Abstract
A new {Dy5} cluster compound has been synthesized and structurally characterized from the initial use of the Schiff base ligand N-naphthalidene-2-amino-5-chlorophenol (nacpH2) in coordination chemistry. The 1:1 reaction between Dy(hpd)3∙2H2O and nacpH2, in a solvent mixture comprising CH2Cl2 and MeOH, afforded orange crystals of [Dy5(OH)2(hpd)3(nacp)5(MeOH)5] (1) in 70% yield, where hpd− is the anion of 3,5-heptadione. The {Dy5} complex can be described as two vertical {Dy3(μ3-OH)}8+ triangles sharing a common vertex; such a metal topology is unprecedented in 4f-metal cluster chemistry. Direct current (dc) magnetic susceptibility studies revealed the presence of some weak ferromagnetic exchange interactions between the five DyIII ions at low temperatures. Alternating current (ac) magnetic susceptibility measurements at zero applied dc field showed that complex 1∙3MeOH∙CH2Cl2 exhibits temperature- and frequency-dependent out-of-phase signals below ~20 K, characteristics of a single-molecule magnet (SMM). The resulting relaxation times were used to construct an Arrhenius-type plot and determine an effective energy barrier, Ueff, of 100 K for the magnetization reversal. The application of a small dc field of 200 Oe resulted in the surpassing of the quantum tunneling process and subsequently the increase of the Ueff to a value of 170 K. The reported results are part of a long-term program aiming at the preparation of structurally and magnetically interesting lanthanide complexes bearing various Schiff base chelating/bridging ligands.
Highlights
The coordination chemistry of 4f -metal ions has recently re-attracted the interest of the scientific community for three primary reasons: (i) their ability to form oligo- and polynuclear metal complexes with unprecedented and nanosized structures [1], (ii) the unusual photoluminescence properties they exhibit [2], arising from forbidden 4f -4f electronic transitions that emerge when coordinated organic ligands are involved, and (iii) their pivotal role in the development of efficient single-molecule magnets (SMMs) [3]
SMMs are individual molecular compounds that exhibit slow relaxation of their magnetization in the absence of an external magnetic field [4]. Such a magnetization reversal is accomplished by the presence of an anisotropic energy barrier, U, which operates through various mechanisms that are either spin-lattice processes (Raman, Orbach and direct mechanism) or quantum tunneling of magnetization (QTM) [5]
Due to their molecular properties, SMMs have been proposed as promising candidates for various modern technological advancements, such as in information and data storage, molecular spintronics and quantum computing [6]
Summary
The coordination chemistry of 4f -metal ions has recently re-attracted the interest of the scientific community for three primary reasons: (i) their ability to form oligo- and polynuclear metal complexes (clusters) with unprecedented and nanosized structures [1], (ii) the unusual photoluminescence properties they exhibit [2], arising from forbidden 4f -4f electronic transitions that emerge when coordinated organic ligands are involved, and (iii) their pivotal role in the development of efficient single-molecule magnets (SMMs) [3]. SMMs are individual molecular compounds that exhibit slow relaxation of their magnetization in the absence of an external magnetic field [4] Such a magnetization reversal is accomplished by the presence of an anisotropic energy barrier, U, which operates through various mechanisms that are either spin-lattice processes (Raman, Orbach and direct mechanism) or quantum tunneling of magnetization (QTM) [5]. Assisted assisted by by the ligand-field around the metal ion(s), which can stabilize the largest projection of the total angular the ligand-field around the metal ion(s), which can stabilize the largest projection of the total angular Based on on these these prerequisites, prerequisites,ititbecomes becomesapparent apparentwhy whyDy. 15/2)) is to III the synthesis of SMMs with interesting properties. Structural formulas and abbreviations of the Schiff base ligands discussed in the text; the blue box encloses the tridentate ligand ligand nacpH nacpH22 used in the present work
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