Monofluoride Bridged, Binuclear Metallacycles of First Row Transition Metals Supported by Third Generation Bis(1-pyrazolyl)methane Ligands: Unusual Magnetic Properties

Daniel L. Reger*, Elizabeth A. Foley, Russell P. Watson, Perry J. Pellechia and Mark D. Smith
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, 29208
Fernande Grandjean
Department of Physics, B5, University of Lige, B-4000 Sart-Tilman, Belgium
Gary J. Long*
Department of Chemistry, Missouri University of Science and Technology,University of Missouri, Rolla, Missouri 65409-0010
Inorg. Chem., 2009, 48 (22), pp 10658–10669
DOI: 10.1021/ic901352p
Publication Date (Web): October 14, 2009
Copyright © 2009 American Chemical Society
*To whom correspondence should be addressed. reger@mail.chem.sc.edu (D.L.R.), glong@mst.edu (G.J.L.).

Abstract

Abstract Image

The reaction of M(BF4)2·xH2O, where M is Fe, Co, Cu, and Zn, and the ditopic, bis(pyrazolyl)methane ligand m-[CH(pz)2]2C6H4, Lm, where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear [M2(μ-F)(μ-Lm)2](BF4)3 complexes. In contrast, a similar reaction of Lm with Ni(BF4)2·6H2O yields dibridged [Ni2(μ-F)2(μ-Lm)2](BF4)2. The solid state structures of seven [M2(μ-F)(μ-Lm)2](BF4)3 complexes show that the divalent metal ion is in a five-coordinate, trigonal bipyramidal, coordination environment with either a linear or nearly linear M−F−M bridging arrangement. NMR results indicate that [Zn2(μ-F)(μ-Lm)2](BF4)3 retains its dimeric structure in solution. The [Ni2(μ-F)2(μ-Lm)2](BF4)2 complex has a dibridging fluoride structure that has a six-coordination environment about each nickel(II) ion. In the solid state, the [Fe2(μ-F)(μ-Lm)2](BF4)3 and [Co2(μ-F)(μ-Lm)2](BF4)3 complexes show weak intramolecular antiferromagnetic exchange coupling between the two metal(II) ions with J values of −10.4 and −0.67 cm−1, respectively; there is no observed long-range magnetic order. Three different solvates of [Cu2(μ-F)(μ-Lm)2](BF4)3 are diamagnetic between 5 and 400 K, thus showing strong antiferromagnetic exchange interactions of −600 cm−1 or more negative. Mssbauer spectra indicate that [Fe2(μ-F)(μ-Lm)2](BF4)3 exhibits no long-range magnetic order between 4.2 and 295 K and isomer shifts that are consistent with the presence of five-coordinate, high-spin iron(II).

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History

  • Published In Issue November 16, 2009
  • Article ASAPOctober 14, 2009
  • Received: July 11, 2009

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