255 research outputs found
An EPR investigation of binding environments by N-donor chelating exchange resins for Cu extraction from aqueous media
EPR and UVâvis spectroscopy were collectively used to characterize a series of Cu(II) binding environments within two chelating exchange resins, Dowex and CuWRAM, used for Cu(II) extraction from aqueous media. A series of well-defined intra- and intermolecular binding sites have been identified as responsible for Cu(II) uptake
Probing the structure of copper(II)-casiopeina type coordination complexes [Cu(O-O)(N-N)]+ by EPR and ENDOR spectroscopy
Although copper based complexes have been widely used in homogeneous catalysis, more recently they are attracting considerable attention as pharmaceutical therapeutic agents. Of paramount importance in their efficacy of use is their structure and electronic properties, which can be thoroughly probed using advanced EPR techniques. In this study, a series of [Cu(acac)(N-N)]+ Casiopeina type complexes were investigated, bearing a series of diimine N-N ligands (including bipy, phen, Py-bipy and dppz). All complexes displayed rhombic g and CuA tensors, although the extent of rhombicity was dependent on the N-N ligand. Greater Cu(II)-N2 in-plane distortion, away from the square planar arrangement, was detected by CW W-band EPR for the smaller bipy and phen ligands compared to the larger Py-bipy and dppz ligands. Changes in ligand spin density distributions (over the 1H and 14N nuclei) were revealed by CW Q-band ENDOR. The largest components of the 1H imine and 14N hyperfine coupling decreased as the ligand size increased, following the trend bipy > phen > Py-bipy > dppz. These results indicate how even small structural and electronic (spin density) perturbations within the Casiopeina family of Cu(II) complexes can be probed by advanced EPR methods
Monitoring the substrate-induced spin-state distribution in a Cobalt(II)-Salen complex by EPR and DFT
Ground state changes of (R,Râ)-N,Nâ-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co(II), following coordination of various pyridyl substrate has been examined by CW EPR, pulsed relaxation measurements and DFT. The solution-based Co(II) complex possesses a low spin (LS) state urn:x-wiley:14341948:media:ejic202101071:ejic202101071-math-0001 (with g-values of 1.96, 1.895, 3.14). Upon coordination of the pyridyl substrate, the resulting bound adduct reveals a distribution of LS âbase-onâ species, possessing a urn:x-wiley:14341948:media:ejic202101071:ejic202101071-math-0002 electronic ground state (with g-values of 2.008, 2.2145, 2.46) and a high spin (HS) species (with geff = 4.6). DFT indicated that the energy gap between the LS and HS state is dramatically lowered (ÎE < 25â
kJmolâ1) following substrate coordination. DFT suggests the main geometrical difference between the LS and HS systems is the severe puckering of the N2O2 ligand backbone. The results revealed a tentative dependency on the pKaâH of the substrates for the spin distribution where, in most cases, the higher pKaâH substrate values favoured the HS species
Understanding the coordination modes of [Cu(acac)2(imidazole)n=1,2] adducts by EPR, ENDOR, HYSCORE, and DFT analysis
The interaction of imidazole with a [Cu(acac)2]
complex was studied using electron paramagnetic resonance (EPR),
electron nuclear double resonance (ENDOR), hyperfine sublevel
correlation spectroscopy (HYSCORE), and density functional
theory (DFT). At low Im ratios (Cu:Im 1:10), a 5-coordinate
[Cu(acac)2Imn=1] monoadduct is formed in frozen solution with the
spin Hamiltonian parameters g1 = 2.063, g2 = 2.063, g3 = 2.307, A1 =
26, A2 = 15, and A3 = 472 MHz with Im coordinating along the axial
direction. At higher Im concentrations (Cu:Im 1:50), a 6-
coordinate [Cu(acac)2Imn=2] bis-adduct is formed with the spin
Hamiltonian parameters g1 = 2.059, g2 = 2.059, g3 = 2.288, A1 = 30,
A2 = 30, and A3 = 498 MHz with a poorly resolved 14N
superhyperfine pattern. The isotropic EPR spectra revealed a distribution of species ([Cu(acac)2], [Cu(acac)2Imn=1], and
[Cu(acac)2Imn=2]) at Cu:Im ratios of 1:0, 1:10, and 1:50. The superhyperfine pattern originates from two strongly coordinating
N3 imino nitrogens of the Im ring. Angular selective 14N ENDOR analysis revealed the NA tensor of [34.8, 43.5, 34.0] MHz, with
e2qQ/h = 2.2 MHz and η = 0.2 for N3. The hyperfine and quadrupole values for the remote N1 amine nitrogens (from
HYSCORE) were found to be [1.5, 1.4, 2.5] MHz with e2qQ/h = 1.4 MHz and η = 0.9. 1H ENDOR also revealed three sets of
HA tensors corresponding to the nearly equivalent H2/H4 protons in addition to the H5 and H1 protons of the Im ring. The spin
Hamiltonian parameters for the geometry optimized structures of [Cu(acac)2Imn=2], including cis-mixed plane, trans-axial, and
trans-equatorial, were calculated. The best agreement between theory and experiment indicated the preferred coordination is
trans-equatorial [Cu(acac)2Imn=2]. A number of other Im derivatives were also investigated. 4(5)-methyl-imidazole forms a
[Cu(acac)2(Im-3)n=2] trans-equatorial adduct, whereas the bulkier 2-methyl-imidazole (Im-2) and benzimidazole (Im-4) form
the [Cu(acac)2(Im-2,4)n=1] monoadduct only. Our data therefore show that subtle changes in the substrate structure lead to
controllable changes in coordination behavior, which could in turn lead to rational design of complexes for use in catalysis,
imaging, and medicine
An EPR Investigation of defect structure and electron transfer mechanism in mixed-conductive LiBO2-V2O5 glasses
Continuous Wave (CW) Electron Paramagnetic Resonance (EPR) spectroscopy was used to study the defect structure and electron transfer mechanism in a series of LiBO2-V2O5 mixed conductive glasses of varying V2O5 content. These glassy materials are attracting growing interest for energy storage devices. At low V2O5 content (VLB1), an isolated S = œ vanadium defect centre is found at a network modifying position within the LiBO2 matrix. The observed spin Hamiltonian parameters are consistent with a V4+ centre possessing a distorted octahedral configuration and dxy orbital ground state. At high V2O5 content (VLB3), the vanadium hyperfine structure is absent indicative of a distinct exchange-narrowed signal. A model was developed to analyse the linewidth and g-tensor component of the EPR signals, revealing a marked temperature dependent behaviour, consistent with a polaron hopping mechanism of electron transfer and inter-electronic exchange along the g3 direction, coincident with the electron transfer axis. The activation energy (Ea) was estimated to be 0.0805 eV, consistent with other conducting glasses. A relaxation-dominated line broadening mechanism was further supported by multi-frequency EPR measurements, which also identified unresolved features at high frequencies due to unaccounted for anisotropic exchange / speciation within the disordered network. This analysis provides a straight-forward method for the use of EPR to investigate solid-state glassy materials
The health profile of people living with Parkinson\u27s Disease managed in a comprehensive care setting
Background: Globally there are few reports of the impairments, disabilities and medications used in people living with idiopathic Parkinson’s disease. Caregiver characteristics and caregiver burden have seldom been reported. We examined the health status in a large cohort of people living with Parkinson’s disease and their caregivers managed in a comprehensive health care setting. Methods/Design: A prospective, cross sectional analysis of impairments, disabilities and Parkinson’s disease medication use was conducted in a sample of 100 people with Parkinson’s disease rated I-IV on the modified Hoehn & Yahr scale. Participants were recruited from the Victorian Comprehensive Parkinson Program in Melbourne, Australia. Their caregivers were invited to provide their views on the burden of care, services provided and support received. Results: The severity of impairments and disabilities was strongly associated with disease duration (mean of 5.5 years). Those with long standing disease or more severe disease also used more Parkinson’s disease medications and participated in fewer social roles than people who were newly diagnosed or mildly affected. The severity of impairments was strongly correlated with limitations in performing activities of daily living. Limitations in performing daily activities were also found to be a significant contributing factor for health-related quality of life (PDQ-39 SI β=0.55, p=0.000; EQ-5D SI β=0.43, p=0.001). People with Parkinson’s disease lived at home with relatives. The average caregiver was a spouse or child providing approximately 3.5 hours of care per day, with the capacity to provide 9.4 hours per day and had provided care for four years. Additional support was high (63%) for 2.5 hours per day. Conclusion: The comprehensive care setting of this cohort describes a relatively benign condition despite a wide range of disease duration and severity. This report provides a baseline with which to compare other delivery models
A continuous-wave EPR investigation into the photochemical transformations of the chromium(I) carbonyl complex [Cr(CO)4bis(diphenylphosphino)]+ and reactivity with 1-hexene
Chromium complexes containing a bis(diphenylphosphino) ligand have attracted significant interest over many years due to their potential as active catalysts for ethylene oligomerisation when combined with suitable co-catalysts such as triethylaluminium (TEA) or methylaluminoxane (MAO). While there has been considerable attention devoted to the possible reaction intermediates and the nature of the Cr oxidation states involved, the potential UV photoactivity of the Cr(I) complexes has so far been overlooked. Therefore, to explore the photoinduced transformations of bis(diphenylphosphino) stabilized Cr(I) complexes, we used continuous-wave (CW) EPR to study the effects of UV radiation on a cationic [Cr(CO)4(dppp)]+[Al(OC(CF3)3)4]â complex (1), where dppp represents the 1,3 bis-(diphenylphosphino)propane ligand, Ph2P(C3H6)PPh2. Our preliminary investigations into the photochemistry of this complex revealed that [Cr(CO)4(dppp)]+ (1) can be readily photo-converted into an intermediate mer-[Cr(CO)3(Îș1-dppp)(Îș2-dppp)]+ complex (2) and eventually into a trans-[Cr(CO)2(dppp)2]+ complex (3) in solution at room temperature under UV-A light. Here, we show that the intermediate species (2) involved in this transformation can be identified by EPR at much lower temperature (140 K) and at a specific wavelength (highlighting the wavelength dependency of the reaction). In addition, small amounts of a âpiano-stoolâ-type complex, namely [Cr(CO)2(dppp-η6-arene)]+ (4), can also be formed during the photoconversion of [Cr(CO)4(dppp)]+ using UV-A light. There was no evidence for the formation of the [Cr(L-bis-η6-arene)]+ complex (5) in these UV irradiation experiments. For the first time, we also evidence the formation of a 1-hexene coordinated [Cr(CO)3(dppp)(1-hexene)]+ complex (6) following UV irradiation of [Cr(CO)4(dppp)]+ in the presence of 1-hexene; this result demonstrates the unprecedented opportunity for exploiting light activation during Cr-driven olefin oligomerisation catalysis, instead of expensive, difficult-to-handle, and hazardous chemical activators
Mono- and dinuclear Ni(I) products formed upon bromide abstraction from the Ni(I) ring-expanded NHC complex [Ni(6-Mes)(PPh<sub>3</sub>)Br]
Bromide abstraction from the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complex [Ni(6-Mes)(PPh3)Br] (1; 6-Mes = 1,3-bis(2,4,6-trimethylphenyl) 3,4,5,6-tetrahydropyrimidin-2-ylidene) with TlPF6 in THF yields the T-shaped cationic solvent complex, [Ni(6-Mes)(PPh3)(THF)][PF6] (2), whereas treatment with NaBArF4 in Et2O affords the dimeric Ni(I) product, [{Ni(6-Mes)(PPh3)}2(”-Br)][BArF4] (3). Both 2 and 3 act as latent sources of the cation [Ni(6-Mes)(PPh3)]+, which can be trapped by CO to give [Ni(6-Mes)(PPh3)(CO)]+ (5). Addition of [(Et3Si)2(”-H)][B(C6F5)4] to 1 followed by work up in toluene results in the elimination of phosphine as well as halide to afford a co-crystallised mixture of [Ni(6-Mes)(η2-C6H5Me)][B(C6F5)4] (4), and [6MesHâ
C6H5Me][B(C6F5)4]. Treatment of 1 with sodium salts of more strongly coordinating anions leads to substitution products. Thus, NaBH4 yields the neutral, diamagnetic dimer [{Ni(6-Mes)}2(BH4)2] (6), whereas NaBH3(CN) gives the paramagnetic monomeric cyanotrihydroborate complex [Ni(6-Mes)(PPh3)(NCBH3)] (7). Treatment of 1 with NaOtBu/NHPh2 affords the three-coordinate Ni(I) amido species, [Ni(6-Mes)(PPh3)NPh2] (8). The electronic structures of 2, 5, 7 and 8 have been analysed in comparison to that of previously reported 1 using a combination of EPR spectroscopy and density functional theory. <br/
periâxanthenoxanthene (PXX): a versatile organic photocatalyst in organic synthesis
Recent years have witnessed a continuous development of photocatalysts to satisfy the growing demand of photophysical and redox properties in photoredox catalysis, with complex structures or alternative strategies devised to access highly reducing or oxidising systems. We report herein the use of periâxanthenoxanthene (PXX), a simple and inexpensive dye, as an efficient photocatalyst. Its highly reducing excited state allows activation of a wide range of substrates, thus triggering useful radical reactions. Benchmark transformations such as the addition of organic radicals, generated by photoreduction of organic halides, to radical traps are initially demonstrated. More complex dual catalytic manifolds are also shown to be accessible: the ÎČâarylation of cyclic ketones is successful when using a secondary amine as organocatalyst, while crossâcoupling reactions of aryl halides with amines and thiols are obtained when using a Ni coâcatalyst. Application to the efficient twoâstep synthesis of the expensive fluoroâtetrahydroâ1Hâpyrido[4,3âb]indole, a crucial synthetic intermediate for the investigational drug setipiprant, has been also demonstrated
EPR and SQUID interrogations of Cr(III) trimer complexes in the MIL-101(Cr) and bimetallic MIL-100(Al/Cr) MOFs
Herein, electron paramagnetic resonance (EPR) spectroscopy at X- (9.4 GHz), Q- (34 GHz) and W-band (95 GHz), and superconducting quantum interference device (SQUID) measurements on antiferromagnetically coupled metal trimers in MIL-101(Cr) and MIL-100(Al
0.8
Cr
0.2
) MOFs were investigated. At low temperatures, the Cr(III) trimers exhibit a Dzyaloshinsky-Moriya (D-M) interaction, and have a total spin state S
T
=
1
/
2
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