Two MnIII4MnII8 clusters from the use of tripodal ligands showing single-molecule magnet behavior

The reaction of manganese(II) acetylacetonate (Mn(acac)2), 1,1,1-tris(hydroxymethyl)ethane (H3thme), tris(hydroxymethyl)aminomethane (H3thma), and (CH3)3CCO2H, adamantane-1-carboxylic acid (Hada) in solvothermal method leads to two mixed-valence MnIII4MnII8 clusters, [Mn(III)4Mn(II)8(μ5-O)2(μ3-MeO)2(thme)4(Me3CCO2)10(H2O)2]·2H2O (1) and [Mn(III)4Mn(II)8(μ5-O)2(μ3-MeO)2(thma)4(ada)10(H2O)2]·4H2O (2). The MnIII4MnII8 cores of the complexes can be described as a central rhomboid [Mn4O6] layer sandwiched by two [Mn4O7] layers, or capped edge-sharing bioctahedra. The co-parallel alignment of four JT axes of the MnIII ions enhances the magnetic anisotropy of the Mn12 molecules. For the population of low-lying excited states, the attempts to fit the direct current (dc) data of two complexes were failed, while rough spin ground state S = 4 for 1 and S = 2 or 3 for 2 were obtained from alternating current (AC) magnetization studies. The two compounds show clearly nonzero and frequency-dependent out-of-phase (χM′′) ac signal below 3 K, indicating a slow relaxation of the magnetization, confirming 1 and 2 to be SMMs, though out-of-phase AC peak above 1.8 K was not observed. The substitution of tripodal ligands and carboxylate ligands leads to different coordinate modes of the pivalate ligands in the Mn12 clusters and varies the packing modes of Mn12 molecules in the crystal.

Graphical abstractTwo valence-sandwich-type MnIII4MnII8 clusters exhibiting SMM behavior were obtained via the use of the tripodal ligands H3thme (1,1,1-tris(hydroxymethyl)ethane) and H3thma (tris(hydroxymethyl)aminomethane) in Mn carboxylate chemistry.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two mixed-valence Mn clusters built using tripodal ligands and carboxylates. ► These two clusters were confirmed as SMMs. ► Substitution of ligands leads to different structures and magnetic properties.