A mixed-valence Mn6 cluster capped by nitronyl nitroxide units

Kazuya Nakata, Hitoshi Miyasaka, Fumiyasu Iwahori, Ken Ichi Sugiura, Masahiro Yamashita

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Abstract

A mixed-valence Mn6 cluster, [Mn6O 2(t-BuCO2)10(H2O)(NNPy) 2] (2), has been synthesized by the assembly of [Mn6O 2(t-BuCO2)10(THF)4]·THF (1) with a nitronyl nitroxide radical molecule, 2-(p-pyridyl)-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide (NNPy). Complex 2 consists of [Mn 6O2]10+ core and two NNPy radical attachments, where the [Mn6O2]10+ core is composed of two MnIII ions (i.e., the inner Mn ions) bridged by two μ4-O2- and four MnII ions (i.e., the outer Mn ions) surrounding the inner MnIII ions via the two μ4-O2-, forming an edge-shared double-tetrahedral polygon (vertices: Mn ions, centers: μ4-O2-). Bridges by pivalate groups in μ2- and μ3-modes assist the coordination spheres around these Mn ions. Two of the outer MnII ions in trans position are, to the sixth coordination site, occupied by NNPy molecule (pyridine-N coordination). One of the outer MnII ions is occupied by a water molecule to complete octahedral geometry, but the rest of them is vacancy taking a square-pyramidal geometry. The variable-temperature direct current (DC) magnetic susceptibility was collected in the temperature range of 1.81 to 300 K at a 1 kOe appled field. The molar magnetic susceptibility (χM) steadily increases from 0.053 emu mol -1 at 300 K to 0.29 emu mol-1 at 20 K, showing a kink (peak), and then increases rapidly to 0.70 emu mol-1 at 1.81 K. The profile of this magnetic behavior indicates that the intracluster spin cancellation takes place bellow 20 K to derive an SMn6 = 0 by strong antiferromagnetic interaction between Mn ions. This is consequently leading to paramagnetic isolation of only the two nitronyl nitroxide units as if remaining as exchange-uncorrelated spin carriers. The variable-temperature ESR spectra show a sharp signal below 30 K with g = 2.00, proving the presence of free nitronyl nitroxide radical, in which double integral of such signal obeys the Curie-Weiss law that follows the susceptibility result in the low-temperature region.

Original languageEnglish
Pages (from-to)2250-2256
Number of pages7
JournalPolyhedron
Volume24
Issue number16-17
DOIs
Publication statusPublished - 2005 Nov 17

Keywords

  • DC magnetic susceptibility
  • ESR study
  • Magnetic properties
  • Manganese cluster
  • Nitronyl nitroxide radical
  • Single-crystal X-ray analysis

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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  • Cite this

    Nakata, K., Miyasaka, H., Iwahori, F., Sugiura, K. I., & Yamashita, M. (2005). A mixed-valence Mn6 cluster capped by nitronyl nitroxide units. Polyhedron, 24(16-17), 2250-2256. https://doi.org/10.1016/j.poly.2005.03.086