Tris(ethylenediamine) cobalt(II) and manganese(II) nitrates

Miguel Cortijo (1) , Ángela Valentín-Pérez (1) , Mathieu Rouzieres (1) , Rodolphe Clérac (1) , Patrick Rosa (2) , Elizabeth Hillard (1)

1 CRPP - Centre de Recherche Paul Pascal
2 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

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.

Mots clés: phase transition; coordination complexes; enantiomorphic space groups; X-ray crystallography; chirality; conglomerate crystallization

Domaines: Matériaux

Miguel Cortijo, Ángela Valentín-Pérez, Mathieu Rouzieres, Rodolphe Clérac, Patrick Rosa, et al.. Tris(ethylenediamine) cobalt(II) and manganese(II) nitrates. Crystals, 2020, 10 (6), 472 (14 p.). ⟨10.3390/cryst10060472⟩. ⟨hal-02868896⟩