Magnetic Properties of Aromatic Compounds and Aromatic Transition States

Herges, Rainer

doi:10.1002/9783527664658.ch13

Cited by 10 publications

(9 citation statements)

References 155 publications

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“…A reasonable correlation has been observed between the exchange coupling coefficient J and aromaticity indices NICS zz (+1) and HOMA, which is consistent with our earlier study. 18 Although studies of magnetic properties of organic aromatic molecules have a very long history, 150 it is very satisfying to observe the manifestation of a relationship between magnetism and aromaticity in such diverse complexes as investigated in this study.…”

Section: Discussionmentioning

confidence: 92%

Toward Molecular Magnets of Organic Origin via Anion−π Interaction Involving m-Aminyl Diradical: A Theoretical Study

et al. 2016

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Here we study a set of novel magnetic organic molecular species with different halide ions (fluoride, chloride, bromide) absorbed ∼2 Å above or below the center of an aromatic π-ring in an m-aminyl diradical. Focus is on the nature of anion-π interaction and its impact on magnetic properties, specifically on magnetic anisotropy and on intramolecular magnetic exchange coupling. In the development of single molecule magnets, magnetic anisotropy is considered to be the most influential factor. A new insight regarding the magnetic anisotropy that determines the barrier height for relaxation of magnetization of m-aminyl diradical-derived anionic complexes is obtained from calculations of the axial zero-field-splitting (ZFS) parameter D. The noncovalent anion-π interaction strongly influences magnetic anisotropy in m-aminyl-halide diradical complexes. In particular, the change of D values from positive (for the m-aminyl diradical, m-aminyl diradical/fluoride, and m-aminyl diradical/chloride complexes) to negative D-values in m-aminyl diradical complexes containing bromide signals a change from oblate to prolate type of spin-density distribution. Furthermore, the noncovalent halide-π interactions lead to large values of intramolecular magnetic exchange coupling coefficients J exhibiting a ferromagnetic sign. The magnitude of J steadily increases going from anionic complexes containing fluoride to chloride and then to bromide. Relations are sought between the magnetic exchange coupling coefficients J and aromaticity, namely structural HOMA (harmonic oscillator model of aromaticity) and magnetic NICS (nucleus independent chemical shift) aromaticity indices, in particular, the NICS(+1) component. Finally, possible numerical checks on the conditions relating to validity of the well-known Yamaguchi's formula for calculating the exchange coupling coefficient J in diradical systems are discussed.

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Section: Discussionmentioning

confidence: 92%

Toward Molecular Magnets of Organic Origin via Anion−π Interaction Involving m-Aminyl Diradical: A Theoretical Study

et al. 2016

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“…Cyclic aromatic systems exhibit ring currents in the presence of a magnetic field, and this has been studied extensively for Möbius aromatic molecules 47 , 51 , 53 , 54 , 87 , 92 , 93 and transition states. 94 − 98 What intriguing effects are waiting to be found in coarctate Möbius systems with helical orbitals?…”

Section: Discussionmentioning

confidence: 99%

“…We hope that our clarification of the electrohelicity effect or helicogenecity will motivate further studies in electronic and magnetic effects in this peculiar class of molecules. Cyclic aromatic systems exhibit ring currents in the presence of a magnetic field, and this has been studied extensively for Möbius aromatic molecules ,,,,,, and transition states. − What intriguing effects are waiting to be found in coarctate Möbius systems with helical orbitals?…”

Section: Discussionmentioning

confidence: 99%

Coarctate and Möbius: The Helical Orbitals of Allene and Other Cumulenes

et al. 2018

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As brought to the attention of the community by Hendon et al. and noted by previous workers, the π orbitals of the equilibrium geometry odd-carbon (even number of double bonds = n) [n]cumulenes may be written in either rectilinear or helical form. We trace the origins and detailed composition of the helical orbitals of cumulenes, which emerge in the simplest Hückel model and are not much modified in advanced computations. For the α,ω-disubstituted even [n]cumulenes, the helical representation is obligatory as the symmetry is reduced from D2d to C2. A relationship is apparent between these helical orbitals of the even [n]cumulenes, seen as a Herges coarctate system, and the corresponding Möbius cyclic polyene orbitals. The twist of the orbitals varies in interesting ways along the helix, and so does the contribution of the component atomic orbitals. Though the electronic structures of even [n]cumulenes and Möbius cyclopolyenes are closely related, they differ for higher n in intriguing ways; these are linked to the constrained rotation of the basis orbitals along the helical twist itinerary. Relations are constructed between the level patterns of the π-systems of even [n]cumulenes and ideas of Hückel and Möbius aromaticity.

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“…Following Herges and Geuenich, , the anisotropy of the induced current density is given by The ACID function ( ) is a scalar function that does not depend on the magnitude nor the direction of the applied magnetic field. can be used for visualization and it provides information about the electron mobility and the aromatic pathways in molecules.…”

Section: Anisotropy Of the Current Induced Densitymentioning

confidence: 99%

Gauge-Origin Independent Calculations of the Anisotropy of the Magnetically Induced Current Densities

2016

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Gauge-origin independent current density susceptibility tensors have been computed using the gauge-including magnetically induced current (GIMIC) method. The anisotropy of the magnetically induced current density (ACID) functions constructed from the current density susceptibility tensors are therefore gauge-origin independent. The ability of the gauge-origin independent ACID function to provide quantitative information about the current flow along chemical bonds has been assessed by integrating the cross-section area of the ACID function in the middle of chemical bonds. Analogously, the current strength susceptibility passing a given plane through the molecule is obtained by numerical integration of the current flow parallel to the normal vector of the integration plane. The cross-section area of the ACID function is found to be strongly dependent on the exact location of the integration plane, which is in sheer contrast to the calculated ring-current strength susceptibilities that are practically independent of the chosen position of the integration plane. The gauge-origin independent ACID functions plotted for different isosurface values show that a visual assessment of the current flow and degree of aromaticity depends on the chosen isosurface. The present study shows that ACID functions are not an unambiguous means to estimate the degree of molecular aromaticity according to the magnetic criterion and to determine the current pathway of complex molecular rings.

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Magnetic Properties of Aromatic Compounds and Aromatic Transition States

Cited by 10 publications

References 155 publications

Toward Molecular Magnets of Organic Origin via Anion−π Interaction Involving m-Aminyl Diradical: A Theoretical Study

Toward Molecular Magnets of Organic Origin via Anion−π Interaction Involving m-Aminyl Diradical: A Theoretical Study

Coarctate and Möbius: The Helical Orbitals of Allene and Other Cumulenes

Gauge-Origin Independent Calculations of the Anisotropy of the Magnetically Induced Current Densities

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