Relaxation dynamics in see-saw shaped Dy() single-molecule magnets

• Published in: Inorganic chemistry frontiers Vol. 7; no. 24; pp. 485 - 4812
• Main Authors: Harriman, Katie L. M, Murillo, Jesse, Suturina, Elizaveta A, Fortier, Skye, Murugesu, Muralee
• Format: Journal Article
• Language: English
• Published: London Royal Society of Chemistry 17.12.2020; Royal Society of Chemistry (RSC)
• Subjects: Angles (geometry); Coordination compounds; Crystal structure; Crystallography; Dysprosium; Inorganic chemistry; Ligands; Magnetic anisotropy; Magnets; Quantum tunnelling
• ISSN: 2052-1553; 2052-1545; 2052-1553
• DOI: 10.1039/d0qi01007c

Utilizing a terphenyl bisanilide ligand, two Dy( iii ) compounds [K(DME) n ][L Ar Dy(X) 2 ] (L Ar = {C 6 H 4 [(2,6- i PrC 6 H 3 )NC 6 H 4 ] 2 } 2− ), X = Cl ( 1 ) and X = I ( 2 ) were synthesized. The ligand imposes an unusual see-saw shaped molecular geometry leading to a coordinatively unsaturated metal complex with near-linear N-Dy-N (avg. 159.9° for 1 and avg. 160.4° for 2 ) angles. These compounds exhibit single-molecule magnet (SMM) behavior with significant uniaxial magnetic anisotropy as a result of the transverse coordination of the bisanilide ligand which yields high energy barriers to magnetic spin reversal of U eff = 1334 K/927 cm −1 ( 1 ) and 1278 K/888 cm −1 ( 2 ) in zero field. Ab initio calculations reveal that the dominant crystal field of the bisanilide ligand controls the orientation of the main magnetic axis which runs nearly parallel to the N-Dy-N bonds, despite the identity of the halide ligand. Analysis of the relaxation dynamics reveals a ca. 14-fold decrease in the rate of quantum tunneling of the magnetisation when X = I ( 2 ). Most notably, the relaxation times were on average 5.6× longer at zero field when the heavier group 17 congener was employed. However, no direct evidence of a heavy atom effect on the Orbach relaxation was obtained as the height of the barrier is defined by the dominant bisanilide ligand. Unusual see-saw shaped Dy( iii ) single-molecule magnets, [K(DME) n ][L Ar Dy(X) 2 ] (L Ar = {C 6 H 4 [(2,6- i PrC 6 H 3 )NC 6 H 4 ] 2 } 2− ), X = Cl ( 1 ) and X = I ( 2 ) were synthesized and display high effective energy barriers ( U eff = 1278-1334 K) in zero field.