From geometric to charge-distribution symmetry:deeper insights into lifting the performance of dysprosium single-ion magnets

Crystal-field symmetry of lanthanide ions plays a critical role in suppressing quantum tunneling of magnetization(QTM)in single-molecule magnets(SMMs),but high-performance SMM design and modulation remain challenging only in view of the geometric symmetry of the first coordination sphere.Herein,two bis(semicarbazone)/bis(thiosemicarbazone)dysprosium singleion magnets with pentagonal bipyramid geometry were reported,and bis(thiosemicarbazone)lanthanide complexes have never been reported to the best of our knowledge.They served as good archetypes to study the magneto-structural relationships based on the charge distribution.The complex with more ideal geometric symmetry displays fast zero-field QTM with negligible“effective barrier”,owing to the defective charge distribution.By modulating the transverse crystal field via the replacement of the O sites with the less charged and larger radius S atoms,it results in lower geometric but higher charge-distribution symmetry,giving rise to the significant suppression of QTM and the enhancement of reversal barrier up to ca.1,000 K.These results demonstrate that the charge-distribution symmetry can be chemically tailored by modification of the crystal field,which is essential for designing high-performance SMMs.