From antiferromagnetic to ferromagnetic exchange in a family of oxime-based MnIII dimers: a magneto-structural study

Abstract

The reaction of Mn(ClO4)2·6H2O, a derivatised phenolic oxime (R-saoH2) and the ligand tris(2-pyridylmethyl)amine (tpa) in a basic alcoholic solution leads to the formation of a family of cluster compounds of general formula [Mn(III)2O(R-sao)(tpa)2](ClO4)2 (1, R = H; 2, R = Me; 3, R = Et; 4, R = Ph). The structure is that of a simple, albeit asymmetric, dimer of two Mn(III) ions bridged through one μ-O(2-) ion and the -N-O- moiety of the phenolic oxime. Magnetometry reveals that the exchange interaction between the two Mn(III) ions in complexes 1, 3 and 4 is antiferromagnetic, but that for complex 2 is ferromagnetic. A theoretically developed magneto-structural correlation reveals that the dominant structural parameter influencing the sign and magnitude of the pairwise interaction is the dihedral Mn-O-N-Mn (torsion) angle. A linear correlation is found, with the magnitude of J varying significantly as the dihedral angle is altered. As the torsion angle increases the AF exchange decreases, matching the experimentally determined data. DFT calculations reveal that the dyz|π*|dyz interaction decreases as the dihedral angle increases leading to ferromagnetic coupling at larger angles.

Modelling spin Hamiltonian parameters of molecular nanomagnets

“…Although the magnitude of the D values are comparatively smaller for the Mn III ions (in the range of ±4 cm -1 ) 192 , the sign is predictable (<0 cm -1 for elongated octahedral complexes) and thus it is a popular choice for the synthetic chemists. 30 The complexes studied are categorized as type-I (see Figure 3a) and possess strong antiferromagnetic interactions, as expected. In relevance to this, we have probed three different types of bis-µ-alkoxo bridged Mn III dimeric complexes are rationalized based on the MO analysis where in type III dimers, due to the perpendicular orientation of the J-T distortions, significant orbital overlaps are avoided and cross interaction between empty and the single-occupied orbital enhances leading to a strong ferromagnetic coupling (see Figure 2b).…”

Selective Formation, Reactivity, Redox and Magnetic Properties of MnIII and FeIII Dinuclear Complexes with Shortened Salen-Type Schiff Base Ligands

“…The family of dimeric species [Mn 2 O(R-sao)(tpa) 2 ](ClO 4 )] 2 (R-saoH 2 = R-salicylaldoxime, with R = H, Et and Ph, and tpa = tris (2-pyridylmethyl)amine) have been recently reported, where the manganese(III) ions are linked by a Mn–N–O–Mn oxime and an Mn–O–Mn oxido bridge leading to AFM coupling with J = −4.94, −3.87, −5.17 cm −1 for R = H, Et, Ph, respectively [ 45 ]. The related complexes (Mn 2 (R-sao) 2 (dpa) 2 )(ClO 4 ) 2 (R = H, Me, Et and Ph, and dpa = di(2-picolyl)amine), having two Mn–N–O–Mn oxime bridges, display AFM coupling with J = −5.73, −3.63, −5.63, –2.05 cm −1 for R = H, Me.…”

Magneto-structural correlations in a family of di-alkoxo bridged chromium dimers

“…We have previously established a computational approach for reliably computing exchange coupling constants in dinuclear complexes using broken-symmetry DFT and this methodology has been employed here. [54][55][56] Results and discussion…”