Thiosemiquinoid Radical-Bridged Cr III 2 Complexes with Strong Magnetic Exchange Coupling

Carol Hua, Jordan A. Degayner, T. David Harris*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Semiquinoid radical bridging ligands are capable of mediating exceptionally strong magnetic coupling between spin centers, a requirement for the design of high-temperature magnetic materials. We demonstrate the ability of sulfur donors to provide much stronger coupling relative to their oxygen congeners in a series of dinuclear complexes. Employing a series of chalcogen donor-based bis(bidentate) benzoquinoid bridging ligands, the series of complexes [(TPyA) 2 Cr 2 ( R L 4- )] 2+ ( O LH 4 = 1,2,4,5-tetrahydroxybenzene, OS LH 4 = 1,2-dithio-4,5-dihydroxybenzene, S LH 4 = 1,2,4,5-tetrathiobenzene, TPyA = tris(2-pyridylmethyl)amine) was synthesized. Variable-temperature dc magnetic susceptibility data reveal the presence of weak antiferromagnetic superexchange coupling between Cr III centers in these complexes, with exchange constants of J = -2.83(3) ( O L 4- ), -2.28(5) ( OS L 4- ), and -1.80(2) ( S L 4- ) cm -1 . Guided by cyclic voltammetry and spectroelectrochemical measurements, chemical one-electron oxidation of these complexes gives the radical-bridged species [(TPyA) 2 Cr 2 ( R L 3-• )] 3+ . Variable-temperature dc susceptibility measurements in these complexes reveal the presence of strong antiferromagnetic metal-semiquinoid radical coupling, with exchange constants of J = -352(10) ( O L 3-• ), - 401(8) ( OS L 3-• ), and -487(8) ( S L 3-• ) cm -1 . These results provide the first measurement of magnetic coupling between metal ions and a thiosemiquinoid radical, and they demonstrate the value of moving from O to S donors in radical-bridged metal ions in the design of magnetic molecules and materials.

Original languageEnglish (US)
Pages (from-to)7044-7053
Number of pages10
JournalInorganic chemistry
Volume58
Issue number10
DOIs
StatePublished - May 20 2019

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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