Synthesis and characterization of homo- and heterodinuclear M(ii)-M′(iii) (M(ii) = Mn or Fe, M′(iii) = Fe or Co) mixed-valence supramolecular pseudo-dimers. the effect of hydrogen bonding on spin state selection of M(ii)

Cynthia T. Brewer, Greg Brewer, Ray J. Butcher, Everett E. Carpenter, Ann Marie Schmiedekamp, Carl Schmiedekamp, Alison Straka, Carol Viragh, Yevgeniy Yuzefpolskiy, Peter Zavalij

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Abstract

Reaction of H3L1, the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3- carboxaldehyde, with manganese(ii)perchlorate or iron(ii)tetrafluoroborate results in the isolation of [MH3L1]X2 (M = Mn and X = ClO4 and M = Fe and X = BF4). These complexes are high spin d5 and d6, respectively, as inferred from the long M-N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and Mössbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH3L 1]2+ with three equivalents of potassium hydroxide produced [CoL1]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH3L1](BF4)2 with 1.5 equivalents of potassium hydroxide to give {[FeH1.5L 1](BF4)}2 or by the metathesis reaction of [FeH2L1][FeHL1](ClO4)2 with sodium hexafluorophosphate to give [FeH3L1][FeL 1](PF6)2. The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal xray diffraction and Mössbauer spectroscopy. The iron(iii) atom is low spin while the iron(ii) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1:1 reaction of [FeH3L1](BF4)2 or [MnH3L1](ClO4)2 with [CoL 1]. [MH3L1][CoL1](X)2 (M = Fe and X = BF4 or M = Mn and X = ClO4), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and Mössbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(ii) and manganese(ii), respectively. DFT calculations demonstrate that the spin state of the iron(ii) atom in {[FeH3L1][FeL1]}2+ changes from high spin to low spin as the iron(ii)-iron(iii) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(ii)-N pyrazole bond distances.

Original languageEnglish (US)
Pages (from-to)181-194
Number of pages14
JournalDalton Transactions
Volume40
Issue number1
DOIs
StatePublished - Jan 7 2011

All Science Journal Classification (ASJC) codes

  • Inorganic Chemistry

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