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According to the high-order perturbation formulae of 3d

A new species of Cymbidium (Orchidaceae), Cymbidium xichouense, from Yunnan Province, China, is described and illustrated based on morphological evidence and molecular analyses. The new orchid is morphologically similar to C. qinbeiense, but it has several morphological features that distinguish it from C. qiubeinense and all other recognized species in Cymbidium. Phylogenetic analyses based on nuclear (ITS) and plastid DNA (matK) were conducted, and the results also supported the status of C. xichouense as a new species, which is sister to C. qiubeiense.

The mixed-metal pillar-layered metal–organic frameworks of Zn(bdc)(DABCO)0.5, Zn0.5Cu0.5(bdc)(DABCO)0.5 and Cu(bdc)(DABCO)0.5 (bdc = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane) are investigated for their local structures and gas adsorption properties. According to the obtained electron paramagnetic resonance (EPR) spectra, the distorted structures around Cu2+ are proposed to be tetragonally and orthorhombically elongated [CuO4N] with the well fitted high-order perturbation formulae of the EPR parameters. Due to the doped Cu2+, the adsorption isotherms of industrially relevant gases (CO2, CO, CH4 and N2) and lower alkanes (CH4, C2H6, C3H8, C4H10 and C5H12) are different, especially at different temperatures. By combining the structural properties and adsorption isotherms, a comprehensive study suggests that the ZnDABCO series can be a controllable tool in gas storage and separation.

Electron paramagnetic resonance (EPR) technology had been adopted to analyze the structures and properties of Cu2+ and VO2+ in Biochar (BG1 and BG2), but the local structural properties have not been clarified up to now. In present work, three possible structures (orthorhombically, rhombically and tetragonally elongated octahedra) are proposed for Cu2+ in BG1 and BG2 samples, and the former seems most reasonable in view of the best agreement between the theoretical EPR parameters based on the perturbation formulae and the experimental data. As for the VO2+ center, unlike the previous assignment of the tetragonally elongated [VO5]6− cluster based on the simple formulae of EPR parameters, presently proposed tetragonally compressed [VO6]8− cluster and the high order perturbation formulae of the EPR parameters yields good agreement with the observed values. This point is also supported by the d-d optical absorption 2B1g →2B2g for tetragonally compressed octahedral 3 d1 systems.

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 C 4 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.

The local angular distortions Δθ are theoretically studied for the various Ni3+ centers in LiAly Co1-y O2 at different Al concentrations (y = 0, 0.1, 0.5, and 0.8) based on the perturbation calculations of electron paramagnetic resonance g factors for a trigonally distorted octahedral 3d7 cluster with low spin (S = 1/2). Due to the Jahn-Teller effect, the [NiO6 ]9- clusters are found to experience the local angular distortions (Δθ ≈ 5°-9°) along the C3 axis. The variation trend of Δθ with y is in accordance with that of anisotropy (Δg = g|| - g⊥ ). As the substitutions can weaken bond strengths between transition metal and oxygen and the structural stability plays an important role in cathode performances, detailed investigations on the structural properties of the cathode materials LiAly Co1-y O2 can be practically helpful to understand the performances of these materials. The oxy-redox properties of LiAly Co1-y O2 systems are comprehensible in the framework of Ni3+ /Ni4+ couples, and the trigonally compressed octahedral [NiO6 ]9- clusters are applicable to the clarification of the electrochemical properties of lithium nickel oxide batteries. It appears that LiAl0.8 Co0.2 O2 with the largest Al concentration may correspond to the smallest distortion among the mixing systems.

This work presents a systematic density functional theory (DFT) study for geometrical and electronic structures, g factors and UV–vis spectra of three Cu(II) coordination polymers (CPs) [Cu(XL)(NO3)2]n (1), {[Cu(XL)(4,4′-bpy)(NO3)2]∙CH3CN}n (2) and {[Cu(XL)3](NO3)2·3.5H2O}n (3) based on the ligand N,N′-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide bi(1,2,4-triazole) (XL) with the linker triazole coordinated with copper to construct the CPs. For three CPs with distinct ligands, the optimized molecular structures with PBE0 hybrid functional and the 6-311g basis set agree well with the corresponding XRD data. Meanwhile, the electronic properties are also analyzed for all the systems. The calculated g factors are found sensitive to the (Hartree-Fock) HF character due to the significant hybridization between copper and ligand orbitals. The calculated UV–visible spectra reveal that the main electronic transitions for CP 1 contain d-d and CT transitions, while those for CPs 2 and 3 largely belong to CT ones. The present CPs seem difficult to adsorb small molecules, e.g., CP 1 with H2O and NO2 exhibit unfavorable adsorption and deformation structures near the Cu2+ site.

The geometric structures, band structures, density of states and optical absorption spectra are studied for cubic and orthorhombic KNbO3 (C- and O-KNO) crystals by using first-principles calculations. Based on the above calculation results, the mechanisms of photocatalytic properties for both crystals are further theoretically investigated to deepen the understandings of their photocatalytic activity from the electronic level. Calculations for the effective masses of electron and hole are carried out to make comparison in photocatalytic performance between cubic and orthorhombic phases. Optical absorption in cubic phase is found to be stronger than that in orthorhombic phase. C-KNO has smaller electron effective mass, higher mobility of photogenerated electrons, lower electron-hole recombination rate and better light absorption capacity than O-KNO. So, the photocatalytic activity of cubic phase can be higher than orthorhombic one. The present work may be beneficial to explore the series of perovskite photocatalysts.

The electron paramagnetic resonance (EPR) parameters and local structures for impurities VO2+ and Cu2+ in RO-Li2O-Na2O-K2O-B2O3 (RLNKB; R = Zn, Mg, Sr and Ba) glasses are theoretically investigated by using the perturbation formulas of the EPR parameters for tetragonally compressed octahedral 3d1 and tetragonally elongated octahedral 3d9 clusters, respectively. The VO2+ and Cu2+ dopants are found to undergo the tetragonal compression (characterized by the negative relative distortion ratios ρ ≈ −3%, −0.98%, −1% and −0.8% for R = Zn, Mg, Sr and Ba) and elongation (characterized by the positive relative distortion ratios ρ ≈ 29%, 17%, 16% and 28%), respectively, due to the Jahn-Teller effect. Both dopants show similar overall decreasing trends of cubic field parameter Dq and covalency factor N with decreasing electronegativity of alkali earth cation R. The conventional optical basicities Λth and local optical basicities Λloc are calculated for both systems, and the local Λloc are higher for Cu2+ than for VO2+ in the same RLNKB glass, despite the opposite relationship for the conventional Λth. This point is supported by the weaker covalency or stronger ionicity for Cu2+ than VO2+ in the same RLNKB system, characterized by the larger N in the former. The above comparative analysis on the spectral and local structural properties would be helpful to understand structures and spectroscopic properties for the similar oxide glasses with transition-metal dopants of complementary electronic configurations.

The electron paramagnetic resonance parameters and local structures for V4 + in xV2O5-(100 − x)[0.8NaPO3-0.2ZnO] glasses are theoretically investigated by using the perturbation formulas for tetragonally compressed octahedral 3d1 clusters. Polynomial, custom and power law functions are applied to describe the concentration variations of covalency factor N, relatively tetragonal compression ratio ρ, core polarization constant κ and reduction factor H. The concentration dependences of the measured electron paramagnetic resonance parameters are suitably reproduced, and the PL functions are found to be the optimal with the lowest mean absolute percentage deviation from the experimental data. The [VO6]8 − clusters exhibit moderately decreasing N, rapidly increasing ρ, slightly decreasing κ and moderately increasing H with x. The calculated decreasing local optical basicity Λloc also supports the declining trend of covalency factor. The theoretical study of the microscopic mechanisms for the concentration dependences of the relevant quantities are discussed in view of the impurity local behaviors with x due to mixed alkali effect.

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.

Based on the perturbation formulas of the spin Hamiltonian parameters (i.e., g factors and hyperfine structure constants A), the electron paramagnetic resonance (EPR) spectra (labeled as: signals a, b and c) are comprehensively investigated, from which the local environments of three different doped Ag2+ sites can be obtained and are characterized by coordinated and electronic structures. Meanwhile, the adsorption properties of CO, CO2 and O2, as well as the catalytic behaviors of CO, are simultaneously verified, which are conducted by comparing the adsorption energy ∆H, the reaction barrier ∆E of pure and the Ag doped CeO2 surface (111). In addition, the micro-mechanism and role of doped Ag2+ in CeO2 are explored from the interactions between the central Ag2+ and ligand oxygen ions, which are represented as covalence factor N and partial density of states (PDOS).

Making use of the perturbation formulae for 3d1 ions (Ti3+ and V4+ ) under orthorhombically compressed octahedra, the spin Hamiltonian parameters (g factors: gx , gy , gz and hyperfine structure constants: Ax , Ay , Az ) and local structures of the 3d1 impurity centres C1 , C2 , and C3 in KTiOPO4 crystals are theoretically analyzed in a consistent way. The remarkable local distortions (i.e., the relative axial compression ratios 11.2%, 7.0%, and 5.5% along Z axis and the relative planar bond length variation ratios 15.9%, 7.0%, and 6.0%) are obtained for the [Ti2O6 ]9- cluster on Ti2 site and [VO6 ]8- clusters on Ti1 and Ti2 sites, respectively, in view of the Jahn-Teller effect. The above local orthorhombic distortion parameters in the impurity centres are found to be more significant than the host Ti1 and Ti2 sites in pure KTiOPO4 . The sequences (C1 > C2 > C3 ) of the local orthorhombic distortion parameters ρ and τ are in accordance with those of the axial and perpendicular anisotropies Δg and δg of g factors, respectively.

A new bibenzyl derivative, dendrocandin V (1) and a new sesquiterpene amino ether, wardianumine A (2), together with eleven known compounds, including phenanthrenes (denbinobin (3), 9,10-dihydro-denbinobin (4), mostatin (5), loddigesiinols A (6)), bibenzyls (moscatilin (7), 5-hydroxy-3,4'-dimethoxybibenzyl (8), 3,4-dihydroxy-5,4'-dimethoxy bibenzyl (9), dendrocandin A (10), gigantol (11), dendrocandin U (12)) and an alkaloids (dihydroshihunine, 13) were isolated from the EtOH extraction of stems of Dendrobium wardianum Warner. Isolation of the new compound 2 indicated that N,N-dimethylethanolamine as the key adduction in the synthesis of dendroxine and its analogs in Dendrobium species. The hypothetical biosynthetic pathway of 2 was then postulated. Inspired by literature and traditional usage of the herbal medicine, some compounds were sent for cytotoxic activity and the results indicated that compounds 1, 3, 4, 5 showed cytotoxic activities against five human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480) with IC50 from 2.33-38.48μM. Among those compounds, 3 and 4 showed cell line selectivity with strong activity comparable to DDP.

Density functional theory (DFT) calculations of the structures and the Cu2+ g factors (g x , g y and g z ) and hyperfine coupling tensor A (A x , A y and A z ) were performed for the paddle-wheel (PW)-type binuclear copper(II) complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) powder and single crystal. Calculations were carried out with the ORCA software using the functionals BHandHlyp, B3P86 and B3LYP with five different basis sets: 6-311g, 6-311g(d,p), VTZ, def-2 and def2-TZVP. Results were tested by the MPAD analysis to find the most suitable functional and basis sets. The electronic structure and covalency between copper and oxygen were investigated by the electron localisation function and the localised orbital locator as well as the Mayer bond order for the [CuO5] group. The optical spectra were theoretically calculated by the time-dependent DFT module and plotted by the Multiwfn program for the [CuO5] group and reasonably associated with the local structure in the vicinity of the central ion copper. In addition, the interactions between the OCNH2CH3, NH3 and H2O molecules and the uncoordinated PW copper(II) complex were studied, and the corresponding adsorption energies, the frequency shifts with respect to the free molecules and the changes of the Cu–Cu distances were calculated and compared with the relevant systems.

The local structures and spin Hamiltonian parameters are theoretically studied for Cu2+ in alkali barium borate glasses 20A2O ∙ 24.5BaO · 55B2O3 · 0.5CuO, where A = Li, Na and K by the quantitative calculations of these parameters for tetragonally elongated octahedral 3d 9 clusters. The [CuO6]10‒ clusters are subject to the local relative tetragonal elongation ratios 7.8, 8.1 and 8.4% in Li, Na and K barium borate glasses, respectively, owing to the Jahn–Teller effect. The increasing (Li < Na < K) local relative elongation ratio and decreasing cubic field parameter and covalency factor are discussed in a consistent way.

The defect structures for Co 2+ in ZnO microwires, thin films and bulks are theoretically investigated by analyzing the electron paramagnetic resonance (EPR) parameters (zero-field splitting D, g factors g // and g ⊥ and hyperfine structure constants A // and A ⊥ ) for trigonally distorted tetrahedral 3d 7 clusters in a consistent way. The impurities Co 2+ are found to suffer the displacements (≈0.046, 0.044 and 0.045 A) away from the ligand triangles along the C 3 axis in ZnO microwires, thin films and bulks, respectively, which considerably reduce the trigonal distortions of the Zn 2+ sites in the hosts. Apart from the contributions from the conventional crystal-field (CF) mechanism, those from the charge-transfer (CT) mechanism are important and should be included in the EPR analysis. The defect structures and spectral properties of the three ZnO:Co 2+ systems are discussed.

The spin Hamiltonian parameters (SHPs) (i.e., g factors, hyperfine structure constants and superhyperfine parameters) are theoretically investigated for the irradiation induced Rh2+ and Rh0 centres in NH4Cl by use of the perturbation calculations. The tetragonally compressed Rh2+ centre in the form of [RhCl4(H2O)2]2‾ group originates from interstitial Rh2+ (reduced from original Rh3+ of doped RhCl3 by capturing one electron during gamma irradiation) associated with two adjacent axial NH4+ cations substituted by two H2O molecules due to charge compensation. The orthorhombically compressed Rh0 centre in the form of [RhCl4(H2O)2]4‾ group arises from interstitial Rh0 (reduced from Rh3+ by capturing three electrons during gamma irradiation) with two adjacent axial NH4+ replaced by two H2O molecules as charge compensators and the planar Rh0-Cl‾ bond length variation of about 0.042 Ǻ along [011] and [ 0 1 ¯ 1 ] axes due to the Jahn-Teller effect. The calculated SHPs are in good agreement with the observed values. The EPR spectra and local structures are discussed for both centres.

Doping transition metal ions in LiCoO2 batteries has been proved an efficient method to improve the electrochemical properties in experiment, which is deeply related with the distorted local structure of impurities ions. According to the observed EPR spectra, the distorted local structures for 3d3 (Mn4+), 3d5 (Fe3+) and 3d7 (Ni3+) ions in LiCoO2 batteries are theoretically studied based on the perturbation calculations of Spin Hamilton Parameters (g factors, hyperfine structure constants A and Zero-field splittings parameters D and E). By considering the Jahn-Teller effect and mismatch radius of above transition metal ions (TMs), the formed [MnO6]8-, [FeO6]9- and [NiO6]9- clusters in LiCoO2 exhibit various distorted symmetries compared with experimental single one, characterized by trigonal distortion parameter Δθ as well as rhombic distortion parameters ΔZ and Δϕ in the 3d3 center and the 3d5 center and tetragonal distortion parameter ΔZ in the 3d7 center. In addition, compared with asymmetrical signal of EPR spectra at 30K, the role of relatively high temperature for 100K is investigated by dynamic Jahn-Teller, making the isotropic EPR signal and regular octahedron for Ni3+ center. Comparing with the obtained structure properties of isolate-doped transition metal ion, the co-doped Mg in LiCoO2 makes the further elongated distortion of local structure. Based on the well fitted EPR parameters and obtained local environment of doped transition metal ions, the inactive of electrochemical properties of Mn4+ can be attribute to the largest crystal field (Dq) and the smallest difference with host Co3+ site. Therefore, a comprehensively study of the local structure may be helpful to understand and predict the electrochemical behaviors of batteries.

The electron paramagnetic resonance (EPR) parameters and defect structures for Cu 2+ in alkaline earth zinc borate glasses 10RO + 30ZnO + 60B 2 O 3 (RZB, where R = Mg, Ca and Sr) are quantitatively investigated from the consistent analysis of these parameters for a tetragonally elongated octahedral 3d 9 complex. The studied [CuO 6 ] 10− complexes are found to undergo the relative tetragonal elongation ratios of about 5.8%, 4.5% and 8.6% in MgZB, CaZB and SrZB glasses, respectively, due to the Jahn-Teller effect. The increasing tendencies (MgZB // is attributed to the decreasing (MgZB > CaZB > SrZB) cubic field parameter Dq and increasing orbital reduction factor k , while the increasing magnitudes of hyperfine structure constants are illustrated by the increases of the reduction factor H arising from the tetragonal elongation distortions. The defect structures and the properties of the EPR parameters are discussed.

The local lattice distortions of the various rhombic Ru3+ centres (A, A′, B, B′, X and X′) in AgX (X = Cl and Br) are quantitatively investigated from the perturbation calculations of the anisotropic g factors and hyperfine structure constants for a 4d5 ion in rhombically distorted octahedra. Centre A or A′ is assigned to the substitutional Ru3+ on Ag+ site associated with one nearest neighbor silver vacancy VAg in the [1 1 0] axis and one next nearest neighbor VAg in the [ 1 ¯ 0 0] axis due to charge compensation. Ru3+ is found to undergo the off-centre displacement 0.022 or 0.017 A along the [1 1 0] axis, while the halide ligands closest to the VAg move away from the vacancies by 0.030 or 0.005 A in AgBr or AgCl, respectively, due to the electrostatic interactions of the VAg. Centre B or B′ is ascribed to Ru3+ associated with each nearest neighbor VAg in the [1 1 0] and [ 1 ¯ 1 ¯ 0] axes. The two axial ligands experience the displacement 0.036 or 0.015 A along the Z (or [0 0 1]) axis, and the four planar ligands shift away from the vacancies by about 0.006 or 0.001 A, respectively. Centre X or X′ can be described as Ru3+ associated with one nearest neighbor VAg and one next nearest neighbor VAg in the [1 1 0] and [0 0 1] axes, respectively. Ru3+ may undergo the off-centre displacement 0.019 or 0.015 A along the [1 1 0] axis, while the ligands closest to the VAg move away from the VAg by 0.022 or 0.006 A. The present studies would be helpful to the investigations on the structures and properties for Ru3+ in AgX and similar halides.

The electron paramagnetic resonance (EPR) g factors and local structures for Ni3+ in LiAlyCo1–yO2 as the cathode materials for lithium-ion batteries are theoretically investigated at various Al concentrations y (= 0.1, 0.5, 0.8 and 1.0). The [NiO6]9– clusters are subject to the tetragonal elongation distortions along the C4 axis owing to the Jahn–Teller effect and the different degrees of distortions are characterised by the slightly increasing relative elongation ratio ρ (and also crystal-field strength and covalency) with y. In pure LiAlO2 (y = 1.0), the [NiO6]9– cluster exhibits the largest ρ (≈1.4%) and an additional relative variation ratio τ (≈1.4%) of the planar bond lengths, responsible for the perpendicular g anisotropy δg = (gx – gy). The number of impurity Ni3+ centres increases from one at y = 0 and 1.0 to two at y = 0.1 and 0.8 and reaches the maximum four at y = 0.5, in accordance with the increasing degree of disorder of the systems. The distinct impurity centres for the same y may ...

The quantum correlation in open quantum systems is of fundamental and practical importance for quantum information processing and controllable nanometer devices. And the properties of quantum correlation can be influenced by the information flow between systems and environments. In this study, we investigated the geometric measure discord of quantum correlation of a two qubits system, interacting with two independent and intrinsic interacting spin-environments, respectively. Based on the asymmetry environments with comparable parameters, the different properties of the geometric measure of entanglement and quantum discord are displayed and discussed for initial Bell states.

The local structures and spin Hamiltonian parameters (SHPs, g factors, hyperfine structure constants and superhyperfine parameters) are theoretically investigated for the two orthorhombic Rh2+centers R4 and R5 in AgCl microcrystals. Center R4 is ascribed to the impurity Rh2+substituted for Ag+ with two H2O molecules substituted for the nearest neighbor ligands Cl− along the [100] and [010] axes, each with one next nearest neighbor Ag+ vacancy (VAg) due to charge compensation. The impurity Rh2+is found to experience a small off-center displacement 0.006 A along the [ 1 ¯ 1 ¯ 0 ] axis because of the electrostatic interactions of the substitutes and the VAg. Center R5 is attributed to the impurity Rh2+substituted for Ag+ associated with one H2O molecule substituted for the nearest neighbor ligand Cl− along the [100] axis and one next nearest VAg along the [010] axis. Due to the effective positive charge of the substitute, Rh2+ is repulsed away from the substitute by about 0.008 A along the [ 1 ¯ 00 ] axis, while the intervening ligand Cl− in Rh2+and VAg suffers a small inward displacement 0.010 A towards the center of octahedron. The calculated SHPs based on the above local structures show good agreement with the experimental data for both centers.

The local distortions and electron paramagnetic resonance (EPR) parameters for Cu2+ in 40MgO–(10−x)PbF2–50SiO2–xCuO (MPSC) glasses are theoretically studied at various impurity CuO concentrations x (= 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 mol %) in a consistent way. Due to the Jahn-Teller effect, the [CuO6]10− clusters are found to experience the moderate tetragonal elongation distortions (characterized by the moderate relative tetragonal elongation ratios ρ ≈ 3%) along C4 axis. With only five adjusted coefficients a1, a2, b1, b2 and ω, the relevant model parameters (Dq, k, ρ, κ and H) are described by the Fourier type functions, which suitably reproduce the corresponding overall varying tendencies and fluctuations of the measured d–d transition bands and EPR parameters with x. The microscopic mechanisms of the varying rules of the relevant quantities with x are discussed in view of the whole decreasing ability of Si4+ to accept electrons and the reverse tendencies due to partial Cu2+ reduced to Cu+ at x ≥ 0.7 mol %. The monotonically increasing tendency of the calculated optical basicity reveals decreasing covalency of the whole glass systems with x.

The electron paramagnetic resonance (EPR) g factors for Cu2+ in [Cu(CH3NHCH2CH2NH2)2(BF4)2] are calculated using the high-order perturbation formulas of g factors for a 3d 9 ion in rhombically elongated octahedra. The calculated g factors show good agreement with the experimental data. The ligand orbital and spin-orbit coupling contributions are taken into account from the cluster approach in consideration of significant covalency due to the short and strongly covalent Cu2+–N3– bonds. The EPR behaviors and structural properties of [Cu(CH3NHCH2CH2NH2)2(BF4)2] are analyzed on the basis of the present perturbation calculations.

The spin Hamiltonian parameters (g factors g//, g⊥, hyperfine structure constants A//, A⊥ and superhyperfine parameters A z ′ , A x ′ and A y ′ ) and defect structures for Ag2+ in NaF and CsCdF3 crystals are theoretically studied using the improved perturbation formulas of these quantities for a 4d9 ion in a tetragonally elongated octahedron. The contributions from both the crystal-field and charge transfer mechanisms are taken into account, and the relevant model parameters are quantitatively obtained from the cluster approach in a consistent way. The impurity centers are found to undergo the relative tetragonal elongations of about 9.4% and 8.2% for Ag2+ in NaF and CsCdF3, respectively, along the C4 axis due to the Jahn–Teller effect. By employing the few adjustable parameters, the calculated spin Hamiltonian parameters based on the above uniform formulas and the local tetragonal elongation distortions agree well with the experimental data. Despite dominant ionicity of the hosts, the charge transfer contributions are actually important to the spin Hamiltonian parameters (e.g., about 20% for the g-shifts) due to strong covalency of impurity Ag2+.

The spin Hamiltonian parameters ( g factors and hyperfine structure constants) are theoretically studied for the two interstitial Cu 2+ centers I and II in the ZnO nanocrystals from the perturbation formulas of these parameters for a tetragonally elongated octahedral 3d 9 cluster. The ligand spin–orbit coupling and orbital contributions are involved from the cluster approach in view of moderate covalency. The two Cu 2+ centers demonstrate slight tetragonal elongation distortions (denoted by the relative elongation parameters ρ ≈ 3.4% and 3.2% for centers I and II, respectively) due to the Jahn–Teller effect. The calculated spin Hamiltonian parameters and three optical transition bands are in good agreement with the observed values. The differences in EPR and optical spectra for both centers can be ascribed to the weaker covalency (higher N ), stronger tetragonal elongation distortion (larger ρ ) and slightly larger core polarization constant κ as well as almost identical crystal-fields (nearly the same Dq ) for center I as compared to center II. The above delicate discrepancies in spectroscopic behaviors may be attributed to the tiny differences in local structures and electronic states for Cu 2+ at dissimilar parts of the ZnO nanocrystals.

4d1 (Mo5+) and 5d1 (W5+) impurities doped into nonlinear optical crystals KTiOPO4 (KTP) can occupy the inequivalent Ti1 and Ti2 sites and exhibit orthorhombically compressed octahedral nd1 (n = 4, 5) centres arising from the Jahn–Teller effect. Closely relevant to the electronic levels as well as optical and magnetic properties of these materials, the above local distortions can be suitably reflected by the anisotropic electron paramagnetic resonance (EPR) signals with the paramagnetic nd1 probes. This work stresses on the theoretical studies of the EPR parameters (g factors gx, gy, gz and hyperfine structure constants Ax, Ay, Az) and local distortions for the above nd1 impurity centres in a consistent way. The local distortions are characterised by the relative axial compression ratios ρ (≈0.040, 0.032 and 0.031) and the relative planar bond length variation ratios τ (≈0.030, 0.015 and 0.012) for Mo5+ centre I and W5+ centres II and III, respectively, which are larger than those of host Ti1 and Ti2 sites.

The local distortions and electron paramagnetic resonance (EPR) parameters for Cu2+in lithium sodium borate (LNB) glassesxLi2O·(30–x)·Na2O·69.5B2O3(5≤x≤25 mol%) are theoretically studied at various concentrationsxin a consistent way. Owing to the Jahn–Teller effect, the [CuO6]10−clusters are found to experience the significant tetragonal elongations of 16% along C4axis. Despite the nearly unchanging observedgfactors, measured d–d transition band (or cubic field parameterDq) shows remarkable linear increases with concentrationx, whose influences ong‖andg⊥are actually cancelled by the linearly increasing covalency factorNand relative elongation ratioηwithx. The almost unvarying hyperfine structure constants are attributed to the fact that the influences of the linearly increasingNand the linearly decreasing core polarisation constantκlargely cancel one another. The microscopic mechanisms of the above concentration dependences for these quantities are illustrated from mixed alkali effect (modification of B2O3network by transforming some BO3units into BO4ones with variations in modifier Li2O concentration).

The local structures and electron paramagnetic resonance (EPR) parameters as well as their composition (x) dependences for Cu 2 + in xMgO·(30 − x)·Na 2 O·69B 2 O 3 (5 ≤ x ≤ 17 mol%) glasses are theoretically studied by analyzing these parameters for tetragonally elongated 3d 9 complexes. The nonlinear variations of the EPR spectra with modifier MgO composition x can be ascribed to the approximately parabolic relationships between cubic field parameter Dq , orbital reduction factor k , local relative tetragonal elongation ratio ρ, core polarization constant κ and reduction factor H with x. The [CuO 6 ] 10 − complexes may experience the slight relative elongations of about 0.4% due to the Jahn–Teller effect. The theoretical d–d transition bands and EPR parameters for the various composition x are in good agreement with the observed results. The above composition dependences of the relevant quantities are illustrated as the modifications of the local crystal-fields and electronic states in the vicinity of the Cu 2 + dopants with x.

The electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants) for Cu2+ in [Cu(ipt)(dap)H2O] n •nH2O (ipt is isophthalic acid, dap–1,3-diaminopropane) are theoretically investigated from the high order perturbation formulas of these parameters for a 3d 9 ion in a rhombically elongated octahedron. The ligand orbital and spin-orbit coupling contributions are included from the cluster approach because of strong covalency of the system. The nearly axial anisotropies of the g factors and hyperfine structure constants are correlated to the significant elongation distortion of the five-fold coordinated Cu2+ (in a distorted square pyramidal [CuN2O3] group). Nevertheless, the perpendicular anisotropies arising from the nonequivalent planar ligands are largely concealed by the experimental uncertainties. The theoretical analysis of the EPR behaviours for [Cu(ipt)(dap)H2O] n •nH2O would be helpful to understand the local structures and properties of this and relevant systems.

The defect structures and spin Hamiltonian parameters (SHPs) for three Rh2+ centres (denoted C1 in KTiOAsO4 and C2 and C3 in KTiOPO4) are theoretically investigated by utilising the perturbation formulae for a 4d7 ion under orthorhombically (D2h) elongated octahedra. The defect structures are characterized by the axial elongation ratios of 4.91%, 4.93% and 4.90% along the Z axis and the planar bond length variation ratios of 0.05%, 0.01% and 0.04% for centres C1, C2 and C3, respectively, owing to the Jahn–Teller effect. The nearly identical moderate axial elongation ratios and the slightly different tiny planar bond length variation ratios may suitably account for the comparable moderate axial g anisotropies ∆g (≈0.6087, 0.6124 and 0.6067) and the slightly dissimilar tiny perpendicular g anisotropies δg (≈0.0649, 0.0097 and 0.0509) of the three centres, respectively. All centres demonstrate similar strong crystal-field interactions and moderate covalence arising from the comparable short impurity-ligand distances.

Local structure and g factors for (20-x)CaF2-10CaO-5Y2O3-10B2O3-55P2O5: xTiO2(x = 0.2, 0.4, 0.6, 0.8 and 1.0 mol%) glasses are theoretically studied by using the perturbation formulae for a tetragonally elongated octahedral 3d1 cluster. Six coordinated [TiO6]9‒ and five coordinated [TiO5]7‒ clusters are evaluated in view of the Jahn-Teller effect and the charge compensation of impurity Ti3+ for host Ti4+. d -d transition bands of E2 (2B2g→2A1g) and E3 (2B2g→2B1g) of the [TiO5]7‒ cluster is obtained with the piecewise linear fitting function of x. The microscopic mechanisms of the varying rules of relevant quantities g//, E2 and N with x are related with NBO. The role of various TiO2 concentrations in local structure and optical spectra is also comprehensively studied from the local optical basicity Λloc, which can represent the local environment and covalency of the Ti3+ center.

The local angular distortions Δθ are theoretically studied for the various Ni

The perturbation formulas of the spin Hamiltonian parameters (zero-field splitting and g factor g// and g⊥) are established for a 3d8 ion in trigonally distorted tetrahedra for the first time. In the theoretical treatments, the contributions from the Jahn–Teller effect, the ligand orbital and spin–orbit coupling interactions and configuration interactions are taken into account from the cluster approach in a uniform way. The above formulas are applied to the studies of the spin Hamiltonian parameters for the three CoCl(PPh3)3 molecules, and the experimental electron paramagnetic resonance spectra of all the molecules are satisfactorily explained. The significant compressions of the ligand tetrahedra with mixed chlorine and PPh3 groups around Co+ are analysed for three distinct CoCl(PPh3)3 compounds, characterised by the Cl–Co–P bond angles θ larger than the tetrahedral angle of 109.47°. The local trigonal distortions are discussed in view of the Jahn–Teller effect.

The local lattice distortions and the electron paramagnetic resonance (EPR) parameters (g factors, hyperfine structure constants and zero-field splittings) for Cu2+, Mn2+ and Fe3+ in ZnWO4 are theoretically studied based on the perturbation calculations for rhombically elongated octahedral 3d9 and 3d5 complexes. The impurity centres on Zn2+ sites undergo the local elongations of 0.01, 0.002 and 0.013 A along the C2 axis and the planar bond angle variations of 8.1°, 8.0° and 8.6° for Cu2+, Mn2+ and Fe3+, respectively, due to the Jahn–Teller effect and size and charge mismatch. In contrast to the host Zn2+ site with obvious axial elongation (∼0.31 A) and perpendicular (angular) rhombic distortion, all the impurity centres demonstrate more regular octahedral due to the above local lattice distortions. The copper centre exhibits significant Jahn–Teller reductions for the spin-orbit coupling and orbital angular momentum interactions, characterised by the Jahn–Teller reduction factor J (≈0.29 ≪ 1). The calculat...

The spin Hamiltonian parameters ( g factors and hyperfine structure constants) and local structures are theoretically studied for the tetragonal Cu 2+ centers in the ZnX (X=O and S) nanocrystals from the perturbation formulas of these parameters for a 3d 9 ion in tetragonally distorted tetrahedra. The ligand orbital and spin–orbit coupling contributions are considered in view of strong covalency. Due to the Jahn–Teller effect, the local Cu 2+ ‒X 2− bond angles between the four equivalent impurity-ligand bonds and the four-fold axis are found to be about 2.47° and 1.68° larger than that (≈54.74°) for an ideal tetrahedron. This induces tetragonally compressed [CuX 4 ] 6− clusters on tetrahedral substitutional Zn 2+ sites, different from the assignments (i.e., Cu 2+ on tetragonally elongated octahedral and tetrahedral substitutional sites in the ZnO and ZnS nanocrystals, respectively) in the previous works. The calculated g factors for both systems and the parallel component of the hyperfine structure constants for the ZnS:Cu 2+ nanocrystals based on the above local angular distortions are in good agreement with the observed values. The validity of the present assignments for the local structures of the Cu 2+ centers is analyzed.

The spin Hamiltonian parameters (g factors and hyperfine structure constants) for Cu2+ in NaCl and AgCl are investigated theoretically for the case of the 3d 9 ion in tetragonally elongated octahedra using high-order perturbation formulas for these parameters. Due to the Jahn–Teller effect, the impurity Cu2+ centers are found to experience relative elongations along the four-fold axis of about 0.15 and 0.08 A in NaCl and AgCl, respectively. The calculated spin Hamiltonian parameters are in good agreement with the experimental data. The local structures and EPR spectra of the systems are discussed.

The improved perturbation formulas of the spin Hamiltonian parameters (zero-field splitting D and g factors) for a 3d5 ion in trigonally distorted tetrahedra are constructed from the cluster approach by including both the crystal-field and charge-transfer contributions. These formulas are applied to the studies of the local structures and the electron paramagnetic resonance (EPR) spectra for Fe3+ in CdX (X = S, Se, Te). The impurity Fe3+ is found not to occupy exactly the host Cd2+ sites but to experience the small outward shifts 0.014 and 0.006 A away from the ligand triangles along the C3 axis in CdS and CdSe, respectively. The charge-transfer contributions to the spin Hamiltonian parameters are important and increase significantly with increasing atomic number of the ligand (i.e., S2− < Se2− < Te2−) arising from the decreases of charge-transfer energy levels and the increases of ligand spin–orbit coupling coefficients. The results are discussed.