Title

Molecular Wheels: New Mn12 Complexes As Single-Molecule Magnets

Abstract

The preparation, structure and magnetic properties of three new wheel-shaped dodecanuclear manganese complexes, [Mn12(Adea) 8(CH3COO)14]·7CH3CN (1·7CH3CN), [Mn12(EdBa)8(CH 3CH2COO)14] (2) and [Mn12(Edea) 8(CH3COO)2-(CH3CH 2COO)12] (3), are reported, where Adea2- and Edea 2- are dianions of the N-allyl diethanolamine and the N-ethyl diethanolamine ligands, respectively. Each complex has six Mn(II) and six Mn(III) ions alternating in a wheel-shaped topology, with eight n-substituted diethanolamine dianions. All variable-temperature direct current (DC) magnetic susceptibility data were collected in 1, 0.1, or 0.01 T fields and in the 1.8-300 K temperature range. Heat capacity data, collected in applied fields of 0-9 T and in the 1.8-100 K temperature range, indicate the absence of a phase-transition due to long-range magnetic ordering for 1 and 3. Variable-temperature, variable-field DC magnetic susceptibility data were obtained in the 1.8-10 K and 0.1-5 T ranges. All complexes show out-of-phase signals in the AC susceptibility measurements, collected in a 50-997 Hz frequency range and in a 1.8-4.6 K temperature range. Extrapolation to 0 K of the in-phase AC susceptibility data collected at 50 Hz indicates an S = 7 ground state for 1, 2, and 3. Magnetization hysteresis data were collected on a single crystal of 1 in the 0.27-0.9 K range and on single crystals of 2 and 3 in the 0.1 -0.9 K temperature range. Discrete steps in the magnetization curves associated with resonant quantum tunneling of magnetization (QTM) confirm these complexes to be single-molecule magnets. The appearance of extra QTM resonances on the magnetic hysteresis of 1 is a result of a weak coupling between two Mn ions at opposite ends of the wheel, dividing the molecule into two ferromagnetic exchange-coupled S = 7/2 halves. The absence of these features on 2 and 3, which behave as rigid spin S = 7 units, is a consequence of different interatomic distances. © 2008 American Chemical Society.

Publication Date

10-20-2008

Publication Title

Inorganic Chemistry

Volume

47

Issue

20

Number of Pages

9569-9582

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1021/ic801374u

Socpus ID

55249113423 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/55249113423

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