Title

Nanomodulation Of Molecular Nanomagnets

Abstract

Detailed synthetic, structural, and magnetic characterizations for a family of six [Mn3Zn 2] 13+ complexes are presented. These complexes have planar [Mn 3'"-(μ 3-oxo)] 7+ core magnetic units and have formulas represented by [cation] 3[Mn 3Zn 2(R-salox) 30(N 3) 6X 2], where [cation]+ = [NEt 4]3 + or [AsPh 4] 3+; R = H or Me; and X = CI -, Br -, l-, or N 3-. Least-squares fits to the magnetic susceptibility data for these complexes indicate large negative values of the axial zero field splitting (ZFS) parameter D (≈ -1.1 K) and spin ground states ranging from a highly spin-mixed S≈ 1 to a reasonably isolated S = 6 (?E S = 5 = 69.2 K). The strength and magnitude of the intramolecular exchange interactions have been observed to change with the crystal packing as a result of systematic variations in the co-crystallizing cation, terminal ion, and oximate ligand. Alternating current susceptibility data were collected from 1.8-7 K at 10-997 Hz, revealing strong frequency-dependent peaks in the out-of-phase susceptibility (χ"M) for ferromagnetic S = 6 complexes 1, 2, and 6. Fitting of these data to the Arrhenius equation gave U eff = 44.0 K and τ 0 = 3.8 × 10- 8 s for [NEt 4] 3[Mn 3Zn 2(salox) 30(N 3) 6CI 2] (1), and U eìt = 45.6 K and τ 0 = 2.1 × 10- 7 s for [NEt4] 3[Mn 3Zn 2(Me-salox) 30(N 3) 6CI 2] (6). The enhanced relaxation behavior in complex 6 is associated with stronger ferromagnetic exchange interactions and a more isolated S = 6 ground state than in 1 and 2. Comprehensive high-frequency electron paramagnetic resonance (HFEPR) experiments were conducted on single crystals of complexes 1, 2, and 6, revealing sharp absorption peaks and allowing for the precise determination of ZFS parameters. Similar experiments on [AsPh 4] 3[Mn 3Zn 2(salox) 30(N 3) 6CI 2] (4) resulted in the observation of a broad absorption peak, consistent with the highly spin-mixed ground state. Single crystal magnetization hysteresis measurements on complexes 1 and 2 indicate SMM behavior via temperature- and sweep-rate dependent hysteresis loops and the observance of very sharp quantum tunneling resonances. Additionally, the Hamiltonian parameters derived from the magnetic data, HFEPR, and hysteresis measurements are in good agreement and highlight the relationships between superexchange, spin-orbit interactions, and the varied relaxation behavior in these complexes. © 2009 American Chemical Society.

Publication Date

4-20-2009

Publication Title

Inorganic Chemistry

Volume

48

Issue

8

Number of Pages

3480-3492

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1021/ic802336k

Socpus ID

65349102324 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/65349102324

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