Impact of anionic co-ligands on nuclearity and single-molecule magnetism in a {CoIII2Dy III } trimeric and two {CoIII2DyIII2} tetrameric complexes

R - and S -isomers of H 3 L yield tri- and tetranuclear Co III –Dy III complexes showing zero-field slow relaxation, one of which shows the highest U eff (200 K). Ab initio studies reveal anisotropy and relaxation pathways, advancing Co III –Dy III -based SMMs.