Structures and magnetic properties of several phenoxo-O bridged dinuclear lanthanide complexes: Dy derivatives displaying substituent dependent magnetic relaxation behavior†
Nine dinuclear Ln(III) complexes, [Ln(dbm)2(L)]2 (Ln = Eu (1), Tb (2), Dy (3), Ho (4), Er (5)) and [Ln(dbm)2(L′)]2 (Ln = Tb (6), Dy (7), Ho (8), Er (9)) (dbm = 1,3-diphenyl-1,3-propanedione, HL = 2-[[(4-methoxy-phenyl)imino]methyl]-8-hydroxy-quinoline and HL′ = 2-[[(4-ethoxyphenyl)imino]methyl]-8-hydroxyquinoline) have been synthesized, and structurally and magnetically characterized. The nine complexes are all phenoxo-O bridged binuclear complexes, in which Ln1 and Ln1a are in an eight-coordinated environment bridged by two phenoxido oxygen atoms of two 8-hydroxyquinoline Schiff base ligands. Although complexes 3 and 7 have very similar structures, magnetic studies reveal that they exhibit different magnetic relaxation behaviors with the effective barriers (ΔE/kB) of 34.5 K for 3 and 67.6 K for 7. The dissimilar dynamic magnetic behaviors of 3 and 7 mostly result from the different electron-donating effect induced by the two alkoxy (–OCH3 and –OC2H5) of the 8-hydroxyquinoline Schiff base ligands. Meanwhile, for complexes 2, 5, 6 and 9, there are no observed magnetic relaxation behaviors under a zero dc field. In addition, the luminescence properties of 1, 2 and 6 were studied.