Heterometallic CoII-CoIII-MII alkoxido-bridged heptanuclear motifs (M = Cu, Zn). Syntheses, crystal structures and magnetic properties

Abstract

Abstract Two new alkoxido-bridged heterometallic complexes of formula [CoIICoIII3CuII3(dea)6(CH3COO)3](ClO4)0.75(CH3COO)1.25 (1) and [CoII2CoIII2ZnII3(tea)2(piv)6(CH3O)2(OH)2(CH3OH)2]·H2O 2 (H2dea = diethanolamine, H3tea = triethanolamine and Hpiv = pivalic acid) have been assembled using aminoalcohol ligands. The cationic core in 1 possesses a threefold crystallographic axis, and it exhibits a set of three copper(II), one cobalt(II) and three cobalt(III) ions arranged as a hexagon of alternating copper(II) and cobalt(III) ions around the central cobalt(II) ion. Each edge of the hexagon is defined by a double alkoxido bridge, the outer one being bis-monodentate with copper(II)-cobalt(III) pair whereas the inner one adopts a tris-monodentate coordination mode linking the Cu(II)-Co(III) pair with the central cobalt(II) ion. The acetate groups act as bidentate ligands towards the copper(II) ions. The intramolecular cobalt(II)-copper(II) separation is 3.157 A. A hexagon of two cobalt(II), two cobalt(II) and two zinc(II) ions distributed along three types of edges with a central zinc(II) ion occurs in 2. A tris-modentate alkoxido bridge is involved in all edges together with another bis-monodentate alkoxido bridge (CoIII-CoII and CoII-ZnII pairs) and a carboxylate-pivalate bridge in the syn-syn conformation. The five coordination at each peripheral zinc(II) ion is completed by a monodentate carboxylate-pivalate ligand whereas a methoxo group allows to achieve the six-coordination at each cobalt(III) ion. The intramolecular cobalt(II)-cobalt(II) separation through the inner zinc(II) ion is 6.309 A. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–300 K. The exchange interaction between the six-coordinate cobalt(II) and copper(II) ions through the double alkoxido bridges in 1 and that between the six-coordinate cobalt(II) ions across the diamagnetic zinc(II) ion in 2 are found to be ferromagnetic [J = +5.39(5) (1) and +1.05(2) cm−1 (2)], the accidental orthogonality between the interacting magnetic orbitals accounting for this behaviour in the two cases.