Design, synthesis and study of coordination complexes with spin crossover or single-molecule magnet properties
[eng] Spin crossover (SCO) complexes and single-molecule magnets (SMMs) are promising prototypes that can reach magnetic bistability within the molecular scale required for data storage. Despite the extensive library of versatile compounds exhibiting SCO and SMM behaviour, continuous growth in the k...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/182768 |
| Acceso en línea: | https://hdl.handle.net/2445/182768 http://hdl.handle.net/10803/673305 |
| Access Level: | acceso abierto |
| Palabra clave: | Química supramolecular Nanotecnologia Magnetisme Lligands Compostos de coordinació Supramolecular chemistry Nanotechnology Magnetism Ligands Coordination compounds |
| Sumario: | [eng] Spin crossover (SCO) complexes and single-molecule magnets (SMMs) are promising prototypes that can reach magnetic bistability within the molecular scale required for data storage. Despite the extensive library of versatile compounds exhibiting SCO and SMM behaviour, continuous growth in the knowledge of such molecular magnetic complexes is pursued to understand its fundamental insights. Here, we contribute on unveiling crucial aspects on their magnetic foundations. Starting from the synthesis of 3-bpp (bpp: 2-(pyrazol-1-yl)-6-(1H-pyrazol-3- yl)pyridine) derivatives, diverse mononuclear compounds of Fe(II) were accessed. The magnetic study of these compounds offered fruitful opportunities to unveil specific insights related to the SCO (Chapters 2 to 4). In chapter 2, we can drastically modulate the SCO temperature for a series of three Fe(II) derivatives of 1,3-bpp: [Fe(1,3-bpp)2](ClO4)2 (1), [Fe(met1,3-bpp)2](ClO4)2 (2), [Fe(dimet1,3-bpp)2] (ClO4)2 (3). The direct influence of the methyl substituents on the SCO temperature (with TSCO (3) > TSCO (1) > TSCO (2)), was observed through by magnetic studies in sold-state. In solution, the crystal packing is excluded as a contributor to their overall macroscopic properties, being the T1/2 tuned through ligand design. In Chapter 3, we studied the metal composition effects on the SCO thermal transition of compound [Fe(met1,3-bpp)2](ClO4)2 (2). For such purpose, the isostructural [Zn(met1,3-bpp)2](ClO4)2 (4) complex and the series [Fe1-xZnx(Me-1,3bpp)2](ClO4)2 (5x; 0.1, 0.153, 0.219, 0.333, 0.412, 0.476, 0.559 and 0.636) were synthesized. The structural study unveils the gradual evolution of the crystallographic parameters with the metal composition at three levels: at the local, at the level of intermolecular interactions and in terms of the crystal lattice parameters. We observed a decrease on the SCO temperature and an increase of the residual HS Fe (II) ascribed to the negative chemical pressure induced by the Zn(II). We quenched the samples at 2K, observing that the relaxation temperature of the metastable state, T(TIESST), is unaffected by the composition. In Chapter 4, an unprecedented heteroleptic compound, [FeL(bpp)](ClO4)2 (6), showing four markedly different magnetic responses at the same temperature range (300-340K) near room temperature is presented. The system undergoes a succession of irreversible phase transitions 6·ac → 6α → 6β → 6γ in the solid-state upon several thermal cycles. An intimate connection between the SCO and structural phase transitions (SPTs) through single-crystal X-ray diffraction (SCXRD) is described. Compound (7·ac) is presented as good candidate for similar study. We tried to elucidate some insights on the importance of the N-H interactions within complex 6 by using its methylated derivative. Nevertheless, it was not possible since homoleptic [FeL2](ClO4)2·2H2O (8), [Fe(Me2bbp)2](ClO4)2 (9) complexes and the [FeL(H2O)2(C3H6O)](ClO4)2 ·2C3H6O (10) were obtained. The design of polytopic ligands containing pyrazolyl-pyridine moieties is discussed in chapter 5. Five new organic ligands (H2L3 to H2L7) were synthesized and fully characterized. A new promising synthetic route to access multitopic ligands, which allows to obtain satisfactorily ligand H2L8, is also proposed. A triple-stranded helicate [Co2(H2L)3]4+ (11) containing Co(II), which often behaves as SMM, was synthesized (Chapter 6). The metal displays an adequate geometry between the trigonal prismatic (TP) and the trigonal antiprismatic (TAP) to study its small axial anisotropy through solution paramagnetic 1H NMR and solid-state magnetometry. The study of the [CoZn(H2L)3]4+ (13) helicate allows to discard the intramolecular magnetic interactions as a source of the low magnetic anisotropy. Two new [Fe9] grid-like clusters composed of an unprecedented flat nanosheet with the formula [Fe9O4(OH)8] as an inorganic core are described in Chapter 7. Both polynuclear coordination complexes with the proposed molecular formula Fe9O4(OH)10(H2L2)6(H2O)4](BF4)5 (17) and [Fe9O4Cl6(OH)8(H2L2)6]4(Cl) (18) display an interesting magnetic behaviour. Considering its first formation together with triple-stranded helicates with the general formula Fe(C2O4)3@[Fe2(H2L2)3] (14, 15 and 16), their obtaining and isolation is discussed. In chapter 8, we describe the first attempt on identifying the dynamics of a broken symmetry states, [HS-LS] and [LS-HS], of a binuclear X@[Fe2(H2L)3]3+ (19 and 20) helicates on the millisecond timescale by using paramagnetic NMR spectroscopy. New synthetically addressed jellyfish-like compounds, ([X@Fe(H2L5)3]2)3+ (24 to 27) were obtained by using the appropriate ligand H2L5 with additional aromatic groups concerning the original ditopic H2L ligand. Such compounds are attractive for studying in solution. |
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