Tetragonal Elongation Research Articles

Impact of counter anions on structural and magnetic properties of iron(III) meso-tetraphenylporphyrin tetrahydrofurane solvates

Intensively researched iron meso-tetraphenylporphyrin (FeTPP) complexes are central to the functionalities of many biological systems while at the same time they possess intriguing magnetic properties. Here we report on the synthesis and structural characterization of FeTPP complexes with axial tetrahydrofuran (THF) ligand and different non-coordinating counter anions. Structurally, the most interesting feature of these complexes is the stretching of the distance between the iron(III) and the oxygen atom of the THF ligand for different counter anions. This parameter affects the magnetic anisotropy of FeTPP as studied here with magnetic susceptibility, χm, and X-band electron paramagnetic resonance (EPR). Both magnetic probes are consistent with the iron(III) in its high-field state S = 5/2. Simulations of temperature dependencies of χm and EPR spectra show that the zero-field splitting magnetic anisotropy parameter D decreases with the tetragonal elongation of the hexa-coordinated iron(III) geometry, which is qualitatively discussed within the ligand field theory.

Investigations on the local structure and the spin Hamiltonian parameters for Cu2+ in xCuO-(68-x)V2 O5 -32TeO2 glasses.

The defect structure, spin Hamiltonian parameters (SHPs: anisotropic factors and and the hyperfine structure constants and ), and their compositional dependence of in ( = 5, 10, 20, 30 mol%) glasses are quantitatively analyzed by using the higher-order perturbation formula of octahedral complex with tetrahedral elongation distortion. Due to the Jahn-Teller effect, the group is subjected to tetragonal elongation distortion of varying degrees. , and show nonlinear changes with the concentrations of . When = 10 mol% CuO, the degree of distortion ( ) is the smallest; when = 30 mol% CuO, the degree of distortion ( ) is the largest, which indicates that excessive distortion leads to the appearance of -axis oxygen vacancies and the coordination number of copper ions from six to four. The increasing tendency of the evaluated and reveals decreasing covalency of the whole glass system. Present theoretical studies would be useful to the explore the structural properties and optical applications of glass with different concentrations.

A comparable study of the optical spectra and EPR parameters for 3d1 - and 3d9 -doped MgNH4 PO4 ·6H2 O.

VO2+ (3d1 ) and Cu2+ (3d9 ) are the two complementary states that usually show opposite distortions when they are doped in crystals. In this work, the optical absorption spectra (OAS), electron paramagnetic resonance (EPR) parameters, and local structure (LS) for VO2+ (and Cu2+ ) in MgNH4 PO4 ·6H2 O (MPPH) are uniformly investigated on the basis of the high-order perturbation formulas for a 3d1 (and 3d9 ) ion in tetragonally compressed (and elongated) octahedra, respectively. In the calculated formulas, the required crystal-field parameters can be obtained from the superposition model and reasonably linked with the LS distortion for VO2+ and Cu2+ centers. Based on the calculations, the tetragonal compressed [VO(H2 O)5 ]2+ cluster (and tetragonal elongated [Cu(H2 O)6 ]2+ cluster) is found to suffer tetragonal compression ratio of 1.65% and tetragonal elongation ratio of 3.8% along C4 -axis, respectively, due to the Jahn-Teller (JT) effect. The theoretical EPR parameters based on the above lattice distortions agree well with the experimental data, and the LS of the VO2+ and Cu2+ centers in MPPH is discussed.

Local-electrostatics-induced oxygen octahedral distortion in perovskite oxides and insight into the structure of Ruddlesden\u2013Popper phases

As the physical properties of ABX3 perovskite-based oxides strongly depend on the geometry of oxygen octahedra containing transition-metal cations, precise identification of the distortion, tilt, and rotation of the octahedra is an essential step toward understanding the structure–property correlation. Here we discover an important electrostatic origin responsible for remarkable Jahn–Teller-type tetragonal distortion of oxygen octahedra during atomic-level direct observation of two-dimensional [AX] interleaved shear faults in five different perovskite-type materials, SrTiO3, BaCeO3, LaCoO3, LaNiO3, and CsPbBr3. When the [AX] sublayer has a net charge, for example [LaO]+ in LaCoO3 and LaNiO3, substantial tetragonal elongation of oxygen octahedra at the fault plane is observed and this screens the strong repulsion between the consecutive [LaO]+ layers. Moreover, our findings on the distortion induced by local charge are identified to be a general structural feature in lanthanide-based An + 1BnX3n + 1-type Ruddlesden–Popper (RP) oxides with charged [LnO]+ (Ln = La, Pr, Nd, Eu, and Gd) sublayers, among more than 80 RP oxides and halides with high symmetry. The present study thus demonstrates that the local uneven electrostatics is a crucial factor significantly affecting the crystal structure of complex oxides.

A comparable study of the EPR spectra and local structures for 3d1‐ and 3d9‐doped halo‐borate glasses

AbstractThe spin Hamiltonian parameters (SHPs) of Cu2+‐doped halo‐glasses PbX2–PbO–B2O3 (X = F and Br) are investigated by means of the perturbation method where the impact of the halides and the local structure of the dopants, that is, the [CuO6]10− clusters suffering the tetragonal elongation distortions, is involved. By comparing with the obtained results of the 3d1 system (VO2+), Cu2+ and V4+ are complementary state, which show opposite distortions. Furthermore, the d‐d transition bands and the sign of anisotropy g factors also show whole opposite concentration variation trends with similar fluctuations due to the increase of non‐bridging oxygen (NBO). The values of the optical basicity Λth referring to the Pauling electronegativity, whose influence on E1 and g factors are also discussed. The above correlations would be beneficial to analyze and predict the properties of analogous borate glasses and ceramics when doped with different transition metal ions.

Theoretical studies of the EPR spectra and local structures for Cu2+ and V4+ doped halo-borate glasses

Local structure and the effect of halide on MX∙M2O∙B2O3 (M = Pb, Ba; X = F, Cl, Br) glasses doped with Cu2+ and VO2+ are investigated by means of the perturbation calculations of the spin Hamiltonian parameters (SHPs). Based on the fitted EPR results, [CuO6]10− and [VO6]8− clusters prefer to suffer the tetragonal elongation and compression distortions, respectively. Compare the ionic radius of Cu2+ with V4+ and Pb2+ with Ba2+ in MX∙M2O∙B2O3, the glasses with larger ionic radius of metal may induce larger tetragonal distortions and larger g anisotropies. The d-d transition bands show whole opposite trends for 3d9 and 3d1 impurities with the similar fluctuations due to the increase of non-bridging oxygen. The d-d transition bands and g factorsare are also analyzed from the electronegativities of incorporated halides. The values of basicities Λth of BCBBV are found larger than PCPBC and PbX-PbO-B2O3 glasses due to stronger ionicity of Ba than Pb.

Theoretical study of the local distortions and the EPR parameters for VO2+ and Cu2+ centers in oxyfluoroborate glasses

Theoretical calculations of the local structures and the electron paramagnetic resonance (EPR) parameters for the impurities VO2+ and Cu2+ centers in oxyfluoroborate glasses (OFG) were performed by using the perturbation formulas of the EPR parameters for tetragonally compressed octahedral [VO6]8- and tetragonally elongated octahedral [CuO6]10− clusters, respectively. In the calculations, the required crystal-field (CF) parameters are estimated from the superposition model which enables correlation of the CF parameters and hence the EPR parameters with the tetragonal distortion (characterized by the relative tetragonal elongation (or compression) ratio τ along the C4 axis) of [VO6]8- (or [CuO6]10−) cluster. Based on the calculations, the [VO6]8- and [CuO6]10− clusters are found to undergo the tetragonal compression (τ ≈ 1.7%) and elongation (τ ≈ 2.9%) along the C4 axis, the signs of A|| and A⊥ for VO2+ and Cu2+ centers in OFG were also determined. The above theoretical approach on local structural properties would enhance the understanding of the structural properties for other oxide glasses with transition-metal (TM) dopants.

Theoretical studies of the electron paramagnetic resonance parameters and local structures for Cu2+ in (100-2x)TeO2-xAg2O-xWO3 glasses

The electron paramagnetic resonance (EPR) parameters and local structures for Cu2+ in (100-2x)TeO2-xAg2O-xWO3 (TAW) (7.5 ≤ x ≤ 30 mol %) glasses are quantitatively studied for distinct modifier concentrations x. The octahedral Cu2+ centers are subject to the medium tetragonal elongations of about 2% along the C4 axis due to the Jahn-Teller effect. By utilizing only three adjusted coefficients a, b and ω, the quantities (Dq, k, t and κ) can be suitably characterized by the Fourier type functions, which reasonably account for the experimental concentration dependences of the d-d transition bands and EPR parameters. The calculation results are discussed, and the mechanisms of the above concentration dependences of these quantities are illustrated by the modifications of the local structures and the electron cloud distribution around the Cu2+ dopant with the variations of the concentration x.

Studies of the EPR parameters and tetragonal distortion for the Cu2+ center in aluminium oxide

The electronic paramagnetic resonance (EPR) parameters (g factor gi , and hyperfine structure constants Ai , with i = || and ⊥) and tetragonal distortion of the Cu2+ center in Al2O3 are unified interpreted from the perturbation formulas for a 3d9 ion in tetragonally elongated octahedral. In the calculations, the impurity Cu2+ is found to occupy the host trigonally-distorted octahedral Al3+ site with the tetragonal elongation distortion due to the Jahn–Teller effect, despite the original trigonal distortion of the host cation site. The contributions to EPR parameters from both the spin–orbit coupling of the central ion and that of the ligands are taken into account. The defect structure of the Cu2+ center (characterized by the relative tetragonal elongation ratio η ≈ 4.3% along the C 4 axis) was determined from the calculation. Furthermore, the calculated results agree well with the experimental data and need fewer adjustable parameters than the previous studies.

Anisotropic lattice compression and pressure-induced electronic phase transitions in Sr2IrO4

The crystal lattice of ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ is investigated with synchrotron x-ray powder diffraction under hydrostatic pressures up to $P=43$ GPa and temperatures down to 20 K. The tetragonal unit cell is maintained over the whole investigated pressure range, within our resolution and sensitivity. The $c$-axis compressibility ${\ensuremath{\kappa}}_{c}(P,T)\ensuremath{\equiv}\ensuremath{-}(1/c)(dc/dP)$ presents an anomaly with pressure at ${P}_{1}=17$ GPa at fixed $T=20$ K that is not observed at $T=300$ K, whereas ${\ensuremath{\kappa}}_{a}(P,T)$ is nearly temperature independent and shows a linear behavior with $P$. The anomaly in ${\ensuremath{\kappa}}_{c}(P,T)$ is associated with the onset of long-range magnetic order, as evidenced by an analysis of the temperature dependence of the lattice parameters at fixed $P=13.7\ifmmode\pm\else\textpm\fi{}0.5$ GPa. At fixed $T=20$ K, the tetragonal elongation $c/a(P,T)$ shows a gradual increment with pressure and a depletion above ${P}_{2}=30$ GPa that indicates an orbital transition and possibly marks the collapse of the ${J}_{\text{eff}}=1/2$ spin-orbit-entangled state. Our results support pressure-induced phase transitions or crossovers between electronic ground states that are sensed, and therefore can be probed, by the crystal lattice at low temperatures in this prototype spin-orbit Mott insulator.

Investigations of the temperature-dependent electron paramagnetic resonance spectra and local structures for a cobalt(II) porphyrin complex within a metal-organic framework.

The interaction between an adsorbed CO molecule and the unsaturated coordinated Co2+ center in the metal-organic framework (MOF) PCN-224 is investigated by analyzing the electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants) and the adsorption energies at various temperatures. Six- and five-coordinated octahedral models (four planar N with two and one axial CO molecules, respectively) are constructed to simulate the local structures of the Co2+ centers at different temperatures. Because of the Jahn-Teller effect of the Co2+ centers, the C2-Co-N4 and C-Co-N4 combinations undergo different tetragonal elongation distortions along the C4 axis, characterized by the relative elongation ΔZ and displacement ΔZ' of Co2+ at different temperatures. Given the agreement between the calculated and experimental EPR parameters, as well as the adsorption properties, the six- and five-coordinated models are regarded as suitable for low- and high-temperature systems, respectively. These studies may be helpful to understand the properties of similar MOFs with adsorbed molecules under the effect of ambient temperature.

Water Adsorption on MO2 (M = Ti, Ru, and Ir) Surfaces. Importance of Octahedral Distortion and Cooperative Effects.

Understanding metal oxide MO2 (M = Ti, Ru, and Ir)–water interfaces is essential to assess the catalytic behavior of these materials. The present study analyzes the H2O–MO2 interactions at the most abundant (110) and (011) surfaces, at two different water coverages: isolated water molecules and full monolayer, by means of Perdew–Burke–Ernzerhof-D2 static calculations and ab initio molecular dynamics (AIMD) simulations. Results indicate that adsorption preferably occurs in its molecular form on (110)-TiO2 and in its dissociative form on (110)-RuO2 and (110)-IrO2. The opposite trend is observed at the (011) facet. This different behavior is related to the kind of octahedral distortion observed in the bulk of these materials (tetragonal elongation for TiO2 and tetragonal compression for RuO2 and IrO2) and to the different nature of the vacant sites created, axial on (110) and equatorial on (011). For the monolayer, additional effects such as cooperative H-bond interactions and cooperative adsorption come into play in determining the degree of deprotonation. For TiO2, AIMD indicates that the water monolayer is fully undissociated at both (110) and (011) surfaces, whereas for RuO2, water monolayer exhibits a 50% dissociation, the formation of H3O2– motifs being essential. Finally, on (110)-IrO2, the main monolayer configuration is the fully dissociated one, whereas on (011)-IrO2, it exhibits a degree of dissociation that ranges between 50 and 75%. Overall, the present study shows that the degree of water dissociation results from a delicate balance between the H2O–MO2 intrinsic interaction and cooperative hydrogen bonding and adsorption effects.

Evaluation of EPR parameters for compressed and elongated local structures of VO2+ and Cu2+ spin probes in BaO-TeO2-B2O3 glasses

EPR parameters and the local configurations of the transition metal (TM) ions VO2+ and Cu2+ in BaO-TeO2-B2O3 glasses were experimentally evaluated and also theoretically verified. From the recorded X-band EPR spectra the spin-Hamiltonian parameters (SHP) were determined. The optical spectra of vanadium doped glass samples revealed a single absorption band at 596 nm which was assigned to 2B2g → 2B1g transition, whereas copper doped glasses revealed two absorption bands around 818 and 602 nm which were assigned to 2B1g → 2B2g and 2B1g → 2E2g transitions respectively. Theoretical studies were accomplished on the EPR and optical factors from perturbation theory. It was observed from both the experimental and theoretical SHP values of vanadium containing glasses that the VO2+ ions are in tetragonally compressed octahedral sites with dxy (2B2g) ground state, while the copper containing glasses found to be in tetragonally elongated octahedral sites with dx2−y2 (2B1g) as the ground state. It is found that the magnitude of the relative tetragonal compression ratio (φ) of vanadium ion is less than the relative tetragonal elongation ratio (τ) of copper ion. The nature of the bonding between TM ions (i.e. vanadium and copper) and their ligands was assessed. Theoretical and experimental EPR parameters are in great concurrence with each other.

Theoretical studies of the Spin Hamiltonian parameters and local structures for Cu2+ centers in MNB ternary glasses

ABSTRACTThe spin Hamiltonian parameters (g factors g|| and g⊥ and the hyperfine structure constants A|| and A⊥) for the doped Cu2+ ion (in the form of CuO) in ternary glasses (i.e. xMgO·(30-x)Na2O·69B2O3·CuO, with 5 < x < 17 mol%) are theoretically investigated based on the high-order perturbation formulas for a tetragonally elongated octahedral 3d9 complex. In these formulas, the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the spin Hamiltonian parameters with the tetragonal distortion (characterized by relative tetragonal elongation δ along the C4 axis due to the Jahn–Teller effect) of [CuO6]10− cluster. The concentration dependences of the spin Hamiltonian parameters are illustrated by the approximately linear increases of the cubic field parameter Dq and the covalency factor N as well as the relative elongation δ with increasing the MgO concentration x. Based on the calculation, the [CuO6]10− clusters in the MNB glasses are found to suffer the relative elongations of about δ (≈ 0.125 Å) along the tetragonal axis due to the Jahn–Teller effect. The theoretical results show good agreement with the experimental data. And the improvement is also achieved in present work with respect to the previous theoretical analysis based on the conventional crystal-field model formulas by including the ligand orbital and spin–orbit coupling contributions.

Calculations of defect structures and spin Hamiltonian parameters of copper in (70 − x)Bi2O3–xLi2O–30 (ZnO–B2O3) glasses at different compositions

Defect structures and spin Hamiltonian parameters (SHPs) and the corresponding composition dependencies are quantitatively analyzed for divalent copper in ([Formula: see text])Bi2O3–[Formula: see text]Li2O–30(ZnO–B2O3) ([Formula: see text] mol.%) glasses by means of the relevant perturbation formulas of an octahedral 3d9 cluster with tetragonal elongation distortion. The [CuO6][Formula: see text] groups are subject to the moderate tetragonal elongation distortions of 4% due to the Jahn–Teller effect. The cubic crystal-field (CF) parameter, orbital reduction factor, tetragonal elongation ratio and core polarization constant exhibit respective piecewise linear functions of Li2O composition [Formula: see text], which suitably account for the experimental optical spectra and the SHPs at various compositions. Mechanisms of these composition dependencies for the related quantities can be explained as the variations of immediate CFs strength and copper–oxygen electron cloud admixtures with increasing Li2O composition.

Diboron Porphyrins: The Raman Signature of the In-Plane Tetragonal Elongation of the Macrocycle.

We describe an unusual in-plane type of porphyrin core distortion, tetragonal elongation (TE), observed experimentally in diboron porphyrins. The vibrational spectra of several of these complexes exhibit shifts that we have assigned to this TE distortion by comparing experimental spectra with DFT computational findings. The influence of TE in porphyrin systems was isolated using DFT analysis of the well-known model compounds Ni(II)porphine and Zn(II)porphine, with the macrocycle ring constrained to eliminate the influence of out-of-plane (OOP) distortions. A significant down-shift in frequencies was observed for porphyrin normal vibrational modes, particularly the in-plane A1g/B1g modes that are dominated by contributions from stretching and bending of Cα-Cm coordinates. In contrast, TE had little effect on the v(Pyrhalfring) and δ(Pyrdef) modes, though the lowered symmetry of the system resulted in significant splitting of the B2u and B3u modes. The impact of the TE distortion upon the diboron porphyrin vibrational spectrum was probed experimentally using Raman spectroscopy of B2O2(BCl3)2(TTP), B2OF2(TTP), and B2OPhOH2(TTP) (TTP = 5,10,15,20-(tetra- p-tolyl)porphyrin). Comparing the experimentally obtained spectral signatures to the computational findings allowed us to assign the large shifts observed for the v2 and v3 modes to the TE distortion in diboron porphyrins.

Evaluation of Spin Hamiltonian Parameters and Local Structure of Cu2+-doped Ion in xK2SO4–(50 – x)Na2SO4–50ZnSO4 Glasses with Various K2SO4 Concentrations

The spin Hamiltonian parameters (SHPs), i.e., g factors and hyperfine structure constants, and local structures are theoretically studied by analyzing tetragonally elongated 3d9 clusters for Cu2+ in xK2SO4–(50 – x)Na2SO4–50ZnSO4 glasses with various K2SO4 concentrations x. The concentration dependences of the SHPs are attributed to the parabolic decreases of the cubic field parameter Dq, orbital reduction factor k, relative tetragonal elongation ratio τ, and core polarization constant κ with x. The [CuO6]10– clusters are found to undergo significant elongations of about 17% due to the Jahn–Teller effect. The calculated cubic field splittings and the SHPs at various concentrations agree well with the experimental data.

Theoretical studies of the local structures and spin Hamiltonian parameters for Cu2+ in alkaline earth alumino borate glasses

The local structures and spin Hamiltonian parameters are theoretically studied for Cu[Formula: see text] in alkaline earth alumino borate (XAB, X = Mg, Ca and Sr) glasses by using the perturbation calculations for tetragonally elongated octahedral 3d9 groups. The [Formula: see text] groups are subject to the large relative tetragonal elongation ratios of 15.4%, 13.4% and 13.0% for MgAB, CaAB and SrAB glasses, respectively, arising from the Jahn–Teller effect. The decreasing cubic field parameter Dq, orbital reduction factor k and relative elongation ratio with the increase of the radius of alkaline earth ion X from Mg to Ca or Sr are analyzed for the studied systems in a uniform way.

Investigations of the local distortions and EPR parameters for Cu2+ in xNa2 O-(30-x)K2 O-70B2 O3 (5≤x≤25mol%) glasses.

The local distortions and electron paramagnetic resonance parameters for Cu2+ in the mixed alkali borate glasses xNa2 O-(30-x)K2 O-70B2 O3 (5≤x≤25mol%) are theoretically studied with distinct modifier Na2 O compositions x. Owing to the Jahn-Teller effect, the octahedral [CuO6 ]10- clusters show significant tetragonal elongation ratios p ~19% along the C4 axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi-linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi-linearly increasing rule with some fluctuations, leading to the minima of g factors at x=10mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi-linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal-fields and the electronic cloud distribution around Cu2+ with the variation of the composition of Na2 O.

Interpretation of the Electron Paramagnetic Resonance Spectra of Copper(II)–Tyrosine Complex

Abstract The electron paramagnetic resonance (EPR) spectra of [Cu(l-tyrosine)2] n (CuA) were interpreted based on the fourth-order perturbation treatments where the contributions due to the local distortion, ligand orbit and spin-orbit coupling were included. The calculated band transitions d x 2 − y 2 ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}}$ to dxy (≈16412 cm−1) and d z 2 ${{\text{d}}_{{{\text{z}}^2}}}$ (≈14845 cm−1) agree well with the band analysis results (d x 2 − y 2 → d xy ${\text{(}}{{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{xy}}}}$ ≈16410 and d x 2 − y 2 → d z 2 ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{{\text{z}}^2}}}$ ≈14850 cm−1). The unresolved separations d x 2 − y 2 → d xz ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{xz}}}}$ and d x 2 − y 2 → d yz ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{yz}}}}$ in the absorption spectra were evaluated as 26283 and 26262 cm−1, respectively. For CuA, copper chromophores in 1,3-diaminorpropane isophtalate copper(II) complex (CuB) and N-methyl-1,2-diaminoetaane-bis copper(II) polymer (CuC), the transition d x 2 − y 2 → d xy ${{\text{d}}_{{{\text{x}}^2} - {{\text{y}}^2}}} \to {{\text{d}}_{{\text{xy}}}}$ (=E1≈10Dq) suffered an increase with a decrease in R̅L which was evaluated as the mean value of the copper-ligand bond lengths. The correlations between the tetragonal elongation ratio ρ (=(R z–R̅L)/R̅L) (or the ratio G=(g z–g e)/((g x+g y)/2–g e)) and the g isotropy g av (=(g x+g y+g z)/3) (or the covalency factor N) for CuA, CuB and CuC were acquired and all the results were discussed.