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Article

Wheel-Shaped Mn ₁₆ Single-Molecule Magnets

Supporting Info

Sonali J. Shah, ^†, Christopher M. Ramsey, ^§, Katie J. Heroux, ^†, James R. O’Brien^‡, Antonio G. DiPasquale, ^†, Arnold L. Rheingold, ^†, Enrique del Barco, ^§ and David N. Hendrickson, *^†

Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California 92093, Quantum Design, San Diego, California 92121, and Department of Physics, University of Central Florida, Orlando, Florida 32765

Inorg. Chem., 2008, 47 (14), pp 6245–6253

DOI: 10.1021/ic800277j

Publication Date (Web): June 21, 2008

†

University of California at San Diego.

University of Central Florida.

‡

Quantum Design.

* To whom correspondence should be addressed. E-mail: dhendrickson@ucsd.edu.

Abstract

The syntheses, structures, and magnetic properties of two new single-stranded hexadecanuclear manganese wheels [Mn ₁₆(CH ₃COO) ₈(CH ₃CH ₂CH ₂COO) ₈(teaH) ₁₂]·10 MeCN ( 1·10 MeCN) and [Mn ₁₆((CH ₃) ₂CHCOO) ₁₆(teaH) ₁₂]·4CHCl ₃ ( 2·4CHCl ₃), where teaH ²⁻ is the dianion of triethanolamine, are reported. 1 crystallizes in the tetragonal I4 ₁/ a space group [ a = b = 33.519(4) Å and c = 16.659(2) Å]. 2 crystallizes in the monoclinic C2/ c space group [ a = 21.473(5), b = 26.819(6), c = 35.186(7), and β = 93.447(5)°]. Both complexes consist of 8 Mn(II) and 8 Mn(III) ions alternating in a wheel-shaped topology with 12 monoprotonated triethanolamine ligands. Variable-temperature direct current (DC) magnetic susceptibility data were collected in 1 T, 0.1 and 0.01 T fields, and in the 1.8−300 K temperature range for 1 and 2. Variable-temperature variable-field DC magnetic susceptibility data were obtained in the 1.8−10 K and 0.1−5 T ranges and least-squares fitting of these reduced magnetization versus H/ T data indicates a S = 13 ground-state for 1 and 2. Single-crystal magnetization hysteresis measurements were performed in a 0.04−1 K temperature range for complex 2. Hysteresis loops were observed that showed a temperature dependence, which indicates that 2 exhibits magnetization relaxation and is a SMM. Both 1 and 2 show frequency-dependent out-of-phase signals in the AC susceptibility measurements, collected in a temperature range of 1.8−5 K and in the frequency range of 50−10 000 Hz. Extrapolation of the in-phase component of the AC susceptibility data to 0 K indicates an S = 12 ground state for 1 and an S = 11 ground-state for 2. Complex 1 has the highest-spin ground state reported to date for a single-stranded manganese wheel and is likely to be an SMM based on a frequency-dependent out-of-phase signal in the AC susceptibility. The AC susceptibility as well as magnetization hysteresis data for 2 confirm that this species is an SMM.