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.

Phenyl 2‐Pyridyl Ketone and Its Oxime in Manganese Carboxylate Chemistry: Synthesis, Characterisation, X‐ray Studies and Magnetic Properties of Mononuclear, Trinuclear and Octanuclear Complexes

“…The (11), N(12), O(11) and N(11Ј), N(12Ј), O(11Ј) each bridge two Mn III ions; in both cases the deprotonated oximate oxygen atom is terminally ligated to a Mn III ion (Figure 4).…”

“…Ϫ and (2-py) 2 CO 2 2Ϫ do not exist as free species -they exist only in their metal complexes in Mn carboxylate chemistry gave the new family of valence-trapped, mixed-valence complexes [11] [Mn 2 II Mn 2 III -(O 2 CR) 2 X 2 {(2-py) 2 CNO} 2 {(2-py) 2 CO 2 } 2 ], where X Ϫ is Cl Ϫ , Br Ϫ or RCO 2 Ϫ ; it has been of great interest that an appreciable quantity of the oxime ligand undergoes transformation to yield the coordinated dianion of the gem-diol form of (2-py) 2 CO. The mechanism of this transformation probably involves reaction(s) of the electrophilically activated coordinated oxime group.…”

The Effect of Crystal Packing and ReIV Ions on the Magnetisation Relaxation of [Mn6]‐Based Molecular Magnets

“…In recent years, a large body of work has involved the use of derivatised salicylaldoxime (R-saoH 2 ) [16][17][18][19][20][21][22] and salicylamidoxime (H 2 N-saoH 2 ) [23][24][25][26][27] ligands in Mn III coordination chemistry. This has led to the isolation of an extensive family of hexanuclear Mn III SMMs, many of them possessing spin ground states as large as S = 12 and energy barriers to magnetisation reversal and blocking temperatures that are the largest reported for polynuclear transition-metal complexes.…”

“…This has led to the isolation of an extensive family of hexanuclear Mn III SMMs, many of them possessing spin ground states as large as S = 12 and energy barriers to magnetisation reversal and blocking temperatures that are the largest reported for polynuclear transition-metal complexes. [16][17][18][19][20][21][22][23] The solution stable, magnetically tuneable [Mn 3 ] building blocks from which these hexamers are constructed are appealing candidates for building novel molecule-based magnets, because nearest neighbour magnetic exchange (J) is controlled by the twisting of the Mn-N-O-Mn torsion angle, and this in turn is controlled through simple organic chemistry through derivitisation of the oxime ligand. [16][17][18][19][20][21][22][23][24][25][26][27] Very recently, the first example of a cationic salicylamidoxime-based [Mn 6 ] 2 + SMM of formula [Mn 6 (m 3 -O) 2 (H 2 Nsao) 6 (py) 6 (EtOH) 2 ][ClO 4 ] 2 ·4 EtOH possessing a S = 12 ground state, was reported.…”

Lanthanide Complexes with Multidentate Oxime Ligands as Single‐Molecule Magnets and Atmospheric Carbon Dioxide Fixation Systems

“…Herein, the synthesis of a new family of lanthanide complexes from oxime ligands with multiple coordination sites are reported. Oxime‐based ligands are particularly known for stabilizing manganese‐based SMMs and related systems,11 which have been extensively studied for their tunable antiferro/ferromagnetic interactions 11a,b. Herein, dinuclear lanthanide‐based complexes have been synthesized from 2‐hydroxyimino‐ N ‐[1‐(2‐pyridyl)ethylidene]propanohydrazone (Hpop) or 1‐(1‐hydroxynaphthalen‐2‐yl)‐ethanone oxime (naphthsaoH 2 ) ligands: 1 : [La 2 (pop) 2 (acac) 4 (CH 3 OH)]; 2 : [Dy 2 (pop)(acac) 5 ]; 3 : [Dy 2 (naphthsaoH) 2 (acac) 4 H(OH)]⋅0.85 CH 3 CN⋅1.58 H 2 O and 4 : [Tb 2 (naphthsao) 2 (acac) 4 H(OH)]⋅0.52 CH 3 CN⋅1.71 H 2 O. Complexes 2 and 3 show slow dynamics of their magnetization, in agreement with SMM properties.…”