Special Issue "High Spin Molecules"

A special issue of Crystals (ISSN 2073-4352).

Deadline for manuscript submissions: closed (30 March 2016)

Special Issue Editor

Guest Editor
Dr. Martin T. Lemaire

Department of Chemistry, Brock University, St. Catharines, Ontario, Canada
Website | E-Mail
Interests: synthesis; redox-active ligands; stable radicals; molecule-based magnets; spin-crossover; high-spin molecules

Special Issue Information

Dear Colleagues,

The field of molecule-based magnetic materials relies, in part, on the creativity of synthetic chemists to design and prepare new molecules with desirable magnetic properties. This is challenging work but tremendous strides have been made over the past 35 years in the understanding of how unpaired electrons communicate with each other within organic molecules, transition- or lanthanide ion complexes, and more recently, in the understanding of the essential role that magnetoanisotropy plays in molecular magnetism and learning to control and enhance magnetic exchange and anisotropy in new molecular designs. In this Special Issue of Crystals, we will celebrate some of these recent efforts in the field of molecule-based magnetism with a focus on creativity in the design and synthesis of new molecular materials.

Dr. Martin T. Lemaire
Guest Editor

Manuscript Submission Information

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Keywords

  • single molecule/ion magnets
  • molecular spintronics
  • magnetoanisotropy
  • stable organic radicals
  • magnetic exchange coupling mechanism
  • spin crossover and valence tautomerism
  • redox active ligands

Published Papers (6 papers)

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Research

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Open AccessArticle The Role of Coulomb Interactions for Spin Crossover Behaviors and Crystal Structural Transformation in Novel Anionic Fe(III) Complexes from a π-Extended ONO Ligand
Crystals 2016, 6(5), 49; doi:10.3390/cryst6050049
Received: 30 March 2016 / Revised: 27 April 2016 / Accepted: 28 April 2016 / Published: 3 May 2016
Cited by 3 | PDF Full-text (3129 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
To investigate the π-extension effect on an unusual negative-charged spin crossover (SCO) FeIII complex with a weak N2O4 first coordination sphere, we designed and synthesized a series of anionic FeIII complexes from a π-extended naphthalene derivative ligand. Acetonitrile-solvate
[...] Read more.
To investigate the π-extension effect on an unusual negative-charged spin crossover (SCO) FeIII complex with a weak N2O4 first coordination sphere, we designed and synthesized a series of anionic FeIII complexes from a π-extended naphthalene derivative ligand. Acetonitrile-solvate tetramethylammonium (TMA) salt 1 exhibited an SCO conversion, while acetone-solvate TMA salt 2 was in a high-spin state. The crystal structural analysis for 2 revealed that two-leg ladder-like cation-anion arrays derived from π-stacking interactions between π-ligands of the FeIII complex anion and Coulomb interactions were found and the solvated acetone molecules were in one-dimensional channels between the cation-anion arrays. A desolvation-induced single-crystal-to-single-crystal transformation to desolvate compound 2’ may be driven by Coulomb energy gain. Furthermore, the structural comparison between quasi-polymorphic compounds 1 and 2 revealed that the synergy between Coulomb and π-stacking interactions induces a significant distortion of coordination structure of 2. Full article
(This article belongs to the Special Issue High Spin Molecules)
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Open AccessArticle High-Spin Chains and Crowns from Double-Exchange Mechanism
Crystals 2016, 6(4), 39; doi:10.3390/cryst6040039
Received: 5 December 2015 / Revised: 23 March 2016 / Accepted: 28 March 2016 / Published: 6 April 2016
Cited by 1 | PDF Full-text (1845 KB) | HTML Full-text | XML Full-text
Abstract
This article addresses the question of the possibility of obtaining high-spin chains and crowns of magnetic units s = 1 from doped (by a hole) antiferromagnetic architectures. It aims at determining the range of values of the double-exchange model interactions for which these
[...] Read more.
This article addresses the question of the possibility of obtaining high-spin chains and crowns of magnetic units s = 1 from doped (by a hole) antiferromagnetic architectures. It aims at determining the range of values of the double-exchange model interactions for which these molecules exhibit a high-spin ground state. Several chains and crowns of sizes varying between three to seven magnetic sites have been studied using a refined double-exchange model. It is shown that, for physical values of the parameters, linear chains of three, four and five sites are likely to adopt the highest spin state. For chains of six sites, small values of magnetic couplings are needed to get the highest spin, but it would be easy to get an S = 3/2 ground state. For systems of seven (or slightly more) sites, the highest spin state becomes non accessible but S = 5/2 states are likely to be obtained. Surprisingly, the physics of crowns is substantially different. The same trends are observed for even-number systems but with a larger double-exchange regime. At variance, odd-number systems do not exhibit a double-exchange mechanism for low values of the magnetic couplings. These observations are rationalized from an analysis of the computed spectra and wave functions. Full article
(This article belongs to the Special Issue High Spin Molecules)
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Open AccessArticle Thermally Activated Paramagnets from Diamagnetic Polymers of Biphenyl-3,5-diyl Bis(tert-butyl Nitroxides) Carrying Methyl and Fluoro Groups at the 2’- and 5’-Positions
Crystals 2016, 6(3), 30; doi:10.3390/cryst6030030
Received: 15 February 2016 / Revised: 12 March 2016 / Accepted: 15 March 2016 / Published: 22 March 2016
Cited by 2 | PDF Full-text (3035 KB) | HTML Full-text | XML Full-text
Abstract
Three new biradicals—2’,5’-dimethyl-, 2’-fluoro-5’-methyl-, and 5’-fluoro-2’-methyl- biphenyl-3,5-diyl bis(tert-butyl nitroxides)—were synthesized. The magnetic susceptibility measurements revealed their diamagnetism below and around room temperature. The nitroxide groups are located close to each other in an intermolecular fashion to form a weakly covalent head-to-tail
[...] Read more.
Three new biradicals—2’,5’-dimethyl-, 2’-fluoro-5’-methyl-, and 5’-fluoro-2’-methyl- biphenyl-3,5-diyl bis(tert-butyl nitroxides)—were synthesized. The magnetic susceptibility measurements revealed their diamagnetism below and around room temperature. The nitroxide groups are located close to each other in an intermolecular fashion to form a weakly covalent head-to-tail (NO)2 ring. Biradical molecules are connected on both radical sites, constructing a diamagnetic chain. The dimethyl derivative underwent a structural phase transition at 83 °C, clarified via differential scanning calorimetry and powder X-ray diffraction, and a paramagnetic solid phase with S = 1 irreversibly appeared. The other analogues exhibited a similar irreversible upsurge of the magnetic susceptibility on heating, but the transition was characterized as the melting. Full article
(This article belongs to the Special Issue High Spin Molecules)
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Open AccessFeature PaperArticle A New Method for the Synthesis of Heterospin Complexes
Crystals 2015, 5(4), 634-649; doi:10.3390/cryst5040634
Received: 21 September 2015 / Revised: 17 November 2015 / Accepted: 20 November 2015 / Published: 2 December 2015
Cited by 3 | PDF Full-text (1281 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The interaction of binuclear Co(II) pivalate [Сo2(H2O)Piv4(HPiv)4] with nitronyl nitroxide HL1 (2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) in organic solvents led to the formation of a pentanuclear heterospin complex [Co5(Piv)4L14L22
[...] Read more.
The interaction of binuclear Co(II) pivalate [Сo2(H2O)Piv4(HPiv)4] with nitronyl nitroxide HL1 (2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) in organic solvents led to the formation of a pentanuclear heterospin complex [Co5(Piv)4L14L22]. A nontrivial peculiarity of the complex is the presence of both the starting nitronyl nitroxide L1 and its deoxygenated derivative imino nitroxide L2 (HL2: 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl) in its coordination sphere. Based on this, a new synthetic approach was developed, which suggests the use of both the starting radical and the product of its reduction in the reaction with the metal. The suggested approach is a new method for the synthesis of heterospin compounds, including those that cannot be obtained by other methods. It was shown that the reaction of Co(II) pivalate with a mixture of HL1 and HL2 can give a trinuclear heterospin complex [Co3(Piv)2L12L22]. The replacement of Co(II) by Ni(II) completely suppresses the reduction of HL1 into HL2, and Ni(II) pivalate does not react with HL1. The use of a known mixture of HL1 and HL2 in the reaction with [Ni2(H2O)Piv4(HPiv)4], however, led to the formation of a heterospin complex [Ni3L1L22(Piv)3(HPiv)3] also containing both nitronyl nitroxide and imino nitroxide. Full article
(This article belongs to the Special Issue High Spin Molecules)
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Review

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Open AccessReview The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes
Crystals 2016, 6(5), 58; doi:10.3390/cryst6050058
Received: 22 April 2016 / Revised: 11 May 2016 / Accepted: 13 May 2016 / Published: 18 May 2016
Cited by 6 | PDF Full-text (5432 KB) | HTML Full-text | XML Full-text
Abstract
The relationship between chemical structure and spin state in a transition metal complex has an important bearing on mechanistic bioinorganic chemistry, catalysis by base metals, and the design of spin crossover materials. The latter provide an ideal testbed for this question, since small
[...] Read more.
The relationship between chemical structure and spin state in a transition metal complex has an important bearing on mechanistic bioinorganic chemistry, catalysis by base metals, and the design of spin crossover materials. The latter provide an ideal testbed for this question, since small changes in spin state energetics can be easily detected from shifts in the spin crossover equilibrium temperature. Published structure-function relationships relating ligand design and spin state from the spin crossover literature give varied results. A sterically crowded ligand sphere favors the expanded metal–ligand bonds associated with the high-spin state. However, steric clashes at the molecular periphery can stabilize either the high-spin or the low-spin state in a predictable way, depending on their effect on ligand conformation. In the absence of steric influences, the picture is less clear since electron-withdrawing ligand substituents are reported to favor the low-spin or the high-spin state in different series of compounds. A recent study has shed light on this conundrum, showing that the electronic influence of a substituent on a coordinated metal ion depends on its position on the ligand framework. Finally, hydrogen bonding to complexes containing peripheral N‒H groups consistently stabilizes the low-spin state, where this has been quantified. Full article
(This article belongs to the Special Issue High Spin Molecules)
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Open AccessReview Role of Water Molecules to the Electronic States of M-DNA
Crystals 2015, 5(4), 475-490; doi:10.3390/cryst5040475
Received: 20 September 2015 / Revised: 6 October 2015 / Accepted: 10 October 2015 / Published: 20 October 2015
PDF Full-text (1732 KB) | HTML Full-text | XML Full-text
Abstract
Various kinds of roles of the water molecules in the electronic states of the complexes of metal ions (M) and deoxyribonucleic acid (DNA) are reviewed. Divalent metal ions M like Fe, Mn, Zn and so on, form Metal-DNA complexes (M-DNA) with each metal
[...] Read more.
Various kinds of roles of the water molecules in the electronic states of the complexes of metal ions (M) and deoxyribonucleic acid (DNA) are reviewed. Divalent metal ions M like Fe, Mn, Zn and so on, form Metal-DNA complexes (M-DNA) with each metal ion between the bases of a base pair of DNA. The electronic states of the complexes depend on the species of ions in M-DNA. Metal ions in Fe-DNA and Mn-DNA possess 3d magnetic moments, but those in Zn-DNA do not. Interestingly, the magnetic property of the complexes, especially the magnetic interaction between the metal ions, is dominated by water molecules in the complexes. In Fe-DNA, the water molecules play a role of ligands for the iron ions, which controls the spin states of Fe3+, whereas they govern the magnetic interaction between the Mn2+ ions in Mn-DNA. In contrast, Zn-DNA has no 3d magnetic moment, but the water molecules dominate the bonding states of the Zn ions and the magnetic states of the Zn-DNA system. Full article
(This article belongs to the Special Issue High Spin Molecules)
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