Structural distortion in a Mn6 complex switches the magnetic exchange from antiferro- to ferromagnetic, resulting in a single-molecule magnet with a record anisotropy barrier.
We have structurally and magnetically characterized a total of 12 complexes based on the Single-Molecule Magnet (SMM) MnIII 6O2(sao)6(O2CH)2(MeOH) 4 (1) (where sao2- is the dianion of salicylaldoxime ...or 2-hydroxybenzaldeyhyde oxime) that display analogous structural cores but remarkably different magnetic behaviors. Via the use of derivatized oxime ligands and bulky carboxylates we show that it is possible to deliberately increase the value of the spin ground state of the complexes Mn6O2(Me-sao)6(O2CCPh3)2(EtOH)4 (2), Mn6O2(Et-sao)6(O2CCMe3)2(EtOH)5 (3), Mn6O2(Et-sao)6(O2CPh2OPh)2(EtOH)4 (4), Mn6O2(Et-sao)6(O2CPh4OPh)2(EtOH)4(H2O)2 (5), Mn6O2(Me-sao)6(O2CPhBr)2(EtOH)6 (6), Mn6O2(Et-sao)6(O2CPh)2(EtOH)4(H2O)2 (7), Mn6O2(Et-sao)6{O2CPh(Me)2}2(EtOH)6 (8), Mn6O2(Et-sao)6(O2C11H15)2(EtOH)6 (9), Mn6O2(Me-sao)6(O2C-th)2(EtOH)4(H2O)2 (10), Mn6O2(Et-sao)6(O2CPhMe)2(EtOH)4(H2O)2 (11), and Mn6O2(Et-sao)6(O2C12H17)2(EtOH)4(H2O)2 (12) (Et-saoH2 = 2-hydroxypropiophenone oxime, Me-saoH2 = 2-hydroxyethanone oxime, HO2CCPh3 = triphenylacetic acid, HO2CCMe3 = pivalic acid, HO2CPh2OPh = 2-phenoxybenzoic acid, HO2CPh4OPh = 4-phenoxybenzoic acid, HO2CPhBr = 4-bromobenzoic acid, HO2CPh(Me)2 = 3,5-dimethylbenzoic acid, HO2C11H15 = adamantane carboxylic acid, HO2C-th = 3-thiophene carboxylic acid, HO2CPhMe = 4-methylbenzoic acid, and HO2C12H17 = adamantane acetic acid) in a stepwise fashion from S = 4 to S = 12 and, in-so-doing, enhance the energy barrier for magnetization reorientation to record levels. The change from antiferromagnetic to ferromagnetic exchange stems from the “twisting” or “puckering” of the (−Mn−N−O−)3 ring, as evidenced by the changes in the Mn−N−O−Mn torsion angles.
Reaction of Gd(OAc)3·4H2O, salicylaldehyde and CH3ONa in MeCN/MeOH affords Gd12Na6(OAc)25(HCO2)5(CO3)6(H2O)12·9H2O.0.5MeCN (1·9H2O.0.5MeCN), whose structure describes a quadruple-wheel consisting of ...two {Na3} and two {Gd6} rings. The magnetic properties of 1 reveal very weak antiferromagnetic interactions between the GdIII ions, which give rise to a record magnetocaloric effect at low applied magnetic fields and low temperatures. The magnetic entropy change reaches −ΔS m= 29.3 J kg–1 K–1 for full demagnetization from B = 1 T at T = 0.5 K.
The use of derivatised salicylaldoximes in Mn chemistry has led to the isolation of a plethora of beautiful new SMMs ranging in nuclearity from three to eight and with spin ground states as large as ...S = 12-including a Mn6 complex with the largest energy barrier to magnetisation reversal yet reported. The deliberate chemically-induced structural distortion of the Mn6 molecule allows the isolation of analogous family members displaying remarkably different magnetic properties and this in turn allows for a rare semi-quantitative magneto-structural correlation which enables prediction of the magnetic properties of new family members.
An octahedral {DyIII6} cage within a diamagnetic {ZnII4} rectangle is reported, with magnetic relaxation studies revealing single-molecule magnet behaviour for the complex under zero external dc ...field with Ueff = 43 K and τo = 1 × 10-5 s.
The employment of 2-(β-naphthalideneamino)-2-(hydroxymethyl)-1-propanol and 2-aminoisobutyric acid in dysprosium chemistry has led to the isolation of a novel heptanuclear DyIII 7 cluster displaying ...single-molecule-magnetism behavior and blue-emitting properties.
A [Mn] wheel-of-wheels Coletta, Marco; Tziotzi, Thomais G; Gray, Mark ...
Chemical communications (Cambridge, England),
04/2021, Letnik:
57, Številka:
34
Journal Article
Recenzirano
Odprti dostop
A Mn
18
wheel of wheels is obtained from the reaction of MnBr
2
·4H
2
O and LH
3
in MeOH. The metallic skeleton reveals two asymmetric Mn
III
6
Mn
II
2
square wheels connected into a larger wheel
...via
two Mn
II
ions. Magnetic susceptibility and magnetisation data reveal competing exchange interactions, supported by computational studies.
A Mn
18
wheel of wheels is constructed from a simple reaction incorporating a triazatriol ligand.
The use of derivatised salicylaldoximes in manganese chemistry has led to the synthesis of a family of approximately fifty hexanuclear (Mn
III
6
) and thirty trinuclear (Mn
III
3
) Single-Molecule ...Magnets (SMMs). Deliberate, targeted structural distortion of the metallic core afforded family members with increasingly puckered configurations, leading to a switch in the pairwise magnetic exchange from antiferromagnetic to ferromagnetic. Examination of both the structural and magnetic data revealed a semi-quantitative magneto-structural correlation, from which the factors governing the magnetic properties could be extracted and used for predicting the properties of new family members and even more complicated structures containing analogous building blocks. Herein we describe an overview of this extensive body of work and discuss its potential impact on similar systems.
Mn
III
6
and Mn
III
3
complexes can have their magnetic behaviour changed
via
structural distortion and be used as building blocks for the construction of discrete and infinite architectures.
Spin Switching via Targeted Structural Distortion Milios, Constantinos J; Vinslava, Alina; Wernsdorfer, Wolfgang ...
Journal of the American Chemical Society,
05/2007, Letnik:
129, Številka:
20
Journal Article
Recenzirano
The deliberate “stepwise” structural distortion of the MnIII 6O2(sao)6(O2CR)2L4 (S = 4, U eff = 28 K) family of SMMs (where sao2- is the dianion of salicylaldoxime or 2-hydroxybenzaldeyhyde oxime and ...L = MeOH, EtOH) via the use of derivatized oxime ligands and bulky carboxylates leads to a family of single-molecule magnets with larger spin ground states and enhanced blocking temperatures. Replacing sao2- and HCO2 - in the molecule MnIII 6O2(sao)6(O2CH)2(MeOH)4 (1), with Et-sao2- (Et-saoH2 = 2-hydroxypropiophenone oxime) and Me3CCO2 - (pivalate), produces the complex MnIII 6O2(Et-sao)6(O2CCMe3)2(EtOH)5 (2) that displays an S = 7 ground state with U eff = 30 K. Replacing Me3CCO2 - with PhCO2 - produces the complex MnIII 6O2(Et-sao)6(O2CPh)2(EtOH)4(H2O)2 (3) that displays an S = 12 ground state with U eff = 53 K. The ligand substitution invokes a subtle structural distortion to the core of the molecule evidenced by an increased “twisting” of the oxime moiety (Mn−N−O−Mn) and a change in carboxylate ligation, which, in turn, invokes a dramatic change in the observed magnetic properties by switching weak antiferromagnetic exchange to weak ferromagnetic exchange.
The 1:1 reaction of trans-ReIIICl3(PPh3)2(MeCN) with 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol, H3L, in toluene gave the dinuclear complex ReIII 2Cl4(HL)(PPh3)·2C7H8 (1·2C7H8), while the ...1:2 reaction led to the formation of complex ReIVCl2(HL)(PPh3) (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL2–, forming chelate rings around the metallic centers. In addition, 1·2C7H8 displays a unique triple metal-to-metal bond between the two trivalent rhenium ions separated at a 2.229(1) Å bond distance, while in complex ReIVCl2(HL)(PPh3) (2) the two aromatic ligands, HL2– and PPh3, occupy axial positions, with the terminal Cl– ions in the trans position. Investigation of the magnetic properties revealed a Curie paramagnetic behavior (S = 1/2) with a pronounced temperature independent paramagnetism (TIP) for 1·2C7H8 and 2. Both the geometry and the electronic structure of both compounds have been studied by means of density functional theory (DFT) calculations, confirming the triplet and doublet spin ground state of the complexes and furthermore establishing an electron-rich σ2π4δ1δ*1 bond order of 3 for 1·2C7H8. In addition, the absorption spectrum of 1·2C7H8 in CH2Cl2 was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C7H8 is the first dinuclear rhenium complex with a triple metal–metal bond between trivalent rhenium centers.
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