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Keywords = angular overlap model (AOM)

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20 pages, 3585 KiB  
Article
Assessing Quantum Calculation Methods for the Account of Ligand Field in Lanthanide Compounds
by Ana Maria Toader, Bogdan Frecus, Corneliu Ioan Oprea and Maria Cristina Buta
Physchem 2023, 3(2), 270-289; https://doi.org/10.3390/physchem3020019 - 16 Jun 2023
Cited by 1 | Viewed by 2344
Abstract
We obtained thorough insight into the capabilities of various computational methods to account for the ligand field (LF) regime in lanthanide compounds, namely, a weakly perturbed ionic body and quasidegenerate orbital multiplets. The LF version of the angular overlap model (AOM) was considered. [...] Read more.
We obtained thorough insight into the capabilities of various computational methods to account for the ligand field (LF) regime in lanthanide compounds, namely, a weakly perturbed ionic body and quasidegenerate orbital multiplets. The LF version of the angular overlap model (AOM) was considered. We intentionally took very simple idealized systems, the hypothetical [TbF]2+, [TbF2]+ and [Tb(O2NO)]2+, in order to explore the details overlooked in applications on complex realistic systems. We examined the 4f and 5d orbital functions in connection to f–f and f–d transitions in the frame of the two large classes of quantum chemical methods: wave function theory (WFT) and density functional theory (DFT). WFT methods are better suited to the LF paradigm. In lanthanide compounds, DFT faces intrinsic limitations because of the frequent occurrence of quasidegenerate ground states. Such difficulties can be partly encompassed by the nonstandard control of orbital occupation schemes. Surprisingly, we found that the simplest crystal field electrostatic approximation, reconsidered with modern basis sets, works well for LF parameters in ionic lanthanide systems. We debated the largely overlooked holohedrization effect that inserts artificial inversion symmetry into standard LF Hamiltonians. Full article
(This article belongs to the Section Theoretical and Computational Chemistry)
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12 pages, 2818 KiB  
Article
Crystal Structures and Magnetic Properties of Diaquatetrapyridinenickel(II) and Diaquatetrapyridinecobalt(II) Complexes
by Hiroshi Sakiyama, Yuya Yamamoto, Ryusei Hoshikawa and Ryoji Mitsuhashi
Magnetochemistry 2023, 9(1), 14; https://doi.org/10.3390/magnetochemistry9010014 - 30 Dec 2022
Cited by 2 | Viewed by 1965
Abstract
Metal complexes with pyridine ligands (py) have not been crystallographically characterized in large numbers, while a large number of 2,2′-bipyridine (bpy) complexes have been structurally characterized. Against this background of scarcity of py complexes, the aim of this study was to characterize the [...] Read more.
Metal complexes with pyridine ligands (py) have not been crystallographically characterized in large numbers, while a large number of 2,2′-bipyridine (bpy) complexes have been structurally characterized. Against this background of scarcity of py complexes, the aim of this study was to characterize the structures and magnetic properties of complexes with pyridine ligands. In this study, new py complexes, trans-[Ni(H2O)2(py)4][BPh4]2·4py (1) and trans-[Co(H2O)2(py)4][BPh4]2·4py (2), were prepared and characterized by the single-crystal X-ray diffraction method and magnetic measurements. In the crystal structure analysis, both complexes were found to have octahedral trans-N2O4 coordination geometry, and the coordination of the trans-aqua ligands was found to be enhanced by the hydrogen-bonded pyridine molecules as a base. In the simultaneous analysis of magnetic susceptibility and magnetization, both complexes were found to show strong magnetism in one direction (χz > χx, χy; Mz > Mx, My), and this was explained by the enhancement of the axial aqua ligands. In the nickel(II) complex, the strong axial ligand field was found to cause negative zero-field splitting (D < 0) to show the magnetic behavior, while in the cobalt(II) complex, the strong axial π-orbital effect was found to cause negative ligand field splitting (Δ) in the 4T1 ground state to show the magnetic behavior. Full article
(This article belongs to the Special Issue Characterization of Coordination Compounds)
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