Functional coordination materials from scorpionate and heterotopic ligands
Creators: name: Hall, Gregory Stuart
Publisher: name: Monash University
Year: 2017
Subjects: Uncategorized

description: This thesis examines the chemistry of the self-assembly process and how it may be used to produce organic and coordination materials. A new class of pyridyl and carboxylic acid containing heterotopic molecules has been designed, synthesised and characterised. An analysis of their hydrogen bonding networks was conducted to determine the effect of varying the relative positions of the pyridyl nitrogen atom and the carboxylic acid group. The networks produced varied from 1- to 3-dimensional with a large variation in topologies. The low symmetry pyridyl/carboxylic acid heterotopic molecules were successfully utilised to form a large number of diverse coordination compounds. The coordination compounds were synthesised by the controlled deprotonation of the carboxylic acid by the slow thermal decomposition of DMF. The topology and connectivity of the coordination polymers were shown to be heavily influenced by the relative position of the pyridyl nitrogen atom and the carboxylic acid/carboxylate group. In addition to a small number of 1- and 3-dimensional coordination polymers, the directional heterotopic ligands were used to produce a variety of non-centrosymmetric, 2-dimensional sheets (3.1, 3.3, 3.5, 3.6). In some cases, the helical-type packing of the polar sheets caused the formation of chiral coordination systems (3.3, 3.5 and 3.6). A heterotopic ligand bearing a carboxylic acid at one terminus and a 2,2'-dipyridyl group at the other was used to successfully synthesise a number of hydrogen bonding and coordination compounds including an unusual, discrete M₄L₄ polyhedron (4.6). This compound demonstrates the unusual ability to form distorted polyhedra using low symmetry dipyridyl/carboxylate ligands. A number of isostructural supramolecular 'nanoball' metal analogues of the formula [(Tp4-pyCuIMeCN)₈(MII(ClO₄)₂)₁₀/₃(MII(ClO₄)(MeCN))₈/₃](ClO₄)₈/₃∙xMeCN were synthesised and structurally characterised. The materials consist of discrete supramolecular species which are approximately 2.9 nm in van der Waal diameter. These supramolecules pack in a fashion which causes the material to have a large void volume, which comprises approximately 29 % of the overall crystal volume. The metal analogues were subjected to gas sorption analysis, with some of the materials being shown to successfully absorb H₂, N₂, CO₂ and CH₄ gases. A weight % uptake for H₂ of 1.22 % was recorded for the iron variant (5.1FeClO₄). The greatest enthalpy of binding achieved for the metal analogues was 8.75 kJ mol-1 (5.1CuClO₄). The isostructural Cu(II) nanoballs produced using perchlorate and tetrafluoroborate anions were subjected to gas storage analysis with some promising results. The tetrafluoroborate containing analogue (6.1CuBF₄) was able to achieve a weight % uptake of 1.39 % for H₂ which was 0.14 % greater than that of the perchlorate containing material (5.1CuClO₄). Additionally, 6.1CuBF4 had a calculated enthalpy of binding which was 0.10 kJ mol-1 greater than that of 5.1CuClO₄. The robust structure and modular nature of the supramolecular nanoballs led to the investigation of two anion nanoball variants, 6.2CuPF₆ and 6.3CuNO₃. Both materials contained the same nanoball topology and connectivity as the metal variants (Fe, Co, Cu, Zn and Cd), however, the variation in the anion present in the structure caused a significant difference in the solid-state packing structure, giving rise to materials with void volumes of 10 % and 41 % for the hexafluorophosphate- and nitrate-containing materials, respectively. The variation in the packing structure was shown to influence both the stability and effectiveness of the materials to absorb a number of gaseous guests. 6.3CuNO₃ had a maximum weight % uptake of H₂ of 1.05 % with a maximum enthalpy of binding of 7.19 kJ mol-1. Finally, a series of nanoballs was produced using different nitrile-containing solvents. As with the counterion variants, the overall basic nanoball topology and connectivity was identical to the previous divalent metal variants, however, the variation in the solvent material in the structure was shown to have a profound effect on the solid-state packing of the materials and, consequently, the solvent accessible void volume of the crystal. Void volumes of the solvent variants ranged from 23 % for the trimethylacetonitrile containing nanoball (7.5CuValCN) to 41 % for the propionitrile containing material (7.2CuPrCN). The materials also contained a number of unique structural features such as the presence of a single copper cation in the centre of the nanoball (7.3CuButCN and 7.4CuIso-ButCN) and [Cu(iso-ButCN)₄] cations in the interstitial space (7.4CuIso-ButCN).