The Intricate Determination of Magnetic Anisotropy in Quasi-octahedral Vanadium(III): An HF-EPR and Magnetic Study

We report here the synthesis and a preliminary characterization of the tetranuclear complex of formula [Ga3V(LEt)2(dpm)6], Ga3VEt, in which H3LEt = 2-Ethyl-2-(hydroxymethyl)-propane-1,3-diol and Hdpm = dipivaloylmethane, containing a single paramagnetic vanadium(III) center, from a structural, magnetic, and spectroscopic point of view. Structural characterization by X-ray diffraction evidenced that this derivative is isostructural with the star-shaped Single-Molecule Magnet [Fe3V(LEt)2(dpm)6], Fe3VEt, and can, thus, be considered a model to analyze the magnetic anisotropy of the vanadium(III) ion in that system. The observed results confirm the complexity in obtaining a rationalization of the magnetic behavior of this metal ion, with magnetization data and High Field Electron Paramagnetic Resonance (HF-EPR) spectroscopy providing apparently conflicting results. Indeed, the former were rationalized assuming a rhombic distortion of the ligand field and a dominant easy-axis type anisotropy (equivalent to D ≈ −14.1 cm−1, E ≈ 1.2 cm−1), while a simple axial Spin Hamiltonian approach could explain HF-EPR data (|D| ≈ 6.98 cm−1).

Поведение кобальтовой и редкоземельной подсистем в фрустрированных кобальтитах DyBaCo-=SUB=-4-=/SUB=-O-=SUB=-7+x-=/SUB=-

Structural, elastic, and magnetic properties of cobaltites DyBaCo_4O_7 + _ x produced by various technologies and distinguished by oxygen excess x are experimentally studied. It was found that rhombic distortion of the crystal structure of annealed stoichiometric samples with x = 0 results in frustration removal and elastic property anomalies in the T _ N region, caused by cobalt subsystem ordering. At an insignificant oxygen nonstoichiometry, no structural distortions occur in quenched samples, and anomalies in elastic characteristics in the T _ N region smooth and disappear. The studies of DyBaCo_4O_7 + _ x magnetic properties show that the rare-earth (RE) subsystem remains paramagnetic and its contribution exceeds the contribution of the Co-subsystem with strong antiferromagnetic couplings by an order of magnitude. The magnetic susceptibility of the stoichiometric sample does not exhibit an appreciable anomaly at T _ N , since cobalt subsystem ordering is not accompanied by the formation of a noticeable effective field on RE ions.

EPR, Nexafs Study and Magnetic Properties of Fe-Doped Ferroelectric Ceramics

Magnetic susceptibility and EPR of iron-containing solid solutions with layered perovskite-like structure Bi2BaNb2-2xFe2xO9-δ and Bi5Nb3-3xFe3xO15-δ have been studied. The solid solutions Bi2BaNb2-2xFe2xO9-δ as well as iron oxides FeO, Fe2O3, and Fe3O4 were studied by the NEXAFS spectroscopy. The formation of exchange-bound aggregates of Fe(III) atoms with antiferroand ferromagnetic exchange types has been found in the solid solutions. In the ESR spectra of the solid solution samples, the lines with g ≈ 2.0 and g = 4.27 having a weak shoulder at g ~ 8 were attributed to Fe(III) atoms in the octahedral field with strong rhombic distortion.

The studies of the spin Hamiltonian parameters and local structures for various 3d3 hexacyanometallates of paramagnetic salts with diluents

The spin Hamiltonian parameters (SHPs) ([Formula: see text] factors, hyperfine structure constants and zero-field splittings (ZFSs)) and local structures for various [Formula: see text] hexacyanometallates of paramagnetic salts K3Cr(CN)6 and K4V(CN)[Formula: see text]3H2O with the diluents K3Co(CN)6, K3Mn(CN)6 and K4Fe(CN)[Formula: see text]3H2O are theoretically investigated from the perturbation calculations of these parameters for a rhombically distorted octahedral [Formula: see text] cluster. The paramagnetic systems are found to undergo the local axial distortions [Formula: see text] [Formula: see text]0.19, −0.18 and 0.09 Å[Formula: see text] and the planar bond angle variations [Formula: see text] [Formula: see text] 3.5[Formula: see text], 5.3[Formula: see text] and 1.4[Formula: see text] for K3Cr(CN)6 with K3Co(CN)6, K3Cr(CN)6 with K3Mn(CN)6 and K4V(CN)[Formula: see text]3H2O with K4Fe(CN)[Formula: see text] 3H2O, respectively. The signs for ZFSs [Formula: see text] and [Formula: see text] are analyzed in the light of those for [Formula: see text] and the rhombic distortion angle [Formula: see text] [Formula: see text] related to an ideal octahedron. Microscopically, the magnitudes of [Formula: see text] and [Formula: see text] can be conveniently illustrated by the axial (ADD) and perpendicular distortion degrees (PDD), respectively, for the paramagnetic systems with the corresponding diluents. The local structural properties are analyzed from the relative ionic radius deviation [Formula: see text] of the equivalent diluent cation from the host paramagnetic cation, the axial and perpendicular ZFS variations [Formula: see text] and [Formula: see text] for ZFSs with the diluent related to the host, the relative deviation [Formula: see text]Dq of the cubic crystal-field parameter for the diluent related to the host. The above studies would be helpful to the investigations on synthesis, structures and properties of [Formula: see text] hexacyanometallates in paramagnetic salts.

Charge density study of the first mixed-valent tetraphosphete

The first λ3,λ5-tetraphosphete contains a 4π-electron four-membered ring as the central structural unit of a dispirocyclic system and can thus be classified as an analogue to diphosphetes and cyclodiphosphazenes. According to its crystal structure the central P4unit exhibits not only P–P bonds which are of equal length (P1–P2 2,139(1) Å, P1–P2A 2,142(1) Å), but also rhombic distortion (P1–P2–P1A 79,4(1)0, P2–P1–P2A 100,6(1)0).[1] Therefore its electronic structure cannot be described as 'Phosphacyclobutadiene' but either as a bis(ylide) or as a system with delocalized double bonds. After various quantum chemical calculations and an extensive examination of its reaction and coordination behavior failed to answer this question, we addressed the problem via a detailed analysis of its charge density distribution. The experimental charge density based on high resolution X-ray diffraction data collected at low temperature is determined by multipole least squares refinement using the program packageXD2006.[2] In a first step, the static deformation density exhibits charge density which is located mainly outside of the P4ring plane at the λ3-phosphorus atoms but simultaneously redistributed into the P–P bond area. In addition to that, a study of its topological properties and an inspection of the Laplacian of the electron density according to Bader's `Quantum Theory of Atoms in Molecules' (QTAIM)[3] further highlight the bonding features. They reveal polar Si–N, Si–C and P–N bonds with a decreasing amount of electrostatic contribution as well as four valence shell charge concentrations (thus sp3hybridization) at each of the phosphorus atoms. Finally supported by theoretical calculations, the results illustrate the unique bonding situation in the P4unit combining a high ylidic character with unusual not exclusively sigma-like P–P bonds.

Dichlorido(5,10,15,20-tetraphenylporphyrinato-κ4N)antimony(V) hexachloridoantimonate(V)

The asymmetric unit of the title compound, [Sb(C44H28N4)Cl2][SbCl6], consists of one half of an antimony(V) tetraphenylporphyrin complex cation and one half of an hexachloridoantimonate(V) anion. In the complex cation, the SbVatom lies on an inversion center and is octahedrally coordinated by four N atoms from a macrocyclic tetraphenylporphyrinate ligand and two chloride ions. The complex cation has approximately a planar core with a maximum deviation of 0.018 (5) Å from the porphyrin mean plane. The average Sb—N distance is 2.062 (11) Å, while the Sb—Cl distance is 2.355 (1) Å. The SbVatom of the anion is also located on an inversion center. The [SbCl6]−octahedron exhibits rhombic distortion characterized by the Sb—Cl bond lengths [2.311 (3), 2.374 (2) and 2.393 (4) Å]. In the crystal, the cations and anions are linked C—H... Cl hydrogen bonds, forming a layer parallel to (211).

INVESTIGATIONS OF THE SPIN HAMILTONIAN PARAMETERS AND THE LOCAL STRUCTURE FOR THE RHOMBICCu2+CENTER IN RUTILE

The spin Hamiltonian parameters (the anisotropic g factors and the hyperfine structure constants) and the local structure for the rhombic Cu2+center in rutile ( TiO2) are theoretically investigated using the formulas of these parameters for a 3d9ion in rhombically elongated octahedra. From the studies, the planar impurity-ligand bond angle is found to be about 5.8° larger than that for the host Ti4+site due to the Jahn–Teller effect via bending the planar Cu2+– O2-bonds, which yields much smaller rhombic distortion in the impurity center. The theoretical spin Hamiltonian parameters based on the above local angular distortion show good agreement with the experimental data, and the improvement of the calculation results are also achieved as compared with those of the previous works.

Theoretical investigations on the spin Hamiltonian parameters and the local structure for Rh2+ in rutile

The spin Hamiltonian parameters, the g factors gi (i = x, y, z) and the hyperfine structure constants Ai, and the local structure for Rh2+ in rutile (TiO2) are theoretically investigated from the perturbation formulas of these parameters for a 4d7 ion under rhombically elongated octahedra. In view of the covalency, the ligand orbital and spin-orbit coupling contributions are taken into account from the cluster approach. The planar bond angle in the impurity center is found to be 7.5° larger than that of the host Ti4+ site because of the Jahn–Teller effect via bending of the planar Rh2+-O2– bonds, leading to much smaller rhombic distortion. The theoretical spin Hamiltonian parameters based on the above Jahn–Teller angular distortion show reasonable agreement with the experimental data.