A study by E.S.R. of Mn2+ in potassium chromate

Divalent manganese ions are found in potassium chromate single crystals after heating at 600°C in the presence of iodine. These ions occupy three differently oriented sites with the same spin Hamiltonian parameters: g_z = 2·000, g_x = 2·008, g_y = 2·015; A_z = ?88·4 G, A_x = A_y = ?91 G; D = 190 and E = ?30 G.The authors suggest that Mn²⁺ occupies a substitutional (K⁺) position rather than an interstitial one. The influence of iodine is discussed.     

EMR and optical study of Mn2+ doped potassium trihydrogen selenite

The EMR study of Mn2+ doped potassium trihydrogen selenite is performed and the site of Mn2+ in the lattice is discussed. The zero field parameters providing good fit to the observed EMR spectra are estimated. The spin-Hamiltonian parameters g, A, B, D, and a are (2.0003 +/- 0.0002), (31 +/- 2) x 10(-4), (20 +/- 2) x 10(-4), (87 +/- 2) x 10(-4), and (-9 +/- 1) x 10(-4) cm(-1), respectively. The percentage of covalency of the metal-ligand bond is also determined. The optical absorption study suggests the lattice distortion in the crystal. The electron repulsion and crystal field parameters having good fit to the observed optical spectra are evaluated. The band positions are fitted with the Racah parameters (B and C), the cubic crystal field splitting parameters (Dq), and the Trees correction (alpha). The values of B, C, Dq, and alpha are 871, 2967, 670, and 76 cm(-1), respectively.     

Neutron diffraction study of ammonium tartrate (NH4)2C4H4O6

A neutron diffraction study of ammonium tartrate has been carried out. Using the diffractometer in symmetrical setting, intensities of 750 reflections have been measured. The positions of all the hydrogen atoms have been determined. A good agreement is noticed between the present neutron and the earlier x-ray heavy atom parameters. The tartrate ion consists of two nearly identical planar halves, with an interplanar angle of 62°. Tre structure is stabilized by a net-work of hydrogen bonds. Details of hydrogen bonding and the ammonium ions environment are discussed.     

Investigation of the Cu2+ and VO2+states in synthetic ion-exchange resins of varying sorts by E.P.R. method

The interaction of Cu²⁺ and VO²⁺ ions with high-molecular ligands of the sulpho, carboxyl, phosphor, amino and aminophosphorus resins were studied by E.P.R. The influence of an active resin group on the formation of the intra complex compounds with metal ions and, hence, on the sorption selectivity has been investigated; the influence of moisture content and temperature on the state of the paramagnetic ions in the resin has been studied. Inhomogeneous distribution of metal ions in the resin matrix which leads to the formation of both individual and exchange-coupled systems has been established. The influence of changes in polymer conformation on the stability of ion-exchange complexes is shown.

The data obtained from the E.P.R. spectra of Cu²⁺ and VO²⁺ complexes in a high polymeric matrix were compared with the corresponding monomeric systems having identical structures for the complex sites.     

Spectrophotometric and E.P.R. study of TCNE charge-transfer complexes

Liquid state charge-transfer complexes formed from the strong acceptor tetracyanoethylene (TCNE) and four donors of like donor properties are studied by spectrophotometric and E.P.R. techniques. If the enthalpy of complex formation ΔH is sufficiently large, the triplet state of the complex ³C will be appreciably populated thermally during complex formation. The E.P.R. signal of the TCNE anion promptly arises because of a dissociation of ³C, reaches a maximum, and then follows second-order decay kinetics. The higher the dielectric constant of the donor, the slower the decay rate. The initial intensity of the E.P.R. signal is proportional to the original TCNE concentration in the donor-solvent. Reversible photoinduced TCNE anions are formed by irradiating the complexes in the charge-transfer band. The relationship between the prompt and photoinduced E.P.R. signals is shown. Singlet-triplet separation energies are estimated.     

Optically detected E.P.R. of Mn2+ in faulted cubic ZnS

We have performed optically detected E.P.R. of Mn²⁺ in faulted cubic ZnS. This experiment permits the identification of the two axial E.P.R. spectra observed in these crystals. This identification allows an estimate of the D parameter of Mn²⁺ in wurtzite.     

Spectroscopic and E. P. R Studies of the Crystal and Molecular Structure of Cu(2-Benzoylpyridine)2(NO3)2.H2O

Abstract

Solid Cu(2-Benzoylpyridine)₂(NO₃)₂ has been studied by UV-Vis, IR, and EPR (X-band, Q-band) techniques. Monoclinic crystal symmetry was determined with two molecules per unit cell. Copper (II) is coordinated by two benzoylpyridine ligands and a single NO₃ group in the chromophore CuN₂O₃ of distorted trigonal bypiramidal stereochemistry. Exchange coupling values were determined from EPR spectra as |J| = 0.0026(2) cm^?1 between magnetically nonequivalent copper (II) sites, and |J| < O.3 cm^?1 between equivalent sites.

Results are discussed by a comparison with Cu(II)-benzoyl-pyridine complexes coordinated with azide N₃ ^? anions.     

BaMgAl10O17:R2+(R=Eu,Mn)的真空紫外光谱特性

采用高温固相反应法合成了BaMgAl10O17:R(R＝Eu,Mn)荧光体，测量了荧光体的真空紫外激发光谱和相应的发射光谱，观察到基质吸收带位于165nm附近，Mn^2 离子的吸收位于170－240nm范围，Eu^2 离子的4f→5d吸收位于210－400nm范围。真空紫外光谱特性的研究表明基质与激活离子之间存在较好的能力传递。     

Electron paramagnetic resonance study of Mn2+ in ferroelectric lithium ammonium tartarate monohydrate

EPR studies of Mn²⁺ in ferroelectric lithium ammonium tartarate monohydrate (LAT) show that there are four Mn²⁺ complexes, which group themselves into two chemically different sets each containing two physically related sites at room temperature. It is inferred that Mn²⁺ enters into NH₄⁺ site. The hyperfine separation of the central group ($\text{1}\text{2}$ → ? $\text{1}\text{2}$) is found to be constant, which is not observed usually. It is suggested that the space group of LAT below T_c is P2₁.     

E. P. R Study Of Copper (II) - Doped Triglycine Selenate (TGSe)

The angular dependence of EPR of the Cu²⁺ ion in the ferroelectric TGSe crystal has been investigated. The coordination of the Cu²⁺ ion and the number of complexes were found to be the same as in the isomorphous copperdoped TGS crystal. The spin density on the central metal ion indicates a more covalent nature of the Cu-ligand bond in TGSe. The spectroscopic splitting factor exhibits an anomaly near the ferroelectric transition point.     

Ac conductivity study of lithium and potassium diphosphate LiK3P2O7 using impedance spectroscopy

In this work, a LiK₃P₂O₇ ceramic material was prepared by the solid-state reaction method and identified by X-ray diffractometry. The dielectric properties, impedance characteristics, and modulus were studied over a range of frequency (200 Hz to 5 MHz) and temperature (615–708 K). The frequency and temperature dependence of dielectric permittivity, dielectric loss, and electric modulus is studied. The frequency analysis of modulus properties showed a distribution of relaxation times. Conductivity plots against frequency at a higher frequency suggested the response obeying the universal power law. The temperature behavior of the frequency exponents shows that the correlated barrier hopping CBH model is well adapted to this material. The activation energy associated with the impedance relaxation and the electric modulus spectra is close to the activation energy for dc conductivity indicating the similar nature of relaxation and conductivity. Thermodynamic parameters such as free energy of activation, enthalpy, and entropy have been calculated.     

The reactions of Cl+ (3P) and Cl+ (1D) with hydrogen sulphide. A G2 molecular orbital study

G2 ab initio molecular orbital calculations have been performed to study the potential energy surfaces (PESs) associated with the reactions of Cl⁺ in its ³P ground state and in its ¹D first excited state with hydrogen sulphide. [H₂, Cl, S]⁺ singlet and triplet state cations present very different bonding characteristics. The latter are systematically ion-dipole or hydrogen-bonded weakly bound species, while the former are covalent molecular ions. As a consequence, although the Cl⁺(³P) is 34.5 kcal mol^?1 more stable than Cl⁺(¹D), the global minimum of the singlet PES lies 37.3 kcal mol^?1 below the global minimum of the triplet PES. Both singlet and triplet potential energy surfaces show significant differences with respect to those associated with Cl⁺ + H₂O reactions as well as with SH₂ reactions with F⁺. In both cases, the major product should be SH⁺ ₂; SH⁺ and HCl⁺ being the minor products, in agreement with the experimental evidence. The estimated heat of formation for the most stable H₂SCl⁺ singlet state species is 198 ± 1 kcal mol^?1.     

P.E.HSQC: a simple experiment for simultaneous and sign-sensitive measurement of (1JCH+DCH) and (2JHH+DHH) couplings

The angular information content of residual dipolar couplings between nuclei of fixed distance makes the accurate and sign-sensitive measurement of (¹J_CH + D_CH) and (²J_HH + D_HH) couplings highly desirable. Experiments published so far are typically highly specialized for the effective measurement of a subset of couplings. The P.E.HSQC presented here, is an E.COSY based experiment which allows the simultaneous measurement of all heteronuclear and homonuclear couplings within CH, CH₂, and CH₃ groups in a single spectrum with the necessary precision and sign information. The simplicity of the approach and the absence of artefacts like phase distortions due to antiphase evolution make it ideally suited for coupling determination of organic molecules at natural abundance.     

An E.P.R. study of the anion radical of diplieadane

A study of radiation damping e ects in inhomogeneously broadened systems leads to an analytical theorem that relates the time integral area of the nuclear magnetic resonance signal to the tipping angle of the magnetization caused by the circuit generated reaction field. The theorem is applied to predict relative signal areas in examples of pulse sequences. In a few selected cases these predictions are also checked by experiment.     

E.P.R. study of dimeric forms of Cu(II)-monoazaporphyrin and of the radical cations of Cu(II) octaethylporphyrin and -octaethylchlorin

It has been shown in the present work that one can obtain dimers from the 1-electron oxidation product of Cu-porphyrin and Cu-chlorin. The E.P.R. study of these dimers has yielded valuable structural information in terms of the symmetry of the dimer as well as the distance between the two porphyrin planes. A qualitative estimate of the different exchange interactions present in the systems has been attempted.     

Proton N.M.R. study of the dynamics of the ammonium ion in ferroelectric langbeinite, (NH4)2Cd2(SO4)3

The proton N.M.R. lineshape of polycrystalline Langbeinite, (NH₄)₂Cd₂(SO₄)₃, has been studied in the temperature range 300 K to 1·8 K. The resonance line is motionally narrowed over the entire temperature range, and the low temperature proton line shows clear evidence for tunnelling motion of the ammonium ion between spin-symmetry states. From a computer simulation of the lineshape, we obtain an estimate for the tunnelling splitting parameter, J, of the torsional ground state of the ammonium ion, as 375 ± 125 gauss. For an undistorted tetrahedral crystal field this corresponds to a tunnelling splitting Δ = 4J = 6·3 ± 2·1 MHz.

Pulsed proton N.M.R. studies have also been carried out on the above compound at 30·8 MHz and 48·2 MHz and the spin-lattice relaxation time (T ₁) has been measured by the π - t - π/2 pulse sequence as a function of temperature down to 77 K. At 30·8 MHz, a T ₁ minimum of 13 ms occurs at 105·8 K, and is ascribed to random reorientations of the NH₄ ⁺ ion. An activational energy barrier of 0·74 ± 0·1 kcal/mole and an associated pre-exponential factor of 8·0 × 10^-13 s are calculated for the above motional process, and the value of the activation energy is correlated with the tunnelling splitting of the torsional ground state.

An anomaly in T ₁ has been observed at the ferroelectric Curie point (95 K), indicating the order-disorder nature of the transition. This is the first experimental evidence relating to the nature of the transition in Langbeinite.     

On the magnetic order in R(57Fe)Mn2

In the present study,⁵⁷Fe is used as a local probe in order to monitor both the development of the Mn moment and its temperature dependence. The different crystal structures present (C15 and C14) were found to only insignificantly influence the hyperfine pattern. Both the simultaneous presence of magnetic and non-magnetic Mn atoms and the specific easy axis of magnetization in a given compound is found to lead to the occurrence of additional subspectra. Within the Mössbauer effect time window, no substantial magnetic correlations could be detected aboveT _C.     

Electronic absorption spectrum of Ni2+ in lithium potassium sulphate single crystal

Single crystals of nickel-doped lithium potassium sulphate were grown by slow evaporation method at room temperature. From the nature and position of the bands observed, a successful interpretation of all the bands could be made assumingO _h symmetry for the Ni²⁺ ion in the crystal. The bands have been assigned transitions from the ground³A_2g(F) state to the excited³T_2g(F),¹E_g(D),³T_1g(F),¹T_2g(D) and³T_1g(P) states. The crystal field parameters derived areDq=910cm^–1,B=890cm^–1 andC=3560cm^–1.The authors wish to express their thanks to Prof. K. Sreerama Murthy for his constant encouragement throughout this investigation. The authors are also thankful to Prof. Mihir Chowdhury, Indian Association for the cultivation of Science, Calcutta for giving permission to take the spectra.