Syntheses, Structures, and Magnetic Properties of a Family of Tetranuclear Hydroxido-Bridged Ni2IILn2III (Ln = La, Gd, Tb, and Dy) Complexes: Display of Slow Magnetic Relaxation by the Zinc(II)-Dysprosium(III) Analogue.

A new family of [2 × 2] tetranuclear 3d—4f heterometallic complexes have been synthesized. These are [Zn2Dy2L2(μ3-OH)2(μ4-OH)(dbm)2(MeOH)2]-(NO3)·2H2O·MeOH (3), [Ni2Dy2L2(μ3-OH)2(μ4-OH)-(dbm)2(MeOH)2](NO3)·MeOH (4), [Ni2La2L2(μ3-OH)2-(μ4-OH)(dbm)2(MeOH)2](CIO4)·H2O·2MeOH (5), [Ni2Tb2L2(μ3-OH)2(μ4-OH)(dbm)2 (MeOH)2]-(NO3)·MeOH (6), and [Ni2Gd2L2(μ2-OH)2(μ4-OH)-(dbm)2(MeOH)2](NO3)·MeOH (7), [H2L = N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyi)ethylenediamine and Hdbm = dibenzoylmethane] obtained through a single-pot synthesis using [Zn(HL)(dbm)] (for 3)/[Ni(HL)(dbm)] -2CH3OH (for 4, 5, 6, and 7) as 3d-metal ion precursors. Single-crystal X-ray diffraction analysis and electrospray ionization (ESI) mass spectroscopy have been used to establish their identities. Compounds are isostructural, in which the metal ions are all connected together by a bridging hydroxido ligand in a rare /i4-mode. In complexes 3–7, the metal ions are antiferromagnetically coupled. Taking a cue from the results of 3 and 5, precise estimations have been made for the antiferromagnetic Ni···Ni (JNi = –50 cm–1), Ni···Gd (JNiGd = –4.65 cm-1), and Gd···Gd (JGd = –0.02 cm–1) exchange interactions in 7, involving the gadolinium(III) ions. The Zn2IIDy2IIIcompound 3 has shown the tail of an out-of-phase signal in alternating current (AC) susceptibility measurement, indicative of slow relaxation of magnetization. Interestingly, the Ni2IIDy2II compound 4 in which both the participating metal ions possess large single ion anisotropy, has foiled to show up any slow magnetic relaxation [ABSTRACT FROM AUTHOR]