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

Abstract

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