Metal organic framework (MOF) liquid crystals. 1D, 2D and 3D ionic coordination polymer structures in the thermotropic mesophases of metal soaps, including alkaline earth, transition metal and lanthanide soaps

Abstract

Taken together, the body of existing literature on metal soap crystal structures and mesophases supports the view that much is to be gained by treating the soaps as metal organic frameworks (MOF's) when relating their structure and liquid crystallinity. We argue that metal soaps mesophases often consist of disordered metal organic (carboxylate) frameworks (MOF's). Metal atoms are linked by bridging carboxylates, and the metal-oxygen networks form semi-flexible rods, chains and sheets of M-O polyhedra within their co-bonded, mesotructured, self-assemblies of lipidic chains. The packing of the molten hydrocarbon chains allows otherwise unconnected MOF networks to coexist as spatially isolated units in the same unit cell. For instance the lamellar phases are true 2D MOF's or layers of 1-D MOF's. The phase transitions can then be regarded as coupled disordering/re-ordering transitions involving rotational and conformational disordering of the hydrocarbon chains balanced with disordering of MOF symmetries, MOF topological transformations, depolymerizations and dimensionality reductions ultimately leading to anisotropic melts. By way of demonstration, thermotropic phase transitions of homologous series of lanthanide soaps are systematically studied using a variety of experimental methods, and the data are used in a topological model for testing the consistency with the MOF concept of metal soap crystal structures and thermotropic mesophases. Finally, an interpenetrating bicontinuous MOF comprised of SrO 6 polyhedral rods is presented as an atomically resolved model for the network topology of the cubic mesophase of strontium soaps. Metal soaps are therefore shown to afford a bridge between liquid crystals and metal organic framework (MOF) materials.

Solventless synthesis of cerium oxide nanoparticles and their application in UV protective clear coatings

“…For other organic coordinated metal compounds, the path is controlled by the structure of the organic chain and the coordinated metal. Some metal-oxygen bonds can be decomposed at temperatures lower than 300 C and others remain stable up to 520 C. 28,37,38 The powder X-ray diffractograms in Fig. 4 show three distinct phases in the growth of ceria during this process.…”

Cooperative loading of multisite receptors with lanthanide containers: an approach for organized luminescent metallopolymers

“…lanthanide-containing polymers) because of the versatile coordination behavior of these metallic centers. 5 In order to avoid this pitfall, coordination chemists have restricted the concept of metallopolymers to infinite crystalline assemblies made of anionic ligand strands and cationic nodes forming extended 3D-networks, originally referred to as Wolf-type III metallopolymers 4 or coordination polymers, 9 and nowadays often named metal–organic frameworks (MOFs). 10 These infinite assemblies resemble ionic solids in their essence and lead to robust and inert scaffolds possessing variable porosities.…”

Polycontinuous geometries for inverse lipid phases with more than two aqueous network domains

“…29 The theoretical possibilty of polycontinuous metal organic frameworks has been mentioned in ref. 88 The experimental realisation of a tricontinuous system that is most closely related to the predictions of this article is the tricontinuous mesoporous silicate IBN-9 with hexagonal symmetry reported by Han et al 18,[43][44][45] This material has been reported to contain three hollow channels following the nets of the 3etc(187 193) structure (see Fig. 3) with a solid ''matrix'' of amorphous silicate forming a periodic branched sheet, with a unit cell size a z 8.9 nm and c z 8.4 nm.…”