Cameron J Kepert

University of Sydney, Sydney, New South Wales, Australia

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Publications (147)677.22 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The metalloligand [Ni(pedt)2]- (pedt = 1-(pyridine-4-yl)ethylene-1,2-dithiolate) has been incorporated into two multi-dimensional structures for the first time. These coordination frameworks represent highly unusual interpenetration isomers and exhibit solid state redox and optical properties that reflect the electronically delocalised nature of the metalloligand.
    Chemical Communications 09/2014; · 6.38 Impact Factor
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    ABSTRACT: The structures of the AxLnM(CN)6·nH2O (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; x = 0, 1; 0 <= n <= 5) cyanide frameworks, their thermal expansion behaviour, and their transformations upon dehydration are explored using X-ray and neutron single crystal diffraction and X-ray powder diffraction. Modification from positive to negative thermal expansion in the LnCo(CN)6·nH2O phases is achieved by removal of the guest water molecules. Most notable is the unprecedented flexibility demonstrated by the "coiling" of KLnFe(CN)6·nH2O frameworks upon their dehydration, wherein the lanthanoid coordination geometry reversibly converts from a 9-coordinate tri-capped trigonal prism to a 6-coordinate octahedron via a single-crystal-to-single-crystal process, accompanied by a large (14–16%) decrease in unit cell volume.
    Chemical Science 09/2014; 5(9):3409-3417. · 8.31 Impact Factor
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    ABSTRACT: Eight platinum complexes with anticancer potential have been synthesised and characterised. These complexes are of the type [Pt(IL)(AL)]2+, where IL¬ is either dipyrido[3,2-f:2ʹ,3ʹ-h]quinoxaline (dpq) or 2,3-dimethyl-dpq (23Me2dpq) and AL is one of the R,R or S,S isomers of either 1,2-diaminocyclohexane (SS-dach or RR-dach) or 1,2-diaminocyclopentane (SS-dacp or RR-dacp). The CT-DNA binding of these complexes and a series of other complexes were assessed using fluorescent intercalator displacement assays, resulting in unexpected trends in DNA binding affinity. The cytotoxicity of the eight synthesised compounds was determined in the L1210 cell line; the most cytotoxic of these were [Pt(dpq)(SS-dach)]Cl2 and [Pt(dpq)(RR-dach)]Cl2, with IC50 values of 0.19 and 0.80 μM, respectively. The x-ray crystal structure of the complex [Pt(dpq)(SS-dach)](ClO4)2•1.75H2O is also reported.
    Dalton Transactions 09/2014; · 3.81 Impact Factor
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    ABSTRACT: The properties of atmospheric CO2 fixation, metamagnetism, reversible guest adsorption and zero thermal expansion have been combined in a single robust MOF, [Cu3(bpac)3(CO3)2](ClO4)2·H2O (·H2O). This compound is a ditopically-bridged copper carbonate kagome lattice where desolvation of the MOF allows subtle tuning of the metamagnetic and uniaxial ZTE behaviour.
    Dalton Transactions 08/2014; · 3.81 Impact Factor
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    ABSTRACT: Covalent post-synthetic modification is a versatile method for gaining high-level synthetic control over functionality within porous metal–organic frameworks and for generating new materials not accessible through one-step framework syntheses. Here we apply this topotactic synthetic approach to a porous spin crossover framework and show through detailed comparison of the structures and properties of the as-synthesised and covalently modified phases that the modification reaction proceeds quantitatively by a thermally activated single-crystal-to-single-crystal transformation to yield a material with lowered spin-switching temperature, decreased lattice cooperativity, and altered color. Structure–function relationships to emerge from this comparison show that the approach provides a new route for tuning spin crossover through control over both outer-sphere and steric interactions.
    Angewandte Chemie 07/2014;
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    ABSTRACT: Covalent post-synthetic modification is a versatile method for gaining high-level synthetic control over functionality within porous metal–organic frameworks and for generating new materials not accessible through one-step framework syntheses. Here we apply this topotactic synthetic approach to a porous spin crossover framework and show through detailed comparison of the structures and properties of the as-synthesised and covalently modified phases that the modification reaction proceeds quantitatively by a thermally activated single-crystal-to-single-crystal transformation to yield a material with lowered spin-switching temperature, decreased lattice cooperativity, and altered color. Structure–function relationships to emerge from this comparison show that the approach provides a new route for tuning spin crossover through control over both outer-sphere and steric interactions.
    Angewandte Chemie International Edition 07/2014; · 11.34 Impact Factor
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    ABSTRACT: Crystalline salts of a series of cationic multimetallic cobalt complexes reversibly, selectively and stoichiometrically chemisorb dioxygen in a process involving the two electron oxidation of dimetallic sites with concurrent reduction of two equivalents of sorbed O2 to form μ-η1,η2-peroxide ligands. The coordinating ability of counteranions, ClO4−, PF6−, BF4−, CF3SO3− and NO3− determine the O2 affinity of the deoxygenated forms, and the nitrate and triflate salts sorb dioxygen at a significantly slower rate compared to the PF6− and BF4− salts (hours versus sub-seconds at ambient temperature and pressure). Single crystal X-ray structural determination for a nitrate salt of the 2-aminoterephthalato-linked deoxy system, [{(bpbp)Co2II(NO3)}2(NH2bdc)](NO3)2·2H2O (bpbp− = 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato, NH2bdc2− = 2-amino-1,4-benzenedicarboxylato) shows that nitrate ions are coordinated as bridging ligands. These crystals undergo reversible single-crystal-to-single-crystal (SC-to-SC) transformations on the stoichiometric uptake of O2. During this process O2 replaces the two nitrate ligands. Thus the Co ions are six coordinated in both the oxy and deoxy states. This SC-to-SC process involves the concerted fast migration of neutral dioxygen through the crystal lattice and the translational movement by 4–6 Å of at least two of nitrate anions. Rapid hydration/dehydration processes involving several molecules of co-crystallized water per unit cell accompany the reaction. Besides large atom movements involving O2, NO3− and H2O, these impressive examples of consecutive SC-to-SC-to-SC transformations involve the cleavage of four bonds, and the creation of four new bonds, in one single molecule. The solid state structural rearrangements observed provide an explanation for the slower rates of dioxygen uptake for the complexes isolated as nitrate salts, and by inference, the triflate salts, compared to the salts of more weakly coordinating counteranions, ClO4−, PF6− and BF4−.
    Chemical Science 07/2014; · 8.31 Impact Factor
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    ABSTRACT: The expected 3D and 2D topologies resulting from combining approximately linear bis- or monopyridyl ligands with [Fe(II)M(II)(CN)4] (M(II) = Pt, Pd, Ni) 4,4-grid sheets are well established. We show here the magnetic and structural consequences of incorporating a bent bispyridyl linker ligand in combination with [Fe(II)Pt(II)(CN)4] to form the material [Fe(H2O)2Fe(DPSe)2(Pt(CN)4)2]·3EtOH (DPSe = 4,4'-dipyridylselenide). Structural investigations reveal an unusual connectivity loosely resembling a 3D Hofmann topology where (1) there are two distinct local iron(II) environments, [Fe(II)N6] (Fe1) and [Fe(II)N4O2] (Fe2), (2) as a consequence of axial water coordination to Fe2, there are "holes" in the [Fe(II)Pt(II)(CN)4] 4,4 sheets because of some of the cyanido ligands being terminal rather than bridging, and (3) bridging of adjacent sheets occurs only through one in two DPSe ligands, with the other acting as a terminal ligand binding through only one pyridyl group. The magnetic properties are defined by this unusual topology such that only Fe1 is in the appropriate environment for a high-spin to low-spin transition to occur. Magnetic susceptibility data reveal a complete and abrupt hysteretic spin transition (T1/2↓ = 120 K and T1/2↑ = 130 K) of this iron(II) site; Fe2 remains high-spin. This material additionally exhibits a photomagnetic response (uncommon for Hofmann-related materials), showing light-induced excited spin-state trapping [LIESST; T(LIESST) = 61 K] with associated bistability evidenced in a hysteresis loop (T1/2↓ = 60 K and T1/2↑ = 66 K).
    Inorganic chemistry. 07/2014;
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    ABSTRACT: Two new isostructural iron(II) spin-crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)2(NCX)2] (dpms=4,4′-dipyridylmethyl sulfide; X=S (SCOF-6(S)), X=Se (SCOF-6(Se))) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF-6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high-spin (HS) to low-spin iron(II) sites over the temperature range 300–4 K (T1/2=75 K). In contrast, the NCSe− analogue, SCOF-6(Se), displays a complete SCO transition (T1/2=135 K). Photomagnetic characterizations reveal quantitative light- induced excited spin-state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF-6(S) and SCOF-6(Se), respectively. Variable-pressure magnetic measurements were performed on SCOF-6(S), revealing that with increasing pressure both the T1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF-6(S) at ambient pressure due to an interplay between close T1/2 and T(LIESST) values.
    Chemistry 05/2014; · 5.93 Impact Factor
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    ABSTRACT: Metal-organic framework materials (MOFs) have recently been shown in some cases to exhibit strong negative thermal expansion (NTE) behavior, while framework interpenetration has been found to reduce NTE in many materials. Using powder and single-crystal diffraction methods we investigate the thermal expansion behavior of interpenetrated Cu3 (btb)2 (MOF-14) and find that it exhibits an anomalously large NTE effect. Temperature-dependent structural analysis shows that, contrary to other interpenetrated materials, in MOF-14 the large positive thermal expansion of weak interactions that hold the interpenetrating networks together results in a low-energy contractive distortion of the overall framework structure, demonstrating a new mechanism for NTE.
    Angewandte Chemie International Edition 04/2014; · 11.34 Impact Factor
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    ABSTRACT: The abrupt and hysteretic two-step spin crossover in a new triazole-based 2-D Hofmann-type complex shows a record breaking 120 K intermediate plateau (IP) region stabilized by negative cooperative interactions.
    Chemical Communications 03/2014; · 6.38 Impact Factor
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    ABSTRACT: A rare, discrete, mixed-valent, heterometallic Fe(III)/Cu(II) cage, [Cu6Fe8L8](ClO4)12·χsolvent (H3L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine), was designed and synthesized via metal-ion-directed self-assembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by X-ray crystallography, ESI mass spectrometry, FT-IR, and UV-vis-NIR spectroscopy.
    Inorganic Chemistry 01/2014; · 4.59 Impact Factor
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    ABSTRACT: Dehydration of the isostructural three-dimensional (3D) octacyanometallate-based materials Mn2M(CN)8·7H2O (M = Mo, 1·7H2O; W, 2·7H2O) generates robust porous frameworks (1 and 2). In the structure, the [M(CN)8]4− units are linked via octahedral Mn2+ centers to form an open 3D framework with 1D channels, in which the non-coordinated and coordinated water molecules are involved. The permanent porosities have been confirmed by thermogravimetric analysis, variable-temperature X-ray diffraction and Raman spectra, and adsorption (H2O, N2 and H2) measurements. H2 adsorption at 1.1 bar and 77 K was 0.60 wt% for 1 and 0.49 wt% for 2. At initial loading ΔHads has the value of ca. 10.0 kJ mol−1 for both materials, which represents the highest value reported for any cyanide-based assemblies. The high enthalpy can be attributed to the presence of coordinatively-unsaturated Mn2+ sites left exposed by the removal of coordinated water molecules in the structure.
    International Journal of Hydrogen Energy 01/2014; 39(2):884–889. · 3.55 Impact Factor
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    ABSTRACT: Neutron powder diffraction measurements were carried out on the evacuated and CO2-loaded Prussian blue analogue, Fe3[Co(CN)6]2, identifying two distinct CO2 adsorption sites: site A, in which CO2 uniquely bridges between two bare-metal sites, and site B, in which it interacts in a face capping motif. The saturation of site A at low loadings of CO2 demonstrates the favourable nature of the interaction of CO2 with bare-metal sites within the material.
    Chemical Communications 09/2013; · 6.38 Impact Factor
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    ABSTRACT: A new coordination framework material, [Zn{MnN(CN)4(H2O)}]·2H2O·MeOH, has been characterised crystallographically and the effect of a terminal nitride on the N2, H2 and CO2 sorption capacities of the material assessed through porosimetery measurements and DRIFTS.
    Dalton Transactions 08/2013; · 3.81 Impact Factor
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    ABSTRACT: RUM mit Kick: Das Ausmaß der negativen thermischen Ausdehnung (NTE) in LnCo(CN)6‐Koordinationsgerüsten nimmt mit steigendem Radius des Lanthanoidions (r Ln) zu. Die Strukturen enthalten ungewöhnliche lokal instabile trigonal‐prismatische LnN6‐Einheiten, die an einer zur NTE beitragenden Schwingungsmode beteiligt sind. Hier zeigt sich ein Unterschied zu den Schwingungsmoden mit starren Einheiten (RUMs), die in anderen Systemen vorherrschen.
    Angewandte Chemie 05/2013; 125(20).
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    ABSTRACT: RUM with a twist: The magnitude of negative thermal expansion (NTE) in the LnCo(CN)6 coordination frameworks increases with Ln ion radius rLn . The framework structure contains an unusual locally unstable trigonal prismatic LnN6 unit that participates in an NTE-contributing vibrational mode by twisting about its axis at low energies. This contrasts with the rigid unit modes (RUMs) prevalent in other systems.
    Angewandte Chemie International Edition 04/2013; · 11.34 Impact Factor
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    ABSTRACT: A new microporous framework, Zn(NDC)(DPMBI) (where NDC = 2,7-naphthalene dicarboxylate and DPMBI = N,N'-di-(4-pyridylmethyl)-1,2,4,5-benzenetetracarboxydiimide), containing the redox-active benzenetetracarboxydiimide (also known as pyromellitic diimide) ligand core has been crystallographically characterised and exhibits a BET surface area of 608.2 ± 0.7 m(2) g(-1). The crystallinity of the material is retained upon chemical reduction with sodium naphthalenide (NaNp), which generates the monoradical anion of the pyromellitic diimide ligand in the framework Zn(NDC)(DPMBI)·Nax (where x represents the molar Na(+)/Zn(2+) ratio of 0.109, 0.233, 0.367 and 0.378 from ICP-AES), as determined by EPR, solid state Vis-NIR spectroelectrochemistry and UV-Vis-NIR spectroscopy. The CO2 uptake in the reduced materials relative to the neutral framework is enhanced up to a Na(+)/Zn(2+) molar ratio of 0.367; however, beyond this concentration the surface area and CO2 uptake decrease due to pore obstruction. The CO2 isosteric heat of adsorption (|Qst|) and CO2/N2 selectivity (S), obtained from pure gas adsorption isotherms and Ideal Adsorbed Solution Theory (IAST) calculations, are also maximised relative to the neutral framework at this concentration of the alkali metal counter-ion. The observed enhancement in the CO2 uptake, selectivity and isoteric heat of adsorption has been attributed to stronger interactions between CO2 and both the radical DPMBI ligand backbone and the occluded Na(+) ions.
    Dalton Transactions 03/2013; · 3.81 Impact Factor
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    ABSTRACT: Dynamically porous metal-organic frameworks (MOFs) with a chiral quartz-based structure have been synthesized from the multidentate ligand 2,2'-dihydroxybiphenyl-4,4'-dicarboxylate (H(2)diol). Compounds [Ni(ii)(H(2)diol)(S)(2)]·xS (where S = DMF or DEF) show marked changes in 77 K N(2) uptake between partially desolvated [Ni(ii)(H(2)diol)(S)(2)] (only the pore solvent is removed) and fully desolvated [Ni(ii)(H(2)diol)] forms. Furthermore, [Ni(ii)(H(2)diol)(DMF)(2)] displays additional solvent-dependent porosity through the rotation of DMF molecules attached to the axial coordination sites of the Ni(ii) centre. A unique feature of the four coordinate Ni(ii) centre in [Ni(ii)(H(2)diol)] is the dynamic response to its chemical environment. Exposure of [Ni(ii)(H(2)diol)] to H(2)O and MeOH vapour leads to coordination of both axial sites of the Ni centres and to the generation of a solvated framework, whereas exposure to EtOH, DMF, acetone, and MeCN does not lead to any change in metal coordination or structure metrics. MeOH vapour adsorption was able to be tracked by time-dependent magnetometry as the solvated and desolvated structures have different magnetic moments. Solvated and desolvated forms of the MOF show remarkable differences in their thermal expansivities; [Ni(ii)(H(2)diol)(DMF)(2)]·DMF displays marked positive thermal expansion (PTE) in the c-axis, yet near to zero thermal expansion, between 90 and 450 K, is observed for [Ni(ii)(H(2)diol)]. These new MOF architectures demonstrate a dynamic structural and colourimetric response to selected adsorbates via a unique mechanism that involves a reversible change in the coordination environment of the metal centre. These coordination changes are mediated throughout the MOF by rotational mobility about the biaryl bond of the ligand.
    Dalton Transactions 02/2013; · 3.81 Impact Factor
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Publication Stats

2k Citations
677.22 Total Impact Points

Institutions

  • 2003–2014
    • University of Sydney
      • School of Chemistry
      Sydney, New South Wales, Australia
  • 2012
    • Aarhus University
      • Centre for Materials Crystallography CMC
      Aars, Region North Jutland, Denmark
    • Chinese Academy of Sciences
      Peping, Beijing, China
  • 2001–2010
    • University of Liverpool
      • Department of Chemistry
      Liverpool, England, United Kingdom
    • University of Western Australia
      • School of Chemistry and Biochemistry
      Perth, Western Australia, Australia
  • 1997–2010
    • University of Oxford
      • • Inorganic Chemistry Laboratory
      • • Department of Physics
      Oxford, England, United Kingdom
    • The Royal Institution
      Street, England, United Kingdom
  • 2009
    • Australian Nuclear Science and Technology Organisation
      Kirrawee, New South Wales, Australia
    • National Institute of Standards and Technology
      • NIST Center for Neutron Research
      Gaithersburg, MD, United States
    • University of Cambridge
      • Department of Earth Sciences
      Cambridge, ENG, United Kingdom
  • 2007–2009
    • Monash University (Australia)
      • School of Chemistry, Clayton
      Melbourne, Victoria, Australia
  • 2005
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2002–2003
    • Institut de Physique et Chimie des Matériaux de Strasbourg
      Strasburg, Alsace, France
  • 1994–1999
    • The Royal Institution of Great Britain
      Londinium, England, United Kingdom