6533b852fe1ef96bd12aab26

RESEARCH PRODUCT

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

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Two new Co II /Co III complexes, [{Co II Co III (mea) 3 } 2 (bpe) 3 ](ClO 4 ) 4  · 1.5CH 3 OH · 1.5H 2 O ( 1 ) and [ Co 4 II Co 3 III ( dea ) 6 ( CH 3 COO ) 3 ] ( ClO 4 ) 0.75 ( CH 3 COO ) 1.25 · 0.5 H 2 O ( 2 ) [Hmea = monoethanolamine H 2 dea = diethanolamine and bpe = 1,2-bis(4-pyridyl)ethane], have been obtained by reacting cobalt(II) perchlorate ( 1 and 2 ), Hmea ( 1 )/H 2 dea ( 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 {Co II Co III (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 [ Co 4 II Co 3 III ] cations, with a central Co II 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.