Two Mn III4Mn II8 clusters from the use of tripodal ligands showing single-molecule magnet behavior

Abstract

The reaction of manganese(II) acetylacetonate (Mn(acac) 2), 1,1,1-tris(hydroxymethyl)ethane (H 3thme), tris(hydroxymethyl)aminomethane (H 3thma), and (CH 3) 3CCO 2H, adamantane-1-carboxylic acid (Hada) in solvothermal method leads to two mixed-valence Mn III 4Mn II 8 clusters, [Mn(III) 4Mn(II) 8(μ 5-O) 2(μ 3-MeO) 2(thme) 4(Me 3CCO 2) 10(H 2O) 2]·2H 2O ( 1) and [Mn(III) 4Mn(II) 8(μ 5-O) 2(μ 3-MeO) 2(thma) 4(ada) 10(H 2O) 2]·4H 2O ( 2). The Mn III 4Mn II 8 cores of the complexes can be described as a central rhomboid [Mn 4O 6] layer sandwiched by two [Mn 4O 7] layers, or capped edge-sharing bioctahedra. The co-parallel alignment of four JT axes of the Mn III ions enhances the magnetic anisotropy of the Mn 12 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 ( χ M′′) 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 Mn 12 clusters and varies the packing modes of Mn 12 molecules in the crystal.