Magnetic molecules that present a slow decay of their magnetization (molecular magnets) are very interesting both from a fundamental and applied points of view. While many approaches focus strongly on finding systems with strong magnetic anisotropy giving rise to large spin-reversal barriers, less is known on the behavior of magnetic tunnelling, which is also a fundamental component of molecular magnet behavior. In this work, we propose a model to describe both the spin-reversal barrier and magnetic tunnelling in Ni(II) trigonal bipyramidal complexes, which could be easily extended to other transition-metal systems. Based on this model, we show the criteria that lead to the optimal complexes to find molecular magnet behavior. We test our proposal with multi-reference configuration-interaction (MRCI) and ligand-field-density-functional-theory (LF-DFT) first-principles calculations applied over several families of mononuclear Ni(II) complexes. As a salient result, we find that the complex [NiCl₃(Hdabco)₂]⁺ (dabco is 1,4-diazabicyclo[2.2.2]-octane) displays both a very large magnetic anisotropy energy, 524 cm⁻¹, and a small tunnelling splitting, 0.2 cm⁻¹, when compared to other systems containing the same metal. We expect molecular magnet behaviour to be observed when small magnetic fields are employed to disrupt tunnelling. These values are reached due to the choice of ligands that favor a complete destruction of the Jahn–Teller distortions through spin–orbit coupling and an unquenched orbital momentum.

Herein, we present the systematic, comparative computational study of the d − d transitions in a series of first row transition metal hexaaqua complexes, [M(H₂O)₆]ⁿ⁺ (M^2+/3+ = V ^2+/3+, Cr^2+/3+, Mn^2+/3+, Fe^2+/3+, Co^2+/3+, Ni²⁺) by the means of Time-dependent Density Functional Theory (TD-DFT) and Ligand Field Density Functional Theory (LF-DFT). Influence of various exchange-correlation (XC) approximations have been studied, and results have been compared to the experimental transition energies, as well as, to the previous high-level ab initio calculations. TD-DFT gives satisfactory results in the cases of d², d⁴, and low-spin d⁶ complexes, but fails in the cases when transitions depend only on the ligand field splitting, and for states with strong character of double excitation. LF-DFT, as a non-empirical approach to the ligand field theory, takes into account in a balanced way both dynamic and non-dynamic correlation effects and hence accurately describes the multiplets of transition metal complexes, even in difficult cases such as sextet-quartet splitting in d⁵ complexes. Use of the XC functionals designed for the accurate description of the spin-state splitting, e.g., OPBE, OPBE0, or SSB-D, is found to be crucial for proper prediction of the spin-forbidden excitations by LF-DFT. It is shown that LF-DFT is a valuable alternative to both TD-DFT and ab initio methods.

Density Functional Theory (DFT) was used to analyse and explain spin state energetics of first-row transition metals (Mn^II, Fe^II, Co^II; Cr^III, Mn^III, Fe^III, Co^III; Mn^IV) in polypyrazolylborato complexes. We explored the effects of substitutions at the 3 and 5 positions of the pyrazolyl rings, as well as the influence of Jahn–Teller (JT) distortions on spin-state switching. Although the stabilizations due to JT distortion are sometimes substantial, this does not lead to switching of the spin ground-state. On the other hand, electron withdrawing or donating substituents do lead to significant changes in the spin-crossover (SCO) properties of the investigated complexes.

The rise of innovation in the electrical industry is driven by the controlled design of new materials. The hybrid materials based on magnetite/nanocellulose are highly interesting due to their various applications in medicine, ecology, catalysis and electronics. In this study, the structure and morphology of nanocellulose/magnetite hybrid nanomaterials were investigated. The effect of nanocellulose loading on the crystal structure of synthesized composites was investigated by XRD and FTIR methods. The presented study reveals that the interaction between the cellulose and magnetic nanoparticles depends on the nanocellulose content. Further, a transition from cellulose II to cellulose I allomorph is observed. SEM and EDS are employed to determine the variation in morphology with changes in component concentrations. By the calculation of magnetic interactions between adjacent Fe³⁺ and Fe²⁺ ions within composites, it is determined that ferromagnetic coupling predominates.

The purpose of this paper is to examine the role of the local community in small-scale sport events in rural areas, from the perspective of contestants and sport event organisers.: Six small-scale ...