Effect of Ligand Substitution on the Exchange Interactions in {Mn₁₂}-Type Single-Molecule Magnets

Abstract

We investigate how ligand substitution affects the intramolecular spin exchange interactions, studying a prototypical family of single-molecule magnets comprising dodecanuclear cluster molecules [Mn(III)(8)Mn(IV)(4)O(12)(COOR)(16)]. We identify a simple scheme based on accumulated Pauling electronegativity numbers (AEN) of the carboxylate ligand groups (R). The redistribution of the electron density, controlled by the AEN of a ligand, changes the degree of hybridization between 3d electrons of manganese and 2p electrons of oxygen atoms, thus changing the exchange interactions. This scheme, despite its conceptual simplicity, provides a strong correlation with the exchange energies associated with carboxylate bridges and is confirmed by the electronic structure calculations taking into account the Coulomb correlations in magnetic molecules.

Two-dimensional molecular magnets with weak topological invariant magnetic moments: mathematical prediction of targets for chemical synthesis

“…However, it may be that J varies in a much more complicated manner within the deformation range in which the model applies. For example, it is known that J also depends on the Mn-O-Mn angles in various MMs [47] and the entire structure of the ligand connecting the two spins [37]. In a future study we will extract the functional form of J from detailed first-principles calculations, and also consider applying similar mathematical approaches to the design of molecules with other highly functional properties.…”

“…the superexchange mechanism through the oxygen atoms [34,35]) or how the coupling strengths are affected by the molecular structure of the MM (e.g. the organic groups attached to the O atoms in Mn 12 -type molecules [36,37]). Spin Hamiltonian models are therefore potentially useful if we are strictly interested in predicting MMs with interesting magnetic properties, such as robustness of the total spin under molecular shape deformations.…”

“…In spin Hamiltonian models, much of the detailed physics of the MM is condensed into the coupling constants J ij . This prevents spin Hamiltonian models from describing certain phenomena such the origin of the spin center-spin center coupling in an MM (such as the superexchange mechanism through the oxygen atoms [34,35]) or how the coupling strengths are affected by the molecular structure of the MM (such as the organic groups attached to the O atoms in Mn 12 -type molecules [36,37]). Spin Hamiltonian models are therefore potentially useful if we are strictly interested in predicting MMs with interesting magnetic properties, such as robustness of the total spin under molecular shape deformations.…”

Single-molecule magnetMn12on graphene

“…12 Mn 12 molecules have been synthesized with various ligands, and prior studies have showed that magnetic properties and exchange interactions of a SMM are strongly R-dependent. [13][14][15][16][17][18][19] To understand the effect of physical environment on properties of SMMs, especially that of a supporting substrate, it is desirable to place Mn 12 on well-defined surfaces and investigate the electronic and magnetic properties of individual molecules and monolayers. Much effort has already been made to deposit Mn 12 on various substrates, such as the metal Au(111), 20,21 the semi-metal Bi(111), 22 and even the ferromagnetic substrate Ni(111).…”

New single-molecule magnet based on Mn12 oxocarboxylate clusters with mixed carboxylate ligands, [Mn12O12(CN-o-C6H4CO2)12(CH3CO2)4(H2O)4]·8CH2Cl2: Synthesis, crystal and electronic structure, magnetic properties

“…It was shown that properties such as size and electronegativity of the substituents in the ligands influence strongly the degree of p-d hybridization, thus the electronic structure of the SMMs. 7,8 Furthermore, incorporation of the additional functional groups into carboxylate ligands can lead to formation of Mn 12 O 12 CR assemblies through various kinds of molecule interactions. 9 The supramolecular SMM dimer [Mn 4 O 3 Cl 4 (EtCO 2 ) 3 ( py) 3 ] 2 held together by close intermolecular Cl⋯Cl contact and C-H⋯Cl hydrogen bonds shows quantum magnetic behavior different from that of the discrete SMMs.…”