Wheel-shaped Mn-16 single-molecule magnets

作者：Shah Sonali J; Ramsey Christopher M; Heroux Katie J; O'Brien James R; DiPasquale Antonio G; Rheingold Arnold L; del Barco Enrique; Hendrickson David N^*

来源：Inorganic Chemistry, 2008, 47(14): 6245-6253.

DOI：10.1021/ic800277j

The syntheses, structures, and magnetic properties of two new single-stranded hexadecanuclear manganese wheels [Mn-16(CH3COO)(8)(CH3CH2CH2COO)(8)(teaH)12]center dot 10 MeCN (1.10 MeCN) and [Mn-16((CH3)(2)CHCOO)(16)(teaH)(12)]center dot 4CHCl(3) (2.4CHCl(3)), where teaH(2-) is the dianion of triethanolamine, are reported. 1 crystallizes in the tetragonal l4(1)/a space group [a = b = 33.519(4) angstrom and c = 16.659(2) angstrom]. 2 crystallizes in the monoclinic C2/c space group [a = 21.473(5), b = 26.819(6), c = 35.186(7), and beta = 93.447(5)degrees]. 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 HIT 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 I 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.

• 出版日期2008-7-21