Special Issue "Single-Molecule Magnets"

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Inorganic Solid-State Chemistry".

Deadline for manuscript submissions: closed (30 April 2018)

Special Issue Editors

Guest Editor
Dr. Liviu Ungur

Theory of Nanomaterials Group and INPAC − Institute of Nanoscale Physics and Chemistry, KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium
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Interests: electronic structure theory; ab initio calculations; crystal and ligand field models; exchange and magnetic interactions; lanthanides; transition metals; single molecule magnets; toroidal magnetic states; magnetic relaxation
Guest Editor
Prof. Dr. Marius Andruh

Inorganic Chemistry Laboratory, Faculty of Chemistry, University of Bucharest, Str. Dumbrava Rosie 23, 020464-Bucharest, Romania
E-Mail
Phone: +40-744 8706563
Fax: +40-21-3159249
Interests: molecular magnetism; crystal engineering; metallosupramolecular chemistry
Guest Editor
Prof. Dr. Liviu F. Chibotaru

Theory of Nanomaterials Group, Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium
Website | E-Mail
Phone: +32 16 327424
Fax: +32 16 327992
Interests: molecular magnetism; magnetic anisotropy; quantum chemistry calculations; single-molecule magnets

Special Issue Information

Dear Colleagues,

Molecular magnets have been attracting increasing attention in recent years, from both experimental and theoretical perspectives. In recent years, we have witnessed significant progress in all aspects of this research area: Top level synthesis, allowing the fine tuning of the crystal field of lanthanide and transition metal compounds, accurate measurements, theoretical routes for obtaining more efficient magnets, joint efforts to solve the complicated problem of magnetic relaxation, etc. These joint efforts allowed for novel molecular magnets, displaying hysteresis at higher temperatures and significantly larger blocking barriers, for temperature-activated relaxation. However, magnetic performance of the current top-performing, single-molecular magnets is preventing their practical application in the field of information storage.The purpose of this Special Issue is to cover latest research in this field from both experimental as well as theoretical sides: Novel synthetic routes and compounds, innovative measurement techniques, as well as theoretical studies unravelling important factors, such as magnetic anisotropy, crystal field splitting, magnetic relaxation, structure–property relationships, etc. Perspectives on using existing and novel molecular magnets in neighboring research domains (quantum computing, luminescent materials, etc.) are highly welcome. 

Dr. Liviu Ungur
Prof. Dr. Marius Andruh
Prof. Dr. Liviu F. Chibotaru
Guest Editors

Manuscript Submission Information

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Keywords

  • transition metal and lanthanide chemistry
  • slow magnetic relaxation
  • magnetic anisotropy
  • exchange interaction
  • crystal (ligand) field theory
  • magnetic properties
  • ab initio calculations
  • magnetic relaxation
  • luminescence
  • metal-radical chemistry and magnetism

Published Papers (10 papers)

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Research

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Open AccessArticle Molecular Engineering of High Energy Barrier in Single-Molecule Magnets Based on [MoIII(CN)7]4− and V(II) Complexes
Received: 1 May 2018 / Revised: 25 May 2018 / Accepted: 28 May 2018 / Published: 30 May 2018
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Abstract
Molecular engineering of high energy barrier Ueff in single-molecule magnets (SMMs) of general composition MoIIIkVIIm based on orbitally-degenerate pentagonal-bipyramidal [MoIII(CN)7]4− complexes with unquenched orbital momentum and high-spin V(II) complexes is discussed. In
[...] Read more.
Molecular engineering of high energy barrier Ueff in single-molecule magnets (SMMs) of general composition MoIIIkVIIm based on orbitally-degenerate pentagonal-bipyramidal [MoIII(CN)7]4− complexes with unquenched orbital momentum and high-spin V(II) complexes is discussed. In these SMMs, the barrier originates exclusively from anisotropic Ising-type exchange interactions −Jxy(SixSjx + SiySjy) − JzSizSjz in the apical cyano-bridged pairs MoIII–CN–VII, which produce a double-well energy profile with a doubly degenerate ground spin state ±MS. It is shown that the spin-reversal barrier Ueff is controlled by anisotropic exchange parameters Jz, Jxy, and the number n of apical MoIII–CN–VII groups in a SMM cluster, Ueff ~ 0.5|JzJxy|n; it can reach a value of many hundreds of wavenumbers (up to 741 cm−1). This finding provides a very efficient straightforward strategy for further scaling Ueff to high values (>1000 cm−1) by means of enhancing exchange parameters Jz, Jxy, and increasing the number of [MoIII(CN)7]4− complexes in a SMM molecule. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessArticle The Exploration and Analysis of the Magnetic Relaxation Behavior in Three Isostructural Cyano-Bridged 3d–4f Linear Heterotrinuclear Compounds
Received: 23 January 2018 / Revised: 19 March 2018 / Accepted: 20 March 2018 / Published: 22 March 2018
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Abstract
Three isostructural cyano-bridged 3d–4f linear heterotrinuclear compounds, (H2.5O)4{Ln[TM(CN)5(CNH0.5)]2(HMPA)4} (Ln = YIII, TM = [FeIII]LS (1); Ln = DyIII, TM = [FeIII
[...] Read more.
Three isostructural cyano-bridged 3d–4f linear heterotrinuclear compounds, (H2.5O)4{Ln[TM(CN)5(CNH0.5)]2(HMPA)4} (Ln = YIII, TM = [FeIII]LS (1); Ln = DyIII, TM = [FeIII]LS (2); Ln = DyIII, TM = CoIII (3)), have been synthesized and characterized by single-crystal X-ray diffraction. Due to the steric effect of the HMPA ligands, the central lanthanide ions in these compounds possess a low coordination number, six-coordinate, exhibiting a coordination geometry of an axially elongated octahedron with a perfect D4h symmetry. Four HMPA ligands situate in the equatorial plane around the central lanthanide ions, and two [TM(CN)5(CNH0.5)]2.5− entities occupy the apical positions to form a cyano-bridged 3d–4f linear heterotrinuclear structure. The static magnetic analysis of the three compounds indicated a paramagnetic behavior of compounds 1 and 3, and possible small magnetic interactions between the intramolecular DyIII and [FeIII]LS ions in compound 2. Under zero dc field, the ac magnetic measurements on 2 and 3 revealed the in-phase component (χ′) of the ac susceptibility without frequency dependence and silent out-of-phase component (χ″), which was attributed to the QTM effect induced by the coordination geometry of an axially elongated octahedron for the DyIII ion. Even under a 1 kOe applied dc field, the χ″ components of 2 were revealed frequency dependence without peaks above 2 K. And under a 2 kOe and 3 kOe dc field, the χ″ components of 3 exhibited weak frequency dependence below 4 K with the absence of well-shaped peaks, which confirmed the poor single-ion magnetic relaxation behavior of the six-coordinate DyIII ion excluding any influence from the neighboring [FeIII]LS ions as that in the analogue 2. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessArticle Field-Induced Slow Relaxation in a Dinuclear Dysprosium(III) Complex Based on 3-Methoxycinnamic Acid
Received: 29 November 2017 / Revised: 2 February 2018 / Accepted: 23 February 2018 / Published: 20 March 2018
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Abstract
We report the synthesis, structure, and magnetic properties of a new dinuclear dysprosium(III) complex based on a 3-methoxycinnamate ligand. The centrosymmetric complex exhibits a field-induced SMM behavior. In contrast to the previously reported lanthanide-based systems with cinnamate derivatives that relax through a combination
[...] Read more.
We report the synthesis, structure, and magnetic properties of a new dinuclear dysprosium(III) complex based on a 3-methoxycinnamate ligand. The centrosymmetric complex exhibits a field-induced SMM behavior. In contrast to the previously reported lanthanide-based systems with cinnamate derivatives that relax through a combination of Raman and direct processes, an Orbach process is also involved in highlighting the role of the structural organization over the spin-lattice relaxations. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessArticle Effect of Low Spin Excited States for Magnetic Anisotropy of Transition Metal Mononuclear Single Molecule Magnets
Received: 14 December 2017 / Revised: 17 January 2018 / Accepted: 25 January 2018 / Published: 27 January 2018
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Abstract
Rational, fine tuning of magnetic anisotropy is critical to obtain new coordination compounds with enhanced single molecule magnet properties. For mononuclear transition metal complexes, the largest contribution to zero-field splitting is usually related to the excited states of the same spin as the
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Rational, fine tuning of magnetic anisotropy is critical to obtain new coordination compounds with enhanced single molecule magnet properties. For mononuclear transition metal complexes, the largest contribution to zero-field splitting is usually related to the excited states of the same spin as the ground level. Thus, the contribution of lower multiplicity roots tends to be overlooked due to its lower magnitude. In this article, we explore the role of lower multiplicity excited states in zero-field splitting parameters in model structures of Fe(II) and Co(II). Model aquo complexes with coordination numbers ranging from 2 to 6 were constructed. The magnetic anisotropy was calculated by state of the art ab initio methodologies, including spin-orbit coupling effects. For non-degenerate ground states, contributions to the zero-field splitting parameter (D) from highest and lower multiplicity roots were of the same sign. In addition, their relative magnitude was in a relatively narrow range, irrespective of the coordination geometry. For degenerate ground states, the contribution from lower multiplicity roots was significantly smaller. Results are rationalized in terms of general expressions for D and are expected to be reasonably transferable to real molecular systems. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessArticle Six-Coordinate Ln(III) Complexes with Various Coordination Geometries Showing Distinct Magnetic Properties
Received: 29 November 2017 / Revised: 14 January 2018 / Accepted: 15 January 2018 / Published: 18 January 2018
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Abstract
The syntheses, structural characterization, and magnetic properties of three lanthanide complexes with formulas [Ln(L1)3] (Ln = Dy (1Dy); Er (1Er)); and [Dy(L2)2] (2Dy) were reported. Complexes 1Dy and 1Er
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The syntheses, structural characterization, and magnetic properties of three lanthanide complexes with formulas [Ln(L1)3] (Ln = Dy (1Dy); Er (1Er)); and [Dy(L2)2] (2Dy) were reported. Complexes 1Dy and 1Er are isostructural with the metal ion in distorted trigonal-prismatic coordination geometry, but exhibit distinct magnetic properties due to the different shapes of electron density for DyIII (oblate) and ErIII (prolate) ions. Complex 1Dy shows obvious SMM behavior under a zero direct current (dc) field with an effective energy barrier of 31.4 K, while complex 1Er only features SMM behavior under a 400 Oe external field with an effective energy barrier of 23.96 K. In stark contrast, complex 2Dy with the octahedral geometry only exhibits the frequency dependence of alternating current (ac) susceptibility signals without χ″ peaks under a zero dc field. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessArticle Photo-Modulation of Single-Molecule Magnetic Dynamics of a Dysprosium Dinuclear Complex via a Diarylethene Bridge
Received: 30 November 2017 / Revised: 11 December 2017 / Accepted: 28 December 2017 / Published: 2 January 2018
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Abstract
A photo-switchable single molecule-magnet (SMM) with two Dy ions bridged by a bis-bipyridine-dithienylethene ligand was synthesised. Isomerisation effects on the magnetic properties were investigated. Particular attention was paid to the slow relaxation of the magnetisation in order to determine precisely the role played
[...] Read more.
A photo-switchable single molecule-magnet (SMM) with two Dy ions bridged by a bis-bipyridine-dithienylethene ligand was synthesised. Isomerisation effects on the magnetic properties were investigated. Particular attention was paid to the slow relaxation of the magnetisation in order to determine precisely the role played by the ligand. Photo-isomerization of the ligand induced a geometric rearrangement of the complex and an electronic reconfiguration. The changes were studied by solid and solution state magnetic measurements. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessArticle Field-Induced Slow Magnetic Relaxation of Mono- and Dinuclear Dysprosium(III) Complexes Coordinated by a Chloranilate with Different Resonance Forms
Received: 14 November 2017 / Revised: 15 December 2017 / Accepted: 28 December 2017 / Published: 30 December 2017
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Abstract
We synthesized the dinuclear and mononuclear dysprosium(III) complexes [{Dy(Tp)2}2(Cl2An)]·2CH2Cl2 (1) and [Co(Cp)2][Dy(Tp)2(Cl2An)] (3), where Cl2An2− and Tp are the chloranilate
[...] Read more.
We synthesized the dinuclear and mononuclear dysprosium(III) complexes [{Dy(Tp)2}2(Cl2An)]·2CH2Cl2 (1) and [Co(Cp)2][Dy(Tp)2(Cl2An)] (3), where Cl2An2− and Tp are the chloranilate and hydrotris(pyrazolyl)borate ligand, respectively. In addition, the magnitude of the magnetic coupling between the lanthanide centers through the Cl2An2− bridge has been probed through the synthesis of [{Gd(Tp)2}2(Cl2An)]·2CH2Cl2 (2), which is a gadolinium(III) analogue of 1. Complexes 13 were characterized by infrared (IR) spectroscopy, elemental analysis, single-crystal X-ray diffraction, and SQUID measurements. IR and single-crystal X-ray structural analyses confirm that the coordination environments of the lanthanide(III) centers in 1 and 3 are similar to each other; i.e., eight-coordinated metal centers, each occupied by an N6O2 donor set from two Tp ligands and one Cl2An2− ligand. The coordination geometries of the lanthanide(III) centers in 1 and 2 are distorted triangular dodecahedral, while that in the mononuclear complex 3 is square antiprismatic, where the Cl2An2− ligand takes the bi-separated delocalized form in 1 and 2, and the o-quinone form in 3. Alternating-current (AC) magnetic studies clearly reveal that both 1 and 3 exhibit field-induced slow relaxations of magnetization that occur via Raman and direct processes. Complexes 1 and 3 exhibit different spin relaxation behavior, which reflects the coordination geometry around each DyIII center and its nuclearity, as well as the molecular packing in the crystal lattice. Although the magnetic analysis of 2 revealed negligible magnetic coupling, Cl2An2− bridges with small biases may form in the dinuclear complexes, which play roles in the spin relaxation dynamics through dipolar interactions. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessArticle Field-Induced Single-Ion Magnet Behaviour in Two New Cobalt(II) Coordination Polymers with 2,4,6-Tris(4-pyridyl)-1,3,5-triazine
Received: 28 November 2017 / Revised: 10 December 2017 / Accepted: 11 December 2017 / Published: 15 December 2017
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Abstract
We herein reported the syntheses, crystal structures, and magnetic properties of a two-dimensional coordination polymer {[CoII(TPT)2/3(H2O)4][CH3COO]2·(H2O)4}n (1) and a chain compound {[CoII(TPT)
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We herein reported the syntheses, crystal structures, and magnetic properties of a two-dimensional coordination polymer {[CoII(TPT)2/3(H2O)4][CH3COO]2·(H2O)4}n (1) and a chain compound {[CoII(TPT)2(CHOO)2(H2O)2]}n (2) based on the 2,4,6-Tris(4-pyridyl)-1,3,5-triazine (TPT) ligand. Structure analyses showed that complex 1 had a cationic hexagonal framework structure, while 2 was a neutral zig-zag chain structure with different distorted octahedral coordination environments. Magnetic measurements revealed that both complexes exhibit large easy-plane magnetic anisotropy with the zero-field splitting parameter D = 47.7 and 62.1 cm−1 for 1 and 2, respectively. This magnetic anisotropy leads to the field-induced slow magnetic relaxation behaviour. However, their magnetic dynamics are quite different; while complex 1 experienced a dominating thermally activated Orbach relaxation at the whole measured temperature region, 2 exhibited multiple relaxation pathways involving direct, Raman, and quantum tunneling (QTM) processes at low temperatures and Orbach relaxation at high temperatures. The present complexes enlarge the family of framework-based single-ion magnets (SIMs) and highlight the significance of the structural dimensionality to the final magnetic properties. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Review

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Open AccessReview Ferromagnetic Cluster Spin Wave Theory: Concepts and Applications to Magnetic Molecules
Received: 23 March 2018 / Revised: 14 May 2018 / Accepted: 16 May 2018 / Published: 19 May 2018
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Abstract
Ferromagnetic cluster spin wave theory (FCSWT) provides an exact and concise description of the low-energy excitations from the ferromagnetic ground state in finite magnetic systems, such as bounded magnetic molecules. In particular, this theory is applicable to the description of experimental inelastic neutron
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Ferromagnetic cluster spin wave theory (FCSWT) provides an exact and concise description of the low-energy excitations from the ferromagnetic ground state in finite magnetic systems, such as bounded magnetic molecules. In particular, this theory is applicable to the description of experimental inelastic neutron scattering (INS) spectra at low temperatures. We provide a detailed conceptual overview of the FCSWT. Additionally, we introduce a pictorial representation of calculated wavefunctions, similar to the usual depiction of vibrational normal modes in molecules. We argue that this representation leads to a better intuitive understanding of the excitations, their symmetry properties, and has links to the energy and wavevector dependence of intensity in the neutron scattering experiments. We apply FCSWT and illustrate the results on a series of examples with available low-temperature INS data, ranging from the Mn10 supertetrahedron, the Mn7 disk to the Mn6 single molecule magnet. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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Open AccessReview Future Directions for Transuranic Single Molecule Magnets
Received: 18 January 2018 / Revised: 6 February 2018 / Accepted: 8 February 2018 / Published: 13 February 2018
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Abstract
Single Molecule Magnets (SMMs) based on transition metals and rare earths have been the object of considerable attention for the past 25 years. These systems exhibit slow relaxation of the magnetization, arising from a sizeable anisotropy barrier, and magnetic hysteresis of purely molecular
[...] Read more.
Single Molecule Magnets (SMMs) based on transition metals and rare earths have been the object of considerable attention for the past 25 years. These systems exhibit slow relaxation of the magnetization, arising from a sizeable anisotropy barrier, and magnetic hysteresis of purely molecular origin below a given blocking temperature. Despite initial predictions that SMMs based on 5f-block elements could outperform most others, the results obtained so far have not met expectations. Exploiting the versatile chemistry of actinides and their favorable intrinsic magnetic properties proved, indeed, to be more difficult than assumed. However, the large majority of studies reported so far have been dedicated to uranium molecules, thus leaving the largest part of the 5f-block practically unexplored. Here, we present a short review of the progress achieved up to now and discuss some options for a possible way forward. Full article
(This article belongs to the Special Issue Single-Molecule Magnets)
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