RESUMEN
Three new cyano-bridged FeII-MoIII complexes assembled from the [MoIII(CN)7]4- unit, FeII ions, and three pentadentate N3O2 ligands, namely {[Fe2H3(dapab)2][Mo(CN)6]}n·2H2O·3.5MeCN (1), [Fe(H2dapb)(H2O)][Fe(Hdapb)(H2O)][Mo(CN)6]·4H2O·3MeCN (2), and [Fe(H2dapba)(H2O)]2[Mo(CN)7]·6H2O (3) (H2dapab = 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone), H2dapb = 2,6-diacetylpyridine bis(benzoylhydrazone), H2dapba = 2,6-diacetylpyridine bis(4-aminobenzoylhydrazone)), have been synthesized and characterized. Single-crystal structure analyses suggest that complex 1 contains a one-dimensional (1D) chain structure where two FeII ions are bridged by the in situ generated [MoIII(CN)6]3- unit through two trans-cyanide groups into trinuclear Fe2IIMoIII clusters that are further linked by the amino of the ligand into an infinite chain. Complexes 2 and 3 are cyano-bridged Fe2IIMoIII trinuclear clusters with two FeII ions connected by the [MoIII(CN)6]3- and [MoIII(CN)7]4- units, respectively. Direct current magnetic studies confirmed the ferromagnetic interactions between the cyano-bridged FeII and MoIII centers and significant easy-axis magnetic anisotropy for all three complexes. Furthermore, complexes 1-3 exhibit slow magnetic relaxation under a zero dc field, with relaxation barriers of 42.3, 21.6, and 14.4 K, respectively, making them the first examples of cyano-bridged FeII-MoIII single-molecule magnets.
RESUMEN
Three new cyanide-bridged compounds {[Mn((S,S)-Dpen)]3[Mn((S,S)-Dpen)(H2O)][Mo(CN)7]2·4H2O·4C2H3N}n (1-SS), {[Mn((R,R)-Dpen)]3[Mn((R,R)-Dpen)(H2O)][Mo(CN)7]2·4.5H2O·4C2H3N}n (1-RR), and {[Mn(Chxn)][Mn(Chxn)(H2O)0.8][Mo(CN)7]·H2O·4C2H3N}n (2) (SS/RR-Dpen = (S,S)/(R,R)-1,2-diphenylethylenediamine and Chxn = 1,2-cyclohexanediamine) have been successfully synthesized from the self-assembly reaction of the [MoIII(CN)7]4- unit, the MnII ions, and two chiral bidentate chelating ligands. Single-crystal structure determinations show that compounds 1-SS and 1-RR containing ligands SS/RR-Dpen are enantiomers and crystallize in the chiral space group P21. On the other hand, compound 2 crystallizes in the achiral centrosymmetric space group P1Ì due to the racemization of the SS/RR-Chxn ligands during the growth of the crystals. Despite their different space groups and ligands, all three compounds exhibit similar framework structures consisting of cyano-bridged MnII-MoIII two-dimensional layers separated by the bidentate ligands. The circular dichroism (CD) spectra have further demonstrated the enantiopure character of compounds 1-SS and 1-RR. Magnetic measurements revealed that all three compounds display ferrimagnetic ordering with similar critical temperatures of about 40 K. The chiral enantiomers 1-SS and 1-RR exhibit the magnetic hysteresis loop with a coercive field of about 8000 Oe at 2 K, which is by far the highest for all known MnII-[MoIII(CN)7]4- magnets. Analyses of their structures and magnetic properties indicated that their magnetic properties depend on the anisotropic magnetic interactions between the MnII and MoIII centers, which are closely related to the C-N-M bond angles.
RESUMEN
A molecular dysprosium(III) complex [Dy(DClQ)3(H2O)2] (1) was used as a building unit for the construction of lanthanide SMMs, leading to the isolation of two dinuclear Dy(III) complexes, namely [Dy2(DClQ)6(MeOH)2] (2) and [Dy2(DClQ)6(bpmo)2]·6MeCN (3) (DClQ = 5,7-dichloro-8-hydroxyquinoline, bpmo = 4,4'-dipyridine-oxide). Structural analyses revealed the same N3O5 coordination environment of the Dy(III) centers with a distorted biaugmented trigonal prism (C2V symmetry) and triangular dodecahedron (D2d symmetry) for 2 and 3, respectively. Magnetic studies revealed the presence of ferromagnetic and weak antiferromagnetic exchange interactions between the Dy3+ centers in 2 and 3, respectively. Interestingly, slow relaxation of magnetization at zero fields was evidenced with an Ueff of 51.4 K and 159.0 K for complexes 2 and 3, respectively. The detailed analysis of relaxation dynamics discloses that the Orbach process is dominant for 2 whereas Raman and QTM play an important role in 3. Theoretical calculations were carried out to provide insight into the magnetic exchange interactions and relaxation dynamics for the complexes. Due to a single-ion magnet (SIM) of 1, the foregoing results demonstrate a SIM modular synthetic route for the preparation of dinuclear lanthanide SMMs.
RESUMEN
Ginseng is a traditional Chinese medicine and has the extensive pharmacological activity. Ginsenosides are the major constituent in ginseng and have the unique biological activity and medicinal value. Ginsenosides have the good effects on antitumor, anti-inflammatory, antioxidative and inhibition of the cell apoptosis. Studies have showed that the major ginsenosides could be converted into rare ginsenosides, which played a significant role in exerting pharmacological activity. However, the contents of some rare ginsenosides are very little. So it is very important to find the effective way to translate the main ginsenosides to rare ginsenosides. In order to provide the theoretical foundation for the transformation of ginsenoside in vitro, in this paper, many methods of the transformation of ginsenoside were summarized, mainly including physical methods, chemical methods, and biotransformation methods.
