Search

Actinide +VI complexes (AnVI =UVI , NpVI and PuVI) with dipicolinic acid derivatives were synthesized and characterized by powder XRD, SQUID magnetometry and NMR spectroscopy. In addition, NpVI and PuVI complexes were described by first principles CAS based and two‐component spin‐restricted DFT methods. The analysis of the 1H paramagnetic NMR chemical shifts for all protons of the ligands according to the X‐rays structures shows that the Fermi contact contribution is negligible in agreement with spin density determined by unrestricted DFT. The magnetic susceptibility tensor is determined by combining SQUID, pNMR shifts and Evans' method. The SO‐RASPT2 results fit well the experimental magnetic susceptibility and pNMR chemical shifts. The role of the counterions in the solid phase is pointed out; their presence impacts the magnetic properties of the NpVI complex. The temperature dependence of the pNMR chemical shifts has a strong 1/T contribution, contrarily to Bleaney's theory for lanthanide complexes. The fitting of the temperature dependence of the pNMR chemical shifts and SQUID magnetic susceptibility by a two‐Kramers‐doublet model for the NpVI complex and a non‐Kramers‐doublet model for the PuVI complex allows for the experimental evaluation of energy gaps and magnetic moments of the paramagnetic center. [ABSTRACT FROM AUTHOR]

Two series of lanthanide complexes have been chosen to analyze trends in the magnetic properties and crystal field parameters (CFPs) along the two series: The highly symmetric LnZn16(picHA)16 series (Ln=Tb, Dy, Ho, Er, Yb; picHA=picolinohydroxamic acid) and the [Ln(dpa)3](C3H5N2)3⋅3H2O series (Ln=Ce–Yb; dpa=2,6‐dipicolinic acid) with approximate three‐fold symmetry. The first series presents a compressed coordination sphere of eight oxygen atoms whereas in the second series, the coordination sphere consists of an elongated coordination sphere formed of six oxygen atoms. The CFPs have been deduced from ab initio calculations using two methods: The AILFT (ab initio ligand field theory) method, in which the parameters are determined at the orbital level, and the ITO (irreducible tensor operator) decomposition, in which the problems are treated at the many‐electron level. It has been found that the CFPs are transferable from one derivative to another, within a given series, as a first approximation. The sign of the second‐order parameter B02 differs in the two series, reflecting the different environments. It has been found that the use of the strength parameter S allows for an easy comparison between complexes. Furthermore, in both series, the parameters have been found to decrease in magnitude along the series, and this decrease is attributed to covalent effects. [ABSTRACT FROM AUTHOR]

By using complementary experimental techniques and first-principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C2 v, has been investigated. Four complexes have the general formula [Ni(bpy)X2] n+ (bpy=2,2′-bipyridine; X2=bpy ( 1), (NCS−)2 ( 2), C2O42− ( 3), NO3− ( 4)). In the fifth complex, [Ni(HIM2-py)2(NO3)]+ ( 5; HIM2-py=2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazolyl-1-hydroxy), which was reported previously, the two bpy bidentate ligands were replaced by HIM2-py. Analysis of the high-field, high-frequency electronic paramagnetic resonance (HF-HFEPR) spectra and magnetization data leads to the determination of the spin Hamiltonian parameters. The D parameter, corresponding to the axial magnetic anisotropy, was negative (Ising type) for the five compounds and ranged from −1 to −10 cm−1. First-principles SO-CASPT2 calculations have been performed to estimate these parameters and rationalize the experimental values. From calculations, the easy axis of magnetization is in two different directions for complexes 2 and 3, on one hand, and 4 and 5, on the other hand. A new method is proposed to calculate the g tensor for systems with S=1. The spin Hamiltonian parameters ( D (axial), E (rhombic), and gi) are rationalized in terms of ordering of the 3 d orbitals. According to this orbital model, it can be shown that 1) the large magnetic anisotropy of 4 and 5 arises from splitting of the eg-like orbitals and is due to the difference in the σ-donor strength of NO3− and bpy or HIM2-py, whereas the difference in anisotropy between the two compounds is due to splitting of the t2g-like orbitals; and 2) the anisotropy of complexes 1- 3 arises from the small splitting of the t2g-like orbitals. The direction of the anisotropy axis can be rationalized by the proposed orbital model. [ABSTRACT FROM AUTHOR]

A novel ester-functionalized bi-compartmental Schiff-base ligand and its dinuclear Zn-Ln complexes [Ln = Dy ( 1), Tb ( 2), Gd ( 3)] are reported herein. Athough electron-withdrawing substituents at the para position of the phenol moieties do not change the coordination environment of the Ln centers in comparison with the nonfunctionalized ligand, they have a clear steric effect on the crystal packing and alter the coordination strength of the central ligand core. This is illustrated by the atypical reactivity of the bi-compartmental Schiff-base ligand towards Ln coordination and corroborated by its longer bond lengths to the rare-earth ions in comparison with the nonfunctionalized ligand. Crystal structures, magnetic behavior, and ab initio calculations for the two series of complexes are reported. A slow relaxation of the magnetization with an energy barrier of 96 K was found for Dy derivative 1 in zero field. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetic properties of neptunyl(VI), NpO22+, and two neptunyl complexes, [NpO2(NO3)3]− and [NpO2Cl4]2−, were studied with a combination of theoretical methods: ab initio relativistic wavefunction methods and density functional theory (DFT), as well as crystal-field (CF) models with parameters extracted from the ab initio calculations. Natural orbitals for electron density and spin magnetization from wavefunctions including spin-orbit coupling were employed to analyze the connection between the electronic structure and magnetic properties, and to link the results from CF models to the ab initio data. Free complex ions and systems embedded in a crystal environment were studied. Of prime interest were the electron paramagnetic resonance g-factors and their relation to the complex geometry, ligand coordination, and nature of the nonbonding 5f orbitals. The g-factors were calculated for the ground and excited states. For [NpO2Cl4]2−, a strong influence of the environment of the complex on its magnetic behavior was demonstrated. Kohn-Sham DFT with standard functionals can produce reasonable g-factors as long as the calculation converges to a solution resembling the electronic state of interest. However, this is not always straightforward. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the magnetic coupling in the [CuMCu(pda)4Cl2] complexes with M=Pd, Pt is analyzed. First principles calculations based on the wave function theory are performed (DDCI+SO-RASSI): it is shown that the interaction without spin-orbit coupling is antiferromagnetic while the contribution due to the spin-orbit is ferromagnetic. The agreement between calculations and experiment is very good for the CuPdCu complex but is lesser for the CuPtCu complex. A Hubbard model is used in order to rationalize these results: this shows that the two d frontier orbitals of the central atom play a key role in these two interactions. Although the model parameters extracted from CASCI calculations do not permit to recover the order of magnitude of the interactions, it allows understanding the main interactions that give physical insight. [Copyright &y& Elsevier]