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Metal organic frameworks (MOFs) have been well-known and extensively researched due to the high storage /good selectivity for gas molecules. Herein, the structures and electron paramagnetic resonance (EPR) spectra for dicopper paddle wheel MOF compound (Cu2(µ2-O2CCH3)4 with various gas molecule are theoretically investigated by density functional theory (DFT) calculations. The adsorption energies and isotherms (including pure gas molecules and the mixed ones) are calculated for the gas molecules interacting with the unsaturated Cu2(µ2-O2CCH3)4. Both quantities exhibit the roughly consistent orders (e.g. H2S > NH3 > CO2 > CO > H2O > N2 > NO > H2 for isotherms and H2S > NH3 > N2 > CO2 > NO > H2O > H2 > CO for adsorption energies), possibly suggesting that this material may act as a potential adsorbent of these gas molecules. The catalytic property of Cu2(µ2-O2CCH3)4 for oxidation of CO and NO into non-toxic molecules and splitting of H2O into H2 and O2 in the solvent condition are uniformly discussed. Simulation of Grand Canonical Monte Carlo (GCMC) in MS 8.0 and calculations in Langmuir model reveal that Cu2(µ2-O2CCH3)4 has good selectivity for CH4 in natural gas (CH4/CO2/N2) and SO2 in fog (SO2/NO/NO2/H2O/O2), which would exhibit potential environmentally friendly applications. [ABSTRACT FROM AUTHOR]

The local structures for various Rh2+ centers in AgCl are theoretically studied using density functional theory (DFT) with periodic CP2K program. Through geometry optimizing, the stable ground states with minimal energies and electronic structures are obtained for the tetragonally elongated (TE), orthorhombically elongated (OE), and tetragonally compressed (TC) centers, and the corresponding g and hyperfine coupling tensors are calculated in ORCA level. The calculations reveal obvious Jahn–Teller elongation distortions of about 0.109 and 0.110 Å along [001] axis for TE and OE centers without and with 1 next nearest neighbor (nnn) cation vacancy VAg in [100] axis, respectively. Whereas TC center with 1 nnn VAg along [001] axis exhibits moderate axial compression of about 0.066 Å due to the Jahn–Teller effect. For OE and TC centers with 1 nnn VAg, the ligand intervening in the central Rh2+ and the VAg is found to displace away from the VAg by about 0.028 and 0.024 Å, respectively. The present results are discussed and compared with those of the previous calculations based on the perturbation formulas by using the improved ligand field theory. [ABSTRACT FROM AUTHOR]

The copper electron paramagnetic resonance gyromagnetic factors are theoretically studied for three novel Cu2+ coordination polymers [Cu(XL)(NO3)2]n ( 1), {[Cu(XL)(4,4′-bpy)(NO3)2]•CH3CN}n (1a) and {[Cu(XL)3](NO3)2•3.5H2O}n (2) with bi-triazole ligand (XL) = N, N′-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide bi(1,2,4-triazole) from the high-order perturbation calculations of the g factors for a rhombically elongated octahedral 3d9 group. The order ( 1 ≤ 1a < 2) of g z can be illustrated by the dominant second-order perturbation term roughly proportional to the square of the covalency factor N. g x (and g y) relies on the combination of the contributions from N, cubic field parameter D q, and axial elongation of the copper sites and exhibits the sequence ( 1 ≤ 2 < 1a). As regards the axiality ( g x ≈ g y) of g factors, this is because the perpendicular rhombic contribution from the deviations of the bond lengths and bond angles for the planar ligands with respect to an ideal octahedron and that from the discrepancies between the crystal fields of the planar ligands O2− and N3− largely cancel each other. The present theoretical studies on the copper electron paramagnetic resonance g factors would be helpful to understand the structures and properties of some promising coordination polymers containing copper with the novel bi-triazole ligand XL. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR)gfactors and local structures for Ni3+in LiAlyCo1–yO2as the cathode materials for lithium-ion batteries are theoretically investigated at various Al concentrationsy(= 0.1, 0.5, 0.8 and 1.0). The [NiO6]9–clusters are subject to the tetragonal elongation distortions along theC4axis owing to the Jahn–Teller effect and the different degrees of distortions are characterised by the slightly increasing relative elongation ratioρ(and also crystal-field strength and covalency) withy. In pure LiAlO2(y = 1.0), the [NiO6]9–cluster exhibits the largestρ(≈1.4%) and an additional relative variation ratioτ(≈1.4%) of the planar bond lengths, responsible for the perpendicularganisotropyδg= (gx–gy). The number of impurity Ni3+centres increases from one aty = 0 and 1.0 to two aty = 0.1 and 0.8 and reaches the maximum four aty = 0.5, in accordance with the increasing degree of disorder of the systems. The distinct impurity centres for the sameymay be accompanied by the comparable energies of the ground and near excited states, similar to ‘resonant states’ with slightly different local elongation distortions and tetragonal level splittings. The present studies will be helpful to understand the relationships between local structures and performances of LiAlyCo1–yO2type cathode materials. [ABSTRACT FROM PUBLISHER]

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 Ag 2+ in NaF and CsCdF 3 crystals are theoretically studied using the improved perturbation formulas of these quantities for a 4d 9 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 Ag 2+ in NaF and CsCdF 3 , respectively, along the C 4 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 Ag 2+ . [ABSTRACT FROM AUTHOR]

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 < CaZB < SrZB) of g // 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. [ABSTRACT FROM AUTHOR]

4d 1 (Mo 5+ ) and 5d 1 (W 5+ ) impurities doped into nonlinear optical crystals KTiOPO 4 (KTP) can occupy the inequivalent Ti1 and Ti2 sites and exhibit orthorhombically compressed octahedral n d 1 ( 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 n d 1 probes. This work stresses on the theoretical studies of the EPR parameters ( g factors g x , g y , g z and hyperfine structure constants A x , A y , A z ) and local distortions for the above n d 1 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 Mo 5+ centre I and W 5+ centres II and III, respectively, which are larger than those of host Ti1 and Ti2 sites. [ABSTRACT FROM AUTHOR]

The defect structures and spin Hamiltonian parameters (SHPs) for three Rh 2+ centres (denoted C 1 in KTiOAsO 4 and C 2 and C 3 in KTiOPO 4 ) are theoretically investigated by utilising the perturbation formulae for a 4d 7 ion under orthorhombically (D 2 h ) 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 C 1 , C 2 and C 3 , 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 δ g (≈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. [ABSTRACT FROM AUTHOR]

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)(NO 3 ) 2 ] n (1), {[Cu(XL)(4,4′-bpy)(NO 3 ) 2 ]∙CH 3 CN} n (2) and {[Cu(XL) 3 ](NO 3 ) 2 ·3.5H 2 O} 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 H 2 O and NO 2 exhibit unfavorable adsorption and deformation structures near the Cu 2+ site. [ABSTRACT FROM AUTHOR]

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 Å) 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. [ABSTRACT FROM AUTHOR]

The spin Hamiltonian (SH) parameters (i.e. the zero-field splitting parameters (ZFSPs) and g factors) and local structures of the two Cr 3+ centers I and II at room temperature in KCl single crystals are theoretically investigated from the perturbation calculations for a rhombically distorted octahedral 3d 3 cluster. The impurity systems are attributed to the doped Cr(CN) 6 3− groups into KCl replacing the host KCl 6 5 − ones, associated with two nearest neighbor potassium vacancies V K in [011] and [ 0 1 ¯ 1 ¯ ] axes in center I and one nearest neighbor V K along [ 0 1 ¯ 1 ] and another next-nearest neighbor V K along [100] axis in center II, respectively. In center I, the four coplanar and two axial ligands CN − undergo the shifts ∆ R 1 (≈0.0044 nm) away from the V K and ∆ R 2 ′ (≈0.0144 nm) away from the central ion along Z axis, respectively, because of the electrostatic interactions. In center II, the impurity Cr 3+ is found to undergo the shift ∆ R C (≈0.0063 nm) towards the nearest neighbor V K along [ 0 1 ¯ 1 ] axis, while the two ligands in [001] and [ 0 1 ¯ 0 ] axes closest to the V K undergo the shifts ∆ R 1 (≈0.0081 nm) away from the respective V K , and the ligand intervening in the V K and the central ion experiences the shift ∆ R 2 (≈0.0238 nm) away from the V K along [100] axis. The charge-transfer (CT) contributions to g-shifts are found to be opposite in sign and more than half (characterized by the ratios |Δg CT /Δg CF |>50%) in magnitude compared with the CF ones for both centers. The local structures and the microscopic mechanisms of the relevant impurity and ligand shifts are discussed for the two centers. [ABSTRACT FROM AUTHOR]

The spin Hamiltonian parameters (SHPs) (i.e., g factors, hyperfine structure constants and superhyperfine parameters) are theoretically investigated for the irradiation induced Rh 2+ and Rh 0 centres in NH 4 Cl by use of the perturbation calculations. The tetragonally compressed Rh 2+ centre in the form of [RhCl 4 (H 2 O) 2 ] 2 ‾ group originates from interstitial Rh 2+ (reduced from original Rh 3+ of doped RhCl 3 by capturing one electron during gamma irradiation) associated with two adjacent axial NH 4 + cations substituted by two H 2 O molecules due to charge compensation. The orthorhombically compressed Rh 0 centre in the form of [RhCl 4 (H 2 O) 2 ] 4 ‾ group arises from interstitial Rh 0 (reduced from Rh 3+ by capturing three electrons during gamma irradiation) with two adjacent axial NH 4 + replaced by two H 2 O molecules as charge compensators and the planar Rh 0 -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. [ABSTRACT FROM AUTHOR]

The EPR g factors for the oxygenated and nonoxygenated BaCuO 2+ x are theoretically studied from the perturbation formulas of the g factors for an orthorhombically elongated octahedral 3d 9 complex based on the cluster approach. The relative axial elongation ratios (≈1% and 0.6%) along c axis and the relative planar bond length variations (≈6.9% and 8.9%) are found for the oxygenated and nonoxygenated systems, respectively. The above local orthorhombic distortions of the Jahn–Teller nature around Cu 2+ can suitably account for the axial and perpendicular anisotropies of the observed g factors. The present studies can be useful to understand the influences of this parasitic phase BaCuO 2+ x on the EPR behaviours and superconductivity of the R 123 high T c superconductors. [ABSTRACT FROM AUTHOR]