Syntheses, structures, magnetic and spectroscopic properties of bis(pentane-2,4-dionato)chromium(III) complexes incorporating 3- or 4-pyridyl-substituted nitronyl and imino nitroxides

Atsushi Iino, Takayoshi Suzuki, Sumio Kaizaki

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Abstract

Preparation and characterization by X-ray analysis and 2H NMR spectra have been described for twelve chromium(III)-nitroxide complexes of cis-[Cr(acac)2Cl(L)] and cis- and trans-[Cr(acac)2(L)2]PF6 with monodentate coordination through the pyridyl-N atom in the nitroxides, where acac = pentane-2,4-dionate and L = 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl 3-oxide (NIT3py or NIT4py) and 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl (IM3py or IM4py). An intramolecular magnetic interaction between CrIII and the nitroxide was found to be weakly antiferromagnetic and ferromagnetic, respectively, in the NIT3py or IM3py complexes and the NIT4py or IM4py complexes. The difference in sign of these magnetic interaction constants between the 3- and 4-pyridyl-substituted nitroxides can be interpreted by a spin polarization mechanism for the π-electron system including the nitroxide SOMO π* and CrIII dπ orbitals. The inherently weak magnetic interactions and absence of an intensity enhancement of the spin-forbidden d-d transition band in these nitroxides complexes are in contrast to our previous results for the chelated NIT2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl 3-oxide] and IM2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl] complexes. This may be accounted for by the difference in the mechanism of magnetic interactions; spin-polarization mechanism and exchange mechanism, respectively.

Original languageEnglish
Pages (from-to)4604-4611
Number of pages8
JournalDalton Transactions
Issue number24
Publication statusPublished - Dec 21 2003
Externally publishedYes

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Spin polarization
Magnetic structure
Chromium
Oxides
X ray analysis
Nuclear magnetic resonance
Atoms
Electrons
pentane

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{759ee521ee864a7283a36e76afc5b52c,
title = "Syntheses, structures, magnetic and spectroscopic properties of bis(pentane-2,4-dionato)chromium(III) complexes incorporating 3- or 4-pyridyl-substituted nitronyl and imino nitroxides",
abstract = "Preparation and characterization by X-ray analysis and 2H NMR spectra have been described for twelve chromium(III)-nitroxide complexes of cis-[Cr(acac)2Cl(L)] and cis- and trans-[Cr(acac)2(L)2]PF6 with monodentate coordination through the pyridyl-N atom in the nitroxides, where acac = pentane-2,4-dionate and L = 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl 3-oxide (NIT3py or NIT4py) and 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl (IM3py or IM4py). An intramolecular magnetic interaction between CrIII and the nitroxide was found to be weakly antiferromagnetic and ferromagnetic, respectively, in the NIT3py or IM3py complexes and the NIT4py or IM4py complexes. The difference in sign of these magnetic interaction constants between the 3- and 4-pyridyl-substituted nitroxides can be interpreted by a spin polarization mechanism for the π-electron system including the nitroxide SOMO π* and CrIII dπ orbitals. The inherently weak magnetic interactions and absence of an intensity enhancement of the spin-forbidden d-d transition band in these nitroxides complexes are in contrast to our previous results for the chelated NIT2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl 3-oxide] and IM2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl] complexes. This may be accounted for by the difference in the mechanism of magnetic interactions; spin-polarization mechanism and exchange mechanism, respectively.",
author = "Atsushi Iino and Takayoshi Suzuki and Sumio Kaizaki",
year = "2003",
month = "12",
day = "21",
language = "English",
pages = "4604--4611",
journal = "Dalton Transactions",
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T1 - Syntheses, structures, magnetic and spectroscopic properties of bis(pentane-2,4-dionato)chromium(III) complexes incorporating 3- or 4-pyridyl-substituted nitronyl and imino nitroxides

AU - Iino, Atsushi

AU - Suzuki, Takayoshi

AU - Kaizaki, Sumio

PY - 2003/12/21

Y1 - 2003/12/21

N2 - Preparation and characterization by X-ray analysis and 2H NMR spectra have been described for twelve chromium(III)-nitroxide complexes of cis-[Cr(acac)2Cl(L)] and cis- and trans-[Cr(acac)2(L)2]PF6 with monodentate coordination through the pyridyl-N atom in the nitroxides, where acac = pentane-2,4-dionate and L = 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl 3-oxide (NIT3py or NIT4py) and 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl (IM3py or IM4py). An intramolecular magnetic interaction between CrIII and the nitroxide was found to be weakly antiferromagnetic and ferromagnetic, respectively, in the NIT3py or IM3py complexes and the NIT4py or IM4py complexes. The difference in sign of these magnetic interaction constants between the 3- and 4-pyridyl-substituted nitroxides can be interpreted by a spin polarization mechanism for the π-electron system including the nitroxide SOMO π* and CrIII dπ orbitals. The inherently weak magnetic interactions and absence of an intensity enhancement of the spin-forbidden d-d transition band in these nitroxides complexes are in contrast to our previous results for the chelated NIT2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl 3-oxide] and IM2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl] complexes. This may be accounted for by the difference in the mechanism of magnetic interactions; spin-polarization mechanism and exchange mechanism, respectively.

AB - Preparation and characterization by X-ray analysis and 2H NMR spectra have been described for twelve chromium(III)-nitroxide complexes of cis-[Cr(acac)2Cl(L)] and cis- and trans-[Cr(acac)2(L)2]PF6 with monodentate coordination through the pyridyl-N atom in the nitroxides, where acac = pentane-2,4-dionate and L = 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl 3-oxide (NIT3py or NIT4py) and 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl (IM3py or IM4py). An intramolecular magnetic interaction between CrIII and the nitroxide was found to be weakly antiferromagnetic and ferromagnetic, respectively, in the NIT3py or IM3py complexes and the NIT4py or IM4py complexes. The difference in sign of these magnetic interaction constants between the 3- and 4-pyridyl-substituted nitroxides can be interpreted by a spin polarization mechanism for the π-electron system including the nitroxide SOMO π* and CrIII dπ orbitals. The inherently weak magnetic interactions and absence of an intensity enhancement of the spin-forbidden d-d transition band in these nitroxides complexes are in contrast to our previous results for the chelated NIT2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl 3-oxide] and IM2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl] complexes. This may be accounted for by the difference in the mechanism of magnetic interactions; spin-polarization mechanism and exchange mechanism, respectively.

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