New alkoxo-bridged mixed-valence cobalt clusters: Synthesis, crystal structures and magnetic properties

Two new CoII/CoIII complexes, [{CoIICoIII(mea)3}2(bpe)3](ClO4)4 · 1.5CH3OH · 1.5H2O (1) and [Co4IICo3III(dea)6(CH3COO)3](ClO4)0.75(CH3COO)1.25·0.5H2O (2) [Hmea = monoethanolamine H2dea = diethanolamine and bpe = 1,2-bis(4-pyridyl)ethane], have been obtained by reacting cobalt(II) perchlorate (1 and 2), Hmea (1)/H2dea (2), bpe (1) and sodium acetate (2). The crystal structures of 1 and 2 have been solved by single crystal X-ray diffraction. Crystal 1 contains “Chinese lantern”-like shaped cations, resulting by connecting two {CoIICoIII(mea)3} moieties with three flexible bpe ligands. The coordination sphere of the outer cobalt(III) ions is built by three amino groups arising from the mea− ligands, and by three bridging alkoxo-oxygen atoms whereas that of the inner cobalt(II) ions is constituted by the three alkoxo oxygen atoms and by three nitrogen atoms from three bpe ligands. The crystallographic analysis of 2 shows the occurrence of heptanuclear [Co4IICo3III] cations, with a central CoII ion and six peripheral cobalt atoms, three of them being divalent and the other three being trivalent. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–300 K. A very weak antiferromagnetic interaction [J = −0.061(2) cm−1] between the high-spin cobalt(II) ions bridged by the bpe ligands occurs in 1 whereas a significant intramolecular ferromagnetic interaction [J = +2.6(1) cm−1] between the high-spin cobalt(II) ions is present in two leading to a low-lying S = 6 spin state. No out-of-phase ac signal was detected for this anisotropic high-spin molecule down to 1.9 K.

Two mixed-valence CoII/CoIII clusters have been obtained: a tetranuclear complex, 1, with “Chinese lantern”-like shaped cations and a heptanuclear one, 2, with a star-like topology of the metal centers. Their magnetic properties have been investigated. A ferromagnetic interaction occurs between the cobalt(II) ions in 2.Figure optionsDownload as PowerPoint slide