Organic spin clusters: Ferromagnetin spin coupling through a biphenyl unit in polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals

Andrzej Rajca, Jirawat Wongsriratanakul, Suchada Rajca

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

Polyarylmethyl high-spin polyradicals are designed to possess a structure corresponding to simple spin clusters, where component spins (S') arise from strong ferromagnetic coupling through 1,3-phenylene units and weak ferromagnetic spin coupling between the component spins is mediated via 3,4'-biphenylene (or 3,5,4'-biphenylyne) units. This rational design permits not only modular and highly convergent synthesis of very high-spin molecules but also detailed analysis of their magnetic data. A series of polyether precursors for the corresponding polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals are prepared. The polyradicals are generated and characterized in frozen tetrahydrofuran (or tetrahydrofuran-d8) solutions, using bulk magnetization studies. The measured values of S, from fits of magnetization vs magnetic field data to Brillouin functions at low temperatures, indicate high-spin ground states; e.g., S = 7.2 vs theoretical S = 8 for hexadecaradical. Estimated yields per site for generation of 'unpaired' electrons are as high as 98% for the best samples of penta-, hepta-, and hexadecaradicals. The magnetization vs temperature data are fit to the Boltzman distribution of energy levels, obtained from Heisenberg Hamiltonian; the fits produced ferromagnetic coupling constants (J/k) through 3,4'-biphenylene units. For tri- and pentaradical, for which exact analytical solutions to the Heisenberg Hamiltonian can be obtained by the vector model, values of J/k ~90 K are obtained. Hepta- and hexadecaradical, which could not be exactly solved by the vector model, are approximated as a dimer of the S' = 5/2, 3 and 5/2 component spins, respectively; the corresponding values of J/k, 13 and 4 K, are found to be scaled by the fraction of component spin directly connected through the weak spin coupler (3,4'-biphenylene unit).

Original languageEnglish (US)
Pages (from-to)11674-11686
Number of pages13
JournalJournal of the American Chemical Society
Volume119
Issue number48
DOIs
StatePublished - Dec 1 1997

Fingerprint

Rubiaceae
Hamiltonians
Magnetization
Temperature
Magnetic Fields
Polyethers
Electrons
Dimers
Electron energy levels
Ground state
Magnetic fields
Molecules
diphenyl
tetrahydrofuran
S(8)

ASJC Scopus subject areas

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

Cite this

@article{07e2dd59defa4a348d492932f50b4991,
title = "Organic spin clusters: Ferromagnetin spin coupling through a biphenyl unit in polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals",
abstract = "Polyarylmethyl high-spin polyradicals are designed to possess a structure corresponding to simple spin clusters, where component spins (S') arise from strong ferromagnetic coupling through 1,3-phenylene units and weak ferromagnetic spin coupling between the component spins is mediated via 3,4'-biphenylene (or 3,5,4'-biphenylyne) units. This rational design permits not only modular and highly convergent synthesis of very high-spin molecules but also detailed analysis of their magnetic data. A series of polyether precursors for the corresponding polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals are prepared. The polyradicals are generated and characterized in frozen tetrahydrofuran (or tetrahydrofuran-d8) solutions, using bulk magnetization studies. The measured values of S, from fits of magnetization vs magnetic field data to Brillouin functions at low temperatures, indicate high-spin ground states; e.g., S = 7.2 vs theoretical S = 8 for hexadecaradical. Estimated yields per site for generation of 'unpaired' electrons are as high as 98{\%} for the best samples of penta-, hepta-, and hexadecaradicals. The magnetization vs temperature data are fit to the Boltzman distribution of energy levels, obtained from Heisenberg Hamiltonian; the fits produced ferromagnetic coupling constants (J/k) through 3,4'-biphenylene units. For tri- and pentaradical, for which exact analytical solutions to the Heisenberg Hamiltonian can be obtained by the vector model, values of J/k ~90 K are obtained. Hepta- and hexadecaradical, which could not be exactly solved by the vector model, are approximated as a dimer of the S' = 5/2, 3 and 5/2 component spins, respectively; the corresponding values of J/k, 13 and 4 K, are found to be scaled by the fraction of component spin directly connected through the weak spin coupler (3,4'-biphenylene unit).",
author = "Andrzej Rajca and Jirawat Wongsriratanakul and Suchada Rajca",
year = "1997",
month = "12",
day = "1",
doi = "10.1021/ja972378b",
language = "English (US)",
volume = "119",
pages = "11674--11686",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "48",

}

TY - JOUR

T1 - Organic spin clusters

T2 - Ferromagnetin spin coupling through a biphenyl unit in polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals

AU - Rajca, Andrzej

AU - Wongsriratanakul, Jirawat

AU - Rajca, Suchada

PY - 1997/12/1

Y1 - 1997/12/1

N2 - Polyarylmethyl high-spin polyradicals are designed to possess a structure corresponding to simple spin clusters, where component spins (S') arise from strong ferromagnetic coupling through 1,3-phenylene units and weak ferromagnetic spin coupling between the component spins is mediated via 3,4'-biphenylene (or 3,5,4'-biphenylyne) units. This rational design permits not only modular and highly convergent synthesis of very high-spin molecules but also detailed analysis of their magnetic data. A series of polyether precursors for the corresponding polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals are prepared. The polyradicals are generated and characterized in frozen tetrahydrofuran (or tetrahydrofuran-d8) solutions, using bulk magnetization studies. The measured values of S, from fits of magnetization vs magnetic field data to Brillouin functions at low temperatures, indicate high-spin ground states; e.g., S = 7.2 vs theoretical S = 8 for hexadecaradical. Estimated yields per site for generation of 'unpaired' electrons are as high as 98% for the best samples of penta-, hepta-, and hexadecaradicals. The magnetization vs temperature data are fit to the Boltzman distribution of energy levels, obtained from Heisenberg Hamiltonian; the fits produced ferromagnetic coupling constants (J/k) through 3,4'-biphenylene units. For tri- and pentaradical, for which exact analytical solutions to the Heisenberg Hamiltonian can be obtained by the vector model, values of J/k ~90 K are obtained. Hepta- and hexadecaradical, which could not be exactly solved by the vector model, are approximated as a dimer of the S' = 5/2, 3 and 5/2 component spins, respectively; the corresponding values of J/k, 13 and 4 K, are found to be scaled by the fraction of component spin directly connected through the weak spin coupler (3,4'-biphenylene unit).

AB - Polyarylmethyl high-spin polyradicals are designed to possess a structure corresponding to simple spin clusters, where component spins (S') arise from strong ferromagnetic coupling through 1,3-phenylene units and weak ferromagnetic spin coupling between the component spins is mediated via 3,4'-biphenylene (or 3,5,4'-biphenylyne) units. This rational design permits not only modular and highly convergent synthesis of very high-spin molecules but also detailed analysis of their magnetic data. A series of polyether precursors for the corresponding polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals are prepared. The polyradicals are generated and characterized in frozen tetrahydrofuran (or tetrahydrofuran-d8) solutions, using bulk magnetization studies. The measured values of S, from fits of magnetization vs magnetic field data to Brillouin functions at low temperatures, indicate high-spin ground states; e.g., S = 7.2 vs theoretical S = 8 for hexadecaradical. Estimated yields per site for generation of 'unpaired' electrons are as high as 98% for the best samples of penta-, hepta-, and hexadecaradicals. The magnetization vs temperature data are fit to the Boltzman distribution of energy levels, obtained from Heisenberg Hamiltonian; the fits produced ferromagnetic coupling constants (J/k) through 3,4'-biphenylene units. For tri- and pentaradical, for which exact analytical solutions to the Heisenberg Hamiltonian can be obtained by the vector model, values of J/k ~90 K are obtained. Hepta- and hexadecaradical, which could not be exactly solved by the vector model, are approximated as a dimer of the S' = 5/2, 3 and 5/2 component spins, respectively; the corresponding values of J/k, 13 and 4 K, are found to be scaled by the fraction of component spin directly connected through the weak spin coupler (3,4'-biphenylene unit).

UR - http://www.scopus.com/inward/record.url?scp=0031439624&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0031439624&partnerID=8YFLogxK

U2 - 10.1021/ja972378b

DO - 10.1021/ja972378b

M3 - Article

AN - SCOPUS:0031439624

VL - 119

SP - 11674

EP - 11686

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 48

ER -