A monometallic lanthanide bis(methanediide) single molecule magnet with a large energy barrier and complex spin relaxation behaviour

Gregson, Matthew; Chilton, Nicholas F.; Ariciu, Ana Maria; Tuna, Floriana; Crowe, Iain F.; Lewis, William; Blake, Alexander J.; Collison, David; McInnes, Eric J.L.; Winpenny, Richard E.P.; Liddle, Stephen T.

Abstract

© The Royal Society of Chemistry. We report a dysprosium(iii) bis(methanediide) single molecule magnet (SMM) where stabilisation of the highly magnetic states and suppression of mixing of opposite magnetic projections is imposed by a linear arrangement of negatively-charged donor atoms supported by weak neutral donors. Treatment of [Ln(BIPMTMS)(BIPMTMSH)] [Ln = Dy, 1Dy; Y, 1Y; BIPMTMS = {C(PPh2NSiMe3)2}2-; BIPMTMSH = {HC(PPh2NSiMe3)2}-] with benzyl potassium/18-crown-6 ether (18C6) in THF afforded [Ln(BIPMTMS)2][K(18C6)(THF)2] [Ln = Dy, 2Dy; Y, 2Y]. AC magnetic measurements of 2Dy in zero DC field show temperature- and frequency-dependent SMM behaviour. Orbach relaxation dominates at high temperature, but at lower temperatures a second-order Raman process dominates. Complex 2Dy exhibits two thermally activated energy barriers (Ueff) of 721 and 813 K, the largest Ueff values for any monometallic dysprosium(iii) complex. Dilution experiments confirm the molecular origin of this phenomenon. Complex 2Dy has rich magnetic dynamics; field-cooled (FC)/zero-field cooled (ZFC) susceptibility measurements show a clear divergence at 16 K, meaning the magnetic observables are out-of-equilibrium below this temperature, however the maximum in ZFC, which conventionally defines the blocking temperature, TB, is found at 10 K. Magnetic hysteresis is also observed in 10% 2Dy@2Y at these temperatures. Ab initio calculations suggest the lowest three Kramers doublets of the ground 6H15/2 multiplet of 2Dy are essentially pure, well-isolated |±15/2〉, |±13/2〉 and |±11/2〉 states quantised along the CDyC axis. Thermal relaxation occurs via the 4th and 5th doublets, verified experimentally for the first time, and calculated Ueff values of 742 and 810 K compare very well to experimental magnetism and luminescence data. This work validates a design strategy towards realising high-temperature SMMs and produces unusual spin relaxation behaviour where the magnetic observables are out-of-equilibrium some 6 K above the formal blocking temperature.

Citation

Gregson, M., Chilton, N. F., Ariciu, A. M., Tuna, F., Crowe, I. F., Lewis, W., …Liddle, S. T. (2015). A monometallic lanthanide bis(methanediide) single molecule magnet with a large energy barrier and complex spin relaxation behaviour. Chemical Science, 7(1), 155-165. https://doi.org/10.1039/c5sc03111g

• Journal Article Type: Article
• Acceptance Date: Nov 20, 2015
• Online Publication Date: Nov 23, 2015
• Publication Date: Nov 23, 2015
• Deposit Date: Sep 28, 2017
• Publicly Available Date: Sep 28, 2017
• Journal: Chemical Science
• Print ISSN: 2041-6520
• Electronic ISSN: 2041-6539
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Issue: 1
• Pages: 155-165
• DOI: https://doi.org/10.1039/c5sc03111g
• Public URL: https://nottingham-repository.worktribe.com/output/765581
• Publisher URL: http://pubs.rsc.org/en/Content/ArticleLanding/2016/SC/C5SC03111G#!divAbstract
• Additional Information: : This document is Similarity Check deposited; : Supplementary Information; : Crystal Structure Data; : Nicholas F. Chilton (ORCID); : Alexander J. Blake (ORCID); : Alexander J. Blake (ResearcherID); : The Royal Society of Chemistry has an exclusive publication licence for this journal; OPEN ACCESS: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0); : Single-blind; : Received 21 August 2015; Accepted 20 November 2015; Accepted Manuscript published 23 November 2015; Advance Article published 1 December 2015; Version of Record published 14 December 2015