The interest in engineering and constructing coordination compounds with supramolecular structures has permanently increased during the last two decades. As a matter of fact, coordination polymers (CPs), also comprising metal-organic frameworks (MOFs), seem very promising in a variety of fields of industrial, technological and environmental relevance, e.g., as selective and reversible adsorbents of gases and/or volatile organic compounds, as highly efficient and selective catalysts, as magnetic and photoluminescent materials capable of both metal- and ligand-centered emission, or even as antimicrobial agents. Coordination polymers are generally formed by the self-assembly of metallic centres and bridging organic linkers. Diverse geometries of the metal ions coupled to sizeable, shapeable and functionalizable organic bridging linkers, may give birth to a huge and impressive class of CPs with various architectural topologies and capable to bring a lot of advantages in terms of regularity, designability and versatility. In Chapter 1 of this thesis, a background and main concepts about coordination polymers are presented. A review of some key advances in the field along with a discussion in terms of relationship between the nature and structure of specifically designed organic linkers and the properties of the products is also included. Practical examples demonstrate that the physical and chemical properties of the linkers play a decisive role in the properties of novel functional MOFs. One particular section of Chapter 1 was dedicated to state-of-the-art coordination frameworks incorporating the nitrogen ligand pyrazole and its derivatives, polypyrazoles. This section was included also to anticipate the work of this thesis about new coordination frameworks incorporating different rigid and flexible polypyrazolyl ligands. Their coordinative potentialities have been insistently explored due to the remarkable robustness of the corresponding supramolecular frameworks coupled to other interesting properties, making them suitable candidates as multifunctional materials. Another particular section was dedicated to a brief recall about silver(I) coordination polymers that have demonstrated, through the last two decades, interesting antimicrobial action against different cultures of bacteria, also anticipating the new silver(I)-based coordination polymers with antibacterial action covered in this thesis. An overview of microporous properties followed by an outline of this thesis end up Chapter 1. Chapter 2, dedicated to the experimental work of this thesis, presents the synthesis of forty three new coordination polymers based on five polypyrazolyl ligands as linkers and different late transition metals as connectors. Accordingly, three rigid ligands such as 4,4'-bipyrazole (H2BPZ), 3,3',5,5'-tetramethyl-4,4'-bipyrazole (H2Me4BPZ) and 1,3,5-tris((4-pyrazol-1H-yl)phenyl)benzene ligand (H3BTPP), along with two flexible ones such as 1,4-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)benzene ligand (H2BDMPX) and 4,4'-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)biphenyl (H2DFBDMP) have led, either by conventional paths or following solvothermal routes, to the isolation of coordination polymers of formula [M(BPZ)]âˆ™Solv (M = Zn, 1; Co, 2; Cd, 3; Cu, 5; Ni, 6; Pd, 7; Solv = DMF, MeCN or H2O), [Ag2(BPZ)] (10) and [Ag(H2BPZ)(X)] (X = NO3, 11; ClO4, 12; BF4, 13; PF6, 14; CH3SO3, 15; CF3SO3, 16), [M(Me4BPZ)] (M = Zn, 17; Co, 18; Cd, 19), [Mx(OH)y(BTPP)z]âˆ™Solv (x = 9, y = 12 and z = 2 for M = Ni, 20; x = 12, y = 18 and z = 2 for M = Cu, 21; x = 3, y = 0 and z = 2 for M = Co, 23; Solv = DMF and H2O), [Mx(BDMPX)] (x = 1 for M = Zn, 24; Co, 25; Cd, 26; x = 2 for M = Cu, 27), [Mx(DFBDMP)] (x = 1 for M = Zn, 33; Co, 34; Cd, 35; x = 2 for M = Cu, 36; Ag, 37), [Ag(H2BDMPX)(X)] (X = ClO4, 28; BF4, 29; NO3, 30; CF3CO2, 31; CF3SO3, 32), and [Ag(H2DFBDMP)(X)] (X = NO3, 38; ClO4, 39; BF4, 40; PF6, 41; CF3CO2, 42; CF3SO3, 43). Their structural characterization was done by means of infrared spectroscopy (IR), elemental analysis (EA), thermal gravimetric analysis (TGA) and, in some of the compounds, X-ray powder diffraction (XRPD) coupled to thermodiffractometric studies. Chapter 3, dedicated to results and discussion, show the most important results in view of potential applications. Section 3.1. describes the synthesis of the new coordination polymers, along with a spectroscopic characterization by infrared spectroscopy (IR), revealing the main absorption bands in their spectra. Section 3.2. reveals the molecular structures for some of the synthesized compounds by means of state-of-the-art laboratory powder diffraction methods, allowing to disclose diverse and fascinating architectures, some of them with porous structure, developed by the polypyrazolyl spacers when coordinated to different metal ions. Section 3.3. is dedicated to the thermal behaviour displayed by the new polymeric materials, highlighting in some of them a remarkable thermal robustness, peaking at 500 Â°C in the case of Cd(II) derivatives based on the rigid H2Me4BPZ and the flexible H2BDMPX and H2DFBDMP ligands. A certain framework flexibility in some of the synthesized PCPs, was also studied by means of thermodiffractometric techniques, highlighting, e.g., the permanent porosity of 1-3, 5 and 6, retained along consecutive temperature cycles in all these cases but 3. Species 24, 25, 33 and 34 reppresent a notable example of pro-porous materials, their adsorption performances implying a low-temperature opening of the rhombic motifs, stimulated by the gas probe and facilitated by the nature of the ligand. Prompted by the envisaged molecular structures containing pores, their adsorption properties with N2 at 77 K and CO2 at 298 K are presented in Section 3.4. When excited with an UV radiation, some of the polymeric species proved their photoluminescence properties, which are shown and discussed in Section 3.5. When embedded into polyethylene disks, the silver(I) coordination polymers 10, 11 and 13-16 based on the rigid H2BPZ ligand, demonstrated their activity as topical antibacterial agents against suspensions of E. coli, P. aeruginosa, and S. aureus: a complete reduction of the three bacterial strains is achieved in 24 h, the reduction of S. aureus reaching ca. 90% in only 2 h. The biocidal action was expressed also by contact susceptibility tests, as discussed in Section 3.6. Concluding remarks and future perspectives are given in Chapter 4. The Annexes section was added at the end of this thesis, including different IR spectra, some tables with crystallographic data, graphical results of the Rietveld refinements, thermodiffraction traces, an XRF plot and two SEM images. All these data were attached also as supplementary information in order to give the reader a more complete understanding of the experimental work presented throughout the thesis.
|Titolo:||New Coordination Polymers Incorporating Rigid and Flexible Polypyrazolyl Ligands with Late Transition Metals. Microporosity, Thermal Resistance, Photoluminescence and Antibacterial Action|
|Data di pubblicazione:||19-mar-2013|
|Appare nelle tipologie:||Tesi di dottorato (Pregresso)|