Search PubMed⌕ Search

Biomedical subjects

Dermot O'Hare

Publications and source records attributed to Dermot O'Hare.

At least 19 recordsLinked to original sources
PubMed2006

A kinetic study of the intercalation of lithium salts into Al(OH)3.

The intercalation of five lithium salts into the gibbsite and bayerite polymorphs of Al(OH)3 has been studied using in situ energy-dispersive X-ray diffraction. The kinetics and mechanisms of the reactions have been modeled using the Avrami-Erofe'ev model. The kinetic data suggest that the reaction mechanisms are predominantly nucleation controlled, although the intercalation of LiNO3 into bayerite and of Li2SO4 into gibbsite proceed via two-stage mechanisms, one part of which is diffusion controlled. All the reactions proceed directly from the host to the product, except for the intercalation of Li2SO4 into gibbsite where a more hydrated intermediate form of [LiAl2(OH)6]2SO4 x yH2O is generated prior to the final product.

Journal Article↗
PubMed2005

Unique layered double hydroxide morphologies using reverse microemulsion synthesis.

We report the first controlled synthesis of a layered double hydroxide (LDH) in a water-in-oil reverse microemulsion system. This synthesis of Mg2Al-LDHs was carried out in the reverse microemulsion of NaDDS (sodium dodecyl sulfate)-water-isooctane with water/surfactant molar ratio = 24. This enables us to obtain nanometer sized LDH platelets typically with a 40-50 nm diameter and 10 nm thickness. Further modification of the reverse microemulsion using triblock copolymers during crystallization allowed us to express different growth orientations of the LDH structure. These data show that the aspect ratio of LDHs can be flexibly adjusted over a wide range.

Journal Article↗
PubMed2005

Electronic coupling in mixed-valence dinuclear ferrocenes and cobaltocenes with saturated bridging groups.

We have synthesised a series of new dinuclear metallocenes [{M(Cp*)(C5H4)}2X] (Cp* = eta5-pentamethylcyclopentadienyl; M = Fe, Co, X = CMe2, SiMe2, GeMe2; M = Fe, X = Si2Me4). For the neutral dicobalt complexes, magnetic susceptibility measurements reveal intramolecular antiferromagnetic interactions of -21 and -14 cm(-1) for SiMe2- and GeMe2-bridged species, respectively, but negligible interaction for the CMe2-bridged compound. In contrast, intervalence charge-transfer (IVCT) data for the mixed-valence monocations of both Fe and Co complexes show electronic coupling to decrease in the order CMe2 > SiMe2 > GeMe2. This suggests that electronic coupling is principally through-space in contrast to results found from previous studies. The IVCT data also show much stronger coupling in the dicobalt species versus their diiron analogues.

Journal Article↗
PubMed2005

The role of amine sulfates in hydrothermal uranium chemistry.

A series of novel uranium sulfates containing organic structure directing cations has been synthesized from amine sulfate precursors under hydrothermal conditions. The amine sulfates act as a soluble source of the protonated amines and sulfate ions at low temperature and provide a reaction pathway in which no amine decomposition is observed. The protonated amines act as both space fillers and hydrogen-bond donors in the three-dimensional structure. The factors governing the formation of the observed hydrogen-bonding networks were probed through the use of bond valence sums, which allow the quantification of residual negative charge and determination of the relative nucleophilicity of each oxide ligand. The hydrogen bonding in these new compounds is dependent upon two factors. First, the oxide ligands with the highest nucleophilicities are preferential acceptors with respect to their less nucleophilic counterparts. Second, geometric constraints that result from the formation of multiple hydrogen bonds from a single ammonium center can dictate the donation to oxides with smaller negative charges. Crystal data for [N4C6H12][SO4]2 x 2H2O, a = 7.2651(2) A, b = 7.3012(2) A, c = 8.3877(3) A, alpha = 90.260(1) degrees, beta = 100.323(1) degrees, gamma = 113.0294(15) degrees, triclinic, P-1 (No. 2), Z = 1; for [N4C6H22][UO2(H2O)(SO4)2]2 x 6H2O, a = 6.7318(1) A, b = 9.2975(1) A, c = 13.1457(3) A, alpha = 72.3395(6) degrees, beta = 89.1401(7) degrees, gamma = 70.0267(12) degrees, triclinic, P-1 (No. 2), Z = 1; for [N4C6H22][UO2(SO4)2)2, a = 9.3771(2) A, b = 12.9523(3) A, c = 18.9065(6) A, orthorhombic, Pbca (No. 61), Z = 4; for [N5C8H28]2[(UO2)5(H2O)5(SO4)10] x H2O, a = 7.76380(5) A, b = 14.16890(5) A, c = 56.46930(5) A, orthorhombic, Pbnm (No. 62), Z = 4.

Journal Article↗
PubMed2005

Structural variation in organically templated uranium sulfate fluorides.

The ability of templated uranium sulfate fluorides to adopt diverse inorganic architectures is demonstrated in six novel materials. The inorganic structures present in [N2C6H16][UO2F2(SO4)](USFO-2), [N2C6H16][UO2F(SO4)]2(USFO-3), [N2C3H12][UO2F(SO4)]2.H2O (USFO-4), [N2C5H14][UO2F(H2O)(SO4]2(USFO-5), [N2C6H18]2[UO2F(SO4)]4.H2O (USFO-6) and [N2C3H12][UO2F(SO4)]2.H2O (USFO-7) range from infinite chains to five different layer topologies. The chain, and two of the five layers, have unprecedented structure types. These compounds illustrate the structural diversity within this new family of materials, arising from the varied coordination of the U6+ centres. Each material was synthesised under hydrothermal conditions, through reaction of uranyl acetate, sulfuric acid, HF(aq), water, and the respective organic template.

Journal Article↗
PubMed2004

The effects of hydrofluoric acid addition on the hydrothermal synthesis of templated uranium sulfates.

The effect of employing hydrofluoric acid as a mineraliser in the formation of organically templated uranium sulfate materials has been studied. Variable amounts of HF((aq)) were added to a series of reaction gels in which all other reactant concentrations were invariant, resulting in the formation of three different phases, depending upon the fluoride concentration. Two of these phases are novel; [N(2)C(4)H(14)][UO(2)(H(2)O)(SO(4))(2)] is a new templated uranium sulfate, containing anionic [UO(2)(H(2)O)(SO(4))(2)](2-) chains that hydrogen bond to one-another forming pseudo-layers, and [N(2)C(4)H(14)][UO(2)F(SO(4))](2) is the first example of a templated uranium sulfate fluoride, which consists of uranium fluoride chains linked by sulfate groups to form [UO(2)F(SO(4))](-) layers. The role of F(-) in these reactions is two-fold; it acts as a mineraliser when present in small concentrations, while it is incorporated into the reaction product when present in larger mole fractions. Both of the new materials have been characterised using a range of physical techniques including single crystal X-ray structure analysis.

Journal Article↗
PubMed2004

Mesoporous silica-supported zirconocene catalysts for highly isotactic polypropylene.

A new bis(indenyl)zirconocene bearing a pendant Si-Cl anchor has been grafted onto MCM-41, SBA-15, MCM-48 and a disordered mesoporous silica for the polymerisation of ethylene and propylene, producing polymers with very high molecular weights, low polydispersities and, in the case of polypropylene, higher levels of isotacticity than obtainable with analogous homogeneous systems.

Journal Article↗
PubMed2004

Kinetic and mechanistic investigations of hydrothermal transformations in zinc phosphates.

The room-temperature crystallization of [C(6)N(2)H(18)][Zn(HPO(4))(H(2)PO(4))(2)], an organically templated zinc phosphate containing [Zn(2)(HPO(4))(2)(H(2)PO(4))(4)](4)(-) molecular anions, and its transformation to compounds containing either one- or two-dimensional inorganic components, [C(6)N(2)H(18)][Zn(3)(H(2)O)(4)(HPO(4))(4)], [C(4)N(2)H(12)][Zn(HPO(4))(2)(H(2)O)], or [C(3)N(2)H(6)][Zn(4)(OH)(PO(4))(3)], under hydrothermal conditions were studied in-situ using energy-dispersive X-ray diffraction. The ability to collect data during reactions in a large volume ( approximately 23 mL) Teflon-lined autoclave under real laboratory conditions has allowed for the elucidation of kinetic and mechanistic information. Kinetic data have been determined by monitoring changes in the integrated peak intensities of Bragg reflections and have been modeled using the Avrami-Erofe'ev expression. The crystallization of [C(6)N(2)H(18)][Zn(HPO(4))(H(2)PO(4))(2)] is a diffusion-controlled process, while nucleation is increasingly more important in determining the overall rate of the formation of [C(6)N(2)H(18)][Zn(3)(H(2)O)(4)(HPO(4))(4)], [C(4)N(2)H(12)][Zn(HPO(4))(2)(H(2)O)], and [C(3)N(2)H(6)][Zn(4)(OH)(PO(4))(3)]. The transformation of [C(6)N(2)H(18)][Zn(HPO(4))(H(2)PO(4))(2)] to [C(4)N(2)H(12)][Zn(HPO(4))(2)(H(2)O)] and [C(3)N(2)H(6)][Zn(4)(OH)(PO(4))(3)] occurs via a dissolution-reprecipitation mechanism, while the transformation to [C(6)N(2)H(18)][Zn(3)(H(2)O)(4)(HPO(4))(4)] may be the first observation of a direct topochemical conversion of one organically templated solid to another under hydrothermal conditions.

Journal Article↗
PubMed2003

A novel coordination mode for pentalene in trinuclear chromium complexes.

The first chromium pentalene complexes have been characterized; in these the ligand displays a hitherto-unknown bonding mode whereby a dimeric [Cr(Cp*)](2)(mu-OR) unit is bound (mu:eta(2):eta(2))- to one face, and Cp*Cr is bound eta(5)- to the other. The magnetic properties of these compounds can be understood as the superposition of those of a chromocene and an antiferromagnetically coupled Cr[bond]Cr bonded unit.

Journal Article↗
PubMed2003

Exploration of composition space in templated uranium sulfates.

The phase stability of organically templated uranium sulfates in the [UO(2)(CH(3)CO(2))(2).2H(2)O/homopiperazine/H(2)SO(4)] and [UO(2)(CH(3)CO(2))(2).2H(2)O/N,N-dimethylethylenediamine/H(2)SO(4)] systems has been studied using composition space. Two new compounds were formed in each system; [N(2)C(5)H(14)](2)[UO(2)(SO(4))(3)] (USO-17) and [N(2)C(5)H(14)][UO(2)(H(2)O)(SO(4))(2)] (USO-18) contain homopiperazine, and [N(2)C(4)H(14)][UO(2)(SO(4))(2)] (USO-19) and [N(2)C(4)H(14)][(UO(2))(2)(H(2)O)(SO(4))(3)].H(2)O (USO-20) contain N,N-dimethylethylenediamine. The relative stability of the products from each system is dependent upon the reactant mole fractions in the initial reaction gel. Crystal data: USO-17, a = 14.4975(3) A, b = 11.9109(3) A, c = 13.0157(3) A, beta = 110.475(1) degrees, monoclinic, C2/c (No. 15), Z = 4; for USO-18, a = 7.6955(2) A, b = 11.7717(3) A, c = 14.7038(4) A, orthorhombic, P22(1)2(1) (No. 18), Z = 4; for USO-19, a = 9.3322(1) A, b = 9.7743(2) A, c = 13.8897(3) A, orthorhombic, P2(1)2(1)2(1) (No. 19), Z = 4; and for USO-20, a = 11.2460(2) A, b = 10.5387(2) A, c = 17.0432(3) A, beta = 92.9884(6) degrees, monoclinic, P2(1)/c (No. 14), Z = 4.

Journal Article↗
PubMed2003

[(Th2F5)(NC7H5O4)2(H2O)][NO3]: an actinide-organic open framework.

We believe [(Th2F5)(NC7H5O4)2(H2O)][NO3] is the first three-dimensionally connected, actinide-organic framework solid. The structure is composed of thorium oxyfluoride chains, each of which connected to pyridinedicarboxylate groups to give a 3D cross-linked network with cavities containing nitrate anions.

Journal Article↗
PubMed2003

Controlled structural variations in templated uranium sulfates.

A series of experiments in the UO(2)(CH(3)CO(2))(2).2H(2)O/H(2)SO(4)/1-(2-aminoethyl)piperazine/H(2)O system were conducted to determine the effects of variation in initial reactant concentrations on the reaction products. Several reaction gels were produced, in which the composition varied from 16:80:4:500 UO(2)(CH(3)CO(2))(2).2H(2)O/H(2)SO(4)/1-(2-aminoethyl)piperazine/H(2)O to 4:92:4:500 UO(2)(CH(3)CO(2))(2).2H(2)O/H(2)SO(4)/1-(2-aminoethyl)piperazine/H(2)O. Single crystals of two new organically templated uranium sulfates, [N(3)C(6)H(18)](2)[(UO(2))(5)(H(2)O)(SO(4))(8)].5H(2)O and [N(3)C(6)H(18)][(UO(2))(2)(H(2)O)(SO(4))(3)(HSO(4))].4.5H(2)O, were isolated. Both compounds exhibit structures in which the inorganic frameworks are two-dimensional and the protonated amines reside between layers, participating in extensive hydrogen bonding. The composition and structure of each compound is dependent on the nature of the starting concentrations. Crystal data: for [N(3)C(6)H(18)](2)[(UO(2))(5)(H(2)O)(SO(4))(8)].5H(2)O, monoclinic, space group P2(1)/n (No. 14), a = 21.5597(3) A, b = 10.2901(2) A, c = 22.8403(3) A, beta = 96.7436(7) degrees, and Z = 4; for [N(3)C(6)H(18)][(UO(2))(2)(H(2)O)(SO(4))(3)(HSO(4))].4.5H(2)O, monoclinic, space group P2(1)/a (No. 14), a = 15.7673(4) A, b = 10.5813(3) A, c = 16.7710(5) A, beta = 99.9216(9) degrees, and Z = 4.

Journal Article↗
PubMed2003

Electronic structures of mixed-sandwich complexes of cyclopentadienyl and Hydrotris(pyrazolyl)borate ligands with 3d transition metals.

The electronic and magnetic properties of a series of mixed-sandwich complexes MCp(R)Tp (Cp(R) = Cp or Cp; Tp = hydrotris(pyrazolyl)borate; M = V, Cr, Fe, Co or Ni) have been studied and compared to their homoleptic analogues, MCp(R)(2) and MTp(2). Solid-state magnetic susceptibility measurements and EPR spectroscopic data indicate that complexes with d(3), d(6), and d(8) configurations are similar electronically to their metallocene analogues, except for FeCpTp, which displays a spin equilibrium (S = 0 if S = 2) in solution which was investigated by variable- temperature NMR spectroscopy. The d(2) complex [VCpTp](+) displays magnetic behavior consistent with an orbitally nondegenerate ground state. The d(4) species CrCpTp has a high-spin (S = 2) ground state. The d(7) species CoCpTp is high spin (S = 3/2) whereas its Cp analogue and [NiCpTp](+) are both low-spin (S = 1/2) species. The optical spectra of the d(3), d(6), and d(8) complexes were assigned in a fashion similar to the analogous metallocenes and ligand-field parameters (delta(1) = delta-sigma gap, delta(2) = sigma-pi gap for d-orbitals in axial symmetry) calculated. The analysis shows that for 15-electron species the total ligand-field splitting, delta(TOT), is larger than for their metallocene analogues, whereas for the 18-electron case Delta(TOT) is smaller and for 20-electron systems delta(TOT) is approximately the same. In all cases delta(2) is substantially reduced compared to the metallocenes, and in the majority of cases delta(1) is markedly larger. DFT calculations were performed to investigate further the nature of the ligand environment on the frontier orbitals in these complexes. Orbital energies and compositions were calculated and compared for a series of homoleptic and mixed-sandwich complexes of Ni(II) and across the 1st transition series for MCp(R)Tp species. The ability of Tp (vs Cp) to act as a delta-donor (with respect to the principal molecular axis) imparts significant ligand antibonding character to the delta-orbitals and results in decreased epsilon(pi)-epsilon(delta) values compared to the metallocenes and an increased tendency toward high-spin complexes in the mixed-sandwich complexes. Structure calculations were performed for CrCpTp, [VCpTp](+), and CoCpTp which show substantial distortions from ideal axial symmetry in their crystal structures. The origins of these distortions were confirmed to arise from unequal occupancy of near-degenerate delta- and pi-levels.

Journal Article↗
PubMed2003

Solid-state chelation of metal ions by ethylenediaminetetraacetate intercalated in a layered double hydroxide.

The solid-state chelation of transition metal ions (Co(2+), Ni(2+), and Cu(2+)) from aqueous solutions into the lithium aluminum layered double hydroxide ([LiAl(2)(OH)(6)]Cl x 0.5H(2)O or LDH) which has been pre-intercalated with EDTA (ethylenediaminetetraacetate) ligand has been investigated. The intercalated metal cations form [M(edta)](2)(-) complexes between the LDH layers as indicated by elemental analysis, powder X-ray diffraction, and IR and UV-vis spectroscopies. If metal chloride or nitrate salts are used in the reaction with the LDH then co-intercalation of either the Cl(-) or NO(3)(-) anions is observed. In the case of metal acetate salts the cations intercalate without the accompanying anion. This can be explained by the different intercalation selectivity of the anions in relation to the LDH. In the latter case the introduction of the positive charge into LDH structure was compensated for by the release from the solid of the equivalent quantity of lithium and hydrogen cations. Time-resolved in-situ X-ray diffraction measurements have revealed that the chelation/intercalation reactions proceed very quickly. The rate of the reaction found for nickel acetate depends on concentration as approximately k[Ni(Ac)(2)](3).

Journal Article↗
PubMed2003

Recent results from the in situ study of hydrothermal crystallisations using time-resolved X-ray and neutron diffraction methods.

We present new time-resolved powder diffraction data measured in situ during the hydrothermal crystallisation of two families of crystalline inorganic materials. In the first study, we have used time-resolved energy-dispersive X-ray diffraction (EDXRD) to follow the formation of zeolitic zinc phosphates from amine phosphates and zinc oxide in acidic solutions at 60-150 degrees C. The advantage of this method is the ability to penetrate a laboratory-sized reaction vessel and to measure data in short (< 1 min) time intervals. Integration of the Bragg peak intensities during the crystallisation of the product allows accurate crystallisation curves to be produced. In addition, in a number of cases, we observe the formation of transient crystalline intermediate phases which can be identified by use of a new three-element detector that allows a large amount of diffraction data to be measured during the experiment. We are thus able to show that three-dimensional zinc phosphate architectures often form via low-dimensional chain and layered phases, which is consistent with a recent aufbau model proposed for their formation. In the second study, we focus on the hydrothermal formation of ferroelectric barium titanate from TiO2 and barium salts in alkaline solution using time-resolved neutron diffraction. Although the time resolution of the neutron diffraction experiment is lower than the EDXRD experiment (data are measured in intervals of 5 min), we are able to penetrate reaction mixtures that are highly absorbing towards X-rays, and thus can measure data in a large volume reaction cell. Neutron diffraction data were collected on one of the highest-flux/highest detector-coverage diffractometers currently available; the GEM diffractometer at ISIS, UK. These experiments reveal that BaTiO3 crystallises after a large amount of TiO2 has been consumed; this implies that a dissolution crystallisation mechanism predominates. Additional mechanistic information is inferred by the observation of transient crystalline phases under certain reaction conditions.

Journal Article↗