Karen Robertson

Tetravalent Silicon Connectors MenSi(p-C6H4CO2H)4−n (n = 0, 1, 2) for the Construction of Metal−Organic Frameworks

A series of silicon-centered connecting units, Me(n)Si(p-C6H4CO2H)(4-n) (n = 0, 1, 2), have been prepared and their coordination polymers with Zn(II) metal atoms studied. The tetra-acid L1 (n = 0) acts as a tetrahedral node and reacts with Zn(II) centers to give 1, a novel interpenetrating 3D network containing distorted tetrahedral bimetallic secondary building units (SBUs). The triacid L2 (n = 1) acts as a trigonal pyramidal node and forms an intercalated 2D layered network, 2, with Zn(II) ions, containing distorted octahedral tetranuclear SBUs. Last, the bent diacid L3 (n = 2) reacts with Zn(II) centers to give 3, a corrugated 2D layered structure containing 1D zinc hydroxo chains. Together these three new coordination polymers demonstrate the potential versatility of tetravalent silicon containing connecting ligands for metal-organic framework construction.

An organosilicon hexacarboxylic acid and its use in the construction of a novel metal organic framework isoreticular to MOF-5

A novel hexacarboxylate organo-silicon molecule has been prepared and used in the construction of IMP-15–a Metal Organic Framework (MOF) material of pcu topology, isoreticular to MOF-5 but with half the metal loading.

MgII, CaII, and CoII Metal-Organic Framework Materials with [Si(p-C6H4CO2)3(p-C6H4CO2H)]3– Struts

Three new metal-organic framework materials [Mg3(LH)2(EtOH)2(H2O)]·(EtOH)4.5(H2O)0.25 (IMP-13Mg), [Co3(LH)2(EtOH)2(H2O)]·(EtOH)3 (IMP-13Co), and [Ca3(LH)2(EtOH)4]·(EtOH)6 (IMP-14) have been prepared from the treatment of silanetetrabenzoic acid (L-H4) with MgII, CoII, and CaII salts respectively. In all cases the silanetetrabenzoic acid has been triply deprotonated and the resultant carboxylate groups assemble with trinuclear metal-based nodes to give (3,6)-connected kgd-type two-dimensional layers. These layers are then extended into the third dimension by coordination of the metal nodes by carboxylic acid groups in adjacent layers. In the case of IMP-13Mg/Co, only alternate L-H connectors and metal nodes are involved in these interlayer interactions, leaving some acid groups free within the structure. However, in IMP-14 all L-H connectors and metal nodes participate in interlayer bonding.

Crystallisation and physicochemical property characterisation of conformationally-locked co-crystals of fenamic acid derivatives

Polymorphism in drug compounds can cause significant problems for industrial-scale production and so a method for restricting the conformational freedom of the target compound whilst retaining desired chemical properties is highly beneficial to the pharmaceutical industry. Co-crystallisation is commonly used to alter the structure of an active pharmaceutical ingredient (API) without affecting its activity. A comprehensive co-crystal screen of four fenamic acid derivatives affords a strictly limited number of co-crystals. These show no evidence of polymorphism, although some of the parent APIs exhibit significant polymorphism. Two of these co-crystals, of mefenamic acid and tolfenamic acid with 4,4′-bipyridine, were previously unknown and are studied using X-ray diffraction. Co-crystals from this screen are fully characterised and display comparable solubility and stability with respect to the parent APIs; no phase transformations have been identified. A range of crystallisation techniques, including cooling and grinding methods, are shown to afford single polymorphic forms for each of the co-crystals.

Using flow technologies to direct the synthesis and assembly of materials in solution

In the pursuit of materials with structure-related function, directing the assembly of materials is paramount. The resultant structure can be controlled by ordering of reactants, spatial confinement and control over the reaction/crystallisation times and stoichiometries. These conditions can be administered through the use of flow technologies as evidenced by the growing widespread application of microfluidics for the production of nanomaterials; the function of which is often dictated or circumscribed by size. In this review a range of flow technologies is explored for use in the control of self-assembled systems: including techniques for reagent ordering, mixing control and high-throughput optimisation. The examples given encompass organic, inorganic and biological systems and focus on control of shape, function, composition and size.Graphical abstract.

Poly[(μ6-rac-cis-cyclo-hexane-1,2-di-carboxyl-ato)strontium]

In the title layered coordination polymer, [Sr(C(8)H(10)O(4))](n), the strontium ion adopts a distorted square-antiprismatic SrO(8) geometry, arising from its coordination by six different cis-cyclohexane-1,2-dicarboxylate dianions (two bidentate and four monodentate). Within the dianion, the cyclohexane ring adopts a chair conformation and the dihedral angle between the planes of the -CO(2)(-) groups is 80.4 (6) degrees. The polyhedral linkage pattern leads to (100) sheets in the crystal in which the SrO(8) groups share triangular faces and edges in which the Sr...Sr topological connectivity is a 6(3) net. The crystal studied was a nonmerohedral twin, with the components related by a 180 degree rotation about [100].

Integrated plug flow synthesis and crystallisation of pyrazinamide

We report the integration of flow chemistry with plug flow crystallisation. Catalytic flow hydration of pyrazinecarbonitrile to pyrazinamide was performed in a packed bed column of MnO2. The effluent of this flow reactor was directly linked to a tri-segmented tubular crystalliser (KRAIC), providing a seamless transition from flow synthesis to crystallisation, with control over solid form and particle characteristics.

Exploring effects of intermittent light upon visible light promoted water oxidations

Visible light promoted photocatalytic water oxidations for potential solar fuel production have been studied widely, with many reports on optimization of reagent components. Here we report an exploration on the effects upon ongoing reactions of daylight equivalent light intensity illumination with regulated short dark periods of a few seconds duration as compared to standard continuous illumination. Comparison was made with systems employing synthesized low cost earth abundant iron oxide, calciumoxomanganite and cobalt oxide nanoparticulate catalysts together with a [Ru(bpy)3]2+ light harvesting dye and an electron acceptor. Yields of gaseous O2 and proton production were measured in situ and in real time. The study found that low cost catalysts could give very significantly increased O2 yields, turn over frequency and improved reaction profiles by use of simple on/off illumination. A range of timings with identical overall photon flux were tested and an optimum determined. Analysis of effects upon the light sensitizer under the range of lighting conditions (through mass spectrometry and UV-vis measurements), together with implementation of a continuous flow system as comparison to the batch reactions, were all employed to help elucidate the mechanisms for the clear improvements in reaction yields observed. These are believed to stem from reduction in self-decomposition of excess oxidized sensitizer and better synchronization of cyclic sensitizer oxidation/reductions with water oxidation at the metal oxide surface at specific light on : off timing.

A novel open tubular continuous crystalliser: design and evaluation

The ability to continuously manufacture products can be of huge benefit to industry as it can reduce waste and capital expenditure. Continuous crystallisation has received tepid interest for many years but has come to the fore recently as it holds the potential for a radical transformation in the way crystalline products are manufactured, leading to the development method being embraced by major industries such as pharmaceuticals. In addition to the financial benefits offered by continuous crystallisation over conventional batch methods, a higher level of control over the crystallisation process can also be achieved – allowing improved, more consistent particle attributes to be obtained in the crystallisation process. This control is in part a consequence of the smaller volumes involved in continuous crystallisation, which also has the advantage of reducing any hazards associated with the materials being processed. By using smaller volumes, the mixing efficacy is inherently increased which reduces any disparity between local environments, thereby allowing kinetics to dictate the nature of the products. The EPSRC Centre for Innovative Manufacturing in Continuous Manufacturing and Crystallisation (CMAC [1]) in the UK is a collaborative national initiative to further the knowledge base and understanding of all aspects relating to continuous crystallisation and its use in the manufacturing of crystalline particulate products. In this work we present the design and construction of a novel continuous crystalliser and its evaluation using various model systems such as calcium carbonate (polymorph control [2]) and Bourne reactions (mixing efficacy [3]). The crystalliser will then be used in the co-crystallisation of agrichemical and pharmaceutical compounds with co-formers in an effort to optimise the solid-state properties of these materials such as solubility. Various aspects of the evaluation of the design of the new crystalliser will be presented with reference to these trials, and assessed critically with respect to evolution of this design and potential implementation in manufacturing processes.