Hetero triply-bridged dinuclear copper(II) compounds with ferromagnetic coupling : a challenge for current density functionals

Peer reviewe

Calix[n]arene-based Polyradicals: Enhancing Ferromagnetism by Avoiding Edge Effects

The absence of edges in circular structures derived from 1,3-arylmethyl polyradical results in realistic molecules showing largely stabilized high-spin ground states.</p

Post-B3LYP Functionals Do Not Improve the Description of Magnetic Coupling in Cu(II) Dinuclear Complexes

The accuracy of post-B3LYP functionals is analyzed using an open-shell database of Cu­(II) dinuclear complexes with well-defined experimental values of the magnetic coupling constants. This database provides a sound open-shell training set to be used to improve the fitting schemes in defining new functionals or when reparametrizing the existing ones. For a large set of representative hybrid exchange-correlation functionals, it is shown that the overall description of moderate-to-strong antiferromagnetic interactions is significantly more accurate than the description of ferromagnetic or weakly antiferromagnetic interactions. In the case of global hybrids, the most reliable ones have 25–40% Fock exchange with SOGGA and PBE0 being the most reliable and M06 the exception. For range-corrected hybrids, the long-range corrected CAM-B3LYP and ωB97XD provide acceptable results, and M11 is comparable but more erratic. It is concluded that the reliability of the calculated values is system- and range-dependent, and this fact introduces a serious warning on the blind use of a single functional to predict magnetic coupling constants. Hence, to extract acceptable magnetostructural correlations, a “standardization” of the method to be used is advised to choose the optimal functional

Electronic and magnetic structure of bulk cobalt: The alpha, beta, and epsilon-phases from density functional theory calculations

The geometric, electronic and magnetic properties of the three metallic cobalt phases: hcp(α) , fcc(β) , and epsilon(ε) have been theoretically studied using periodic density functional calculations with generalized gradient approximation (GGA) and plane wave basis set. These results have been compared with those obtained with GGA+U approach which have shown a noticeable improvement with regard to experimental data. For instance, the cohesive energy values predicted by GGA are overestimated by ∼25% , whereas GGA+U underestimate them by 14%–17%. On the other hand, magnetic moment values are underestimated in GGA while are overestimated for GGA+U approach by almost the same amount. Besides, the introduction of U parameter gives rise to an electronic redistribution in the d-band structure, which leads to variations in the magnetic properties. Moreover, a higher attention has been paid in the study of the electronic and magnetic properties of the ε -phase that has not described previously. These studies show that this phase posses special properties that could lead to an unusual behavior in magnetic or catalytic applications

Redox-Induced Gating of the Exchange Interactions in a Single Organic Diradical

Embedding a magnetic electroactive molecule in a three-terminal junction allows for the fast and local electric field control of magnetic properties desirable in spintronic devices and quantum gates. Here, we provide an example of this control through the reversible and stable charging of a single all-organic neutral diradical molecule. By means of inelastic electron tunnel spectroscopy we show that the added electron occupies a molecular orbital distinct from those containing the two radical electrons, forming a spin system with three antiferromagnetically coupled spins. Changing the redox state of the molecule therefore switches on and off a parallel exchange path between the two radical spins through the added electron. This electrically controlled gating of the intramolecular magnetic interactions constitutes an essential ingredient of a single-molecule quantum gate

Biradical Formation by Deprotonation in Thiazole-Derivatives: The Hidden Nature of Dasatinib

The formation of stable organic biradicals by a deprotonation process is reported for a series of conjugated heterocycles that share a Ph-N(H)-2-thiazole structural motif. We characterise the paramagnetic electronic ground state by means of continuous-wave and pulse EPR. We propose a simple valence bond mechanism for a deprotonation-induced formation of paramagnetic organic molecules, based on the interplay between the electronegativity of heteroatomic groups and the recovery of aromaticity to stabilise the biradical species. The Ph-N(H)-2-thiazole motif is found in a variety of biologically active molecules, exemplified here with the anticancer drug Dasatinib, and our results suggest a radical-based mechanism for the protein kinase inhibition activity of the drug. The existence of this structure-property relationship for an elementary chemical motif suggests that biradical species may be more prevalent than previously thought and have an important role in bioorganic chemistry