Issue 1, 2011

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)

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 [CoH3L1]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 {[FeH1.5L1](BF4)}2 or by the metathesis reaction of [FeH2L1][FeHL1](ClO4)2 with sodium hexafluorophosphate to give [FeH3L1][FeL1](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 [CoL1]. [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)-Npyrazole bond distances.

Graphical abstract: 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)

Supplementary files

Article information

Article type
Paper
Submitted
24 Aug 2010
Accepted
30 Sep 2010
First published
19 Nov 2010

Dalton Trans., 2011,40, 181-194

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)

C. T. Brewer, G. Brewer, R. J. Butcher, E. E. Carpenter, A. M. Schmiedekamp, C. Schmiedekamp, A. Straka, C. Viragh, Y. Yuzefpolskiy and P. Zavalij, Dalton Trans., 2011, 40, 181 DOI: 10.1039/C0DT01098G

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