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The X-ray absorption spectroscopy study (EXAFS and XANES) of the local structure of symmetrical and asymmetrical gadolinium and samarium bisporphyrinate complexes is reported. The Gd L3 edge spectra are recorded at room and low temperatures, while the Sm L3 edge spectra are recorded at room temperature. The X-ray absorption fine structure (XAFS) an...
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... 26, 433. (where oep ) octaethylporphyrin and tpp ) tetraphenylporphyrin, see also Figure 1), in an effort to be able to target derivatives which may be used as artificial batteries. ...
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... the cluster of 32 atoms around the Gd, the SS and MS (total 112 paths) calculated spectra within the radius 4.5 Å are shown in Figure S1 in comparison with the experimental one. The SS calculation (32 paths) is surprisingly in good agreement with the experiment. ...
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... modulus and imaginary parts of these FTs coincide well too. The MS signals (80 paths) give only small distortion of the form of the SS contributions ( Figure S1.a). The modulus (see Figure S2.a) and imaginary parts of these FTs coincide well too. ...
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... result is mainly due to the interference effect between MS signals and, possibly, structural and/or thermal disorder. As one can see in Figure S1, the DS and TS signals present the opposite phase that leads to a decrease of the total MS signal amplitude. The most important MS signal generated within the Gd-N-C R chains originates from the eight pyrrolic groups: 32 DS contributions with path lengths of 3.6-3.8 ...
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X-ray absorption spectroscopy (XAS) refers to the details of how X-rays are absorbed by an atom at energies near and above the core-level binding energies of that particular atom. The absorption of X-rays on the high energy side of absorption edges does not vary monotonically in condensed matter but has a complicated behavior which extends past the...
The redistribution of Mn atoms in Ga1-xMnxAs layer during medium-temperature annealing, 250-450 oC, by Mn K-edge X-ray absorption fine structure (XAFS) recorded at ALBA facility, was studied. For this purpose Ga1-xMnxAs thin layer with x=0.01 was grown on AlAs buffer layer deposited on GaAs(100) substrate by molecular beam epitaxy (MBE) followed by...
Fine-grained homogeneous powder samples of thirteen trioctahedral micas, mostly intermediate members of the phlogopite – annite
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examined at the potassium K-edge by X-ray absorption fine structure spectroscopy. The interlayer...
The local coordination environments of Ti in Cretaceous–Paleogene (K–Pg) from Stevns Klint and Devonian–Carboniferous (D–C) boundary from western part of Cat Co Beach on Cat Ba Island sediments are studied by K-edge X-ray absorption fine structure (XAFS) in order to provide local atomic information by X-ray absorption near edge structure (XANES) an...
The magnetic properties and local order of cobalt/silicon nitride metal-insulator multilayered system have been studied. Magnetization characterization reveals an evolution of the magnetic features by varying the metal layer thickness. Results show that multilayers with larger metal thickness (t) present a pure ferromagnetic character, whereas samp...
Citations
... 49,50 Note that these peak positions are not necessarily the exact crystallographic values. 51 Therefore, we further performed curve fitting analysis to obtain the structural parameters. In hexagonal WO 3 structure, the corner-sharing WO 6 octahedra builds up 3D frameworks with hexagonal channels. ...
... (br, ν½ ~ 200 Hz, 12 H, CH(CH 3 ) 2 ), 0.42 (br, ν½ ~ 20 Hz, 72 H, CH(CH 3 ) 2 ). 13 46.26;H,9.06;N,3.00. Found: C,45.83;H,9. ...
... ppm). In contrast to these data, we found that methyl and methine groups were observed in the 13 C{ 1 H} NMR spectra of 2-X and 3 at similar chemical shifts to those seen previously for HN † † , 6 indicating that paramagnetic shifting of these signals by the Sm(III) centres in these complexes is relatively minor. The chemical shifts in the 29 ...
Addition of various oxidants to the near-linear Sm(II) complex [Sm(N††)2] (1), where N†† is the bulky bis(triisopropylsilyl)amide ligand {N(SiiPr3)2}, afforded a family of heteroleptic three-coordinate Sm(III) halide complexes, [Sm(N††)2(X)] (X = F, 2-F; Cl, 2-Cl; Br, 2-Br; I, 2-I). In addition, the trinuclear cluster [{Sm(N††)}3(μ2-I)3(μ3-I)2] (3), which formally contains one Sm(II) and two Sm(III) centres, was isolated during the synthesis of 2-I. Complexes 2-X are remarkably stable towards ligand redistribution, which is often a facile process for heteroleptic complexes of smaller monodentate ligands in lanthanide chemistry, including the related bis(trimethylsilyl)amide {N(SiMe3)2} (N′′). Complexes 2-X and 3 have been characterised by single crystal X-ray diffraction, elemental analysis, multinuclear NMR, FTIR and electronic spectroscopy. The Lα1 fluorescence-detected X-ray absorption spectrum recorded at the Sm L3-edge for 2-X exhibited a resolved pre-edge peak defined as an envelope quadrupole-allowed 2p → 4f transition. The X-ray absorption spectral features were successfully reproduced using time-dependent density functional theoretical (TD-DFT) calculations that synergistically supports the experimental observations as well as the theoretical model upon which the electronic structure and bonding in lanthanide complexes is derived.
As the use of base metals in organometallic chemistry continues to expand, the ability to characterize open shell organometallic compounds with unpaired electrons is essential. This chapter describes four advanced techniques that are particularly powerful for evaluating electronic structure, bonding and reactivity in paramagnetic organometallic complexes: electron paramagnetic resonance, magnetic circular dichroism, X-ray absorption and nuclear magnetic resonance spectroscopies. A discussion of the fundamentals of each spectroscopic method is presented to provide the necessary background and theory central to each technique. This is followed by discussions of key applications of each method for paramagnetic organometallic complexes, using specific examples from the literature to highlight the insight into electronic structure, bonding and reactivity that these methods can provide.
In the present work a series gadolinium porphyrin double deckers and the corresponding monoporphyrinate derivatives were investigated towards photocatalytic hydrogen evolution. The complexes were modified both on the meso- and on the beta- positions of the porphyrin macrocycle. The presence of the double decker structure was proved essential towards the photocatalytic activity since the Gd bisporphyrinate with pyridyl peripheral groups exhibited the higher performance which was 13.8 mmolg⁻¹h⁻¹, while the Gd monoporphyrinate with the same peripheral substitution was totally inactive. A self-assembly investigation of the porphyrin derivatives revealed that different supramolecular architectures can be obtained by varying the solvent mixture and the peripheral substitution, however this did not affect the photocatalytic activity of the complexes.
Incorporating palladium in the first coordination sphere of acetato‐bridged lanthanoid complexes, [Pd2Ln2(H2O)2(AcO)10]·2AcOH (Ln = Gd(1), Y(2), Gd0.4Y1.6(3), Eu(4)), led to significant bonding interactions between the palladium and the lanthanoid ions, which were demonstrated by experimental and theoretical methods. We found that electron density was donated from the d8 Pd2+ ion to Gd3+ ion in 1 and 3, leading to the observed slow magnetic relaxation by using local orbital locator (LOL) and X‐ray absorption near edge structure (XANES). Field induced dual‐slow magnetic relaxation was observed for 1 up to 20 K. Complex 3 and frozen aqueous and acetonitrile solutions of 1 showed only one relaxation peak, which confirms the role of intermolecular dipolar interactions in slowing the magnetic relaxation of 1. The slow magnetic relaxation occurred via a combination of Orbach and Direct processes with the highest pre‐exponential factor (τo = 0.06 s) reported so far for a gadolinium complex exhibiting slow magnetic relaxation. The results revealed that transition metal‐lanthanoid (TM‐Ln) axial interactions indeed could lead to new physical properties by affecting both the electronic and magnetic states of the compounds.
Heterometallic Tb-Pt complex ([Tb2Pt3(SAc)12(H2O)2] (SAc = thioacetate) ) was synthesized. Dual emission was modulated by the presence of a heterometallic Tb-Pt bonding environment. The heterometallic Tb-Pt bond lowers the symmetry of the Tb ion and enhanced the emission efficiency. In addition, the Tb-Pt complex shows field-induced multiple magnetic relaxation pathways. Furthermore, it served as antenna for the observed dual emissions. In other words, the heterometallic Tb-Pt bond has a significant effect on the luminescence and magnetic properties of the complex.
The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)31- (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4f
n
5d1 configurations (not 4f n+1 5d0). In these 4f
n
5d1 complexes, the C3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f
n
5d1 electronic configurations lower in energy than the more typical 4f n+1 5d0 configuration.
Supramolecular chemistry of porphyrins and metalloporphyrins has grown enormously and becomes one of the most important areas of modern chemistry in recent years. Porphyrin and metalloporphyrin assemblies have been attracting wide interest due to various kinds of applications in novel functional materials, for example, photonic materials, electronic materials, nanometer materials, and so on. The functions, properties and potential applications of porphyrin and metalloprophyrin are reviewed in this paper.
The nature of the near-IR band in the electronic absorption spectra of bis(tetrapyrrole) rare earth(III) complexes Y(Pc)2 (1), La(Pc)2 (2), Y(Pc)(Por) (3), Y(Pc)[Pc(α-OCH3)4] (4), Y(Pc)[Pc(α-OCH3)8] (5), and Y(Pc)[Pc(β-OCH3)8] (6) was studied on the basis of time-dependent density functional theory (TD-DFT) calculations. The electronic dipole moment along the z-axis in the electronic transition of the near-IR band in all the studied neutral bis(tetrapyrrole) yttrium(III) and lanthanum(III) double-deckers is well explained on the basis of the composition analysis of the orbitals involved. The electronic transition in the near-IR band causes the reversion of the orbital orientation of one tetrapyrrole ring in both homoleptic and heteroleptic bis(tetrapyrrole) rare earth complexes and induces electron transfer from the tetrapyrrole ring with lower orbital energy to the other ring in the heteroleptic bis(tetrapyrrole) rare earth(III) complexes. The near-IR band can work as an ideal characteristic absorption band to reflect the π–π interaction between the two tetrapyrrole rings in bis(tetrapyrrole) rare earth(III) double-decker complexes because of its peculiar electronic transition nature. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010
