Strong Antiferromagnetic Exchange‐Coupling Observed in Hydride‐Bridged Dimeric Dysprosium(III) Single‐Molecule Magnet

Comprehensive Summary One dihydride‐bridged dimeric Dy(III) guanidinate complex, formulated as [{(Me 3 Si) 2 NC(N i Pr) 2 } 2 Dy( μ ‐H)] 2 ( 1Dy ), was successfully isolated and the introduction of hydride bridges significantly reduces the intramolecular Dy(III)···Dy(III) distance to only 3.688(1) Å. To investigate the effect of such a short Dy(III)···Dy(III) distance on magnetism, we also prepared its dibromide‐bridged analogue [{(Me 3 Si) 2 NC(N i Pr) 2 } 2 Dy( μ ‐Br)] 2 ( 2Dy ), which has a much longer Dy(III)···Dy(III) distance of 4.605(4) Å. Surprisingly, 2Dy demonstrates much larger effective energy barrier for magnetization reversal ( U eff ) and higher blocking temperature ( T B ). The worse performance of 1Dy is attributed to the concerted effect of strong antiferromagnetic interactions between Dy(III) ions ( J total = –2.683 cm –1 ) and the unparallel arrangement of magnetic principle axes of the Dy(III) ions for 1Dy .