Tris(ethylenediamine) cobalt(II) and manganese(II) nitrates Article - Juin 2020

Miguel Cortijo, Ángela Valentín-Pérez, Mathieu Rouzieres, Rodolphe Clérac, Patrick Rosa, Elizabeth Hillard

Miguel Cortijo, Ángela Valentín-Pérez, Mathieu Rouzieres, Rodolphe Clérac, Patrick Rosa, Elizabeth Hillard, « Tris(ethylenediamine) cobalt(II) and manganese(II) nitrates  », Crystals, juin 2020, 472 (14 p.). ISSN 2073-4352

Abstract

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 group P6322 to enantiomorphic P6522 or P6122, 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 with S = 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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