Preparation, electrochemical behavior, and variable-temperature magnetic properties of Co(3,5-DBSQ)₂ complexes of imidazole- or pyrazole-substituted ligands

Abstract

Herein we describe the preparation of four new Co(3,5-DBSQ) 2 containing known 2-(2-pyridyl)benzimidazole 1, 2,2=-bisbenzimidazole 2, or 2,2-(1H-pyrazole-3,5-diyl)dipyridine 3. We investigate the electronic and variable-temperature magnetic susceptibility properties of these complexes. Complexes containing 2 and 3 are bimetallic and variable-temperature magnetic susceptibility data suggest observation of a stable intermediate (high-spin and low-spin) state for the bimetallic complex with 3, which does undergo valence tautomerism. Complexes 4-6 containing imidazole-based ligands 1 and 2 feature high-spin ground states and no valence tautomerism is observed in these materials. This experimental finding is corroborated with density functional theory calculations, which support the existence of a stable high-spin ground state in these complexes. Résumé :Dans le présent article, nous décrivons la préparation de quatre nouveaux complexes de type Co(3,5-DBSQ) 2 dont les ligands connus sont le 2-(2-pyridyl)benzimidazole 1, le 2,2=-bis(benzimidazole) 2 ou la 2,2-(1H-pyrazole-3,5-diyl)dipyridine 3. Nous avons étudié ces complexes sous l'angle de leurs propriétés électroniques et de leurs propriétés de susceptibilité magnétique en fonction de la température. Les complexes comprenant les ligands 2 et 3 sont bimétalliques, et les données de susceptibilité magnétique en fonction de la température laissent supposer qu'on devrait observer un état intermédiaire stable (formes haut-spin et bas-spin) pour le complexe bimétallique avec le ligand 3, qui manifeste effectivement un tautomérisme de valence. Les complexes 4 à 6 comprenant les ligands à base d'imidazole 1 et 2 présentent des états fondamentaux de forme haut-spin, et aucun tautomérisme de valence n'est observé dans ces composés. Ce résultat expérimental est corroboré par des calculs de la théorie de la fonctionnelle de la densité, qui appuient l'existence d'un état fondamental stable de forme haut-spin dans ces complexes. [Traduit par la Rédaction]

A Convenient DFT-Based Strategy for Predicting Transition Temperatures of Valence Tautomeric Molecular Switches

“… , However, this localized unpaired electron can easily leak across the two dioxolene ligands during geometry optimization due to the common self-interaction error (SIE), − an effect where the electrons display unphysical interaction with themselves. Selection of a density functional that prevents such artificial delocalization of the spin density is vital, something not properly considered in the literature despite knowledge of this problem, with methods applied that did not localize the spin. ,,,, In general, generalized gradient approximations (GGA) functionals, such as BP86, , give reliable geometries and are widely used in many computational studies including for valence tautomeric cobalt complexes. ,, However, for [Co­(dbdiox)­(dbsq)­(phen)], the BP86 functional results in delocalized spin distribution in the doublet LS-Co III -(cat)­(SQ) tautomer resulting from high amounts of SIE (Figure ). The 2010 study by Yoshikawa et al employed B3LYP, B3LYP*, BLYP, , BP86 and OPBE , to obtain the relative energy of the VT process and Co–O bond lengths .…”

“…Selection of a density functional that prevents such artificial delocalization of the spin density is vital, something not properly considered in the literature despite knowledge of this problem, with methods applied that did not localize the spin. 27,28,32,35,89 In general, generalized gradient approximations (GGA) functionals, such as BP86, 90,91 give reliable geometries and are widely used in many computational studies including for valence tautomeric cobalt complexes. 35,39,92 However, for [Co(dbdiox)(dbsq)-(phen)], the BP86 functional results in delocalized spin distribution in the doublet LS-Co III -(cat)(SQ) tautomer resulting from high amounts of SIE (Figure 3).…”