Tris(ethylenediamine) Cobalt(II) and Manganese(II) Nitrates
CRYSTALS(2020)
摘要
Octahedral tris(ethylenediamine) coordination complexes demonstrate helicoidal chirality, due to the arrangement of the ligands around the metal core. The enantiomers of the nitrate salts [Ni(en)(3)](NO3)(2)and [Zn(en)(3)](NO3)(2)spontaneously resolve to form a mixture of conglomerate crystals, which present a reversible phase transition from space groupP6(3)22 to enantiomorphicP6(5)22 orP6(1)22, with the latter depending on the handedness of the enantiomer. We report here the synthesis and characterization of [Mn(en)(3)](NO3)(2)and [Co(en)(3)](NO3)(2), which are isostructural to the Zn(II) and Ni(II) derivatives. The Mn(II) analogue undergoes the same phase transition centered at 150(2) K, as determined by single-crystal X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry. The Co(II) derivative does not demonstrate a phase transition down to 2 K, as evidenced by powder X-ray diffraction and heat capacity measurements. The phase transition does not impact the magnetic properties of the Ni(II) and Mn(II) analogues; these high spin compounds display Curie behavior that is consistent withS= 1 and 5/2, respectively, down to 20 K, while the temperature-dependent magnetic moment for the Co(II) compound reveals a significant orbital contribution.
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关键词
chirality,conglomerate crystallization,X-ray crystallography,phase transition,coordination complexes,enantiomorphic space groups
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