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)?

Dalton Transactions Pub Date: 2010-11-19 DOI: 10.1039/C0DT01098G

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 M?ssbauer 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 M?ssbauer 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 M?ssbauer 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)
Recommended Literature