Enhancing the barrier height for magnetization reversal in 4d/4f Ru III 2 L III 2 “butterfly” single molecule magnets (Ln = Gd, Dy)viatargeted structural alterations

Swain, A, Martin, R, Vignesh, KR, Rajaraman, G, Murray, KS and Langley, SK ORCID: https://orcid.org/0000-0002-2241-1551 (2021) Enhancing the barrier height for magnetization reversal in 4d/4f Ru III 2 L III 2 “butterfly” single molecule magnets (Ln = Gd, Dy)viatargeted structural alterations. Dalton Transactions, 50 (35). pp. 12265-12274. ISSN 1477-9226

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Abstract

A series of 4d-4f {Ru>III2Dy>III2} and {Ru>III2Gd>III2} ‘butterfly’ (rhombohedral) complexes have been synthesized and characterized and their magnetic properties investigated. Earlier, we have reported the first 4d/4f SMM - [Ru>III2Dy>III2(OMe)2(O2CPh)4(mdea)2(NO3)2] (1Dy) with aUeffvalue of 10.7 cm−1. As the structural distortion around the DyIIIcentres and the RuIII⋯DyIIIexchange interactions are key to enhancing the anisotropy, in this work we have synthesised three more {Ru2Dy2} butterfly complexes where structural alteration around the DyIIIcentres and alterations to the bridging groups are performed with an aim to improve the magnetic properties. The new complexes reported here are [Ru2Dy2(OMe)2(O2C(4-Me-Ph)4(mdea)2(MeOH)4],2Dy, [Ru2Dy2(OMe)2(O2C(2-Cl,4,5-F-Ph)4(mdea)2(NO3)2],3Dy, and an acac derivative [Ru2Dy2(OMe)2(acac)4(NO3)2(edea)2],4Dy, where acac−= acetylacetonate, edea2−=N-ethyldiethanolamine dianion. Complex2Dydescribes alteration in the DyIIIcenters, while complexes3Dyand4Dyare aimed to alter the RuIII⋯DyIIIexchange pathways. To ascertain the 4d-4f exchange, the Gd-analogues of1Dyand4Dywere synthesised [Ru2Gd2(OMe)2(O2CPh)4(mdea)2(NO3)2],1Gd, [Ru2Gd2(OMe)2(acac)4(NO3)2(edea)2],4Gd. Both ac and dc susceptibility studies were performed on all these complexes, and out-of-phase signals were observed for3Dyin zero-field while2Dyand4Dyshow out-of-phase signals in the presence of an applied field. Complex3Dyreveals a barrier heightUeffof 45 K. To understand the difference in the magnetic dynamic behavior compared to our earlier reported {Ru>III2Dy>III2} analogue, detailed theoretical calculations based onab initioCASSCF/RASSI-SO calculations have been performed. Calculations reveal that theJRu⋯Dyvalue varies from −1.8 cm−1(4Dy) to −2.4 cm−1(3Dy). These values are also affirmed by DFT calculations performed on the corresponding GdIIIanalogues. The origin of the largest barrier and observation of slow magnetic relaxation in3Dyis routed back to the stronger single-ion anisotropy and strongerJRu⋯Dyexchange which quenches the QTM effects more efficiently. This study thus paves the way forward to tune local structure around the LnIIIcenter and the exchange pathway to enhance the SMM characteristics in other {3d-4f}/{4d-4f} SMMs.