What Controls the Magnetic Interaction in bis‐μ‐Alkoxo Mn^III Dimers? A Combined Experimental and Theoretical Exploration

Abstract

The synthesis and magnetic characterisation of a series of bis-μ-alkoxide bridged Mn(III) dinuclear complexes of general formula [Mn(III)(2)(μ-OR)(2)(biphen)(2)(ROH)(x)(L)(y)] (where R = Me, Et; H(2) biphen = 2,2'-biphenol and L = terminally bonded N-donor ligand) is described, doubling the literature basis set for this type of complex. Building on these findings we have categorised all known μ-OR bridged Mn(III) dinuclear complexes into one of three classifications with respect to their molecular structures. We have then employed DFT and MO calculations to assess all potential magneto-structural correlations for this class of compound in order to identify the structural requirements for constructing ferromagnetic family members. Our analysis indicates that the most influential parameter which governs the exchange interaction in this class of compounds is the relative orientation of the JT axes of the Mn(III) atoms. A perpendicular orientation of the JT axes leads to a large ferromagnetic contribution to the exchange. These results also suggest that a large ferromagnetic interaction and a large anisotropy are unlikely to co-exist in such structural types.

Modelling spin Hamiltonian parameters of molecular nanomagnets

“…This is primarily due to the fact that Mn III complexes often yield negative zero-field splitting parameter, a key ingredient in the construction of SMMs. 29 (a) (b) Although the established concept was for {Mn III 2 (OR) 2 } type dimers, the classification was found to have relevance also in other classes of dimers. The negative D values of the Mn III ions are associated with the inherent Jahn-Teller distortions but this distortion not only controls the single-ion and cluster anisotropy but also the intramolecular magnetic exchange interactions.…”

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

“…3 (see Fig. 70 The ligand atoms in the direction of d z 2-orbital, i.e. The Mn III ions are found to possess three unpaired electrons in the t 2g orbitals (metal π-type) which promote a spin polarization mechanism, and one unpaired electron in an e g orbital (metal σ type) favouring a spin delocalization mechanism.…”

Zig-zag [MnIII4] clusters from polydentate Schiff base ligands

“…The use of polyol Schiff base ligands, OH-C 6 H 4 -CH@NC(R)(CH 2-OH) 2 (R = CH 3 , H 3 L 1 ; R = C 2 H 5 , H 3 L 2 ; R = CH 2 OH, H 3 L 3 ), in manganese cluster chemistry afforded tetranuclear complexes [Mn 4 (L 1 ) 2 (HL 1 ) 2 [33] concerning the nature of the magnetic interactions in alkoxo-bridged Mn(III) dimers. The present synthetic approach allows for synthesis of clusters with similar topology.…”

“…Following the classification of this approach, for 2b the outer dimers belong to type III whereas the central dimer belongs to type II. For type III, ferromagnetic interactions are expected whereas for type II the interactions are moderately antiferromagnetic [33]. On the basis of these considerations we simulated the magnetic susceptibility data assuming J > 0 and J 0 < 0.…”

“…In a recent study, magneto-structural correlations were attempted for bis-l-alkoxo bridged dimers [33] depending on the relative orientation of the Jahn-Teller axes within the dimer. Three different types were proposed concerning the relative orientation of the Jahn-Teller axes, i.e.…”