Local C3v Symmetry Research Articles

Insight into the Structural and Emissive Behavior of a Three-Dimensional Americium(III) Formate Coordination Polymer.

We report the structural, vibrational, and optical properties of americium formate (Am(CHO2 )3 ) crystals synthesized via the in situ hydrolysis of dimethylformamide (DMF). The coordination polymer features Am3+ ions linked by formate ligands into a three-dimensional network that is isomorphous to several lanthanide analogs, (e. g., Eu3+ , Nd3+ , Tb3+ ). Structure determination revealed a nine-coordinate Am3+ metal center that features a unique local C3v symmetry. The metal-ligand bonding interactions were investigated by vibrational spectroscopy, natural localized molecular orbital calculations, and the quantum theory of atoms in molecules. The results paint a predominantly ionic bond picture and suggest the metal-oxygen bonds increase in strength from Nd-O<Eu-O<Am-O. The optical properties were probed using diffuse reflectance and photoluminescence spectroscopies. Notably, the rarely reported 5 D1' →7 F0' emission band is observed and dominates the emission spectrum. This behavior is unusual and is attributed to the C3v coordination environment of the metal center.

Synthesis, Spectroscopic Investigations, Thermal Analysis And DFT Calculations Of Some Pentacarbonyl(Mercaptopyrimidine)Metal(0) Complexes Of Group VI B Elements

Pentacarbonyl-N-mercaptopyrimidinemetal(0) complexes of VIB metals (M: Cr, Mo, W) were formed when hexacarbonylmetal(0) complexes are treated photochemically with 4,6-dimethyl-2-mercaptopyrimidine at 10 ºC. The reported organometallic complexes were purified and isolated under an inert atmosphere. All M(CO)5L complexes were characterized in solution by FTIR-, 1H- and 13C-NMR spectroscopies. The FTIR spectroscopy results showed three absorption bands in the carbonyl region which indicates that the pentacarbonyl metal unit of the complexes has a local C4v symmetry. The 1H- and 13C-NMR spectroscopies showed that the mercaptopyrimidine ligand bonded to the metal complex through the mercaptopyrimidine-nitrogen atom symmetrically. The 13C-NMR spectroscopy results also showed a 1:4 ratio of two peaks in the CO-region, the ratio of the peaks proved the C4v symmetry of these complexes. The thermal behavior of these organometallic complexes is investigated by using DTA/TGA methods. The results of thermal analyses showed that the complexes decomposed at three different temperatures. The density functional theory (DFT) calculations were computed in B3PW91 formalism by Gaussian03W Software. The comparison of the experimental data with the theoretical values showed that the results obtained are compatible with each other. Thus, the accuracy of the experimentally given structural proposal of the obtained organometallic complex compounds was also confirmed through theoretical calculations.

Zinc ferrite nanoparticles from industrial waste for Se (IV) elimination from wastewater

The presence of high concentrations of selenium ions in wastewater is considered an environmental problem. However, the mechanism of selenium ions (Se (IV)) removal by the adsorption process has not been investigated in-depth so far. Also, the recovery and conversion of the industrial waste materials into valuable materials is a vital issue. Therefore, in this study, zinc ferrite nanopowders are economically synthesized from steel-making wastes by co-precipitation method for investigating as adsorbents of selenium species. The produced nanopowders were annealed at 150, 300, 500, and 850 °C for 5 h to scrutinize the impact of annealing temperature on their crystallite size. The compositional, optical, and magnetic features of the nanopowders were defined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), UV–Vis. spectrophotometer along with vibrating sample magnetometer (VSM). Optical absorbance spectra were found characteristic due to the electronic structure of Fe3+ (3d5) considering the C3v local symmetry of Fe3+ ions. The prepared nanopowders demonstrated good adsorption capacity toward selenium ions (43.67 mg/g at pH 2.5) from an aqueous medium. Adsorption data were found fitting to Freundlich isotherm model. Thus, ZnFe2O4 can be recommended to effectively eliminate selenium ions from aqueous solutions.

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Substituent-Mediated Transformation of Polynuclear Gold(I)-Sulfido Complexes—From Pentanuclear to Octadecanuclear Cluster-to-Cluster Transformation

Substituent-Mediated Transformation of Polynuclear Gold(I)-Sulfido Complexes—From Pentanuclear to Octadecanuclear Cluster-to-Cluster Transformation

Radical Cyclic [3]Daisy Chains

Summary Mechanically interlocked molecules (MIMs) that undergo controllable internal motions of their component parts in more than one dimension are rare entities in the molecular world. Cyclic [2]daisy chains ([c2]DCs) are a class of MIMs that have been identified as prototypes for molecular muscles. It remains, however, a challenge to synthesize [cn]DCs with n > 2 selectively and efficiently. Herein, we report the design and synthesis of [c3]DCs employing radical and anionic templates. Two mechanically interlocked [c3]DCs with 18 positive charges were obtained in >90% yields. One [c3]DC displayed good air stability in its radical cationic form, while the other underwent reversible “co-conformational” switching between open macrocyclic and closed trisarm-shaped forms under electrochemical control. These findings provide not only two-dimensional MIMs with attractive electronic and switchable properties, but also a starting point for the design of extended molecular arrays, which could become the forerunners of adjustable molecular nets and breathable molecular membranes.

An investigation into the magnetic interactions in a series of Dy2 single-molecule magnets.

Three di-nuclear DyIII complexes [Dy2(H2L)2(tfa)]·Cl·3DMF (1), [Dy2(H2L)2(MeO)(SCN)]·MeOH (2) and [Dy2(H2L)2(MeOH)Cl]·Cl·2MeOH (3) were synthesized and structurally and magnetically characterized. The Dy1/Dy2 centers in these complexes are all nine-coordinate with spherical capped square antiprism (local C4v symmetry) environments. All complexes display single-molecule magnet (SMM) behavior under zero applied dc field with their properties dependent on the nature of the magnetic interactions between the DyIII ions. Ab initio calculations substantiate that all DyIII ions show a weakly axial crystal-field environment with the exception of one of the DyIII ions in complex 2. The ground Kramers doublets show modest amounts of quantum tunneling of magnetization that gets blocked by the interaction between the DyIII ions, leading to a thermally activated slow relaxation of magnetization. The interaction between the ions is ferromagnetic and mostly originates from the dipolar interaction. However, anti-ferromagnetic intermolecular interaction plays an important role and in the case of complex 2 it is sufficiently strong to mask the ferromagnetic intramolecular interaction.

Size-dependent photoluminescence of europium in alumina nanoparticles synthesized by cw CO2 laser vaporization

Nanosized Eu/γ- and/or η-Al2O3 ([Eu2О3] = 0.00, 0.02, 0.45 and 0.92 wt%) powders with the particle size from <10 nm to 21 nm synthesized by cw CO2 laser vaporization were studied. It was shown that photoluminescence (PL) properties of the obtained samples are caused by luminescence of the Eu3+ and Eu2+ ions incorporated to the Al2O3 matrix in crystallographic positions with the C3v local symmetry. A scheme based on the formation of Eu2+ ions in the Al2O3 lattice via the charge compensation by oxygen vacancies (F centers) located in the first coordination sphere of europium was proposed. The influence of size effects on PL of Eu/Al2O3 nanoparticles consists first of all in shortening the lifetime of 4f – 4f transitions in Eu3+ ions as a result of increased probability of nonradiative relaxation owing to OH groups and various structural defects. It was found that the conditions of laser vaporization (gas composition and pressure) can change the structure of the resulting Eu/Al2O3 nanoparticles.

Investigations of the electron paramagnetic resonance parameters and defect structures for Cu2+ ions in BeO crystal with trigonally distorted tetrahedral symmetry

Abstract The electron paramagnetic resonance(EPR) parameters (g factors gi and hyperfine structure constants Ai, where i = x, z) for Cu2+ ions embedded in beryllium oxide (BeO) crystal at Be2+ sites with C3v local symmetry have been calculated by the complete diagonalization method (CDM) and high-order perturbation theory method (PTM). The calculated results from the two methods are in reasonable agreement with the observed data available. The defect structural data of the trigonal Cu2+ center in beryllium oxide are determined from the calculations and analyses. The calculated results show that the Be2+ ions are replaced by Cu2+ ions in BeO crystal and the ligands undergo outward movement.

Syntheses and crystal structures of neodymium(III) and europium(III) complexes bearing dimethyl-, pyrrolidine-, or S-prolinol- dithiocarbamato ligands and their natural and magnetic circular dichroism spectra

A series of NdIII and EuIII complexes containing achiral or chiral dithiocarbamato (dtc) ligands, [Ln(Xdtc)3(NN)] {Ln = Nd or Eu; X = dimethyl- (Me2), pyrrolidine- (pyr), or (S)-prolinol- (S-proOH); NN = 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy)}, were prepared and their crystal structures and spectroscopic properties, in particular the natural circular dichroism (CD) and magnetic circular dichroism (MCD), were investigated. The crystal structures of the complexes analyzed by the X-ray diffraction method showed an 8-coordinate geometry around the LnIII center with comparable structural parameters to one another and to the related complexes reported previously. These complexes exhibited similar spectral patterns in their absorption, natural CD and MCD spectra in solution. Weak but characteristic sharp f–f transition bands were observed in the absorption and MCD spectra, but no CD signals associated with these transitions were observed even in the S-proOHdtc complexes. The MCD spectral pattern of the EuIII complexes revealed a local C2v symmetry around the LnIII center in solution, in contrast to the aqua and the analogous β-diketonato EuIII complexes.

Microwave study of internal rotation in para-tolualdehyde: Local versus global symmetry effects at the methyl-rotor site

The rotational spectrum of para-tolualdehyde (CH3-C6H4-CHO) has been measured using three different microwave spectrometers, with the goal of quantifying the influence of the aldehyde group at the top of the benzene ring on the internal rotation barrier seen by the methyl group at the bottom of the ring. This barrier consists of a six-fold component, which results from the local C2v symmetry of the benzene ring seen by the methyl top (as in toluene), and an additional three-fold component, which results from information on the non-C2v symmetry at the aldehyde site at the top of the ring being transmitted to the methyl-group site at the bottom of the ring. The nearly-free internal rotation of the methyl group splits each of the rotational transitions into two components, one of A and one of E symmetry. Assignment and fit of 786 A-state and E-state transitions to an internal rotation Hamiltonian containing barrier terms of three-fold (V3 = 28.111(1) cm−1) and six-fold (V6 = −4.768(7) cm−1) symmetry with respect to the internal rotation angle, as well as the three rotational constants and a number of higher-order torsion-rotation interaction terms, resulted in residuals equal to experimental measurement uncertainty. Isotopic data from all eight mono-substituted 13C species and the one 18O species were obtained in natural abundance and used to determine an rs substitution structure. Various chemical and physical implications of this structure and the two barrier parameters are discussed.

Substitutional nitrogen in diamond: A quantum mechanical investigation of the electronic and spectroscopic properties

This paper reports the fully-relaxed lattice and electronic structures, vibrational spectra, and hyperfine coupling constants of the substitutional Ns defect in diamond, derived from B3LYP calculations constructed from all-electron Gaussian basis sets and based on periodic supercells. Mulliken analyses of the charge and spin distributions indicate that the defect comprises a single unpaired electron distributed very largely over both the negatively-charged substituted site and one of the four nearest-neighbour carbon sites, which relaxes away from the impurity. This leads to a local C3v symmetry, with the nitrogen ‘lone pair’ lying along the C3 axis and pointed towards the ‘dangling’ bond of the shifted carbon neighbour. The calculated band gap is 5.85 eV, within which a singly-occupied, majority spin donor band is found ∼2.9 eV above the valence band, and an unoccupied, minority spin acceptor band ∼0.9 eV below the conduction band. Atom-projected densities of states of the donor and acceptor levels show that, contrary to a widespread description, ∼30% only of the donor band derives from nitrogen states per se, with the majority weight corresponding to states associated with the shifted carbon atom. The defect formation energy is estimated to be ∼3.6 eV. The calculated IR spectrum of the impurity centre shows several features between 800 and 1400 cm−1, all of which are absent in the perfect crystal, for symmetry reasons. These show substantial agreement with recent experimental observations. The calculated hyperfine constants related to the coupling of the unpaired electron spin to the N and C nuclei, for which the Fermi contact terms vary from over 200 MHz to less than 3 MHz, are generally in good agreement with the largest experimental values, both in terms of absolute magnitudes and site assignments. The agreement is less good for the smallest two values, for which the experimental assignments are less certain. The results lend support to previous suggestions that some of the weaker lines in the observed spectra, notably those below ∼7 MHz, which are difficult to assign unambiguously, might result from the overlap of lines from different sites.

Surface Spectroscopic Signatures of Mechanical Deformation in High-Density Polyethylene (HDPE).

High-density polyethylene (HDPE) has been extensively studied, both as a model for semi-crystalline polymers and because of its own industrial utility. During cold drawing, crystalline regions of HDPE are known to break up and align with the direction of tensile load. Structural changes due to deformation should also manifest at the surface of the polymer, but until now, a detailed molecular understanding of how the surface responds to mechanical deformation has been lacking. This work establishes a precedent for using vibrational sum-frequency generation (VSFG) spectroscopy to investigate changes in the molecular-level structure of the surface of HDPE after cold drawing. X-ray diffraction (XRD) was used to confirm that the observed surface behavior corresponds to the expected bulk response. Before tensile loading, the VSFG spectra indicate that there is significant variability in the surface structure and tilt of the methylene groups away from the surface normal. After deformation, the VSFG spectroscopic signatures are notably different. These changes suggest that hydrocarbon chains at the surface of visibly necked HDPE are aligned with the direction of loading, while the associated methylene groups are oriented with the local C2v symmetry axis roughly parallel to the surface normal. Small amounts of unaltered material are also found at the surface of necked HDPE, with the relative amount of unaltered material decreasing as the amount of deformation increases. Aspects of the nonresonant SFG response in the transition zone between necked and undeformed polymer provide additional insight into the deformation process and may provide the first indication of mechanical deformation. Nonlinear surface spectroscopy can thus be used as a noninvasive and nondestructive tool to probe the stress history of a HPDE sample in situations where X-ray techniques are not available or not applicable. Vibrational sum-frequency generation thus has great potential as a platform for material state awareness (MSA) and should be considered as part of a broader suite of tools for such applications.

Investigation of magneto-structural correlation based on a series of seven-coordinated β-diketone Dy(iii) single-ion magnets with C2v and C3v local symmetry.

A series of four β-diketone mononuclear Dy(iii) complexes, namely Dy(Hthd)3(MeOH)·2,5-Py (1), Dy(Hthd)3(Tppo) (2), Dy(Hthd)3(PyNO) (3), and Dy(Hthd)3(4-PyNO) (4) (Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione, 2,5-Py = 2,5-pyridine, Tppo = triphenylphosphine oxide, PyNO = pyridine N-oxide, 4-PyNO = 4-methylpyridine N-oxide), have been isolated by reactions of Hthd, DyCl3·6H2O and an auxiliary ligand. X-ray crystallographic analysis revealed that complexes 1-4 are all seven-coordinated mononuclear structures with C2v or C3v local symmetry. The magnetic measurements of complexes 1-4 revealed their field-induced single-ion magnet (SIM) behavior, due to mixed low-lying states. The crystal field parameters and orientations of the magnetic easy axes were obtained from simulations of the DC magnetic data and an electrostatic model calculation. The magneto-structural correlation of seven-coordinated Dy(iii) SIMs with low-symmetry coordination environments was further discussed.

Design and Magnetic Properties of a Mononuclear Co(II) Single Molecule Magnet and Its Antiferromagnetically Coupled Binuclear Derivative.

The preparations of related mononuclear and binuclear Co(II) complexes with a quasi-identical local C3v symmetry using a cryptand organic ligand are reported. The mononuclear complex behaves as a single molecule magnet (SMM). A relatively weak antiferromagnetic exchange coupling (J) of the same order of magnitude as the local magnetic anisotropy (D) is determined experimentally and theoretically for the binuclear complex. The weak magnitude of the antiferromagnetic exchange coupling, analyzed using a combination of broken-symmetry density functional theory and wave function based calculations, is ascribed to the weak overlap between the singly occupied orbitals because of the local C3v symmetry of the Co(II) ions; the organic ligand was found to contribute to the exchange coupling as the azido bridge that directly links the Co(II) ions. Calculation of the energy and wave functions of the spin states for the binuclear complex, in the general case, allows analysis of the effect of the |J/D| ratio on the magnetic behavior of the binuclear complex and prediction of the optimum range of values for the complex to behave as two weakly interacting SMMs.

Twenty years of operando IR, X-ray absorption, and Raman spectroscopy: Direct methanol and hydrogen fuel cells

Mixed metal catalysts in polymer electrolyte fuel cell membrane electrode assemblies were characterized by operando infrared, X-ray absorption and Raman spectroscopy. Windowed direct methanol and hydrogen-air fuel cell assemblies allow for spectral acquisition with controlled potential, temperature and flowing reactant streams to the graphite flow fields. Johnson Matthey Pt and PtRu (1:1), in-house prepared PtRu (1:1 and 3:1), PtRuOs (65:25:10), PtNi (1:1), and a melamine-synthesized FeNC catalyst were studied. The near invariant core structure of phase segregated alloy catalysts over practical fuel cell potentials enable a simultaneous fit of metal component EXAFS to quantitatively characterize core structures: JM PtRu is a face centered cubic lattice with 50% of the Ru in an amorphous phase. Stark tuning of COads as a reaction intermediate and as a surface structure probe elucidates potential dependent co-adsorption of Nafion functional groups on Pt. Operando Raman spectroscopic tracking of membrane hydration at a fuel cathode is facilitated by symmetry-based group mode assignments of Nafion IR bands. Fully hydrated Nafion sulfonate groups have C3V local symmetry. Dehydrated sulfonic acid groups have C1 local symmetry. C3V and C1 IR bands coexist at intermediate states of membrane hydration.

Redox flexibility of iron complexes supported by sulfur-based tris(o-methylenethiophenolato)amine relative to its tripodal oxygen-based congener.

Tripodal ligands designed to generate a local C3 symmetry have resulted in novel types of metal complexes that feature unusual bonding and electronic properties. However, most complexes reported to date are characterised by strong field ligands that enforce low or intermediate-spin states for the metal centres. Moreover, anionic sulfur-based tripodal ligands are particularly scarce due to their challenging synthesis. In this context, we herein report the synthesis, spectral characterization, structural, and electronic properties of an iron complex supported by the tripodal, trianionic ligand [N(CH2ArS)3](3-) as the trigonal-bipyramidal complexes [Fe{N(CH2ArS)3}(X)] ((X), X = DMSO, THF). The solid-state structures reveal local C3v symmetry around the Fe(3+) ions, while electron spin resonance measurements established a high-spin state (S = 5/2). Electrochemical studies demonstrate the redox flexibility of the FeS3 fragment by direct comparison with the oxygen-based analogue N(CH2ArOH)3, which displays an irreversible reduction; in contrast, (THF) has a reversible Fe(3+)/Fe(2+) redox process at -0.83 V (relative to the ferrocenium/ferrocene redox couple). The high spin and redox properties of (THF) are attributable to the weak ligand field provided by the NS3 fragment, as confirmed by the electronic structure calculated by density functional theory, which reveals substantial electronic delocalisation and covalency of the Fe-S bonds in (X).

Synthesis and 13C NMR features of N-substituted aziridino[60]fullerenes

An effective cycloaddition of organic azides to fullerene C60 in the presence stoichiometric amounts of Cu(OTf)2 to form individual aziridino[60]fullerenes was developed. Considering the 13C NMR data, it was ascertained that among the synthesized aziridinofullerenes only the compound with the adamantane substituent possessed the local C2v symmetry of the fullerene core. In the 13C NMR spectra of the other compounds, 11 resonances were unexpectedly observed for the fullerene carbon atoms instead of probable 16 signals. The 13C NMR chemical shifts were computed with the high level GIAO-PBE/3ζ technique and the possible reasons of the signal overlap in the 13C NMR spectra were discussed.

Structure, electronic and magnetic properties of hexagonal boron nitride sheets doped by 5d transition metal atoms: First-principles calculations and molecular orbital analysis

A first-principles calculation based on density functional theory is carried out to reveal the geometry, electronic structures and magnetic properties of hexagonal boron nitride sheets (h-BNSs) doped by 5d transitional mental atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) at boron-site (B5d) and nitrogen-site (N5d). Results of pure h-BNS, h-BNS with B vacancy (VB) and N vacancy (VN) are also given for comparison. It is shown that all the h-BNSs doped with 5d atoms possess a C3v local symmetry except for NLu and NHg which have a clear deviation. For the same 5d dopant, the binding energy of B5d is larger than that of N5d, which indicates the substitution of a 5d atom for B is preferred. The total densities of states are presented, where impurity energy levels exist. Besides, the total magnetic moments (TMMs) change regularly with the increment of the 5d atomic number. Theoretical analyses by molecular orbital under C3v symmetry explain the impurity energy levels and TMMs.

Theoretical and experimental infrared spectra of hydrated and dehydrated sulfonated poly(ether ether ketone)

Time-dependent FT-IR spectra of sulfonated poly(ether ether ketone) during dehydration show diminishing 1081 cm−1 and 1023 cm−1 band intensities concurrent with the emergence and shifting of bands at 1362 cm−1 and 898 cm−1. Animations of density functional theory calculated normal modes enable assignment of the 1081 cm−1 and 1023 cm−1 bands as group modes that include a sulfonate exchange site with C3v local symmetry, while the 1362 cm−1 and 898 cm−1 bands are assigned as group modes that include an associated sulfonic acid with no local symmetry (C1). In contrast to analogously assigned Nafion group mode bands, the SPEEK C3v and C1 bands coexist throughout the entire dehydration–hydration cycle, suggesting the presence of associated and dissociated exchange sites in SPEEK at all states-of-hydration. This supports a morphological model for SPEEK featuring branched hydrophilic domains and dead-end aqueous confines.