Browsing by Author "Macreadie, LK"

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    Hydrogen Bonding of O-Ethylxanthate Compounds and Neutron Structural Determination of C–H···S Interactions
    (CSIRO Publishing, 2014-10-10) Macreadie, LK; Edwards, AJ; Chesman, ASR; Turner, DR
    A range of ethylxanthate (EtXn) salts, containing either protic or aprotic cations (guanidinium (1), methylammonium (2), dimethylammonium (3), trimethylammonium (4), tetramethylammonium (5), tetraethylammonium (6), and tetrapropylammonium (7)), have been synthesised and structurally characterised. The cations in these compounds differ in their degree of hydrogen-bonding ability, i.e. the number of donor groups, with significant structural consequences. Compounds 1–4 contain cations that are able to form N–H···S hydrogen bonds, with six, three, two, and one donor groups in 1–4 respectively. The number of donor atoms affects greatly the dimensionality of the hydrogen-bonding networks in the solid state. The structure of 1 has a 3-D hydrogen-bonding network, 2 and 3 form 2-D sheets and 1-D chains respectively, whereas the lone NH donor group in 4 has strong hydrogen bonding only within a discrete cation–anion pair. The tetraalkylammonium salts 5–7 have no strong hydrogen bonding, with only C–H···S and C–H···O interactions possible. To determine unambiguously the presence of such interactions, single-crystal Laue neutron diffraction data were obtained for compound 5, providing a fully anisotropic model, which can be used to rationalise potential close interactions in the other structures. The neutron structure of 5 confirms the existence of C–H···S hydrogen bonds, with the H···S distance falling well within the sum of the van der Waals radii of the atoms. The close-packing in 5–7 is mediated solely through these weak interactions, with the size of the cations influencing the structures. © CSIRO 1996-2020
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    Improving hydrophobicity of MOFs using aliphatic linkers
    (Society of Crystallographers in Australia and New Zealand, 2017-12-03) Macreadie, LK; Brand, HEA; Hill, MR
    Metal-organic frameworks (MOFs) have become renowned throughout the chemistry and materials communities as an exciting suite of porous material, capable of being designed and adapted to suit various objectives and applications [1]. Aromatic ligands with carboxylate functionalities are a commonly selected organic linker when synthesising MOFs due to their commercial availability and the numerous variable coordination modes exhibited by these functionalities, consequently leading to a high degree of framework connectivity [2]. Structurally similar to 1,4-dicarboxybenzene, frequently used as an organic linker in MOF synthesis, is 1,4-dicarboxycubane due to its para coordination capabilities and carboxylate functionalities. Unlike 1,4-dicarboxybenzene, 1,4-dicarboxycubane is nonplanar in nature, features a higher steric bulk and is void of conjugation within the ring (Figure 1). These differing properties can be exploited to modify the local environment within the pores of resultant MOFs to be more hydrophobic. We have substituted 1,4-dicarboxybenzene with 1,4-dicarboxycubane during the synthesis of known and well-characterised MOFs with the aim of modifying the pore environment within the framework. These MOFs were structurally characterised using single crystal X-ray diffraction and Rietveld refinement of synchrotron X-ray diffraction data collected at the MX and PD beamlines at the Australian . Here we will discuss the structural and behavioural differences between the MOF species, pertaining to their selective gas sorption, water retention and thermal stability properties.
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    Lowering the energetic landscape for negative thermal expansion in 3D-linker metal–organic frameworks
    (ACS Publications, 2023-11-30) Chen, C; Maynard-Casley, HE; Duyker, SG; Barbarao, R; Kepert, CJ; Evans, JD; Macreadie, LK
    Tuning the coefficient of thermal expansion (CTE) of functional materials is paramount for their practical implementation. The multicomponent nature of metal–organic frameworks (MOFs) offers an opportunity to finely adjust negative thermal expansion (NTE) properties by varying the metal ions and linkers used. We describe a new strategy to adjust the NTE by using organic linkers that include additional rotational degrees of freedom. Specifically, we employ cubane-1,4-dicarboxylate and bicyclo[1.1.1]pentane-1,3-dicarboxylate to form the MOFs CUB-5 and 3DL-MOF-1, respectively, where each linker has low torsional energy barriers. The core of these nonconjugated linkers is decoupled from the carboxylate functionalities, which frees the relative movement of these components. This results in enhanced NTE compared to the analogous, conjugated system; VT-PXRD results were used to calculate the CTE for 3DL-MOF-1 (αL = −13.9(2) × 10–6 K–1), and CUB-5 (αL = −14.7(3) × 10–6 K–1), which is greater than the NTE of MOF-5 (αL = −13.1(1) × 10–6 K–1). These results identify a new route to enhanced NTE behaviors in IRMOF materials influenced by low energy molecular torsion of the linker. © American Chemical Society