Cameron J. Kepert

University of Sydney, Sydney, New South Wales, Australia

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Publications (169)818.78 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The structures and the electrochemical and spectral properties of a series of discrete [PPh4][MnN(CN)3(diimine)] complexes {diimine = 2,2′-bipyridine [1(bpy)], 4,4′-dimethyl-2,2′-bipyridine [1(4-dmbpy)], 5,5′-dimethyl-2,2′-bipyridine [1(5-dmbpy)], 1,10-phenanthroline [1(phen)] and bipyrimidine [1(bpym)]} have been assessed. These complexes represent potential building blocks for the construction of coordination frameworks. The incorporation of diimine ligands with different π-accepting capacities allows the systematic tuning of the metal-to-ligand charge-transfer (MLCT) band as well as the MnV/MnVI redox potential. The complexes exhibit solvatochromism, and the marked sensitivity of λmax of the MLCT band to polar solvents leads the way towards their potential application in chemical sensing.
    Berichte der deutschen chemischen Gesellschaft 05/2015; DOI:10.1002/ejic.201500012
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    ABSTRACT: Two organic polymers containing alternating electron donating triarylamine and electron accepting thiazolo[5,4-d]thiazole (TzTz) moieties have been synthesized and their redox states investigated. When donor and acceptor units are proximal (polymer 1), electron density is delocalized, leading to a small electrical and optical band gap; these are larger with the inclusion of an adjoining alkynyl-phenyl bridge (polymer 2), where electron density is more localized due to the rotation of the monomer units. As a result, 1 and 2 display different optical and fluorescence properties in their neutral states. Upon chemical and electrochemical redox reactions, radicals form in both 1 and 2, yielding magnetic materials that display temperature independent paramagnetism, attributable to delocalization of radical spins along the polymeric backbones. The ability to convert between diamagnetic and paramagnetic states upon chemical oxidation and/or reduction allows for the materials to display switchable magnetism and fluorescence, imparting multifunctionality to these solid-state purely organic materials.
    Physical Chemistry Chemical Physics 03/2015; 17(17). DOI:10.1039/C5CP00081E · 4.20 Impact Factor
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    ABSTRACT: The electron spin lifetime in an assembly of chemically synthesized graphene sheets was found to be extremely sensitive to oxygen. Introducing small concentrations of physisorbed O2 onto the graphene surface reduced the exceptionally long 140 ns electron spin lifetime by an order of magnitude. This effect was completely reversible: Removing the O2 by using a dynamic vacuum restored the spin lifetime. The presence of covalently bound oxygen also decreased the electron spin lifetime in graphene, although to a far lesser extent compared to physisorbed O2 . The conduction electrons in graphene were found to play a significant role by counter-balancing the spin depolarization caused by oxygen molecules. Our results highlight the importance of chemical environment control and device packing in practical graphene-based spintronic applications.
    Chemistry - A European Journal 01/2015; 21(2). DOI:10.1002/chem.201404309 · 5.70 Impact Factor
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    ABSTRACT: A ligand containing the thiazolo[5,4-d]thiazole (TzTz) core (acceptor) with terminal triarylamine moieties (donors), N,N′-(thiazolo[5,4-d]thiazole-2,5-diylbis(4,1-phenylene))bis(N-(pyridine-4-yl)pyridin-4-amine (1), was designed as a donor–acceptor system for incorporation into electronically active metal–organic frameworks (MOFs). The capacity for the ligand to undergo multiple sequential oxidation and reduction processes was examined using UV/Vis-near-infrared spectroelectrochemistry (UV/Vis-NIR SEC) in combination with DFT calculations. The delocalized nature of the highest occupied molecular orbital (HOMO) was found to inhibit charge-transfer interactions between the terminal triarylamine moieties upon oxidation, whereas radical species localized on the TzTz core were formed upon reduction. Conversion of 1 to diamagnetic 2+ and 4+ species resulted in marked changes in the emission spectra. Incorporation of this highly delocalized multi-electron donor–acceptor ligand into a new two-dimensional MOF, [Zn(NO3)2(1)] (2), resulted in an inhibition of the oxidation processes, but retention of the reduction capability of 1. Changes in the electrochemistry of 1 upon integration into 2 are broadly consistent with the geometric and electronic constraints enforced by ligation.
    Chemistry - A European Journal 12/2014; 20(52). DOI:10.1002/chem.201405089 · 5.70 Impact Factor
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    ABSTRACT: Activation of the secondary assembly instructions in the mononuclear pyrazine imide complexes [Co(III)(dpzca)2](BF4) or [Co(II)(dpzca)2] and [Ni(II)(dpzca)2] has facilitated the construction of two robust nanoporous three-dimensional coordination polymers, [Co(III)(dpzca)2Ag](BF4)2·2(H2O) [1·2(H2O)] and [Ni(II)(dpzca)2Ag]BF4·0.5(acetone) [2·0.5(acetone)]. Despite the difference in charge distribution and anion loading, the framework structures of 1·2(H2O) and 2·0.5(acetone) are isostructural. One dimensional channels along the b-axis permeate the structures and contain the tetrafluoroborate counterions (the Co(III)-based MOF has twice as many BF4(-) anions as the Ni(II)-based MOF) and guest solvent molecules. These anions are not readily exchanged whereas the solvent molecules can be reversibly removed and replaced. The H2, N2, CO2, CH4, H2O, CH3OH, and CH3CN sorption behaviors of the evacuated frameworks 1 and 2 at 298 K have been studied, and modeled, and both show very high selectivity for CO2 over N2. The increased anion loading in the channels of Co(III)-based MOF 1 relative to Ni(II)-based MOF 2 results in increased selectivity for CO2 over N2 but a decrease in the sorption kinetics and storage capacity of the framework.
    Inorganic Chemistry 10/2014; DOI:10.1021/ic501876m · 4.79 Impact Factor
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    ABSTRACT: The synthesis, as well as the electrochemical, optical and magnetic properties of a sulfate bridged Co(II) dimer, [Co2(DMIM)4(μ2 O2,O,O′ SO4)2]•2MeCN (DMIM = 1,2 dimethylimidazole) (2), are reported. The crystal structure consists of two distorted pseudo octahedral Co(II) centres, each ligated by the μ2-(O O′ sulfato) and μ2-(O2 sulfato) bridging modes of the SO42- anions. Magnetic studies have identified significant antiferromagnetic coupling between the high spin Co(II) centres, with J = –28 cm 1. Cyclic voltammetry indicated the presence of a quasi reversible ligand centred oxidation, while the vis NIR spectrum of 2 revealed complex splitting of the absorption bands due to the tetragonal distortion of the octahedral geometry of the Co(II) centres.
    New Journal of Chemistry 09/2014; DOI:10.1039/C4NJ01401D · 3.16 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 09/2014; 126(38). DOI:10.1002/ange.201402951
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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 09/2014; 53(38). DOI:10.1002/anie.201402951 · 11.34 Impact Factor
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    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; 50(84). DOI:10.1039/C4CC05438E · 6.72 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. DOI:10.1039/c4sc00809j · 8.60 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; 43(41). DOI:10.1039/C4DT02133A · 4.10 Impact Factor
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    ABSTRACT: The structure of the nanoporous metal-organic framework Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) with a variety of molecular guests was studied in situ using single crystal X-ray diffraction. By collecting crystal structure data for a series of guests within the same host crystal, insights into the molecular interactions underpinning guest adsorption processes have been gained. Adsorption behaviors are influenced strongly by both enthalpic and entropic thermodynamic, as well as interpore steric (size-exclusion) effects, and we note correlations between guest attributes and these effects. Vapor adsorption measurements revealed a guest uptake capacity inversely proportional to guest size. Correspondingly, structural results show that guests reside in the smallest pores accessible to them. Interpore steric effects for larger guests cause these to be excluded from the smallest pores, and this corresponds to lower total uptake. Both hydrophilic and lipophilic small guests adsorb favorably into the 5 Å diameter smallest pore of the material, with the number of guests in these pores dependent on guest size and their location, in turn dependent upon both guest-guest interactions and competition between hydrogen-bonding interactions at the apertures of the smallest pore and lipophilic interactions at the center of the smallest pore. Hydrophilic guests with lone electron pairs interact preferentially with the coordinatively unsaturated Cu sites of the desolvated framework, with the number of these depending on steric interactions between neighboring bound guests and guest flexibility. Guest coordination at the Cu sites has a significant effect on the framework structure, increasing the Cu···Cu distance in the dinuclear unit, with the Cu3(BTC)2 unit cell being smaller when guests that do not coordinate with the Cu are present, and in the case of cyclohexane, smaller than for the desolvated framework. Overall, our comprehensive structural study reconciles Cu3(BTC)2 adsorption properties with the underlying guest-host and guest-guest interactions that gives rise to these.
    Chemistry of Materials 08/2014; 26(16):4712-4723. DOI:10.1021/cm501138g · 8.54 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; 43(39). DOI:10.1039/c4dt02205j · 4.10 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; 5(10). DOI:10.1039/C4SC01636J · 8.60 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; 53(15). DOI:10.1021/ic500323r · 4.79 Impact Factor
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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 - A European Journal 06/2014; 20(24). DOI:10.1002/chem.201400367 · 5.70 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 03/2014; 126(20). DOI:10.1002/anie.201311055 · 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; 50(29). DOI:10.1039/c4cc01079e · 6.72 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. DOI:10.1016/j.ijhydene.2013.10.143 · 2.93 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; 53(2). DOI:10.1021/ic402686s · 4.79 Impact Factor

Publication Stats

6k Citations
818.78 Total Impact Points

Institutions

  • 2001–2015
    • University of Sydney
      • School of Chemistry
      Sydney, New South Wales, Australia
  • 2009
    • Australian Nuclear Science and Technology Organisation
      • Bragg Institute
      Kirrawee, New South Wales, Australia
  • 2008
    • Universität Basel
      • Department of Chemistry
      Bâle, Basel-City, Switzerland
  • 2007
    • Monash University (Australia)
      • School of Chemistry, Clayton
      Melbourne, Victoria, Australia
  • 2006
    • University of Cambridge
      • Department of Earth Sciences
      Cambridge, England, United Kingdom
  • 1999–2006
    • University of Western Australia
      • School of Chemistry and Biochemistry
      Perth, Western Australia, Australia
  • 2005
    • Argonne National Laboratory
      Lemont, Illinois, United States
  • 2004
    • University of Vic
      Vic, Catalonia, Spain
  • 2003
    • Institut de Physique et Chimie des Matériaux de Strasbourg
      Strasburg, Alsace, France
  • 2000–2002
    • University of Liverpool
      • Department of Chemistry
      Liverpool, ENG, United Kingdom
  • 1998–2000
    • University of Oxford
      • Inorganic Chemistry Laboratory
      Oxford, England, United Kingdom
  • 1994–1999
    • The Royal Institution of Great Britain
      Londinium, England, United Kingdom
  • 1997
    • The Royal Institution
      Londinium, England, United Kingdom
  • 1995
    • University College London
      • Department of Chemistry
      Londinium, England, United Kingdom