The uranyl(V) complexes UO2(dbm)2K(18C6)2 (dbm = dibenzoylmethanate) and UO2(L)3(L = 2-(4-tolyl)-1,3-bis(quinolyl)malondiiminate), exhibiting diamond-shaped U2O2 and triangular-shaped U3O3 cores ...respectively with 5f1–5f1 and 5f1–5f1–5f1 configurations, have been investigated using relativistic density functional theory (DFT). The bond order and QTAIM analyses reveal that the covalent contribution to the bonding within the oxo cores is slightly more important for U3O3 than for U2O2, in line with the shorter U–O distances existing in the trinuclear complex in comparison to those in the binuclear complex. Using the broken symmetry (BS) approach combined with the B3LYP functional for the calculation of the magnetic exchange coupling constants (J) between the magnetic centers, the antiferromagnetic (AF) character of these complexes was confirmed, the estimated J values being respectively equal to −24.1 and −7.2 cm–1 for the dioxo and trioxo species. It was found that the magnetic exchange is more sensitive to small variations of the core geometry of the dioxo species in comparison to the trioxo species. Although the robust AF exchange coupling within the U x O x cores is generally maintained when small variations of the UOU angle are applied, a weak ferromagnetic character appears in the dioxo species when this angle is higher than 114°, its value for the actual structure being equal to 105.9°. The electronic factors driving the magnetic coupling are discussed.
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•- Quantum calculations were carried out on pyrimidopyrimidine tautomeric heterocyclic derivatives.•- The effect of the solvent on the process of tautomerism is analyzed.•- The ...predominance of thedi-ketone form in gas phase and solution is observed.
Quantum calculations were carried out on some pyrimidopyrimidine tautomeric heterocyclic derivatives both in gas phase and in solution in order to study the influence of the migration of hydrogen on their electronic and structural properties as well to highlight the effect of the solvent on the process of tautomerism. Results indicate that the electronic properties of the studied heterocycles are influenced by the nature of the solvent used. All tautomeric forms are more stable in H2O and DMSO than in CHCl3 and in the gas phase. The predominance of the di-ketone form in gas phase and solution is observed.
Electronic structures and magnetic properties of the binuclear bis(μ-oxo) UIV/UIV K2{((nP,MeArO)3tacn)UIV}2(μ-O)2 and UV/UV {((nP,MeArO)3tacn)UV}2(μ-O)2 (tacn = triazacyclononane, nP = neopentyl) ...complexes, exhibiting U(μ-O)2U diamond-core structural motifs, have been investigated computationally using scalar relativistic Density Functional Theory (DFT) combined with the Broken Symmetry (BS) approach for their magnetic properties. Using the B3LYP hybrid functional, the BS ground state of the pentavalent UV(μ-O)2UV 5f1–5f1 complex has been found of lower energy than the high spin (HS) triplet state, thus confirming the antiferromagnetic character in agreement with experimental magnetic susceptibility measurements. The nonmagnetic character observed for the tetravalent K2UIV(μ-O)2UIV 5f2–5f2 species is also predicted by our DFT calculations, which led practically to the same energy for the HS and BS states. As reported for related dioxo diuranium(V) systems, superexchange is likely to be responsible for the antiferromagnetic coupling through the π-network orbital pathway within the (μ-O)2 bridge, the dissymmetrical structure of the U2O2 core playing a determining role. In the case of the UIV species, our computations indicate that the K+ counterions are likely to play a role for the observed magnetic property. Finally, the MO analysis, in conjunction with NPA and QTAIM analyses, clarify the electronic structures of the studied complexes. In particular, the fact that the experimentally attempted chemical oxidation of the UV species does not lead straightforwardly to binuclear complexes UVI is clarified by the MO analysis.
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