Quantum Tunneling of Magnetization in a New [Mn₁₈]²⁺ Single-Molecule Magnet with S = 13

Abstract

The reaction between 2-(hydroxyethyl)pyridine (hepH) and a 2:1 molar mixture of [Mn3O(O2CMe)6(py)3](ClO4) and [Mn3O(O2CMe)6(py)3](py) in MeCN leads to isolation of [Mn18O14(O2CMe)18(hep)4(hepH)2(H2O)2](ClO4)2 (1) in 10% yield. The complex is 2MnII,16MnIII and consists of a Mn4O6 central unit to either side of which is attached a Mn7O9 unit. Magnetization data collected in the 2.0-4.0 K and 20-50 kG ranges were fit to yield S = 13, g = 1.86, and D = -0.13 cm-1 = -0.19 K, where D is the axial zero-field splitting parameter. AC susceptibility studies in the 0.04-4.0 K range at frequencies up to 996 Hz display out-of-phase (chiM' ') signals, indicative of a single-molecule magnet (SMM). Magnetization vs applied DC field scans exhibit hysteresis at <1.0 K, confirming 1 to be a SMM. DC magnetization decay data were collected on both a microcrystalline sample and a single crystal, and the combined data were used to construct an Arrhenius plot. Between 3.50 and 0.50 K, the relaxation rate is temperature-dependent with an effective barrier to relaxation (Ueff) of 14.8 cm-1 = 21.3 K. Below ca. 0.25 K, the relaxation rate is temperature-independent at 1.3 x 10-8 s-1, indicative of quantum tunneling of magnetization (QTM) between the lowest energy Ms = +/-13 levels of the S = 13 state. Complex 1 is both the largest spin and highest nuclearity SMM to exhibit QTM.

Modulating the Slow Relaxation Dynamics of Binuclear Dysprosium(III) Complexes through Coordination Geometry

“…Moreover, the Cole-Cole plots [31,32] (Figure 3 and Figure S11) were generated from the frequency-dependent ac susceptibility data. The fit of the χM″ vs χM′ data using the generalized Debye model [31,32] produced the values of α within the ranges 0.05-0.27 (1) and 0.08-0.32 (2), signifying the narrow distribution of the relaxation time. Effective energy barrier (Ueff) and relaxation time (τ0) were calculated from the Arrhenius Equation (1): [33][34][35] ln(1/τ) = ln(1/τ0) − Ueff/kT (1) where k = Boltzmann constant, and 1/τ0 = pre-exponential factor.…”

“…However, the out-of-phase signals (χ M ") for complex 2 do not show the peak maxima in the mentioned temperature range. Therefore, Debye model and Equation (2) were used to calculate energy barrier and relaxation time [36] ln(χ /χ ) = ln(ωτ 0 ) + U eff /kT (2) From the best fitting, the value of energy barrier and relaxation time were calculated as U eff = 9.7 K and τ 0 = 1.4 × 10 −6 s, respectively ( Figure S11), and found to be in good agreement with the expected value of 10 −6 -10 −11 for a SMM [37][38][39].…”

“…The importance of SMMs is that, even in the absence of an external magnetic field, they can preserve the magnetization for long period of time at low temperatures. After an extensive research on 3d metal complexes in the last decade [2][3][4], a rapid development of Ln based SMMs has been observed in recent years [5][6][7][8][9]. Compared to 3d metals, Ln based SMMs are mostly investigated owing to the fact that the Ln III ions such as Dy III , Tb III , Er III , and Ho III have huge and unquenched orbital angular momentum [10][11][12] which causes substantial magnetic anisotropy.…”

“…If a dinuclear SMM can be designed in a controllable manner, it can be possible to construct larger molecules via a bottom up molecular approach and make SMMs with higher blocking temperatures. Herein two dinuclear complexes [Dy 2 (L) 2 …”

Recent Progress in the Realm of Homonuclear Ln6 Single molecule magnets: Structural Overview and Synthetic Approaches

“…Typically, the first category is represented by symmetric arrangement of the six metal centers to construct a metallic wheel/ring, while the other category is typified by the relatively more familiar combinations of interconnected triangles. Rather than distinguishing these SMM materials based on the symmetry-aspect, it seems more judicious to divide the entire regime of the reported hexanuclear SMMs into two more general broad classifications: First class being the homonuclear Ln 6 series where the metal centers are solely 4f-elements, whereas the second class comprises of the heteronuclear entities composed of both 3d-and 4f-metal centers (Randell et al, 2013;Boskovic et al, 2002;Brechin et al, 2002;King et al, 2004;Zheng et al, 2007;Manoli et al, 2007;Feng et al, 2010;Stamatatos et al, 2011;Nayak et al, 2010;Kotzabasaki et al, 2011;Yang et al, 2011;Costa et al, 2012;Charalambous et al, 2012;Chakraborty et al, 2012;Mukherjee et al, 2014). Hereafter, our discussion will revolve around the first class only.…”