Intramolecular antiferromagnetic vs ferromagnetic spin coupling through the biphenyl unit

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Abstract

Two isomeric triarylmethyl-based diradicals, with 3,3'- and 3,4'-biphenyl as the spin coupling units, were prepared and studied in frozen solutions by ESR spectroscopy and SQUID magnetometry. The 3,3'-isomer was found to be the singlet ground state, with a singlet-triplet energy gap of -0.1 kcal/mol. The 3,4'-isomer was found to be the triplet ground state. This dependence of intramolecular spin coupling (antiferromagnetic vs ferromagnetic) on topology is in agreement with simple theoretical models. The singlet ground state for the 3,3'-isomer, which has two half-filled nonbonding orbitals, is in formal violation of Hund's rule, as applied to molecules.

Original languageEnglish (US)
Pages (from-to)8121-8126
Number of pages6
JournalJournal of the American Chemical Society
Volume118
Issue number34
DOIs
StatePublished - Aug 28 1996

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Magnetometry
Isomers
Ground state
Spectrum Analysis
Theoretical Models
SQUIDs
Paramagnetic resonance
Energy gap
Topology
Spectroscopy
Molecules
diphenyl

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

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title = "Intramolecular antiferromagnetic vs ferromagnetic spin coupling through the biphenyl unit",
abstract = "Two isomeric triarylmethyl-based diradicals, with 3,3'- and 3,4'-biphenyl as the spin coupling units, were prepared and studied in frozen solutions by ESR spectroscopy and SQUID magnetometry. The 3,3'-isomer was found to be the singlet ground state, with a singlet-triplet energy gap of -0.1 kcal/mol. The 3,4'-isomer was found to be the triplet ground state. This dependence of intramolecular spin coupling (antiferromagnetic vs ferromagnetic) on topology is in agreement with simple theoretical models. The singlet ground state for the 3,3'-isomer, which has two half-filled nonbonding orbitals, is in formal violation of Hund's rule, as applied to molecules.",
author = "Andrzej Rajca and Suchada Rajca",
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T1 - Intramolecular antiferromagnetic vs ferromagnetic spin coupling through the biphenyl unit

AU - Rajca, Andrzej

AU - Rajca, Suchada

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N2 - Two isomeric triarylmethyl-based diradicals, with 3,3'- and 3,4'-biphenyl as the spin coupling units, were prepared and studied in frozen solutions by ESR spectroscopy and SQUID magnetometry. The 3,3'-isomer was found to be the singlet ground state, with a singlet-triplet energy gap of -0.1 kcal/mol. The 3,4'-isomer was found to be the triplet ground state. This dependence of intramolecular spin coupling (antiferromagnetic vs ferromagnetic) on topology is in agreement with simple theoretical models. The singlet ground state for the 3,3'-isomer, which has two half-filled nonbonding orbitals, is in formal violation of Hund's rule, as applied to molecules.

AB - Two isomeric triarylmethyl-based diradicals, with 3,3'- and 3,4'-biphenyl as the spin coupling units, were prepared and studied in frozen solutions by ESR spectroscopy and SQUID magnetometry. The 3,3'-isomer was found to be the singlet ground state, with a singlet-triplet energy gap of -0.1 kcal/mol. The 3,4'-isomer was found to be the triplet ground state. This dependence of intramolecular spin coupling (antiferromagnetic vs ferromagnetic) on topology is in agreement with simple theoretical models. The singlet ground state for the 3,3'-isomer, which has two half-filled nonbonding orbitals, is in formal violation of Hund's rule, as applied to molecules.

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