Three new MnII-[MoIII(CN)7]4- molecular magnets constructed from chiral bidentate chelating ligands
Fang-Xue Xu1, Ying-Lian Li1, Xiao-Qin Wei1
1State Key Laboratory of Coordination Chemistry, Collaborative Innovation Center of Advanced Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, China. wangxy66@nju.edu.cn.
Abstract:
Three new cyanide-bridged compounds {[Mn((S,S)-Dpen)]3[Mn((S,S)-Dpen)(H2O)][Mo(CN)7]2·4H2O·4C2H3N} (1-SS), {[Mn((R,R)-Dpen)]3[Mn((R,R)-Dpen)(H2O)][Mo(CN)7]2·4.5H2O·4C2H3N} (1-RR), and {[Mn(Chxn)][Mn(Chxn)(H2O)0.8][Mo(CN)7]·H2O·4C2H3N} (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 P1̄ 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.
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