-H) = 2999 cm-l). Relativistic and correlation effects are analyzed for the vibrational frequencies ~ f i l ( C H , ) ~ +

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  • 2-Methyl-4-hydroxymethyl-5-carboxyethyl-pyridine.

    Boyd, Peter; Lena, G; Spicer, Julie (2008)

    Journal article
    The University of Auckland Library

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  • 5,15-Bis(3,5-di-tert-butylphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetrapropylporphyrin

    Boyd, Peter; Chaker, L; Rickard, Clifton (2006)

    Journal article
    The University of Auckland Library

    The title molecule, C64H86N4 , possesses a crystallographically imposed centre of symmetry with a rectangular distortion of the porphyrin core. In the crystal structure, molecules form laddered assemblies via partial stacking of porphyrins. The assemblies are further formed into layers separated by tertbutyl groups.

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  • (+/-)-2 '-phenylcyclohexanespiro-4 '-(azepano[1,2-b] isoxazolidine)

    crimmins, D; Choi, Ka; Boyd, Peter; Brimble, Margaret (2008)

    Journal article
    The University of Auckland Library

    In the crystal structure of the racemic title isoxazolidine, C19H27NO, the relative stereochemistry between the phenyl group and the bridgehead H atom is shown to be syn. There are two molecules in the asymmetric unit, one of which is the 7R*,13R* enantiomer, and one of which is the 7S*,13S* enantiomer. These enantiomers adopt different orientations of the phenyl ring with respect to the isoxazolidine ring, with C-C-C-C torsion angles of 63.6 (4) and 86.8 (4)??, respectively. In both enantiomers, the six-membered ring adopts a chair conformation, while the seven-membered ring adopts a twist-chair conformation.

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  • (+/-)-Cyclohexane-1,2-diyl bis(4-nitrobenzoate)

    Tong, Sok; Barker, David; Choi, Ka; Boyd, Peter; Brimble, Margaret (2008)

    Journal article
    The University of Auckland Library

    The crystal structure of the title compound, C20H18N2O8, has been investigated to establish the relative stereochemistry between the ester groups. The cyclohexane ring adopts a chair conformation, in which the two ester groups occupy the adjacent equatorial positions in a trans relationship with each other. The molecules assemble in the crystal as chains along the c axis via C-H center dot center dot center dot pi interactions between the cyclohexane ring and a pair of nitrophenyl rings of the neighbouring molecule. Also observed are pi-pi stacking interactions between the nitrophenyl rings of neighbouring chains, with a perpendicular distance between these rings of 3.409 angstrom and a slippage of 0.969 angstrom.

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  • (4R)-4-[(1R)-1,2-dihydroxyethyl]-1-[(1R)-1-phenylethyl]pyrrolidin-2-one

    Blaser, Adrian; Boyd, Peter (2008-09)

    Journal article
    The University of Auckland Library

    The title compound, C14H19NO3, was obtained as one of the two isomers of a Sharpless asymmetric dihydroxylation reaction of (1S)-1-[(1R)-1-phenylethyl]-4-vinylpyrrolidin-2-one. The absolute stereochemistry of this isomer was determined from the known stereochemistry (R) at the bridge C atom between the phenyl and pyrrolidine rings. The molecules form one-dimensional tapes along the b axis via hydrogen bonding between the carbonyl O atom and the alcohol groups of neighbouring molecules. These assemble into sheets via interdigitative stacking of the phenyl rings and C-H center dot center dot center dot O interactions.

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  • Crystal, molecular, and electronic structure of [Ta2Cl 4(??-Cl)4(PMe3)4]: A metal-metal single bond between eight-co-ordinate tantalum atoms

    Boyd, Peter; Jones, TC; Nielson, AJ; Rickard, CEF (1984)

    Journal article
    The University of Auckland Library

    The crystal structure of the title complex shows an MCl4M bridge across a weak Ta???Ta interaction and eight-fold co-ordination about each metal centre; an electronic structure calculation supports the existence of a ?? metal???metal bond.

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  • A double Mannich approach to the synthesis of substituted piperidones-application to the synthesis of substituted E-ring analogues of methyllycaconitine

    Chan, YM; Balle, J; Sparrow, JK; Boyd, Peter; Brimble, Margaret; Barker, David (2010-08-28)

    Journal article
    The University of Auckland Library

    The double Mannich reaction of acyclic alpha,gamma-substituted beta-keto esters and bis(aminol) ethers gives substituted 3,5-substituted-4-piperidones with high levels of diastereoselectivity. These piperdiones can be easily transformed into substituted E-ring analogues of the delphinium alkaloid methyllycacotine. (C) 2010 Elsevier Ltd. All rights reserved.

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  • (+/-)-N-(3-hydroxy-1,2-diphenylpropyl)-4-methylbenzenesulfonamide

    Tong, Sok; Barker, David; Choi, Ka; Boyd, Peter; Brimble, Margaret (2008)

    Journal article
    The University of Auckland Library

    In the title compound, C22H23NO3S, the relative stereochemistry of the two stereogenic centres is anti with respect to the H atoms. The molecular packing of the crystal shows a doublestrand arrangement, consisting of one strand of (S*,S*)enantiomers and one strand of (R*,R*) enantiomers. Both strands lie parallel to each other along the a axis. Each strand is made up of dimers in which the molecules are connected to each other via an intermolecular O-H...O hydrogen bond between the hydroxyl groups and an O-H..pie interaction with the aromatic ring. These units are then connected to neighbouring dimers via N-H...O hydrogen bonds and C-H...O interactions. Intramolecular C-H...O interactions are also observed.

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  • SPIN SPIN INTERACTIONS IN POLYNUCLEAR NICKEL(II) COMPLEXES - A MAGNETIC AND STRUCTURAL STUDY OF BINUCLEAR NICKEL(II) COMPLEXES OF ENOLIC 1,3,5-TRIKETONATES

    Boyd, Peter; LEE, KS; ZVAGULIS, M (1986-01-01)

    Journal article
    The University of Auckland Library

    The bulk magnetic susceptibilities of the binuclear nickel(11) complexes of the 1,3,5- triketonates from diethyl (2-oxocyclopentane-1,3-diy1)bisglyoxylate (H2ecg) (1) and diethyl 2,4,6-trioxoheptanedioate (H2decg) (2) have been measured over the temperature range 6-300 K. Antiferromagnetic spin-spin coupling is observed in each case with Nee1 temperatures in the range 45-65 K. The X-ray crystal structure of [ N i ( e ~ g ) ( p y ) ~ ] ~ . ( p y ) has been solved. The complex crystallize! with one pyridine of solvation in the space group PT [ a 10.507(1), b 13.384(1), c g q 9 9 2 ( 1 ) A, a 103.004(9), /3 115.867(9), y 86.857(10)", Z = 11. The molecule is binuclear with two coplanar triketonate dianions bridging the two six-coordinate nickel atoms through a di-p-0x0 linkage [Ni-Ob-Ni angle 102.0(1)"]. Two pyridine molecules and four triketonate oxygen atoms are bound to each nickel atoms. Magnetostructural correlations are presented in comparison with binuclear copper(11) 1,3,5- triketonates. The marked decrease in spin-spin interaction in the nickel complexes is attributed to increasing metal-bridging oxygen bond lengths that decrease the efficacy of the u antiferromagnetic pathway xyllOb 1 x y and contributions from the ferromagnetic xyllOb / / z2 pathway.

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  • An SCF MS-X?? study of the bonding and nuclear quadrupole coupling in copper(I) and silver(I) halides

    Bowmaker, Graham; Boyd, Peter (1985)

    Journal article
    The University of Auckland Library

    SCF MS-X?? calculations of the electronic structure of diatomic copper(I) and silver(I) halides MX (M = Cu, Ag; X = F, Cl, Br, I) have been carried out to investigate the bonding and nuclear quadrupole coupling in these molecules. Reasonable agreement (to within 30%) is obtained between the calculated and observed halogen coupling constants. The agreement is rather poorer for the copper coupling constants, which are small in magnitude, since they result from near cancellation of large but opposing contributions from the copper 3d and 4p orbitals. However, the calculations reproduce the observed negative sign of the field gradient at the copper nucleus, as well as the observed decrease in the copper coupling constant from CuF to CuI. The reasons for this trend are discussed.

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  • Preparation and Antitumour Properties of the Enantiomers of a Hypoxia-Selective Nitro Analogue of the Duocarmycins

    Tercel, M; Lee, Ho; Yang, S; Liyanage, HDS; Mehta, Sunali; Boyd, Peter; Jaiswal, JK; Tan, KL; Pruijn, FB (2011)

    Journal article
    The University of Auckland Library

    Racemic 2-{[1-(chloromethyl)-5-nitro-3-{5-[2-(dimethylamino)ethoxy]indol-2-carbonyl}-1,2-dihydro-3H-benzo[e]indol-7-yl]sulfonyl}aminoethyl dihydrogen phosphate, a synthetic nitro derivative of the duocarmycins, is a hypoxia-selective prodrug active against radiation-resistant tumour cells at nontoxic doses in mice. An intermediate in the synthesis of this prodrug was resolved by chiral HPLC and the absolute configuration assigned by X-ray crystallography. The intermediate was used to prepare the prodrug???s enantiomers, and also the enantiomers of the active nitro and amino metabolites. In vitro analysis in the human cervical carcinoma cell line SiHa showed that both nitro enantiomers are hypoxia-selective cytotoxins, but the ???natural??? S enantiomer is at least 20-fold more potent. Examination of extracellular amino metabolite concentrations demonstrated no enantioselectivity in the hypoxia-selective reduction of nitro to amino. Low levels of amino derivative were also found in aerobic cell suspensions, sufficient to account for the observed oxic toxicity of the nitro form. At an equimolar dose in SiHa-tumour bearing animals, the (???)-R enantiomer of the prodrug was inactive, while the (+)-S enantiomer caused significantly more hypoxic tumour cell kill than the racemate. At this dose, the combination of (+)-S-prodrug and radiation eliminated detectable colony-forming cells in four out of five treated tumour-bearing animals.

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  • ELECTRON-SPIN-RESONANCE STUDIES OF ONE-ELECTRON REDUCTION PRODUCTS OF NICKEL(II) AND PALLADIUM(II) COMPLEXES CONTAINING TETRATHIOMOLYBDATE, TETRATHIOTUNGSTATE, AND DIALKYLDITHIOCARBAMATE LIGANDS, "[M(M'S4)N(R2NCS2)2-N)]N-(N=0-2,M=NI OR PD,M'=MO OR W)

    Bowmaker, Graham; Boyd, Peter; CAMPBELL, GK; ZVAGULIS, M (1986-06-01)

    Journal article
    The University of Auckland Library

    The redox properties of nickel(II) and palladium(II) complexes of the type [M(M???S4)n(R2NCS2)2 ???n]n???(n= 0???2, M = Ni or Pd, M???= Mo or W) have been studied using d.c. and a.c. cyclic voltammetry at a platinum electrode in dichloromethane solution. The series of complexes show initial reversible or quasi-reversible one-electron reduction to give species containing a single unpaired electron. E.s.r. spectra have been used to identify the species produced after one-electron reduction. In the case of palladium, the reduction potential increases smoothly with increasing n whilst the unpaired electron is increasingly delocalised from the central metal ion with decreasing g anisotropy. In contrast, the reduction potential of the nickel complexes increases sharply from n= 0 to 1 with a corresponding increase in the g anisotropy. The reduction potential increases again for n= 2, however the e.s.r. spectrum shows an unusual ???reversal??? of g anisotropy (g??? < g???) compared to that expected for a d9 planar complex with the unpaired electron in a nickel dxy orbital (g??? > g???). It is suggested that in the case of n= 1 or 2 the unpaired electron is now occupying a molecular orbital composed of the low-lying molybdenum (or tungsten)d orbitals. This is supported by scattered wave X?? calculations of the electronic structure of the model complexes [Ni(H2NCS2)2], [Ni(MoS4)(H2NCS2)]??? and [Ni(MoS4)2]2??? and their oneelectron reduction products.

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  • TRIMETHYLPHOSPHINE COMPLEXES OF NIOBIUM(IV) AND TANTALUM(IV) - CRYSTAL, MOLECULAR, AND ELECTRONIC-STRUCTURES OF [M2CL4(MU-CL)4(PME3)4] (M = NB OR TA)

    Boyd, Peter; NIELSON, AJ; RICKARD, CEF (1987-02-01)

    Journal article
    The University of Auckland Library

    Reaction of [NbCl4(NCMe)3] or [NbCl4(thf)2](thf = tetrahydrofuran) with three equivalents of PMe3 gives the seven-co-ordinate complex [NbCl4(PMe3)3]. In refluxing benzene this complex converts to [Nb2Cl4(??-Cl)4(PMe3)4] which is obtained in good yield by reacting [NbCl4(NCMe)3] with two equivalents of PMe3. [NbCl4(thf)2] reacts with one equivalent of PMe3 in acetonitrile to give [{NbCl4(PMe3)}n]. [Ta2Cl4(??-Cl)4(PMe3)4] was obtained by reacting dilithium t-butyl-phosphide and PMe3 with TaCl5. Reduction of TaCl5 with Na???Hg amalgam in the presence of [NEt4]Cl gave [NEt4]2[TaCl6]. X-Ray structure determinations show the [M2Cl4(??-Cl)4(PMe3)4] complexes (M = Ta or Nb) are isostructural (space group Im3), containing four symmetrical chlorine bridges [Ta???Cl 2.544(2), Nb???Cl 2.545(1)??] across two metal centres [Ta???Ta 2.830(1), Nb???Nb 2.836(1)??] each of which have co-ordinated two terminal chlorines [Ta???Cl 2.497(2), Nb???Cl 2.506(1)??] and two terminal phosphine ligands [Ta???P 2.677(3), Nb???P 2.675(1)??]. Scattered wave X?? calculations on the electronic structure of the dinuclear complexes [M2Cl4(??-Cl)4(PH3)4](M = Nb or Ta) indicate the formation of a metal???metal single ?? bond between the metal atom dz2 orbitals. The ???????* energy separation suggests greater metal???metal interaction for the tantalum complex.

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  • INTENSITY ENHANCEMENTS IN THE IR-SPECTRA OF ORGANIC RADICAL IONS - A THEORETICAL-STUDY

    BRIENNE, SHR; Boyd, Peter; SCHWERDTFEGER, P; Bowmaker, Graham; Cooney, Ralph (1993-08-21)

    Journal article
    The University of Auckland Library

    The IR spectra of the methyl viologen dication and monocation have been calculated by molecular orbital (MO) methods in order to account for the considerable simplification observed in the IR spectra of viologens upon one-electron reduction to the corresponding radical monocations. Similar calculations on p-dicyanobenzene and its radical monoanion were carried out for comparison. The calculations show that a small number of fundamental modes of the reduced species show unusually large intensities and tend to dominate the spectrum, giving rise to the apparent simplicity of the observed spectra. The modes which show the greatest intensity enhancement are those which involve vibrations in the two halves of the molecule which are out of phase with each other. These modes produce a large charge oscillation and thus a large dipole change which gives rise to bands with high IR absorption intensity.

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  • 2-(4-Ferrocenylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

    Boyd, Peter; Paauwe, JD (2008-12)

    Journal article
    The University of Auckland Library

    In the title compound,, [Fe(C5H5)(C17H20BO2)], the two near parallel cyclopentadienyl rings of the ferrocene group are eclipsed. The benzene ring is tilted with respect to the attached cyclopentadiene ring by 17.0 (1)degrees and by 24.2 (1)degrees with respect to the dioxaborolane ring. The molecules assemble in the crystal via C-H center dot center dot center dot pi interactions between the cyclopentadienyl H atoms and the benzene and cyclopentadienyl rings of neighbouring molecules.

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  • Magnetic and structural studies on copper(II) dialkyldithiocarbamates

    Boyd, Peter; MITRA, S; RASTON, CL; ROWBOTTOM, GL; WHITE, AH (1981)

    Journal article
    The University of Auckland Library

    The magnetic susceptibilities of a series of copper(II) dialkyldithiocarbamates have been measured over the range 4???290 K, the alkyl groups being methyl, ethyl, isopropyl, and n-butyl. Contrary to a previous report of strong ferromagnetic interaction in the diethyl derivative, we find no evidence of any significant exchange interaction in this compound. The dimethyl and di-isopropyl analogues show weak antiferromagnetic interactions. Only the di-n-butyl derivative in the dialkyl series shows evidence of strong magnetic exchange interaction but of an antiferromagnetic nature; this effect is peculiar to the phase recrystallized from chloroform???light petroleum (??), the phase obtained from chloroform???ethanol (??) showing no such interaction. To seek the origin of the exchange interaction in the ?? derivative, its crystal structure has been determined by single-crystal X-ray diffraction methods at 295 K and refined by least squares to a residual 0.032 for 1 976 ???observed??? reflections. Crystals are triclinic, P, a= 15.29(1), b= 9.963(7), c= 9.243(7)??, ??= 67.94(7), ??= 82.92(7), ??= 71.55(7)??, and Z= 2. The copper environment is the usual pseudo-square-planar array of four sulphur atoms from two bidentate ligands (???Cu???S???, 2.31 ??), but there is a long fifth interaction [Cu S, 2.899(4)??] through the inversion centre leading to pseudo-dimer formation. Although similar to the diethyl analogue in this respect, differences are observed in regard to (a) the bridging geometry in the ???dimer??? and (b) the proximity to the ???dimer??? sulphur ligands of sulphur atoms from neighbouring dimers at ca. 3.8 ??. The likely relative importance of these two features in determining the origin of the antiferromagnetic coupling is discussed. The structure of the ?? phase has also been determined, the final residual being 0.036 for 1 324 ???observed??? reflections. Crystals are monoclinic, P21/n, a= 14.593(5), b= 7.840(2), c= 10.822(5)??, ??= 101.55(3)??, and Z= 2. The molecules are located with the copper atoms on crystallographic centres of symmetry, and the only significant intermolecular interactions observed are S H contacts. The CuS4 entity is planar with ???Cu???S??? 2.30 ??.

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  • Relativistic effects in gold chemistry. 4. Gold(III) and gold(V) compounds

    Schwerdtfeger, P; Boyd, Peter; Brienne, S; Burrell, AK (1992)

    Journal article
    The University of Auckland Library

    Hartree-Fock (HF) calculations of the electronic structure and bonding in gold(III) and gold(V) compounds (AuH, AuF, AuCl, AuH, AuF, AuCl, AuBr, AuI, AuF, AuH, AuF, AuCl) have been carried out. Non-relativistic and relativistic pseudopotentials were applied using a [Xe4f]-core definition for the gold atom, however, including the 5s and 5p electrons in the valence space. All bond distances and angles were optimized. M??ller-Plesset (MP2-4) calculations on the stability of gold(III) halide complexes were carried out to study the effects of electron correlation at the nonrelativistic and relativistic level of the theory. The relativistic effects in the Au-L bond are analyzed. Relativistic changes in Au(III)-ligand bond distances are calculated to be small compared to those in Au(I) compounds. However, relativistic changes in Au(III)-ligand stretching force constants are very large and of comparable magnitude to that in Au(I) compounds. The preference of the oxidation state III in gold is found to be influenced considerably by relativistic effects and is dependent on the electronegativity of the ligand. The conclusions drawn from previously published HF results (J. Am. Chem. Soc. 1989, 111, 7261) on the stability of AuL (L = F, Cl, Br, I) are confirmed by MP2-4 calculations; i.e., the decomposition AuL ??? AuL + L occurs less easily relativistically than nonrelativistically. Relativistic effects also contribute to the facile decomposition of AuF into Au and AuF. All calculated AuL compounds (L = H, F, Cl) show T-shaped structures as a result of a first-order Jahn-Teller symmetry breaking of the D trigonal planar structure into the C, arrangement. A rationalization for the polymeric helix structure of AuF is provided. The stability and structure of gold(III) hydride is examined in detail. Multiple scattering X?? calculations were carried out on AuF, AuCl, AuBr, and AuI to determine relativistic effects in the nuclear quadrupole coupling constant for Au. AuCl was prepared, and a single-crystal X-ray analysis was carried out to compare with data obtained by the MP2 method (monoclinic, space group P2/c with a = 6.5906 (9) ??, b = 11.007 (2) ??, c = 6.442 (3) ??, Z = 4, 873 reflections, and R = 0.0561). ?? 1992 American Chemical Society.

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