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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]

The magnetic properties of LnIII and AnIII complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single‐crystal X‐ray diffraction (XRD) and extended X‐ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal–ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher‐order terms of the dipolar and contact contributions are required, especially for the lightest LnIII and almost all the studied AnIII. Bleaney's parameters a and CaD relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of a and CaD. However, the CaD values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for LnIII. Other parameters, such as the crystal field parameter and the hyperfine constants Fi obtained from the experimental data of the [An(ethyl‐dpa)3]3− complexes (ethyl‐dpa=4‐ethyl‐2,6‐dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory. Valid for Ln, but for An? Is Bleaney's equation for paramagnetic NMR shifts of LnIII valid for AnIII complexes? (see figure) Several methods have been applied to separate the paramagnetic shifts observed in the NMR spectra of LnIII and AnIII complexes formed with dipicolinate ligands. Discrepancies with Bleaney's equation have been found for the AnIII complexes, and some parameters are at odds with the assumptions underlying Bleaney's theory. [ABSTRACT FROM AUTHOR]

Abstract: The flexibility of first‐principles (ab initio) calculations with the SO‐CASSCF (complete active space self‐consistent field theory with a treatment of the spin‐orbit (SO) coupling by state interaction) method is used to quantify the electrostatic and covalent contributions to crystal field parameters. Two types of systems are chosen for illustration: 1) The ionic and experimentally well‐characterized PrCl3 crystal; this study permits a revisitation of the partition of contributions proposed in the early days of crystal field theory; and 2) a series of sandwich molecules [Ln(ηn‐CnHn)2]q, with Ln=Dy, Ho, Er, and Tm and n=5, 6, and 8, in which the interaction between LnIII and the aromatic ligands is more difficult to describe within an electrostatic approach. It is shown that a model with three layers of charges reproduces the electrostatic field generated by the ligands and that the covalency plays a qualitative role. The one‐electron character of crystal field theory is discussed and shown to be valuable, although it is not completely quantitative. This permits a reduction of the many‐electron problem to a discussion of the energy of the seven 4f orbitals. [ABSTRACT FROM AUTHOR]