Since the last decade, the focus in the area of single‐molecule magnets (SMMs) has been shifting constructively towards the development of single‐ion magnets (SIMs) based on transition metals and lanthanides. Although ground‐breaking results have been witnessed for DyIII‐based SIMs, significant results have also been obtained for some mononuclear transition metal SIMs. Among others, studies based on CoII ion are very prominent as they often exhibit high magnetic anisotropy or zero‐field splitting parameters and offer a large barrier height for magnetisation reversal. Although CoII possibly holds the record for having the largest number of zero‐field SIMs known for any transition metal ion, controlling the magnetic anisotropy in these systems are is still a challenge. In addition to the modern spectroscopic techniques, theoretical studies, especially ab initio CASSCF/NEVPT2 approaches, have been used to uncover the electronic structure of various CoII SIMs. In this article, with some selected examples, the aim is to showcase how varying the coordination number from two to eight, and the geometry around the CoII centre alters the magnetic anisotropy. This offers some design principles for the experimentalists to target new generation SIMs based on the CoII ion. Additionally, some important FeII/FeIII and NiII complexes exhibiting large magnetic anisotropy and SIM properties are also discussed.

The synergistic combination of high pressure techniques with ab initio methods creates a powerful tool to understand giant magnetic anisotropy.

Single‐molecule magnets based on lanthanides are very attractive due to their potential applications proposed in the area of microelectronic devices. Very recent advances in this area are due to the blend of conventional lanthanide chemistry with organometallic ligands, and several breakthrough achievements are attained with this combination. Ab initio methods based on multi‐reference CASSCF calculations are playing a vital role in the design and development of such molecules. In this minireview, we aim to appraise various contributions in the area of organometallic lanthanide complexes (those containing lanthanide‐carbon bonds) and describe how these robust wavefunction‐based methods have played a constructive role not only in rationalizing the observed magnetic properties but also proven to be a potential predictive tool with some selected examples.

Robust and versatile metal−organic frameworks (MOFs) have emerged as sophisticated scaffolds to meet the critical needs of the nuclear community, but their performance depends on their underexplored structural integrities in highradiation fields. The contributions of selected metal nodes in the radiation stability of MOFs within the isostructural M-UiO-66 series (where M = Zr, Ce, Hf, Th, and Pu; Zr-UiO-66 experiments were executed in a previous work) have been determined. Ce-, Hf-, and Th-UiO-66 MOF samples were irradiated via gamma and Heion methodologies to obtain doses up to 3 MGy and 85 MGy, respectively, the latter strikingly higher than that obtained in most other studies. Appreciable self-irradiation constituted the total absorbed doses, up to 31 MGy of the gamma-irradiated Pu-UiO-66 samples. Structural degradation was ascertained by powder X-ray diffraction, X-ray total scattering, vibrational spectroscopy, and, where possible, N 2 physisorption isotherms. Diffuse reflectance infrared Fourier transform spectroscopy provided atomic-level mechanistic insights to reveal that the node-linker connection was most susceptible to radiation damage. Density functional theory calculations were performed on cluster models to evaluate the binding energy of the linkers to each metal node. While the isostructures disclosed the same breakdown signatures, distinct radiation sensitivity as a function of metal selection was evident and followed the trend Hf-UiO-66 ∼ Zr-UiO-66 > Th-UiO-66 > Pu-UiO-66 > Ce-UiO-66. We anticipate that these endeavors will contribute to the rational design of radiation-resistant materials for targeted applications.

Mononuclearf our coordinate Co II complexes have drawn ag reat deal of attention as they often exhibit excellent single-ion magnet (SIM) properties. Among the reported complexes, the axial zero-field splitting parameter (D)w as found to vary drastically both in terms of the sign as well as strength. There are variousp roposals in this respects uch as structural distortions,h eaviera tom substitution, metalligand covalency,t uning secondary coordination sphere, etc. that are expected to control the D values. To assess the importance of structurald istortions vs. heaviera tom substitution effect, herew eh ave undertaken detailed theoretical studies based on the ab initio CASSCF/NEVPT2 methodt o estimate zero-field splitting parameters for twelve complexes reported in the literature. Our test set includes the {Co II X 4 } (where X = O, S, Se) core structure where the D value was found to vary from + 19 to À118cm À1 .B ased on the structural variation, we have classified the complexes into three types (I-III)w here type I complexes were found to exhibit the largestn egative D value as desired for SIMs. The other two types (II and III)o fc omplexes have been found to be inferior with respect to type I. The secondary coordination spherew as also found to influence D,a ss ubstitution on the secondary coordination sphere atom was found to significantly alter the magnitude of D values. Particularly,t wo structuralp arameters, namely,t he dihedrala ngle between the two ligand planes and the ffX-Co-X polar angle were found to heavily influence the sign and strength of D values. Our analysis clearly reveals that these structural factors are much more important than the heavier atom substitution,o r metal-ligand covalency.Alarge variation in the D and E/D values among these complexesd espite possessing av ery close structuralsimilarity offers an exquisite playground for a chemistt odesign and develop new-generation Co II -based SIMs.

Two-dimensional (2D) inorganic materials have emerged as exciting platforms for (opto)electronic, thermoelectric, magnetic, and energy storage applications. However, electronic redox tuning of these materials can be difficult. Instead, 2D metal−organic frameworks (MOFs) offer the possibility of electronic tuning through stoichiometric redox changes, with several examples featuring one to two redox events per formula unit. Here, we demonstrate that this principle can be extended over a far greater span with the isolation of four discrete redox states in the 2D MOFs Li x Fe 3 (THT) 2 (x = 0−3, THT = triphenylenehexathiol). This redox modulation results in 10,000-fold greater conductivity, p-to n-type carrier switching, and modulation of antiferromagnetic coupling. Physical characterization suggests that changes in carrier density drive these trends with relatively constant charge transport activation energies and mobilities. This series illustrates that 2D MOFs are uniquely redox flexible, making them an ideal materials platform for tunable and switchable applications.

A systematic one-step one-pot multicomponent reaction of Co­(ClO4)2·6H2O, H3L (2,6-bis­((2-(2-hydroxyethylamino)­ethylimino)­methyl)-4-methylphenol), and readily available carboxylate salts (RCO2Na; R = CH3, C2H5) resulted in the two structurally novel coordination aggregates [CoIICoIII 4L2(μ1,3-O2CCH3)2(μ-OH)2]­(ClO4)4·4H2O (1) and [CoIICoIII 4L2(μ1,3-O2CC2H5)2(μ-OH)­(μ-OMe)]­(ClO4)4·5H2O (2). At room temperature, reactions of H3L in MeOH with cobalt­(II) perchlorate salts led to coassembly of initially formed ligand-bound {CoII 2} fragments following aerial oxidation of metal centers and bridging by in situ generated hydroxido/alkoxido groups and added carboxylate anions. Available alkoxido arms of the initially formed {L­(μ1,3-O2CCH3)­(μ-OH/OMe)­Co2}+ fragments were utilized to trap a central CoII ion during the formation of [Co5] aggregates. In the solid state, both complexes have been characterized by X-ray crystallography, variable-temperature magnetic measurements, and theoretical studies. Both 1 and 2 show field-induced slow magnetic relaxation that arises from the single pseudo-T d CoII ion present. The structural distortion leads to an easy-axis magnetic anisotropy (D = −31.31 cm–1 for 1 and −21.88 cm–1 for 2) and a small but non-negligible transverse component (E/D = 0.11 for 1 and 0.08 for 2). The theoretical studies also reveal how the O–Co–O bond angles and the interplanar angles control D and E values in 1 and 2. The presence of two diamagnetic {Co2(μ-L)} hosts controls the distortion of the central {CoO4} unit, highlighting a strategy to control single-ion magnetic anisotropy by trapping single ions within a diamagnetic coordination environment.

Symmetry control using DABCO generates a large easy-plane magnetic anisotropy with zero rhombic anisotropy.