Hexanuclear Manganese(III) Single‐Molecule Magnets

Abstract

Single-molecule magnets (SMMs) [1,2] are molecular species that can retain magnetization in the absence of a magnetic field below a blocking temperature. They represent the smallest possible magnetic storage device, which retains information in a single molecule rather than in a magnetic particle or array of particles. Furthermore, such molecules straddle the classical/quantum interface in also displaying quantum tunneling of magnetization and quantum phase interference. The SMM behavior derives from the intrinsic intramolecular properties of a high-spin ground state, and large and negative (easy axis type) magnetoanisotropy. [1,2] Experimentally, a SMM exhibits both a frequency-dependent out-of-phase alternating current (ac) magnetic susceptibility (c'') signal and hysteresis loops in magnetization versus direct current (dc) field studies.[ nÀ (n = 0, 1, 2; x = 3, 4; Mn III 8 Mn IV 4 for n = 0) and their derivatives, [1,2] but there are a number of other examples of SMMs containing manganese (at the oxidation states ii/iii, iii/iv or ii/iii/iv), iron, cobalt, nickel, and vanadium. [1][2][3] Important to the future of the field of SMMs is the development of new synthetic schemes that can yield molecules with a large spin and/or anisotropy. Herein we report access to the first members of a new class of manganese-based SMMs consisting exclusively of Mn III ions with T B (T B = blocking temperature) greater than 2 K.

Inelastic neutron scattering and frequency-domain magnetic resonance studies ofS=4andS=12Pieper1, Guidi2, Carretta3 et al. 2010Phys. Rev. B211160View full textAdd to dashboardCite

“…Mn 6 (1) (S =4) U eff É 28 K Sample ͑1͒ was the first reported member of the Mn 6 family. 16 The building block of the molecule is the ͓Mn 3 3+ O͔ triangular unit where Mn 2 pairs, bridged by the NO oxime, form a -Mn-O-N-Mn-moiety ͑Fig. 2͒.…”

“…16. For our measurements we used incident neutron wavelengths ranging from 3.0 to 5.92 Å with energy resolution between 50 and 360 eV.…”

Electronic structure of aMn6(S=4)single molecule magnet grafted on Au(111)

“…The characteristics of SMMs derive from their intrinsic properties of combining a high-spin ground state with a large and negative ͑easy axis type͒ magnetoanisotropy. 4 Recently, a family of SMMs containing six Mn III atoms has received great attention since one of its members ͑Mn 6 O 2 ͑Et-sao͒ 6 ͓O 2 CPh͑Me͒ 2 ͔ 2 ͑EtOH͒ 6 ͒ showed an effective energy barrier for magnetization relaxation of 86.4 K. 5 Actually, there are two distinct categories of molecules within this family, one with spin ground state S = 4, 6 and other with S = 12, which presents the high energy barrier quoted above. The "switch" from an antiferromagnetic exchange in the former class to a ferromagnetic exchange in the latter appears related to a structural distortion induced in the cluster by the presence of bulky oximato derivatives.…”

“…This phenomenon is more relevant for the 3p → 3d transition, where the two photoemission channels have comparable intensities, and less evident at the 2p → 3d edge, where the indirect channel prevails and the photoemission is particularly large ͑giant resonance͒. For Mn, for example, the 3d electron resonance occurs when the direct photoemission channel ͑mp 6 3d n + h → mp 6 3d n−1 + f ͒ interferes with the Mn mp → 3d excitation followed by a Coster-Kronig decay, mp 6 3d…”

“…6 This compound has been functionalized with two 3-thiophenecarboxylate ligands to enable its grafting on Au͑111͒. As the two 3tpc units have their S atoms in the outer position of the TP ring protruding from the molecular plane in opposite directions, they should force the molecules to graft onto the gold surface with their axis normal to the surface.…”