School of Chemistry - Research Publications

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    Impact of the 2Fe2P core geometry on the reduction chemistry of phosphido-bridged diiron hexacarbonyl compounds
    Selan, OTE ; Cheah, MH ; Abrahams, BF ; Gable, RW ; Best, SP ; Koutsantonis, G (CSIRO PUBLISHING, 2022)
    The effect of core geometry constraints of hydrogenase H-cluster analogues on reduction chemistry have been explored by a combination of structural, electrochemical and IR spectroelectrochemical (IR-SEC) studies. A series of phosphido-bridged diiron hexacarbonyl complexes, Fe2(µ2-PPh2(CH2)xPPh2)(CO)6, x = 2 (2P) and 4 (4P) and previously reported with x = 3 (3P) and the unlinked bis-diphenylphosphido (DP) analogues were investigated. The X-ray structures of the neutral complexes demonstrate the effect of the linking group on the Fe2P2 core geometry with P–Fe–Fe–P torsion angles of 95 (2P), 101 (3P), 108 (4P) and 109° (DP) and a twisting of the Fe(CO)3 fragments from an eclipsed geometry (2P, 3P and DP) for 4P. For all four compounds the primary reduction process involves two close-spaced one-electron reactions (E1 and E2) with a systematic trend to more negative reduction potentials with a shorter link between the bridging phosphorus atoms. This reflects the greater constraint that the bridging group places on the adoption of a planar 2Fe2P geometry. The sensitivity of the core geometry is greater for E2 than E1 and this impacts the stability of the monoanion with respect to disproportion (Kdisp(298 K) = 0.02 (2P), 2.4 (3P) and 3540 (4P and DP)). 4P has a stable dianion and gives reversible cyclic voltammetry at 298 K and is quasi-reversible at 253 K, whereas the response of 2P is irreversible at 298 K, with two distinct daughter products, but becomes quasi-reversible at 253 K. IR-SEC measurements enabled elucidation of the spectra and time evolution of the reduction products. These results are consistent with a bimolecular reaction giving a distinct reduced product modelled as a dimeric, 4Fe species. The sensitivity of the reduction chemistry of the bridged diiron compounds underpins their utility as catalytic proton reduction catalysts and the systematic trends delineated in this investigation provide the framework for charting the path of their redox-coupled chemical reactions.
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    Bulky Ytterbium Formamidinates Stabilise Complexes with Radical Ligands, and Related Samarium "Tetracyclone" Chemistry
    Werner, D ; Zhao, X ; Best, SP ; Maron, L ; Junk, PC ; Deacon, GB (WILEY-V C H VERLAG GMBH, 2017-02)
    Divalent [Yb(DippForm)2 (thf)n ] (n=2 (1 a), or 1 (1 b), DippForm=N,N'-bis(2,6-diisopropylphenyl)formamidinate) complexes were treated with the ketones: 9-fluorenone (fn), or 2,3,4,5-tetraphenylcyclopentadienone (tpc, tetracyclone), giving ketyl complexes: [Yb(DippForm)2 (fn. -O)(thf)] (2), and [Yb(DippForm)2 (tpc. -O)] (3), respectively (ketyl=a radical anion containing a C. -O(-) group. By contrast, when perfluorobenzophenone (pfb) was treated with either 1 a or 1 b, transitory ketyl formation was followed by rapid decomposition through a C-F activation pathway, giving [YbF(DippForm)2 (thf)] (4 a) and a highly unusual fluoride/oxide-bridged species: [Yb5 F6 O2 (DippForm)5 ] (4 b). The reduction of diketones: 3,5-di-tert-butyl-1,2-benzoquinone (tbbq), 9,10-phenanthrenequinone (phen), or 1,2-acenaphthenequinone (acen), was also examined giving ketyl complexes: [Yb(DippForm)2 (tbbq. -O2 )] (5), [Yb(DippForm)2 (phen. -O2 )] (6), and [Yb(DippForm)2 (acen. -O2 )(thf)] (7). An unsolvated derivative of 7, namely [Yb(DippForm)2 (acen. -O2 )] (8), was obtained from PhMe. All ketyl complexes had suitably elongated C. -O bonds, were stable in both polar and non-polar solvents-an uncommon trait for rare-earth ketyl complexes-and, with the exception of 3, showed radical signals in ESR spectra. To investigate the reactivity of the tpc. -O ketyl complex, 3 was treated with oxidants (CS2 , Se) and reducing agents (Mg0 , KH, or [SmI2 (thf)2 ]). Thus 3 was oxidised to tpc by Se. Treatment of 3 with KH led to a ligand exchange process giving an unusual diketyl species [Yb(DippForm)(tpc. -O)2 (thf)2 ] (10), which has two cisoid tpc. -O- ligands in very close proximity. When treated with [SmI2 (thf)2 ], the tpc. -O ketyl was further reduced to a dianion (1-oxido-2,3,4,5-tetraphenylcyclopentadianide2- ), ({C5 Ph4 }-O)2- by [SmI2 (thf)2 ], giving dimeric [{SmI({C5 Ph4 }-O)(thf)2 }2 ] (Sm11) and monomeric complexes [YbI(DippForm)2 (thf)] (11 b) and [YbI2 (DippForm)(thf)2 ] (11 c). Activated Sm metal reduced neutral tetracyclone to the dianion, ({C5 Ph4 }-O)2- , in THF, giving tetranuclear [{SmII2 ({C5 Ph4 }-O)2 (thf)3 }2 ] (Sm13). Treatment of Sm13 with iodine in situ provided access to [{SmI({C5 Ph4 }-O)(thf)2 }2 ] (Sm11), in good yield.
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    Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene
    Best, SP ; Wang, F ; Islam, MT ; Islam, S ; Appadoo, D ; Treyorah, RM ; Chantler, CT (WILEY-V C H VERLAG GMBH, 2016-12-12)
    Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio-calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT-calculated spectra of the eclipsed (D5h ) and staggered (D5d ) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7-300 K), and solid (7-300 K) states. In each case the D5h rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution-phase samples (ca. 6 kJ mol-1 ) than for the gas-phase species (1-3 kJ mol-1 ). The generality of the approach is demonstrated with application to tricarbonyl(η4 -norbornadiene)iron(0), Fe(NBD)(CO)3 . The temperature-dependent coalescence of the ν(CO) bands of Fe(NBD)(CO)3 is well explained by the RCM without recourse to NMR-like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature-dependence of their vibrational spectra.
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    Investigation of biological activity of nickel (II) complex with naproxen and 1,10-phenanthroline ligands
    Mirzaei-Kalar, Z ; Khandar, AA ; White, JM ; Abolhasani, H ; Movahhed, TK ; Best, SP ; Jouyban, A (TAYLOR & FRANCIS INC, 2021-12-12)
    After the accidental discovery of cis-platinum, extensive attempts have centralized on the rational design of metallic compounds for cancer treatment. Here a solvent-dependent complex of nickel (II) with 1,10-phenanthroline and naproxen, [Ni(1,10-phenanthroline)(naproxen)2(solvent)], solvent = 83% H2O and 17% EtOH in the crystal structure, has been synthesized and specified by the X-ray structure analysis. It's in vitro DNA binding was inspected by the multispectroscopic methods and gel electrophoresis. The data of DNA-viscosity and competition fluorimetric test by methylene blue (MB) and Hoechst 33258 confirm groove binding mode of the complex to CT-DNA. Comparison of the results of this binding study with previous work revealed that the mode of binding of small compounds to DNA is highly influenced by the structure of the compounds. The DNA cleavage potency of the complex was appraised by the agarose gel electrophoretic and it was found that the complex does not have any momentous cleavage potency on the pUC18 plasmid DNA. The cytotoxicity of the complex on HT 29, HepG2 and HEK-293 cell lines by MTT method indicates that %inhibition of the complex on HT 29 is better than HepG2, compared with cisplatin drug. On HEK-293 cells, %inhibition growth of normal cells of the complex is less than cisplatin. Flow cytometry analysis of the complex on the HT 29 cells indicated the apoptosis cell death. RT-PCR studies revealed down-regulation of BCL2 expression, while the expression of BAX, caspase 3 and BAX/BCL2 genes was up-regulated in HT 29 cells by the complex. HighlightsA solvent-dependent nickel (II) with naproxen and 1,10-phenanthroline with aqueous solubility was synthesized and characterized.All experimental results indicate a groove mode of binding of the complex to CT-DNA.Potential biological characteristics confirmed that the complex is a promising candidate as anticancer agent.Communicated by Ramaswamy H. Sarma.
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    Neutral, Anionic, and Paramagnetic 1,3,2-Diazaberyllacyles Derived from Reduced 1,4-Diazabutadienes
    Paparo, A ; Best, SP ; Yuvaraj, K ; Jones, C (American Chemical Society, 2020-12-14)
    A series of neutral, bulky diazabutadienediyl-substituted beryllacycles [Be(DipDAB)(L)] (DipDAB = [(DipNCH)2]2-, Dip = 2,6-diisopropylphenyl; L = OEt2, THF,:C(RNCH)2; R = Me (TMC), Pri(IPriMe)) have been prepared and characterized by multinuclear NMR spectroscopy and X-ray crystallography. The preparation of similar complexes bearing the smaller tert-butyl-substituted diazabutadienediyl ligand ([(ButNCH)2]2-, viz. ButDAB) was attempted but gave rise to complex product mixtures, several components of which were isolated in trace yields. This phase of the study did, however, lead to the preparation of the homoleptic beryllium diradical complex [Be(ButDAB•)2], which was characterized by X-ray crystallography and EPR spectroscopy. In efforts to access BeI-BeI-bonded dianions, [(DipDAB)Be-Be(DipDAB)]2-, reductions of [Be(DipDAB)(L)] were pursued, but these instead afforded largely intractable product mixtures. Treating ethereal solutions of [Be(DipDAB)(OEt2)] with lithium alkyls afforded highly reactive, heterocyclic beryllate salts, [Li(OEt2)2,1][Be(DipDAB)R] (R = Me, Bun). Subsequent treatment of [Li(OEt2)][Be(DipDAB)Bun] with either N,N,N′,N′-tetramethylethylenediamine (tmeda) or N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (pmdeta) led to the formation of [Li(tmeda)2][Be(DipDAB)Bun] and [Li(pmdeta)][Be(DipDAB)Bun]. Reactions between two of the heterocyclic beryllate salts and [BeX2(OEt2)2] (X = Br, I) did not lead to clean salt metathesis reactions but gave mixtures of many products, several of which were isolated in very low yields. While the noninnocent nature of the diazabutadienediyl ligands of [Be(DipDAB)(L)], and the [Be(DipDAB)R]-anions, hampered explorations of their further reactivity, these heterocycles hold promise as synthons for beryllium coordination chemistry.
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    Redox state and photoreduction control using X-ray spectroelectrochemical techniques: advances in design and fabrication through additive engineering
    Best, SP ; Streltsov, VA ; Chantler, CT ; Li, W ; Ash, PA ; Hayama, S ; Diaz-Moreno, S (International Union of Crystallography (IUCr), 2021-03-01)
    The design and performance of an electrochemical cell and solution flow system optimized for the collection of X-ray absorption spectra from solutions of species sensitive to photodamage is described. A combination of 3D CAD and 3D printing techniques facilitates highly optimized design with low unit cost and short production time. Precise control of the solution flow is critical to both minimizing the volume of solution needed and minimizing the photodamage that occurs during data acquisition. The details of an integrated four-syringe stepper-motor-driven pump and associated software are described. It is shown that combined electrochemical and flow control can allow repeated measurement of a defined volume of solution, 100 µl, of samples sensitive to photoreduction without significant change to the X-ray absorption near-edge structure and is demonstrated by measurements of copper(II) complexes. The flow in situ electrochemical cell allows the collection of high-quality X-ray spectral measurements both in the near-edge region and over an extended energy region as is needed for structural analysis from solution samples. This approach provides control over photodamage at a level at least comparable with that achieved using cryogenic techniques and at the same time eliminates problems associated with interference due to Bragg peaks.
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    A Heteroaromatically Functionalized Hexamolybdate
    Healey, MR ; Best, SP ; GOERIGK, L ; Ritchie, C (MDPI - Open Access Publishing, 2015-05-08)
    A new heteroaromatic thiophene containing organoimido functionalized hexamolybdate has been synthesized and characterized in both solid form and solution. Structural analysis shows successful introduction of the organoimido ligand through replacement of one terminal oxo site on [Mo6O19]2− to yield the singly functionalized hexamolybdate. Spectroscopic and theoretical analysis indicates charge transfer between the inorganic and organic components, with a significantly red-shifted lowest lying transition of 399 nm vs. the parent Lindqvist ion of 325 nm. Additional characterization includes, thermal gravimetric analysis (TGA), infrared (IR), cyclic voltammetry (CV), nuclear magnetic resonance (NMR) and time-dependent density functional theory (TD-DFT) studies.
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    Artist oil paints in Thailand
    TSE, NA ; Chayabutra, S ; Kamolchote, K ; Panmanee, S ; Khlungwisarn, T ; Puskar, L ; Best, SP (International Council of Museums, 2014-09-14)
    The deterioration of artist paints and paintings in Thailand’s tropical climate is unique. This paper outlines the research and production of Pradit oil paints by Thailand’s Silpakorn University, which are manufactured in collaboration with artists, researchers, scientists and conservators. Following eight years of natural ageing in Thailand and three years in Melbourne, Australia, the paint films were technically and analytically examined to identify the oil paints more susceptible to the effects of climate. Lightfastness, solubility, crack patterns, contact angle and the real time response of oil paint films to moisture identified the more susceptible paints. Fourier transform infrared (FTIR) with attenuated total reflectance (ATR) and synchrotron radiation FTIR microspectroscopy (SR-μFTIR) identified the signatures associated with chemical changes in the paint films. Given the harsh climatic conditions in tropical Thailand, the integrated study aims to provide artists with a wider range of painting choices and for materials scientists and conservators to approach preservation issues in the region from a proactive, informed position.
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    Structural investigation of mM Ni(II) complex isomers using transmission XAFS: the significance of model development
    Islam, MT ; Chantler, CT ; Cheah, MH ; Tantau, LJ ; Tran, CQ ; Best, SP (INT UNION CRYSTALLOGRAPHY, 2015-11)
    High-accuracy transmission XAFS determined using the hybrid technique has been used to refine the geometries of bis(N-n-propyl-salicylaldiminato) nickel(II) (n-pr Ni) and bis(N-i-propyl-salicylaldiminato) nickel(II) (i-pr Ni) complexes which have approximately square planar and tetrahedral metal coordination. Multiple-scattering formalisms embedded in FEFF were used for XAFS modelling of the complexes. Here it is shown that an IFEFFIT-like package using weighting from experimental uncertainty converges to a well defined XAFS model. Structural refinement of (i-pr Ni) was found to yield a distorted tetrahedral geometry providing an excellent fit, χr(2) = 2.94. The structure of (n-pr Ni) is best modelled with a distorted square planar geometry, χr(2) = 3.27. This study demonstrates the insight that can be obtained from the propagation of uncertainty in XAFS analysis and the consequent confidence which can be obtained in hypothesis testing and in analysis of alternate structures ab initio. It also demonstrates the limitations of this (or any other) data set by defining the point at which signal becomes embedded in noise or amplified uncertainty, and hence can justify the use of a particular k-range for one data set or a different range for another. It is demonstrated that, with careful attention to data collection, including the correction of systematic errors with statistical analysis of uncertainty (the hybrid method), it is possible to obtain reliable structural information from dilute solutions using transmission XAFS data.
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    X-Ray Spectroscopy and Structure Elucidation of Reactive Electrogenerated Tri-iron Carbonyl Sulfide Clusters
    Yeo, J ; Cheah, MH ; Bondin, MI ; Best, SP (CSIRO PUBLISHING, 2012)
    The design and operation of electrosynthesis cells for generation of samples for X-ray absorption spectroscopy are described. Optimization of continuous-flow methods allows the generation of highly reducing species, which may be combined with spectroscopic validation of the composition of the electrogenerated solution. It is shown that the large sample volume (10 mL) of the 1–10 mM (in the absorbing element) solution required for such experiments can be reduced to ~100 μL using a strategy in which the in situ electrosynthesis cell is amenable to freeze-quenching and transfer to a beamline cryostat. The working electrode in this case doubles as the X-ray absorption spectroscopy sample cell. The application of these techniques is illustrated by the reduction chemistry of Fe3S2(CO)9, 3Fe2S. Spectra recorded in the near-edge region confirm that quantitative preparation of samples of 3Fe2S, 3Fe2S1– and 3Fe2S2– can be prepared by either approach, but samples of a more reduced form, identified as [Fe3S(CO)9]2–, could only be generated using continuous-flow electrosynthesis techniques. Differences in the structural chemistry of the 3Fe2S0/1–/2– redox series were examined from the perspective of their near-edge spectra and the structures of 3Fe2S1– and 3Fe2S2– forms were deduced by a combination of computational (density functional theory), spectroscopic and X-ray absorption fine-structure analyses. These show that addition of the first electron is predominantly localized in one of the Fe–Fe bonds; cleavage of the Fe–Fe bond by addition of a second electron to the Fe–Fe antibonding orbital is associated with a more substantial rearrangement of the molecule. The reduced compounds have structural similarities to the reduced dithiolate-bridged di-iron hexacarbonyl compounds and this is related to the weak electrocatalytic proton reduction exhibited by Fe3S2(CO)9. The methods described provide a strategy for the collection and analysis of experimental data directed towards structure elucidation of redox-activated solution-state complexes.