A new Mn25 single-molecule magnet with an S = 61/2 ground state arising from ligand-induced ‘spin-tweaking’ in a high-spin molecule

Reactivity studies of a [Mn25]2+ cage of full formula [Mn6IIMn18IIIMnIVO18(OH)2(N3)12(pdm)6(pdmH)6]2+ (1) involving replacement of azide groups with hmp− ones have led to a new, isostructural [Mn25O18(OH)(OMe)(hmp)6(pdm)6(pdmH)6]8+ (2) cluster with new and impressive magnetic properties. The successful ligand (hmp−)-induced structural distortion of the preformed Mn25 cluster (1) with an S = 51/2 ground-state causes the ground-state spin to increase remarkably (∼20%) to S = 61/2. Hysteresis loops are seen below ∼1.0 K whose coercivities increase with increasing sweep rate and with decreasing temperature. This confirms 2 to be an SMM, possessing one of the highest S values ever reported.

The replacement of the 12 azide groups in [Mn25O18(OH)2(N3)12(pdm)6(pdmH)6]2+ with 6 η1:η2:μ2 hmp− groups in MeCN/MeOH gives [Mn25O18(OH)(OMe)(hmp)6(pdm)6(pdmH)6]8+. The resulting small perturbations to the structure and exchange parameters cause a change to the ground state from S = 51/2 to S = 61/2. Hysteresis studies below ∼1.0 K show the new compound to also be a single-molecule magnet.Figure optionsDownload as PowerPoint slide