title: Exploring the Influence of Diamagnetic Ions on the Mechanism of Magnetization Relaxation in {CoIII2LnIII2} (Ln = Dy, Tb, Ho) "Butterfly" Complexes.
abstract: The synthesis and magnetic and theoretical studies of three isostructural heterometallic [CoIII2LnIII2(μ3-OH)2(o-tol)4(mdea)2(NO3)2] (Ln = Dy (1), Tb (2), Ho (3)) "butterfly" complexes are reported (o-tol = o-toluate, (mdea)2-= doubly deprotonated N-methyldiethanolamine). The CoIIIions are diamagnetic in these complexes. Analysis of the dc magnetic susceptibility measurements reveal antiferromagnetic exchange coupling between the two LnIIIions for all three complexes. ac magnetic susceptibility measurements reveal single-molecule magnet (SMM) behavior for complex 1, in the absence of an external magnetic field, with an anisotropy barrier Ueffof 81.2 cm-1, while complexes 2 and 3 exhibit field induced SMM behavior, with a Ueffvalue of 34.2 cm-1for 2. The barrier height for 3 could not be quantified. To understand the experimental observations, we performed DFT and ab initio CASSCF+RASSI-SO calculations to probe the single-ion properties and the nature and magnitude of the LnIII-LnIIImagnetic coupling and to develop an understanding of the role the diamagnetic CoIIIion plays in the magnetization relaxation. The calculations were able to rationalize the experimental relaxation data for all complexes and strongly suggest that the CoIIIion is integral to the observation of SMM behavior in these systems. Thus, we explored further the effect that the diamagnetic CoIIIions have on the magnetization blocking of 1. We did this by modeling a dinuclear {DyIII2} complex (1a), with the removal of the diamagnetic ions, and three complexes of the types {KI2DyIII2} (1b), {ZnII2DyIII2} (1c), and {TiIV2DyIII2} (1d), each containing a different diamagnetic ion. We found that the presence of the diamagnetic ions results in larger negative charges on the bridging hydroxides (1b > 1c > 1 > 1d), in comparison to 1a (no diamagnetic ion), which reduces quantum tunneling of magnetization effects, allowing for more desirable SMM characteristics. The results indicate very strong dependence of diamagnetic ions in the magnetization blocking and the magnitude of the energy barriers. Here we propose a synthetic strategy to enhance the energy barrier in lanthanide-based SMMs by incorporating s- and d-block diamagnetic ions. The presented strategy is likely to have implications beyond the single-molecule magnets studied here.
authors.affiliation: IITB-Monash Research Academy, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Kuduva R
authors.initials: KR
authors.lastname: Vignesh
authors.affiliation: School of Science and the Environment, Division of Chemistry, Manchester Metropolitan University , Manchester M15 6HB, U. K.
authors.forename: Stuart K
authors.initials: SK
authors.lastname: Langley
authors.affiliation: School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
authors.forename: Keith S
authors.initials: KS
authors.lastname: Murray
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Gopalan
authors.identifier: http://orcid.org/0000-0001-6133-3026
authors.initials: G
authors.lastname: Rajaraman