Long-Range Ferromagnetic Exchange Interactions Mediated by Mn–Ce^IV–Mn Superexchange Involving Empty 4f Orbitals

Abstract

Reactions involving reductive aggregation of MnO 4− in methanol in the presence of Ce IV and an excess of carboxylic acid have led to the synthesis of structurally related Ce/ Mn clusters, [Ce 3 Mn 5 O 8 (OMe)(O 2 CBu t ) 13 (MeOH)] (1) and [Ce 2 Mn 3 O 5 (O 2 CPh) 9 (MeOH) 3 ] (2), containing at least one {Mn 2 Ce 2 O 4 } cubane unit. The cores of both clusters contain Mn x units separated by three (1) or two (2) Ce IV ions. Fits of variable-temperature, solid-state dc and ac magnetic susceptibility data reveal dominant ferromagnetic interactions within 1 and 2, resulting in the maximum S = 17 / 2 and S = 5 ground state spins, respectively, and thus suggesting significant ferromagnetic (F) interactions between the Mn x units that are ≥6 Å apart and separated by four intervening bonds through diamagnetic Ce IV . Fits of magnetic susceptibility data also revealed unusual long-range F interactions, and this finding was further supported by high-field EPR measurements and simulations. Density functional theory calculations and a Wannier function analysis confirm long-range interactions and indicate a Mn−Ce−Mn superexchange pathway via Mn-d/Ce-f orbital overlap/hybridization

Structures and magnetic properties of two heterometallic Cu(ii)–Cd(ii) polymers exhibiting antiferromagnetic ordering

“…When considering the possible presence of a weak interchain coupling ( zJ ′), the molecular field correction can be merged into the 1D magnetic model with the expression represented as: 31,32 …”

Long-Range Magnetic Exchange Pathways in Complex Clusters from First-Principles

“…The Mn 5 Ce 3 complex (molecular structure shown in Fig. 1) is experimentally determined to be ferromagnetic, and this is supported by DFT+U calculations [17]. Two important questions about the magnetic coupling remain unanswered.…”

“…The reference state in the CI calculation (Suppl. IV) was constructed as the ferromagnetic symmetry breaking state with charge and spin state for each ion as identified experimentally [17]. Excitations, which are relevant to exchange processes, were selected for the CI calculation.…”

“…Aside from a few single-ion examples, MMs usually contain multiple magnetic transition metal ions whose magnetic interactions can present rich and complex physics, especially when these ions are of mixed valence states such as the Mn m Ce n oxo clusters and the well known SMM [Mn 12 O 12 (O 2 CR) 16 (H 2 O) 4 ] [2][3][4]. Molecular Mn m Ce n oxo clusters, first reported in 2003 [5], have been synthesized recently to study a variety of magnetic interactions involving f -electrons [6,7].…”

“…Analogies to bulk perovskite manganites are drawn [6], where magnetic interactions are rich and complex and later long-range ferromagnetic couplings are observed [7].…”