Exploring Tuning of Structural and Magnetic Properties by Modification of Ancillary β-Diketonate Co-ligands in a Family of Near-Linear Tetranuclear DyIII Complexes

Three tetranuclear Dy-III complexes, [Dy-4(LH)(2)(CH3OH)(4)(acac)(6)] (1), [Dy-4(LH)(2)(CH3OH)(4)(hmacac)(6)]center dot 2CH(3)OH (2), and [Dy-4(LH)(2)(CH3OH)(4)(dpacac)(6)]center dot 2CHCl(3)center dot 2CH(3)OH center dot 2H(2)O (3), have been synthesized and characterized [LH4 = (2E,N'E)-N'-(2,3-dihydroxybenzylidene)-2-(hydroxyimino)propanehydrazide; acacH = acetyl-acetone; hmacacH = 2,2,6,6-tetramethyl-3,5-heptanedione; dpacacH = dibenzoylmethane]. The structural elucidation of these complexes reveals two types of Dy-III centers in terms of the number of ancillary beta-diketonate co-ligands coordinated to the metal centers. Detailed magnetic studies have been carried out on 1-3 which reveal a slow relaxation of magnetization at low temperatures. The relaxation of complexes 2 and 3 is distributed in three temperature ranges: lower temperature process, transition range, and higher temperature process. In the higher temperature range, the best fitting of the data for 2 yields tau(0) = (6.3 +/- 3.6) x 10(-6) s and U-eff = (23.8 +/- 4.0) K, and for 3, tau(0) = (9.4 +/- 5.9) x 10(-6) s, U-eff = (29.0 +/- 6.3) K.