Analysis of the paramagnetic susceptibility of Fe(HCOO)2·2H2O

The paramagnetic susceptibility of powdered Fe(HCOO)₂·2H₂O is analysed by the combined method of high temperature expansion and molecular field approximation. The experimental data are well explained by the consistent model obtained in the previous specific heat analysis.     

Theoretical investigation of ESR spectra and local structure for VO in Ba2Zn(HCOO)6(H2O)

The electron spin resonance spectra (characterized by g factors g_, g_⊥ and hyperfine structure constants A_ and A_⊥) of Ba₂Zn(HCOO)₆(H₂O) (BZFA): VO²⁺ crystal are calculated from high order perturbation formulas. The calculated results are in good agreement with the observed values. The local structure parameters of [VO(H₂O)₅]²⁺ clusters are also obtained from the calculation. The magnitudes of the metal-ligand distances parallel and perpendicular to the C₄-axis are, respectively, R_≈0.163 nm and R_⊥≈0.210 nm. It is shown that the local structure around the V⁴⁺ ion possesses a compressed tetragonal distortion along C₄-axis.     

Electron paramagnetic resonance of Gd3 in YCl3·6H2O

The electron paramagnetic resonance spectrum of Gd³⁺ in YCl₃·6H₂0 with $\text{1}\text{100}$ dilution of Gd/Y ions, has been studied with an X-band spectrometer at 295, 77 and 1.77°K and with a K-band spectrometer at 295 and 77°K. The individual values of all the parameters are evaluated from the data at the three temperatures. In particular, the following values for the g-tensor and the zero-field splitting parameters b₂⁰ and b₂² are obtained from X-band data: at 295°K, g_zz = 1.994±0.005, g_xx = 1.992±0.005, g_yy = 1.997±0.005, b₂⁰ = 1.898 ±0.015 GHz, b₂² = ?2.247 ± 0.015GHz; at 77°K, g_zz = 1.999±0.008, g_xx = 2.000±0.008, b₂⁰= 1.978 ±0.022 GHz, b₂² = ?1.574±0.022GHz; at 1.77°K, g_zz = 2.002±0.010, g_xx = 1.990 ±0.010, b₂⁰ = 2.011 ± 0.025 GHz, b₂² = ?1.650 ±0.025 GHz. (The K-band values are found to be consistent with the X-band values). From the angular dependence of the data in the ZX plane (i) the angle X₀ which the Z axis makes with the a vector of the unit cell, is determined to be 58.00 ±0.25° and (ii) the existence of pseudo-symmetry axes at ±5° from the Z axis in the ZX plane as found by heat capacity and specific heat data has been confirmed. An estimate is also made of the extent of admixture of the excited ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ state with the ground state ${}^8\text{S}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$.     

Electron paramagnetic resonance of Re4+ : (NH4)2 PtCl6

The electron paramagnetic resonance of Re⁴⁺ in single crystals of (NH₄)₂PtCl₆ at frequencies near 10 GHz is reported. The results are interpreted in terms of two types of centre, one with octahedral symmetry and the other with an axial distortion along a trigonal axis. It is suggested that this distortion could be due to variations in the orientations of the ammonium ions.     

Zero-point spin reduction in a two-dimensional Heisenberg antiferromagnet Cu(HCOO)2 · 4H2O

The copper NMR in a two-dimensional Heisenberg antiferromagnet Cu(HCOO)₂ ·4H₂O (T_N = 17 K) was observed using a standard spin- echo method at liquid He temperatures. The field-dependence of the ⁶³Cu NMR frequency was measured for H₀ (? 56 kOe) | b-axis. The result was interpreted by taking into account a zero-point spin reduction of about 35% in addition to the rotation of the antiferromagnetic spin axis. The amount of the observed spin reduction is in good agreement with the prediction of spin-wave theory.     

Studies of thermal decomposition of (NH4)2Fe(SO4)2·6H2O

Thermal decomposition products of the Mohr salt (NH₄)₂Fe(SO₄)₂·6H₂O have been studied and identified using the Mössbauer effect, X-ray diffraction, infrared spectroscopy, and the gravimetric and thermal differential methods. It has been found that the Mohr salt heated for 96 hr. in air at 520K changes to a single substance identified as NH₄Fe(SO₄)₂ with a single Mössbauer line (width 0.30 mm/sec; isomeric shift 0.30 mm/sec). When the Mohr salt is heated for 1 hr. in air at 770 K it changes to Fe₂(SO₄)₃ with a single Mössbauer line (width 0.33 mm/sec; isomeric shift 0.31 mm/sec) strikingly similar to line of NH₄Fe(SO₄)₂.     

Absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O

Optical absorption spectra of Ni²⁺ in (NH₄)₂Mg(SO₄)₂·6H₂O and Co²⁺ in Na₂Zn(SO₄)₂·4H₂O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band in Ni²⁺ and ${}^4\text{T}{}_{\mathrm{2g}}\text{(F)}$ band in Co²⁺ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm^-1 in the case of Ni²⁺ at low temperature has been interpreted to be the superposition of vibrational mode of SO^2-₄ radical on ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ.     

Electron paramagnetic resonance of Mn IN (NH4)2Co2(SO4)3 and (NH4)2Ni2(SO4)3 single crystals

EPR studies are reported on single crystals of ammonium cobalt sulphate and ammonium nickel sulphate containing Mn²⁺ ions. In each case only one magnetic complex of Mn²⁺ ion is found. The resonance lines in the case of Mn²⁺ doped ammonium nickle sulphate are characterised by a strong angular dependence of line intensities. The resonance lines in both the cases are fitted to a spin-Hamiltonian corresponding to orthorhombic symmetry.     

Kinetics of the rehydration of Fe(NH4)2(SO4)2. 4H2O

The kinetics of the reaction of ferrous ammonium tetrahydrate with water has been studied at room temperature using the Mössbauer effect. Data were fitted to two equations and from the results it is concluded that the reaction is diffusion controlled.     

ESR study of phase transitions in single crystals of Cd(BF4)2, 6H2O

From an ESR study of Mn²⁺ doped single crystals of Cd(BF₄)₂, 6H₂O, two first order structural phase transitions at 324 ± 2 K (monoclinic to trigonal) and at 177 ± 2 K (trigonal to monoclinic or triclinic) are detected and studied for the first time.     

EPR study of a new low-temperature phase transition in Zn(ClO4)2·6H2O

From a temperature variation EPR study of Mn²⁺ doped single crystals of Zn(ClO₄)₂·6H₂O phase transition has been detected at T₂~290 K. The phase relationships in this crystal are as follows. Phase I transforms atT₂~346K to Phase II, which in turn transforms to Phase III at T₂ ~ 290K. The latter exists down to at least 220 K. The space group symmetry of crystal may be the same, i.e. Pmn2₁ both above and below T₂. The water-perchlorate sublattice symmetry below T₂ is found to be lower than the P6₃mc symmetry determined previously by X-ray measurements. The onset of a monoclinic or lower symmetry distortion of the water octahedron around a metal ion which starts just below T₂, is reflected through the observed temperature dependence of the rhombic distortion parameter E. It is felt that during this phase transition a change in the degree of configurational disorder associated with the perchlorate tetrahedra takes place, which in turn modifies the hydrogen bonded interaction in the crystal and consequently results in the onset of temperature dependent displacements of the mean positions of the oxygens of the water molecules.     

EPR detection and study of new phase transitions in Mg(ClO4)2·6H2O

A temperature dependent EPR study of Mn²⁺ impurity-doped crystals of Mg(ClO₄)₂·6H₂O has led to the detection of two critical temperatures T₁ ~ 335K and T₂ ~ 324K where the EPR characteristics undergo distinct changes. The monoclinic distortion of the water octahedron around the metal ion shows little temperature dependence between T₁ and T₂ and T₂ and T₃ ~ 272K, while it is found to be comparatively strongly temperature dependent above T₁ and below T₃, decreasing as T approaches T₁ from the high temperature side and as T approaches T₃ from the low temperature side. At room temperature the water-perchlorate symmetry seems to deviate slightly from the perfect P6₃mc symmetry proposed from previous X-ray measurements by West. Although the space symmetry group of the unit cell appears to remain unchanged at T₁ and T₂, the temperatures T₁ and T₂ are suspected to be related to structural phase transitions in this crystal.     

Electron impact ionization of Ar n , (H2O) n , Ar n (H2O) m clusters

Signals from ions forming in a supersonic molecular beam consisting of an argon-water vapor mixture are measured as functions of the exciting electron energy in the range to 120 eV. The thresholds of electron impact excitation of (H₂O) _{n − 1}H⁺ and Ar _n (H₂O _m ⁺ clusters are determined for the first time. It is found that the proton-hydroxyl group binding energy decreases considerably both in the case of water molecule clustering and when mixed Ar _n (H₂O) _m clusters arise.     

Specific heat of Ni(ClO4)26H2O between 2 and 17 K

A specific heat investigation of nickel perchlorate hexahydrate was performed between 2 and 17 K. Lattice vibration and magnetic contributions were separated. The lattice term obeys a Debye αT³ law, with $\text{α = 4.04 × 10}{}^{\mathrm{?3}}\text{J}\text{K}{}^4$ mol. The magnetic contribution comes from the splitting of the ground state triplet of the Ni²⁺ ions, by axial and rhombic crystal field distortions, which can be explained by a Schottky specific heat with D = 1.72 KandE = 0.06 K.     

On the presence of the S4z-term in Fe(HCOO)2 · 2H2O

The magnetic specific heat of ferrous formate dihydrate is analysed on the basis of a model, $\text{S}{}_{\mathrm{A}}\text{=}\text{1}\text{2}$ and S_B = 2. The experimental result turns out to be well explained by the introduction of a large S⁴_z-term for B site ions.     

Temperature evolution of the infrared spectrum of Ni(ClO4)2·6H2O

Temperature evolution of the infrared spectrum of the title compound confirms the phase transition temperatures 223, 311 and 355 K reported earlier and suggests a new phase transition at 180 K. From the spectral evidence, the transitions below the room temperature (～300 K) are attributed to tumbling motion of the metal aquo-complex, while those above the room temperature are attributed to reorientational motion of the water molecule. The space group in low temperature phases is suggested to be C²_s.     

Molecular dynamics and phase transitions in paramagnetic [Mn(H2O)6][SiF6] investigated by H NMR

The temperature dependences of ²H NMR spectra and spin-lattice relaxation time T₁ have been measured for paramagnetic [Mn(H₂O)₆][SiF₆]. The obtained ²H NMR spectra were simulated by considering the quadrupole interaction and paramagnetic shift. The variation of the spectra measured in phase III was explained by the 180° flip of water molecules. The activation energy E_a and the jumping rate at infinite temperature k₀ for the 180° flip of H₂O were obtained as 35 kJ mol⁻¹ and 4×10¹⁴ s⁻¹, respectively. The spectral change in phases I and II was ascribed to the reorientation of [Mn(H₂O)₆]²⁺ around the C₃ axis where the E_a and k₀ values were estimated as 45 kJ mol⁻¹ and 1×10¹³ s⁻¹, respectively. From the almost temperature independent and short T₁ value, the correlation time for electron-spin flip-flops, τ_e, and the exchange coupling constant J were obtained as 3.0×10⁻¹⁰ s and 2.9×10⁻³ cm⁻¹, respectively. The II-III phase transition can be caused by the onset of the jumping motion of [Mn(H₂O)₆]²⁺ around the C₃ axis.     

Structural characterisation of [Cu2(bptd) (H2O) Cl4] and [Ni2(bptd)2(H2O)4] Cl4·3H2O; evidence of null intramolecular exchanges by EPR and magnetic measurements

Using the 2,5-bis(2-pyridyl)-1,3,4-thiadiazole (bptd), we recently prepared [Cu₂(bptd) (H₂O) Cl₄] and [Ni₂(bptd)₂ (H₂O)₄] Cl₄, 3H₂O in which the magnetic centres are connected through one diazine+one chloro and two diazine ligand bridges, respectively. These two compounds are the first examples that show null intramolecular magnetic interactions despite M-M distances close to 3.7 Å within perfectly planar edifices:Down to , [Cu₂(bptd)Cl₄(H₂O)] is paramagnetic while, below T_t, half of the Cu²⁺ions interact, leading to residual paramagnetism of one Cu²⁺/f.u. Magnetic susceptibility measurements, EPR and pulsed EPR study indicate the original intermolecular nature of AF exchanges.[Ni₂(bptd)₂(H₂O)₄]Cl₄·3H₂O susceptibility obeys a Curie-law involving pure paramagnetism. Moreover, its EPR spectrum can be interpreted on the basis of virtual S=1 monomers. Below 70 K, Zero Field Splitting (D∼275 G) due to dipolar interactions without magnetic exchanges could be responsible for the LT spectra splitting. For both compounds, the thia role is suggested as partially responsible for the null-in-plane magnetic exchanges.     

Kβ′ satellite of the Kβ1 X-ray emission line of Fe(NH4)2β(SO4)2β6H2O

The origin of the Kβ′ satellite of the Kβ₁ X-ray emission line of Fe(NH₄)₂β(SO₄)₂β6H₂O, observed by Tsutsumi has been explained for the first time in a more satisfactory way than by any of the previous workers. Plasmon oscillations in solid theory can give a better fit with the experimentally observed values for energy separation and relative intensity than the Molecular Orbital theory of Tsutsumi.     

Complex formation and phosphate-H2O interactions in a concentrated aqueous Mg(H2PO4)2 solution.

X-ray diffraction data from a solution of Mg(H₂PO₄)₂ were examined. The experimental distribution curve shows peaks at about 2.10, 2.7–2.9, 3.6, 3.9 and 4.25 Å. The 3.6 Å peak reveals the formation of inner sphere magnesium-phosphate complexes Mg(H₂O)_6-z(H₂PO₄)^+2-z_z, in which oxygens from phosphate groups substitute z water molecules of the hydrated Mg(H₂O)²⁺₆ ions. Least squares refinements of the i(s) curve are consistent with a structural unit in which the phosphate tetrahedron shares a corner with one magnesium octahedron with MgOP angle of 147 deg. Each phosphate ion interacts with about eight water molecules.