Ln(III) Metallacrown Complexes: Novel Systems and Single-Molecule Magnet (SMM) Properties

Abstract

This Thesis deals with the synthesis and characterization of new Ga/Ln and 3d/Ln 12-Metallacrown-4 complexes, using salicylhydroxamic acid (shaH2) as a bridging-chelating organic ligand. Magnetic studies also took place and evaluation of the magnetic data are presented. The results presented in Chapter 2 and 3 are already published, while the work presented in Chapter 4 has been submitted for publication. Chapter 5 includes a bank of unpublished results, which have been examined and reported. In Chapter 1 an introduction into the topic of Metallacrowns and Single-molecule magnets (SMMs) is provided. Metallacrowns is a special family of complexes that our group finds great interest in since these molecules can retain their integrity in solution, they are easily modified according to our synthetic demands and needs as well as they can be used as excellent candidates at various applications such as molecular recognition, surface applications, etc. As such, the present Thesis has focused on the synthesis of these molecules with a strong interest into their magnetic properties. Chapter 2 deals with the synthesis and magnetic characterization of a new family of 12-MC-4 complexes, namely (tBu4N){[LnIII(O2CBut)4][12-MC-Mn(III)N(shi)-4]}•5CH2Cl2 (Ln = Gd (1) and Tb (2)) and (tBu4N)2{[YIII(O2CBut)4][12-MC-Mn(III)N(shi)-4]}(ClO4) (3). These compounds have been structurally and magnetically investigated, and they do not show any alternating-current (ac) magnetic susceptibility signals. Chapter 3 involves the isolation and characterization of a new family of isostructural {Fe6Ln} complexes, (pipH)3{Fe6Ln(shiH)3(shi)6}·1.5 pip·xH2O (Ln = Gd (1), Dy (2), Tb (3) and Y (4), pip = piperidine, and shi3- = salicylhydroxamic acid). This family of compounds possesses a unique structural metallacrown-like motif, while they also resemble the structure of metallacrypates. Magnetic studies demonstrate that the {Fe6Dy} analogue shows frequency-dependent ac signals. Thus, the Dy-analogue belongs to the SMM family.Chapter 4 focuses on the synthesis and magnetic characterization of the first Ga/Dy double-decker or sandwich 12-MC-4 complex ever to be reported. The compound possesses a general formula of (tBu4N) [GaIII8DyIII(OH)4(shi)8] (1) and the complex does show interest SMM behavior with an anisotropy barrier Ueff = 40 K. Finally, Chapter 5 includes unpublished results that have been synthesized and characterized. Six new compounds are presented, five of which are Ga/Ln-based complexes, whilst a Fe/Ln compound is also introduced.