A series of tetraazalene radical-bridged M2 (M = CrIII, MnII, FeII, CoII) complexes with strong magnetic exchange coupling

Jordan A. Degayner, Ie Rang Jeon, T. David Harris*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


The ability of tetraazalene radical bridging ligands to mediate exceptionally strong magnetic exchange coupling across a range of transition metal complexes is demonstrated. The redox-active bridging ligand N,N',N″,N'′′-tetra(2-methylphenyl)-2,5-diamino-1,4-diiminobenzoquinone (NMePhLH2) was metalated to give the series of dinuclear complexes [(TPyA)2M2(NMePhL2-)]2+ (TPyA = tris(2-pyridylmethyl)amine, M = MnII, FeII, CoII). Variable-temperature dc magnetic susceptibility data for these complexes reveal the presence of weak superexchange interactions between metal centers, and fits to the data provide coupling constants of J = -1.64(1) and -2.16(2) cm-1 for M = MnII and FeII, respectively. One-electron reduction of the complexes affords the reduced analogues [(TPyA)2M2(NMePhL3-•)]+. Following a slightly different synthetic procedure, the related complex [(TPyA)2CrIII2(NMePhL3-•)]3+ was obtained. X-ray diffraction, cyclic voltammetry, and Mössbauer spectroscopy indicate the presence of radical NMePhL3-• bridging ligands in these complexes. Variable-temperature dc magnetic susceptibility data of the radical-bridged species reveal the presence of strong magnetic interactions between metal centers and ligand radicals, with simulations to data providing exchange constants of J = -626(7), -157(7), -307(9), and -396(16) cm-1 for M = CrIII, MnII, FeII, and CoII, respectively. Moreover, the strength of magnetic exchange in the radical-bridged complexes increases linearly with decreasing M-L bond distance in the oxidized analogues. Finally, ac magnetic susceptibility measurements reveal that [(TPyA)2Fe2(NMePhL3-•)]+ behaves as a single-molecule magnet with a relaxation barrier of Ueff = 52(1) cm-1. These results highlight the ability of redox-active tetraazalene bridging ligands to enable dramatic enhancement of magnetic exchange coupling upon redox chemistry and provide a rare opportunity to examine metal-radical coupling trends across a transmetallic series of complexes.

Original languageEnglish (US)
Pages (from-to)6639-6648
Number of pages10
JournalChemical Science
Issue number11
StatePublished - Aug 18 2015

ASJC Scopus subject areas

  • Chemistry(all)


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