Wheel-Shaped [Mn₁₂] Single-Molecule Magnets

Abstract

The reaction of [Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4)].4H(2)O.2CH(3)COOH with n-methyldiethanol amine (H(2)mdea), n-ethyldiethanol amine (H(2)edea), or n-butyldiethanol amine (H(2)bdea) leads to the formation of wheel-shaped Mn(III)(6)Mn(II)(6) complexes with the general formula [Mn(12)(R)(O(2)CCH(3))(14)] (1, R = mdea; 2, R = edea; and 3, R = bdea). Complex 1 crystallizes in the triclinic space group P1, whereas complex 3 crystallizes in the monoclinic space group C(2/c). Complex 1a has the same molecular structure as complex 1 but crystallizes in the monoclinic space group P2(1/n). Complex 3a has the same molecular structure as complex 3 but crystallizes in the triclinic space group P1. Variable-temperature magnetic susceptibility data collected for complexes 1, 2, and 3 indicate that antiferromagnetic exchange interactions are present. The spin ground states of complexes 1, 2, and 3 were determined by fitting variable-field magnetization data collected in the 2-5 K temperature range. Fitting of these data yielded the spin ground-state parameters of S = 8, g = 2.0, and D = -0.47 cm(-1) for complex 1; S = 8, g = 2.0, and D = -0.49 cm(-1) for complex 2; and S = 8, g = 2, and D = -0.37 cm(-1) for complex 3. The ac magnetic susceptibility data were measured for complexes 1, 2, and 3 at temperatures between 1.8 and 10 K with a 3 G ac field oscillating in the range 50-1000 Hz. Slow kinetics of magnetization reversal relative to the frequency of the oscillating ac field were observed as frequency-dependent out-of-phase peaks for complexes 1, 2, and 3, and it can be concluded that these three complexes are single-molecule magnets.

Radical ligand-containing single-molecule magnets

“…After the discovery of the first single-molecule magnet, cluster compound Mn 12 O 12 (O 2 CMe) 16 (H 2 O) 4 [31], efforts to increase the spin relaxation barrier primarily involved research aimed at synthesizing larger metal clusters with higher values of S, typically featuring oxo bridging ligands between metal centers [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. Here, the magnetic interactions between the metal centers occur via superexchange coupling through the diamagnetic oxido unit, and these interactions can indeed reach appreciable magnitudes for such one-atom bridging ligands.…”

Syntheses, Structures, and Properties of Two Dicyanamide‐Bridged Polymers with a Schiff‐base Ligand

“…[32] The plot of χ M -1 vs. T can be fitted by Curie-Weiss law giving the Curie constant C = 9.17 cm 3 ·K·mol -1 and the Weiss constant θ = -23.88 K (Figure 6). The negative θ value confirms the antiferromagnetic interactions between the adjacent Mn 2+ ions.…”

Prediction of Exchange Coupling Constant for Mn12 Molecular Magnet Using Dft+U

“…Among these complexes are the Mn 22 wheel [14] and the Mn 84 wheel, which is the largest wheel-shaped SMM known to date. The largest reported spin ground state for a wheel-shaped SMM is the S=14 ground state reported for the complex [Mn 16 12 ] wheels reported by Rumberger et al [6] in 2005 are also examples of single-stranded wheels.…”