One- and two-dimensional coordination assemblies incorporating 3,2’:6’,3”-terpyridine linkers

In the field of material sciences, coordination polymers represent a topic of interest, due to their extended structures and the associated properties. To date, the formation of these networks is a fascinating but not fully understood phenomenon, and the evidence of structure-property relationships makes the control of this process an issue of major concern. Towards this end, systematic studies in which one parameter is varied at one time could offer a meaningful contribution to gain a better comprehension of the factors that influence the assembly of one kind of structure over the other possibilities. This is especially true when flexible building blocks are chosen. Although a substantial part of the effort in this area has been centered on the use of rigid ligands, there is scope for developing metal coordination assemblies with more flexible components. In particular, in this PhD thesis, homologous series of ditopic 3,2’:6’,3”-terpyridine ligands have been synthesized following the one-pot procedure by Wang and Hanan, fully characterized (as described in Chapter 2) and their coordination chemistry has been explored focusing on two metal salts. Copper(II) acetate (which typically forms dinuclear paddle-wheel motifs) directed the assembly of 1D-chains (Chapter 3), while cobalt(II) thiocyanate led to the formation of 2D-nets with a (4,4) topology (Chapter 4); only one exception for each category is reported. All the obtained coordination polymers have been characterized via single-crystal XRD, solid state FT-IR and powder X-ray diffraction (PXRD), the latter to confirm whether the crystal chosen for structural determination was representative of the bulk sample. A structural determination and description is reported for each of the coordination assemblies, including comparisons to underline similarities and differences between the networks, in terms of topology, packing interactions and lattice solvents. Thermogravimetric analysis coupled with mass spectrometry (TGA-MS) has been conducted on some of the obtained polymers, with the purpose of identifying and quantifying the solvent released from the lattice under mild condition, i.e. without the net losing its crystallinity. Further TGA-MS measurements have been carried out to check whether the process of solvent extraction is reversible and if the removed solvent could be replaced by other small molecules.
In Chapter 5, the notion of “expanded ligands” is introduced, referring to analogs of conventional ligands in which the donor sites are separated by metal-containing groups. With the aim of combining this concept of metalloligands with terpyridine-based building blocks, in the last part of the thesis asymmetric bis(terpyridines) have been prepared, containing the 2,2’:6’,2”-terpyridine bis(chelating) unit on one end and the divergent ditopic 3,2’:6’,3”- or 4,2’:6’,4”- terpyridine unit on the other. Homoleptic iron(II) complexes of the asymmetric bisterpyridine compounds have been synthesized; these are tetratopic metal-containing molecules, which represent a new type of expanded ligands, i.e. the expanded version of the purely organic bis(terpyridines), and are potential building blocks for the assembly of coordination polymers. All the intermediates and the final compounds have been fully characterized, and several crystallization experiments with different metal salts have been carried out in attempts to obtain supramolecular architectures incorporating the newly-prepared expanded ligands.