Three variants of 2-(pyridine-2-yl)-1H-benzimidazole bidentate ligands,with distinct pentyl substituents(n-pentyl(L1),(2S)-2-methylbutyl(L2S),and(2R)-2-methylbutyl(L2R)),were synthesized and employed to prepare magnet...Three variants of 2-(pyridine-2-yl)-1H-benzimidazole bidentate ligands,with distinct pentyl substituents(n-pentyl(L1),(2S)-2-methylbutyl(L2S),and(2R)-2-methylbutyl(L2R)),were synthesized and employed to prepare magnetically bistable cobalt_((II))and iron_((II))complexes.The cobalt_((II))complexes[Co(L1)(κ^(2)-NO_(3))_(2)(CH_(3)CN)](1),[Co(L2S)(κ^(2)-NO_(3))2(H_(2)O)](2S),[Co(L2R)(κ^(2)-NO_(3))2(H_(2)O)](2R)and[Co(L2)(κ^(2)-NO_(3))2(H_(2)O)](2rac)exhibit field supported slow relaxation of magnetisation,while the iron_((II))complexes[Fe(L2S)_(3)](CF_(3)SO_(3))_(2)·H_(2)O·CH_(3)NO_(2)·C_(5)H_(12)O(3S)and[Fe(L2S)_(3)]·1.5H_(2)O(3R)exhibit thermal spin crossover allocated above room temperature.Structural analysis revealed that the heptacoordinated cobalt_((II))complexes adopt a distorted pentagonal bipyramidal geometry,whereas the iron_((II))compounds contain hexacoordinated complex cations.Coordination compounds incorporating the chiral ligands L2S and L2R are optically active,with their enantiomeric relationship confirmed by circular dichroism spectroscopy.Computational studies provided insights into electron density distributions and bonding energetics(DFT and QT-AIM),predicted zero-field splitting parameters(CASSCF/NEVPT2),and quantified energies of the d-orbital,ligand field terms and their multiplets(via AILFT).Magnetic investigations of the cobalt_((II))complexes yielded experimental ZFS parameters and revealed distinct magnetization relaxation mechanisms:1 exhibits relaxation governed by a phonon bottle-neck process,whereas 2S and 2R involve a combination of Raman and direct relaxation processes.Notably,compounds 2S and 2R,despite being enantiomers and isostructural,exhibited distinct relaxation dynamics,attributable to differential phonon coupling pathways modulated by the chiral substituents.This is the first report demonstrating enantiomer-dependent slow relaxation of magnetisation behaviour in cobalt_((II))-based SMMs.These findings underscore the critical role of stereochemistry in modulating spin dynamics and magnetic bistability,providing design principles for future chiral magnetic materials.展开更多
基金support of Slovak Grant Agencies(APVV-23-0006,APVV-22-0172,APVV-19-0087,VV-MVP-24-0039,VEGA 1/0029/22,DS-FR-22-0010)the project“Large Projects for Excellent Researchers”under the Recovery and Resilience Plan of the Slovak Republic(09I03-03-V03-00029)+1 种基金support from the Grant Agency of the Czech Republic Grant No.25-16980Ssupport from the Institutional Sources of the Department of Inorganic Chemistry,PalackýUniversity Olomouc,Czech Republic。
文摘Three variants of 2-(pyridine-2-yl)-1H-benzimidazole bidentate ligands,with distinct pentyl substituents(n-pentyl(L1),(2S)-2-methylbutyl(L2S),and(2R)-2-methylbutyl(L2R)),were synthesized and employed to prepare magnetically bistable cobalt_((II))and iron_((II))complexes.The cobalt_((II))complexes[Co(L1)(κ^(2)-NO_(3))_(2)(CH_(3)CN)](1),[Co(L2S)(κ^(2)-NO_(3))2(H_(2)O)](2S),[Co(L2R)(κ^(2)-NO_(3))2(H_(2)O)](2R)and[Co(L2)(κ^(2)-NO_(3))2(H_(2)O)](2rac)exhibit field supported slow relaxation of magnetisation,while the iron_((II))complexes[Fe(L2S)_(3)](CF_(3)SO_(3))_(2)·H_(2)O·CH_(3)NO_(2)·C_(5)H_(12)O(3S)and[Fe(L2S)_(3)]·1.5H_(2)O(3R)exhibit thermal spin crossover allocated above room temperature.Structural analysis revealed that the heptacoordinated cobalt_((II))complexes adopt a distorted pentagonal bipyramidal geometry,whereas the iron_((II))compounds contain hexacoordinated complex cations.Coordination compounds incorporating the chiral ligands L2S and L2R are optically active,with their enantiomeric relationship confirmed by circular dichroism spectroscopy.Computational studies provided insights into electron density distributions and bonding energetics(DFT and QT-AIM),predicted zero-field splitting parameters(CASSCF/NEVPT2),and quantified energies of the d-orbital,ligand field terms and their multiplets(via AILFT).Magnetic investigations of the cobalt_((II))complexes yielded experimental ZFS parameters and revealed distinct magnetization relaxation mechanisms:1 exhibits relaxation governed by a phonon bottle-neck process,whereas 2S and 2R involve a combination of Raman and direct relaxation processes.Notably,compounds 2S and 2R,despite being enantiomers and isostructural,exhibited distinct relaxation dynamics,attributable to differential phonon coupling pathways modulated by the chiral substituents.This is the first report demonstrating enantiomer-dependent slow relaxation of magnetisation behaviour in cobalt_((II))-based SMMs.These findings underscore the critical role of stereochemistry in modulating spin dynamics and magnetic bistability,providing design principles for future chiral magnetic materials.
