Showing papers on "Spectrochemical series published in 2016"

New insights into the selectivity of four 1,10-phenanthroline-derived ligands toward the separation of trivalent actinides and lanthanides: a DFT based comparison study.

Abstract: Although many heterocyclic N-donor ligands have shown excellent competence for separating actinides from lanthanides, an explanation for why some ligands work whereas others fail is very fundamental but greatly needs to be addressed for designing novel and efficient extractants. In this work, we systematically investigated four phenanthroline-derived ligands, DHDIPhen, BQPhen, Ph2-BTPhen and CyMe4-BTPhen, and their coordination geometrical properties and formation reactions with Am(III) and Eu(III) ions by quasi-relativistic density functional theory. The calculated hardness of ligands, which may help to determine their selectivity toward actinides and lanthanides, yielded an order, from the softest to the hardest, as follows: Ph2-BTPhen < CyMe4-BTPhen < BQPhen < DHDIPhen. It shows that the intramolecular hydrogen bonds and size of a ligand cavity are two dominant factors for metal-ion complexation. Natural population analysis (NPA) reveals that the 5d/6d orbitals of Eu/Am accept significantly more electrons than other orbitals, but partial density of states and molecular orbital analysis prove that the d orbitals with more accepted electrons have little contribution to the metal–ligand bonds. The thermodynamic results suggest that ligand protonation does have a great influence on the complexation of ligands with metal ions but does not change the selectivity of ligands toward metal ions. This work can help in-depth understanding the differences of selectivity of various structurally similar ligands and provide more theoretical insights for designing more innovative ligands for Ln/An separation.

Ion-Specific Effects in Carboxylate Binding Sites

Abstract: Specific ion binding by carboxylates (−COO–) is a broadly important topic because −COO– is one of the most common functional groups coordinated to metal ions in metalloproteins and synthetic polymers. We apply quantum chemical methods and the quasi-chemical free-energy theory to investigate how variations in the number of −COO– ligands in a binding site determine ion-binding preferences. We study a series of monovalent (Li+, Na+, K+, Cs+) and divalent (Zn2+, Ca2+) ions relevant to experimental work on ion channels and ionomers. Of two competing hypotheses, our results support the ligand field strength hypothesis and follow the reverse Hofmeister series for ion solvation and ion transfer from aqueous solution to binding sites with the preferred number of ligands. New insight arises from the finding that ion-binding sequences can be manipulated and even reversed just by constraining the number of carboxylate ligands in the binding sites. Our results help clarify the discrepancy in ion association between mo...

Spin Modulation in Highly Distorted FeIII Porphyrinates by Using Axial Coordination and Their π‐Cation Radicals

Abstract: A series of five-coordinate FeIII octaaryltetraphenylporphyrins [FeIII(por)(X)] (X = Cl, I, I3, ClO4, or SO3CF3) and their 1 e–-oxidized complexes [FeIII(por·)(X)(Y)] (X = Cl, I, ClO4, or SO3CF3; Y = SbCl6, I3, ClO4, or SO3CF3) have been synthesized and characterized. The electronic structures have been confirmed by using UV/Vis, IR, 1H NMR, EPR, and Mossbauer spectroscopy as well as signal-crystal X-ray diffraction studies. The neutral five-coordinate complexes exhibit spin states ranging from essentially pure high spin (S = 5/2 with X = Cl), admixed intermediate spin (S = 5/2, 3/2 with X = I) to an essentially pure intermediate spin (S = 3/2 with X = I3, ClO4, and SO3CF3) depending upon the axial ligand field strength. The average Fe–Np length decreases with decreasing axial ligand strengths, Cl < I < ClO4 < I3 ≈ SO3CF3, which happens to be the order of increasing contributions of the intermediate-spin state to the complexes. DFT calculations demonstrate a dramatic change in the orbital energy levels upon changing the axial ligand strength. Upon 1 e– oxidation, the high-spin chloro complex forms the five-coordinate high-spin FeIII porphyrin π-cation radical, whereas the essentially pure intermediate perchlorato, triflato, triiodo iron(III) porphyrinates produce the corresponding six-coordinate high-spin iron(III) porphyrin π-cation radicals. The oxidation also induces larger separation between the up- and down-field shifted methylene resonances in the 1H NMR spectra owing to the presence of the π-cation radical.

Influence of Halogen Atoms on Spin-Crossover Properties of 1,2,4-Triazole-Based 1D Iron(II) Polymers

Abstract: The introduce of halogen atoms (F, Cl, Br, I) to the triazole-based ligand N-benzyl-4-amino-1, 2, 4-triazole (L) have shown a significant effect on the spin-crossover (SCO) properties of the corresponding one-dimensional (1D) coordination Fe (II) polymers with chemical formula [Fe(4-X–L)3](BF4)2 (X=F, Cl, Br, and I). Compared with the [FeL3](BF4)2, the electronegative halogen atoms have increased the π-acceptor character of these ligands, which thus improved the ligand field strength and induced the occurrence of SCO for the Fe (II) polymers at higher temperatures. The SCO transition temperatures T1/2 have changed from 200 K to 249 (I), 250 (Br), 252 (Cl) and 275 (F) K, respectively. More importantly, the UV-Vis absorption spectrum and density functional theory (DFT) calculations indicated that the transition temperatures and the width of thermal hysteresis loops have shown a positive correlation with the electronegativity of the halogen atoms.

Pentacoordinate and Hexacoordinate Mn(III) Complexes of Tetradentate Schiff-Base Ligands Containing Tetracyanidoplatinate(II) Bridges and Revealing Uniaxial Magnetic Anisotropy

Abstract: Crystal structures and magnetic properties of polymeric and trinuclear heterobimetallic MnIII···PtII···MnIII coordination compounds, prepared from the Ba[Pt(CN)4] and [Mn(L4A/B)(Cl)] (1a/b) precursor complexes, are reported. The polymeric complex [{Mn(L4A)}2{μ4-Pt(CN)4}]n (2a), where H2L4A = N,N’-ethylene-bis(salicylideneiminate), comprises the {Mn(L4A)} moieties covalently connected through the [Pt(CN)4]2− bridges, thus forming a square-grid polymeric structure with the hexacoordinate MnIII atoms. The trinuclear complex [{Mn(L4B)}2{μ-Pt(CN)4}] (2b), where H2L4B = N,N’-benzene-bis(4-aminodiethylene-salicylideneiminate), consists of two [{Mn(L4B)} moieties, involving pentacoordinate MnIII atoms, bridged through the tetracyanidoplatinate (II) bridges to which they are coordinated in a trans fashion. Both complexes possess uniaxial type of magnetic anisotropy, with D (the axial parameter of zero-field splitting) = −3.7(1) in 2a and −2.2(1) cm−1 in 2b. Furthermore, the parameters of magnetic anisotropy 2a and 2b were also thoroughly studied by theoretical complete active space self-consistent field (CASSCF) methods, which revealed that the former is much more sensitive to the ligand field strength of the axial ligands.

Water induced spin-crossover behaviour and magneto-structural correlation in octacyanotungstate(iv)-based iron(ii) complexes.

Abstract: A series of octacyanotungstate(IV)-based iron(II) complexes with the general formula FeII2(L)8[WIV(CN)8]·nH2O [L = (3-pyridyl)methanol (1, 2), 3-methylpyridine (3), (4-pyridyl)methanol (4), and 4-methylpyridine (5); n = 4 for 1, and n = 0 for 2–5] have been synthesized and characterized. Single crystal X-ray diffraction analysis reveals that the FeII ions lie in the centre of the compressed [FeN6] octahedron in all complexes. FeII and WIV ions are alternately bridged by cyano groups forming a three-dimensional (3D) bimetallic framework. Magnetic investigation shows that 1 displays a gradual spin-crossover (SCO) phenomenon with a spin transition temperature (T1/2) of 200 K, and such SCO behaviour is obviously correlated with the lattice water content of the sample. The magnetic measurements of dehydrated samples show that the fractional conversion from the high-spin (HS) to the low-spin (LS) state is reduced with the increasing of dehydration temperature. Complexes 2–5 are in the HS state and do not exhibit SCO properties in the range of 2–300 K. Comparing the octahedral geometry of [FeN6] of five complexes, quantified by using continuous shape measures, the distortion of complex 1 is the highest as a result of the intermolecular hydrogen bonds, which shorten the Fe–N bond distances and thus increase the ligand field strength at the FeII sites. The analysis of correlations between the structural characteristics and magnetic behaviour of 1–5 suggests that the SCO is mainly tuned by the octahedral distortion of the [FeN6] core caused by intermolecular hydrogen bonds. There is an exact correlation between SCO behaviour and the amount of lattice water molecules existing in the crystal. The spin crossover behaviour of these complexes has been computationally studied using the DFT method. The results of the calculations are consistent with the experiments, which prove that complex 1 with severe distortion of the coordination sphere of FeII is prone to exhibit SCO in theory.

Cobalt Kβ valence-to-core X-ray emission spectroscopy: a study of low-spin octahedral cobalt(III) complexes

Abstract: Kβ valence-to-core (V2C) X-emission spectroscopy (XES) has gained prominence as a tool for molecular inorganic chemists to probe the occupied valence orbitals of coordination complexes, as illustrated by recent evaluation of Kβ V2C XES ranging from titanium to iron. However, cobalt Kβ V2C XES has not been studied in detail, limiting the application of this technique to probe cobalt coordination in molecular catalysts and bioinorganic systems. In addition, the community still lacks a complete understanding of all factors that dictate the V2C peak area. In this manuscript, we report experimental cobalt Kβ V2C XES spectra of low-spin octahedral Co(III) complexes with different ligand donors, in conjunction with DFT calculations. Cobalt Kβ V2C XES was demonstrated to be sensitive to cobalt-ligand coordination environments. Notably, we recognize here for the first time that there is a linear correlation between the V2C area and the spectrochemical series for low-spin octahedral cobalt(III) complexes, with strong field π acceptor ligands giving rise to the largest V2C area. This unprecedented correlation is explained by invoking different levels of π-interaction between cobalt p orbitals and ligand orbitals that modulate the percentage of cobalt p orbital character in donor MOs, in combination with changes in the average cobalt–ligand distance.

Electrical component and electronic device

Abstract: An electrical component includes a contact point part that establishes an electrical connection by contact. In addition, the contact point part includes: a substrate having a metal as a constituent material; and a thin film arranged at a surface of the substrate. Moreover, the thin film includes a π-accepting molecule having a π-acceptability, in which the π-accepting molecule has a size of ligand field splitting in a spectrochemical series larger than or equal to a size of ligand field splitting of 2,2′-bipyridyl.

The role of chelating ligands and central metals in the oxygen reduction reaction activity: a DFT study

Abstract: A detailed investigation of oxygen reduction reaction (ORR) catalyzed by various metal chelates has been performed by DFT study. The results indicate that the ORR activity is determined by both of the central metal ions and chelating ligands, among which the former play a key role. For the same ligand, the central metal ions Fe, Co, or Mn give higher ORR activity, while the others almost have no catalytic activity, which is due to the fact that the O2 and oxygen containing species are either excessively adsorbed (on central Cr) or difficult to be adsorbed on the active sites (for central Zn, Cu, or Ni). Furthermore, the ORR activity for Fe chelates is slightly increased with the increase of ligand field strength, while for other metal chelates there seems to be no clear trends between ligand field strength and ORR activity. The origin of the ORR activity for the studied metal chelates is mainly attributed to the appropriate energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).