scholarly journals Effect of Ligand Substitution on the Exchange Interactions in {Mn12}-Type Single-Molecule Magnets

2010 ◽  
Vol 49 (23) ◽  
pp. 10902-10906 ◽  
Author(s):  
Danil W. Boukhvalov ◽  
Viatcheslav V. Dobrovitski ◽  
Paul Kögerler ◽  
Mohammad Al-Saqer ◽  
Mikhail I. Katsnelson ◽  
...  
Keyword(s):  
Single Molecule ◽  
Exchange Interactions ◽  
Ligand Substitution ◽  
Single Molecule Magnets

Anisotropy barrier enhancement via ligand substitution in tetranuclear {CoIII2LnIII2} single molecule magnets

2013 ◽  
Vol 49 (62) ◽  
pp. 6965 ◽  
Author(s):  
Stuart K. Langley ◽  
Nicholas F. Chilton ◽  
Boujemaa Moubaraki ◽  
Keith S. Murray
Keyword(s):  
Single Molecule ◽  
Ligand Substitution ◽  
Single Molecule Magnets

scholarly journals Energy-Barrier Enhancement by Ligand Substitution in Tetrairon(III) Single-Molecule Magnets

2004 ◽  
Vol 116 (9) ◽  
pp. 1156-1159 ◽  
Author(s):  
Andrea Cornia ◽  
Antonio C. Fabretti ◽  
Pierfrancesco Garrisi ◽  
Cecilia Mortalò ◽  
Daniele Bonacchi ◽  
...  
Keyword(s):  
Single Molecule ◽  
Energy Barrier ◽  
Ligand Substitution ◽  
Single Molecule Magnets

Mixed valency in polynuclear Mn II /Mn III , Mn III /Mn IV and Mn II /Mn III /Mn IV clusters: a foundation for high-spin molecules and single-molecule magnets

2007 ◽  
Vol 366 (1862) ◽  
pp. 113-125 ◽  
Author(s):  
Theocharis C Stamatatos ◽  
George Christou
Keyword(s):  
Single Molecule ◽  
Exchange Interactions ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Single Molecule Magnets ◽  
Zero Field Splitting Parameter ◽  
Jahn Teller ◽  
Splitting Parameter ◽  
Molecular Spin ◽  
Molecular Compounds

Mixed-valent Mn/O dinuclear and polynuclear molecular compounds containing Mn III are almost without exception trapped valence. Large differences between the strengths of the exchange interactions within Mn II Mn III , Mn III Mn III and Mn III Mn IV pairs lead to situations where Mn III Mn IV interactions, the strongest of the three mentioned and antiferromagnetic in nature, dominate the intramolecular spin alignments in trinuclear and higher nuclearity mixed-valent complexes and often result in molecules that have large, and sometimes abnormally large, values of molecular spin ( S ). When coupled to a large molecular magnetoanisotropy of the easy-axis-type (negative zero-field splitting parameter, D ), also primarily resulting from individual Jahn–Teller distorted Mn III centres, such molecules will function as single-molecule magnets (molecular nanomagnets). Dissection of the structures and exchange interactions within a variety of mixed-valent Mn x cluster molecules with metal nuclearities of Mn 4 , Mn 12 and Mn 25 allows a ready rationalization of the observed S , D and overall magnetic properties in terms of competing antiferromagnetic exchange interactions within triangular subunits, resulting spin alignments and relative orientation of Mn III JT axes. Such an understanding has provided a stepping stone to the identification of a ‘magnetically soft’ Mn 25 cluster whose groundstate spin S value can be significantly altered by relatively minor structural perturbations. Such ‘spin tweaking’ has allowed this cluster to be obtained in three different forms with three different groundstate S values.

Ferromagnetic [Mn3] Single-Molecule Magnets and Their Supramolecular Networks

2009 ◽  
Vol 62 (9) ◽  
pp. 1108 ◽  
Author(s):  
Ross Inglis ◽  
Giannis S. Papaefstathiou ◽  
Wolfgang Wernsdorfer ◽  
Euan K. Brechin
Keyword(s):  
Single Molecule ◽  
Quantum Physics ◽  
Three Dimensional ◽  
Exchange Interactions ◽  
Molecular Magnets ◽  
Single Molecule Magnets ◽  
Spin Networks ◽  
Quantum Tunnelling ◽  
Field Bias ◽  
Supramolecular Networks

The complexes [MnIII3O(Et-sao)3(O2CPh(Cl)2)(MeOH)3(H2O)] (1), [MnIII3O(Et-sao)3(ClO4)(MeOH)3] (2), [MnIII3O(Et-sao)3(O2Ph(CF3)2)(EtOH)(H2O)3] (3), and [MnIII3O(Ph-sao)3(O2C-anthra)(MeOH)4]·Ph-saoH2 (4·Ph-saoH2) display dominant ferromagnetic exchange interactions leading to molecules with S = 6 ground states. The molecules are single molecule magnets (SMM) displaying large effective energy barriers for magnetization reversal. In each case their crystal structures reveal multiple intermolecular H-bonding interactions. Single crystal hysteresis loop measurements demonstrate that these interactions are strong enough to cause a clear field bias, but too weak to transform the spin networks into classical antiferromagnets. These three-dimensional networks of exchange coupled SMMs demonstrate that quantum tunnelling magnetization can be controlled using exchange interactions, suggesting supramolecular chemistry can be exploited to modulate the quantum physics of molecular magnets.

scholarly journals Asymmetric Dinuclear Lanthanide(III) Complexes from the Use of a Ligand Derived from 2-Acetylpyridine and Picolinoylhydrazide: Synthetic, Structural and Magnetic Studies

Molecules ◽  
2020 ◽  
Vol 25 (14) ◽  
pp. 3153
Author(s):  
Diamantoula Maniaki ◽  
Panagiota S. Perlepe ◽  
Evangelos Pilichos ◽  
Sotirios Christodoulou ◽  
Mathieu Rouzières ◽  
...  
Keyword(s):  
Single Molecule ◽  
Metal Ion ◽  
Ac Susceptibility ◽  
Solvent Molecule ◽  
Exchange Interactions ◽  
Experimental Fact ◽  
Anisotropy Axis ◽  
Magnetic Studies ◽  
Single Molecule Magnets ◽  
Magnetization Relaxation

A family of four Ln(III) complexes has been synthesized with the general formula [Ln2(NO3)4(L)2(S)] (Ln = Gd, Tb, Er, and S = H2O; 1, 2 and 4, respectively/Ln = Dy, S = MeOH, complex 3), where HL is the flexible ditopic ligand N’-(1-(pyridin-2-yl)ethylidene)pyridine-2-carbohydrazide. The structures of isostructural MeOH/H2O solvates of these complexes were determined by single-crystal X-ray diffraction. The two LnIII ions are doubly bridged by the deprotonated oxygen atoms of two “head-to-head” 2.21011 (Harris notation) L¯ ligands, forming a central, nearly rhombic {LnIII2(μ-OR)2}4+ core. Two bidentate chelating nitrato groups complete a sphenocoronal 10-coordination at one metal ion, while two bidentate chelating nitrato groups and one solvent molecule (H2O or MeOH) complete a spherical capped square antiprismatic 9-coordination at the other. The structures are critically compared with those of other, previously reported metal complexes of HL or L¯. The IR spectra of 1–4 are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The f-f transitions in the solid-state (diffuse reflectance) spectra of the Tb(III), Dy(III), and Er(III) complexes have been fully assigned in the UV/Vis and near-IR regions. Magnetic susceptibility studies in the 1.85–300 K range reveal the presence of weak, intramolecular GdIII∙∙∙GdIII antiferromagnetic exchange interactions in 1 [J/kB = −0.020(6) K based on the spin Hamiltonian Ĥ = −2J(ŜGd1∙ ŜGd2)] and probably weak antiferromagnetic LnIII∙∙∙LnIII exchange interactions in 2–4. Ac susceptibility measurements in zero dc field do not show frequency dependent out-of-phase signals, and this experimental fact is discussed for 3 in terms of the magnetic anisotropy axis for each DyIII center and the oblate electron density of this metal ion. Complexes 3 and 4 are Single-Molecule Magnets (SMMs) and this behavior is optimally observed under external dc fields of 600 and 1000 Oe, respectively. The magnetization relaxation pathways are discussed and a satisfactory fit of the temperature and field dependencies of the relaxation time τ was achieved considering a model that employs Raman, direct, and Orbach relaxation mechanisms.

scholarly journals Exchange Interactions at the Origin of Slow Relaxation of the Magnetization in {TbCu3} and {DyCu3} Single-Molecule Magnets

2014 ◽  
Vol 53 (17) ◽  
pp. 8970-8978 ◽  
Author(s):  
Fraser J. Kettles ◽  
Victoria A. Milway ◽  
Floriana Tuna ◽  
Rafael Valiente ◽  
Lynne H. Thomas ◽  
...  
Keyword(s):  
Single Molecule ◽  
Exchange Interactions ◽  
Slow Relaxation ◽  
Single Molecule Magnets

Enhancing the Blocking Temperature in Single-Molecule Magnets by Incorporating 3d-5d Exchange Interactions

2010 ◽  
Vol 16 (45) ◽  
pp. 13458-13464 ◽  
Author(s):  
Kasper S. Pedersen ◽  
Magnus Schau-Magnussen ◽  
Jesper Bendix ◽  
Høgni Weihe ◽  
Andrei V. Palii ◽  
...  
Keyword(s):  
Single Molecule ◽  
Exchange Interactions ◽  
Blocking Temperature ◽  
Single Molecule Magnets

scholarly journals Insensitivity of Magnetic Coupling to Ligand Substitution in a Series of Tetraoxolene Radical-Bridged Fe2 Complexes

2019 ◽  
Author(s):  
Agnes Thorarindottir ◽  
Ragnar Bjornsson ◽  
T. David Harris
Keyword(s):  
Single Molecule ◽  
Magnetic Measurements ◽  
Variable Temperature ◽  
Magnetic Coupling ◽  
Ligand Substitution ◽  
X Ray Diffraction ◽  
Single Molecule Magnets ◽  
Susceptibility Data ◽  
Bridging Ligand ◽  
Exchange Constants

<p>The elucidation of magnetostructural correlations between bridging ligand substitution and strength of magnetic coupling is essential to the development of high-temperature molecule-based magnetic materials. Toward this end, we report the series of tetraoxolene-bridged Fe<sup>II</sup><sub>2</sub> complexes [(Me<sub>3</sub>TPyA)<sub>2</sub>Fe<sub>2</sub>(<sup>R</sup>L)]<i><sup>n</sup></i><sup>+</sup> (Me<sub>3</sub>TPyA = tris(6-methyl-2-pyridylmethyl)amine; <i>n</i> = 2: <sup>OMe</sup>LH<sub>2</sub> = 3,6-dimethoxy-2,5-dihydroxo-1,4-benzoquinone, <sup>Cl</sup>LH<sub>2</sub> = 3,6-dichloro-2,5-dihydroxo-1,4-benzoquinone, Na<sub>2</sub>[<sup>NO2</sup>L] = sodium 3,6-dinitro-2,5-dihydroxo-1,4-benzoquinone; <i>n</i> = 0: <sup>SMe2</sup>L = 3,6-bis(dimethylsulfonium)-2,5-dihydroxo-1,4-benzoquinone diylide) and their one-electron-reduced analogues. Variable-temperature dc magnetic susceptibility data reveal the presence of weak ferromagnetic superexchange between Fe<sup>II</sup> centers in the oxidized species, with exchange constants of <i>J</i> = +1.2(2) (R = OMe, Cl) and +0.3(1) (R = NO<sub>2</sub>, SMe<sub>2</sub>) cm<sup>−1</sup>. In contrast, X-ray diffraction, cyclic voltammetry, and Mössbauer spectroscopy establish a ligand-centered radical in the reduced complexes. Magnetic measurements for the radical-bridged species reveal the presence of strong antiferromagnetic metal–radical coupling, with <i>J</i> = −57(10), −60(5), −58(6), and −65(8) cm<sup>−1</sup> for R = OMe, Cl, NO<sub>2</sub>, and SMe<sub>2</sub>, respectively. The minimal effects of substituents in the 3- and 6-positions of <sup>R</sup>L<i><sup>x</sup></i><sup>−•</sup> on the magnetic coupling strength is understood through electronic structure calculations, which show negligible spin density on the substituents and associated C atoms of the ring. Finally, the radical-bridged complexes are single-molecule magnets, with relaxation barriers of <i>U</i><sub>eff </sub>= 50(1), 41(1), 38(1), and 33(1) cm<sup>−1</sup> for R = OMe, Cl, NO<sub>2</sub>, and SMe<sub>2</sub>, respectively. Taken together, these results provide the first examination of how bridging ligand substitution influences magnetic coupling in semiquinoid-bridged compounds, and they establish design criteria for the synthesis of semiquinoid-based molecules and materials. </p>

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