ic4029645_si_004.pdf (3.66 MB)
Single-Molecule Magnetism in a Family of {CoIII2DyIII2} Butterfly Complexes: Effects of Ligand Replacement on the Dynamics of Magnetic Relaxation
journal contribution
posted on 2014-05-05, 00:00 authored by Stuart
K. Langley, Liviu Ungur, Nicholas F. Chilton, Boujemaa Moubaraki, Liviu F. Chibotaru, Keith S. MurrayThe
synthesis and structural characterization of four related heterometallic
complexes of formulas [DyIII2CoIII2(OMe)2(teaH)2(O2CPh)4(MeOH)4](NO3)2·MeOH·H2O (1a) and [DyIII2CoIII2(OMe)2(teaH)2(O2CPh)4(MeOH)2(NO3)2]·MeOH·H2O (1b), [DyIII2CoIII2(OMe)2(dea)2(O2CPh)4(MeOH)4](NO3)2 (2), [DyIII2CoIII2(OMe)2(mdea)2(O2CPh)4(NO3)2] (3), and [DyIII2CoIII2(OMe)2(bdea)2(O2CPh)4(MeOH)4](NO3)2·0.5MeOH·H2O (4a) and [DyIII2CoIII2(OMe)2(bdea)2(O2CPh)4(MeOH)2(NO3)2]·MeOH·1.5H2O (4b) are reported (teaH3 = triethanolamine,
deaH2 = diethanolamine, mdeaH2 = N-methyldiethanolamine, and bdeaH2 = N-n-butyldiethanolamine). Compounds 1 (≡ 1a and 1b) and 4 (≡ 4a and 4b) both display two unique molecules
within the same crystal and all compounds display a butterfly type
core, with the DyIII ions occupying the central body positions
and the diamagnetic CoIII ions the outer wing-tip sites.
Compounds 1–4 were investigated via
direct current and alternating current magnetic susceptibility measurements,
and it was found that each complex displayed single-molecule magnet
(SMM) behavior. All four compounds display unique coordination and
geometric environments around the DyIII ions and it was
found that each displays a different anisotropy barrier. Ab
initio calculations were performed on 1–4 and these determined the low lying electronic structure
of each DyIII ion and the magnetic interactions for each
cluster. It was found that there was a strong correlation between
the calculated energy gap between the ground and first excited states
of the single-ion ligand-field split DyIII levels and the
experimentally observed anisotropy barrier. Furthermore, the transverse g factors found for the DyIII ions, defining
the tunnelling rates within the ground Kramers doublets, are largest
for 1, which agrees with the experimental observation
of the shortest relaxation time in the high-temperature domain for
this complex. The magnetic exchange between the DyIII ions
revealed overall antiferromagnetic interactions for each compound,
derived from the dominant dipolar exchange resulting in nonmagnetic
ground states for 1–4. The diamagnetic
ground states coupled with small tunneling gaps resulted in quantum
tunneling time scales at zero field of between 0.1 and >1.5 s.
