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Tian H, Ungur L, Zhao L, Ding S, Tang J, Chibotaru LF. Exchange Interactions Switch Tunneling: A Comparative Experimental and Theoretical Study on Relaxation Dynamics by Targeted Metal Ion Replacement. Chemistry 2018; 24:9928-9939. [PMID: 29697161 DOI: 10.1002/chem.201801523] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Indexed: 11/12/2022]
Abstract
The magnetic relaxation and magnetization blocking barriers of tailor-made homo- and heterodinuclear compounds [Dy2 (opch)2 (OAc)2 (H2 O)2 ]⋅MeOH (1) and [DyMn(opch)2 (OAc)(MeOH)(H2 O)2 ] (2), where H2 opch is (E)-N'-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide, were systematically investigated and the change in single-molecule magnet behavior originating from targeted replacement of one dysprosium site in the Dy2 compound with manganese was elucidated through a combination of experimental and theoretical studies. A detailed comparative study on these closely related model compounds revealed remarkable changes of the crystal-field splitting and anisotropy of the Dy site and the total exchange spectrum due to the replacement of Dy by Mn. The blocking barriers of these two compounds, which explain their different relaxation behaviors, were analyzed. The two Ising doublets arising from the magnetic interaction in the case of 1 are strongly uniaxial, with tunneling splittings smaller than 10-6 cm-1 , and this leads to magnetic relaxation at temperatures exceeding the exchange energy (2.14 cm-1 ), which involves transition via the excited states corresponding to local transitions on the excited doublet at the Dy site. The third and fourth exchange doublets in 2 (located at 2.16 and 3.25 cm-1 , respectively) show much larger tunneling splittings (of 10-4 and 10-3 cm-1 , respectively), and thus open an important path for magnetic relaxation.
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Latendresse TP, Vieru V, Wilkins BO, Bhuvanesh NS, Chibotaru LF, Nippe M. Magnetic Properties of a Terbium–[1]Ferrocenophane Complex: Analogies between Lanthanide–Ferrocenophane and Lanthanide–Bis‐phthalocyanine Complexes. Angew Chem Int Ed Engl 2018; 57:8164-8169. [DOI: 10.1002/anie.201804075] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 05/04/2018] [Indexed: 11/10/2022]
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Latendresse TP, Vieru V, Wilkins BO, Bhuvanesh NS, Chibotaru LF, Nippe M. Magnetic Properties of a Terbium–[1]Ferrocenophane Complex: Analogies between Lanthanide–Ferrocenophane and Lanthanide–Bis‐phthalocyanine Complexes. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201804075] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Zhang X, Liu S, Vieru V, Xu N, Gao C, Wang BW, Shi W, Chibotaru LF, Gao S, Cheng P, Powell AK. Frontispiece: Coupling Influences SMM Properties for Pure 4 f Systems. Chemistry 2018. [DOI: 10.1002/chem.201882364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Zhang X, Liu S, Vieru V, Xu N, Gao C, Wang BW, Shi W, Chibotaru LF, Gao S, Cheng P, Powell AK. Coupling Influences SMM Properties for Pure 4 f Systems. Chemistry 2018; 24:6079-6086. [DOI: 10.1002/chem.201705350] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2017] [Indexed: 02/03/2023]
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Mansikkamäki A, Popov AA, Deng Q, Iwahara N, Chibotaru LF. Interplay of spin-dependent delocalization and magnetic anisotropy in the ground and excited states of [Gd 2@C 78] - and [Gd 2@C 80] . J Chem Phys 2017; 147:124305. [PMID: 28964020 DOI: 10.1063/1.5004183] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The magnetic properties and electronic structure of the ground and excited states of two recently characterized endohedral metallo-fullerenes, [Gd2@C78]- (1) and [Gd2@C80]- (2), have been studied by theoretical methods. The systems can be considered as [Gd2]5+ dimers encapsulated in a fullerene cage with the fifteen unpaired electrons ferromagnetically coupled into an S = 15/2 high-spin configuration in the ground state. The microscopic mechanisms governing the Gd-Gd interactions leading to the ferromagnetic ground state are examined by a combination of density functional and ab initio calculations and the full energy spectrum of the ground and lowest excited states is constructed by means of ab initio model Hamiltonians. The ground state is characterized by strong electron delocalization bordering on a σ type one-electron covalent bond and minor zero-field splitting (ZFS) that is successfully described as a second order spin-orbit coupling effect. We have shown that the observed ferromagnetic interaction originates from Hund's rule coupling and not from the conventional double exchange mechanism. The calculated ZFS parameters of 1 and 2 in their optimized geometries are in qualitative agreement with experimental EPR results. The higher excited states display less electron delocalization, but at the same time they possess unquenched first-order angular momentum. This leads to strong spin-orbit coupling and highly anisotropic energy spectrum. The analysis of the excited states presented here constitutes the first detailed study of the effects of spin-dependent delocalization in the presence of first order orbital angular momentum and the obtained results can be applied to other mixed valence lanthanide systems.
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Chen YC, Liu JL, Lan Y, Zhong ZQ, Mansikkamäki A, Ungur L, Li QW, Jia JH, Chibotaru LF, Han JB, Wernsdorfer W, Chen XM, Tong ML. Cover Picture: Dynamic Magnetic and Optical Insight into a High Performance Pentagonal Bipyramidal Dy III
Single-Ion Magnet (Chem. Eur. J. 24/2017). Chemistry 2017. [DOI: 10.1002/chem.201700763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Chen YC, Liu JL, Wernsdorfer W, Liu D, Chibotaru LF, Chen XM, Tong ML. Inside Cover: Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet (Angew. Chem. Int. Ed. 18/2017). Angew Chem Int Ed Engl 2017. [DOI: 10.1002/anie.201702921] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Chen YC, Liu JL, Wernsdorfer W, Liu D, Chibotaru LF, Chen XM, Tong ML. Innentitelbild: Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet (Angew. Chem. 18/2017). Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201702921] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Chen YC, Liu JL, Wernsdorfer W, Liu D, Chibotaru LF, Chen XM, Tong ML. Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201701480] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Chen YC, Liu JL, Wernsdorfer W, Liu D, Chibotaru LF, Chen XM, Tong ML. Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet. Angew Chem Int Ed Engl 2017; 56:4996-5000. [PMID: 28295930 DOI: 10.1002/anie.201701480] [Citation(s) in RCA: 147] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Indexed: 11/09/2022]
Abstract
An extremely rare non-Kramers holmium(III) single-ion magnet (SIM) is reported to be stabilized in the pentagonal-bipyramidal geometry by a phosphine oxide with a high energy barrier of 237(4) cm-1 . The suppression of the quantum tunneling of magnetization (QTM) at zero field and the hyperfine structures originating from field-induced QTMs can be observed even from the field-dependent alternating-current magnetic susceptibility in addition to single-crystal hysteresis loops. These dramatic dynamics were attributed to the combination of the favorable crystal-field environment and the hyperfine interactions arising from 165 Ho (I=7/2) with a natural abundance of 100 %.
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Chen YC, Liu JL, Lan Y, Zhong ZQ, Mansikkamäki A, Ungur L, Li QW, Jia JH, Chibotaru LF, Han JB, Wernsdorfer W, Chen XM, Tong ML. Dynamic Magnetic and Optical Insight into a High-Performance Pentagonal Bipyramidal DyIII
Single-Ion Magnet. Chemistry 2017. [DOI: 10.1002/chem.201700803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Chen YC, Liu JL, Lan Y, Zhong ZQ, Mansikkamäki A, Ungur L, Li QW, Jia JH, Chibotaru LF, Han JB, Wernsdorfer W, Chen XM, Tong ML. Dynamic Magnetic and Optical Insight into a High Performance Pentagonal Bipyramidal DyIII
Single-Ion Magnet. Chemistry 2017; 23:5708-5715. [DOI: 10.1002/chem.201606029] [Citation(s) in RCA: 81] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Indexed: 11/07/2022]
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Ungur L, Chibotaru LF. Ab Initio Crystal Field for Lanthanides. Chemistry 2017; 23:3708-3718. [DOI: 10.1002/chem.201605102] [Citation(s) in RCA: 189] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Indexed: 11/10/2022]
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Long J, Shestakov BG, Liu D, Chibotaru LF, Guari Y, Cherkasov AV, Fukin GK, Trifonov AA, Larionova J. An organolanthanide(iii) single-molecule magnet with an axial crystal-field: influence of the Raman process over the slow relaxation. Chem Commun (Camb) 2017; 53:4706-4709. [DOI: 10.1039/c7cc02213a] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report the synthesis and magnetic properties of a series of new organometallic homoleptic complexes Li(DME)3[Ln(DAD)2] (Ln = Dy (1a, 1b), Tb(2), and Er(3)).
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Zhang K, Liu D, Vieru V, Hou L, Cui B, Guo FS, Chibotaru LF, Wang YY. Transitions of two magnetic interaction states in dinuclear Dy(iii) complexes via subtle structural variations. Dalton Trans 2017; 46:638-642. [DOI: 10.1039/c6dt04490e] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Herein we explored the transitions of two magnetic interaction states (antiferromagnetic or ferromagnetic) upon structural variations in two dinuclear Dy(iii) complexes.
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Moilanen JO, Mansikkamäki A, Lahtinen M, Guo FS, Kalenius E, Layfield RA, Chibotaru LF. Thermal expansion and magnetic properties of benzoquinone-bridged dinuclear rare-earth complexes. Dalton Trans 2017; 46:13582-13589. [DOI: 10.1039/c7dt02565c] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The complexes [BQ(MCl2·THF3)2] (M = Y or Dy) possessing pentagonal bipyramidal environment around metal centers undergo significant thermal expansion as revealed by single-crystal X-ray and powder diffraction experiments.
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Vieru V, Pasatoiu TD, Ungur L, Suturina E, Madalan AM, Duhayon C, Sutter JP, Andruh M, Chibotaru LF. Synthesis, Crystal Structures, Magnetic Properties, and Theoretical Investigation of a New Series of NiII–LnIII–WV Heterotrimetallics: Understanding the SMM Behavior of Mixed Polynuclear Complexes. Inorg Chem 2016; 55:12158-12171. [DOI: 10.1021/acs.inorgchem.6b01669] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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Iwahara N, Chibotaru LF. Orbital disproportionation of electronic density is a universal feature of alkali-doped fullerides. Nat Commun 2016; 7:13093. [PMID: 27713426 PMCID: PMC5059769 DOI: 10.1038/ncomms13093] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 09/01/2016] [Indexed: 11/09/2022] Open
Abstract
Alkali-doped fullerides show a wide range of electronic phases in function of alkali atoms and the degree of doping. Although the presence of strong electron correlations is well established, recent investigations also give evidence for dynamical Jahn–Teller instability in the insulating and the metallic trivalent fullerides. In this work, to reveal the interplay of these interactions in fullerides with even electrons, we address the electronic phase of tetravalent fulleride with accurate many-body calculations within a realistic electronic model including all basic interactions extracted from first principles. We find that the Jahn–Teller instability is always realized in these materials too. In sharp contrast to the correlated metals, tetravalent system displays uncorrelated band-insulating state despite similar interactions present in both fullerides. Our results show that the Jahn–Teller instability and the accompanying orbital disproportionation of electronic density in the degenerate lowest unoccupied molecular orbital band is a universal feature of fullerides. Understanding the electronic phases of alkali-doped fullerides is a long-standing and challenging task for material scientists. Here the authors show that Jahn-Teller instability and orbital disproportionation of electronic density in the lowest unoccupied molecular orbital band is universal in these systems.
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Ungur L, Chibotaru LF. Strategies toward High-Temperature Lanthanide-Based Single-Molecule Magnets. Inorg Chem 2016; 55:10043-10056. [PMID: 27508399 DOI: 10.1021/acs.inorgchem.6b01353] [Citation(s) in RCA: 276] [Impact Index Per Article: 34.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Lanthanide-based single-molecule magnets are leading materials for achieving magnetization blocking at the level of one molecule. In this paper, we examine the physical requirements for efficient magnetization blocking in single-ion complexes and identify the design principles for achieving very high magnetization blocking barriers in lanthanide-based compounds. The key condition is the preponderant covalent binding of the Ln ion to one of the ligand atoms, tremendously enhancing the axial crystal field. We also make an overview of practical schemes for the implementation of this principle. These are (1) the effective lowering of the coordination number via displacement of the Ln ion to one of the atoms in the coordination polyhedron, (2) the design of two-coordinated complexes, and (3) the stabilization of diatomic compounds in cages and on surfaces. The last proposal is appealing in connection to spintronics applications, especially via the exploration of robust and highly anisotropic [LnX] units displaying multilevel blocking barriers of thousands of Kelvin and prospects for room-temperature magnetization blocking.
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Iwahara N, Chibotaru LF. New mechanism of kinetic exchange interaction induced by strong magnetic anisotropy. Sci Rep 2016; 6:24743. [PMID: 27098292 PMCID: PMC4838874 DOI: 10.1038/srep24743] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 04/04/2016] [Indexed: 11/09/2022] Open
Abstract
It is well known that the kinetic exchange interaction between single-occupied magnetic orbitals (s-s) is always antiferromagnetic, while between single- and double-occupied orbitals (s-d) is always ferromagnetic and much weaker. Here we show that the exchange interaction between strongly anisotropic doublets of lanthanides, actinides and transition metal ions with unquenched orbital momentum contains a new s-d kinetic contribution equal in strength with the s-s one. In non-collinear magnetic systems, this s-d kinetic mechanism can cause an overall ferromagnetic exchange interaction which can become very strong for transition metal ions. These findings are fully confirmed by DFT based analysis of exchange interaction in several Ln(3+) complexes.
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Liu J, Chen YC, Liu JL, Vieru V, Ungur L, Jia JH, Chibotaru LF, Lan Y, Wernsdorfer W, Gao S, Chen XM, Tong ML. A Stable Pentagonal Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K. J Am Chem Soc 2016; 138:5441-50. [PMID: 27054904 DOI: 10.1021/jacs.6b02638] [Citation(s) in RCA: 770] [Impact Index Per Article: 96.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Single-molecule magnets (SMMs) with a large spin reversal barrier have been recognized to exhibit slow magnetic relaxation that can lead to a magnetic hysteresis loop. Synthesis of highly stable SMMs with both large energy barriers and significantly slow relaxation times is challenging. Here, we report two highly stable and neutral Dy(III) classical coordination compounds with pentagonal bipyramidal local geometry that exhibit SMM behavior. Weak intermolecular interactions in the undiluted single crystals are first observed for mononuclear lanthanide SMMs by micro-SQUID measurements. The investigation of magnetic relaxation reveals the thermally activated quantum tunneling of magnetization through the third excited Kramers doublet, owing to the increased axial magnetic anisotropy and weaker transverse magnetic anisotropy. As a result, pronounced magnetic hysteresis loops up to 14 K are observed, and the effective energy barrier (Ueff = 1025 K) for relaxation of magnetization reached a breakthrough among the SMMs.
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Vieru V, Chibotaru LF. Redox Switches for Single-Molecule Magnet Activity: An Ab Initio Insight. Chemistry 2016; 22:5309-18. [PMID: 26918833 DOI: 10.1002/chem.201504490] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Indexed: 11/11/2022]
Abstract
A dinuclear Co(II) complex (1) featuring unprecedented anodic and cathodic switches for single-molecule magnet (SMM) activity has been recently investigated (J. Am. Chem. Soc. 2013, 135, 14670). The presence of sandwiched radicals in different oxidation states of this compound mediates magnetic coupling between the high-spin (S=3/2) cobalt ions, which gives rise to SMM activity in both the oxidized ([1(OEt2)](+)) and reduced ([1](-)) states. This feature represents the first example of a SMM exhibiting fully reversible, dual ON/OFF switchability. Here we apply ab initio and broken-symmetry DFT calculations to elucidate the mechanisms responsible for magnetic properties and magnetization blocking in these compounds. It is found that due to the strong delocalization of the magnetic molecular orbital, there is a strong antiferromagnetic interaction between the radical and cobalt ions. The lack of high axiality of the cobalt centres explains why these compounds possess slow relaxation of magnetization only in an applied dc magnetic field.
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Gysler M, El Hallak F, Ungur L, Marx R, Hakl M, Neugebauer P, Rechkemmer Y, Lan Y, Sheikin I, Orlita M, Anson CE, Powell AK, Sessoli R, Chibotaru LF, van Slageren J. Multitechnique investigation of Dy 3 - implications for coupled lanthanide clusters. Chem Sci 2016; 7:4347-4354. [PMID: 30155081 PMCID: PMC6013819 DOI: 10.1039/c6sc00318d] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 03/16/2016] [Indexed: 11/21/2022] Open
Abstract
Torque magnetometry and far-infrared spectroscopy elucidate electronic structure and magnetic properties of Dy3 single molecule magnet.
In-depth investigations of the low energy electronic structures of mononuclear lanthanide complexes, including single molecule magnets, are challenging at the best of times. For magnetically coupled polynuclear systems, the task seems well nigh impossible. However, without detailed understanding of the electronic structure, there is no hope of understanding their static and dynamic magnetic properties in detail. We have been interested in assessing which techniques are most appropriate for studying lanthanide single-molecule magnets. Here we present a wide ranging theoretical and experimental study of the archetypal polynuclear lanthanide single-molecule magnet Dy3 and derive the simplest model to describe the results from each experimental method, including high-frequency electron paramagnetic resonance and far-infrared spectroscopies and cantilever torque magnetometry. We conclude that a combination of these methods together with ab initio calculations is required to arrive at a full understanding of the properties of this complex, and potentially of other magnetically coupled lanthanide complexes.
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Pugh T, Vieru V, Chibotaru LF, Layfield RA. Magneto-structural correlations in arsenic- and selenium-ligated dysprosium single-molecule magnets. Chem Sci 2016; 7:2128-2137. [PMID: 29899940 PMCID: PMC5968533 DOI: 10.1039/c5sc03755g] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Accepted: 12/15/2015] [Indexed: 11/21/2022] Open
Abstract
The structures and magnetic properties of the arsenic- and selenium-ligated dysprosium single-molecule magnets (SMMs) [Cp'3Dy(AsH2Mes)] (3-Dy), [(η5-Cp'2Dy){μ-As(H)Mes}]3 (4-Dy), [Li(thf)4]2[(η5-Cp'2Dy)3(μ3-AsMes)3Li] ([Li(thf)4]2[5-Dy]), and [(η5-Cp'2Dy){μ-SeMes}]3 (6-Dy) are described. The arsenic-ligated complexes 4-Dy and 5-Dy are the first SMMs to feature ligands with metalloid elements as the donor atoms. The arsenide-ligated complex 4-Dy and the selenolate-ligated complex 6-Dy show large anisotropy barriers in the region of 250 cm-1 in zero d.c. field, increasing to 300 cm-1 upon 5% magnetic dilution. Theoretical studies reveal that thermal relaxation in these SMMs occurs via the second-excited Kramers' doublet. In contrast, the arsinidene-ligated SMM 5-Dy gives a much smaller barrier of 23 cm-1, increasing to 35 cm-1 upon dilution. The field-dependence of the magnetization for 4-Dy and 5-Dy at 1.8 K show unusual plateaus around 10 kOe, which is due to the dominance of arsenic-mediated exchange over the dipolar exchange. The effects of the exchange interactions are more pronounced in 5-Dy, which is a consequence of a small but significant increase in the covalent contribution to the predominantly ionic dysprosium-arsenic bonds. Whereas the magnetically non-dilute dysprosium SMMs show only very narrow magnetization versus field hysteresis loops at 1.8 K, the impact of magnetic dilution is dramatic, with butterfly-shaped loops being observed up to 5.4 K in the case of 4-Dy. Our findings suggest that ligands with heavier p-block element donor atoms have considerable potential to be developed more widely for applications in molecular magnetism.
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