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Abstract: Polyoxometalate Molybdenum blue (MBs) complexes typically exist as discrete multianionic clusters and are composed of repeating Mo building units. MB Wheels, such as {Mo176} and {Mo154} are made from pentagon-centered {Mo8} building blocks joined by equal number of {Mo1} units as loin, and {Mo2} dimer units as skirt along the ring edge and the ring sizes of the Mo-blue wheels are modulated by the {Mo2} units. Herein we report a new class of contracted lanthanide-doped MB structures that have replaced all the {Mo2} units with lanthanide ions on the ring edge with the general formula {Mo90+2nLn10-n} (n = 0, 1). We show three examples of this new decameric {Mo90Ln10} (Ln = La, Ce and Pr) framework synthesized by hydrothermal methods, and demonstrate that later Ln ions result in {Mo92Nd9}, conserving one {Mo2} linker unit in its structure, as a consequence of the lanthanide contraction. Remarkably the decameric {Mo90Ln10} compounds are the first examples of charge-neutral molybdenum wheels as confirmed by BVS and redox titrations. We detail our full synthetic optimization for the isolation of these clusters and complete characterization by X-ray, TGA, UV-vis and ICP studies. Finally we show that this fine-tuned self assembly process can be utilised to selectively enrich Ln-Mo Blue wheels for effective separation of lanthanide ions.

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Abstract: The exploration of complex multicomponent chemical reactions leading to new clusters, where discovery requires both molecular self-assembly and crystallization, is a major challenge. This is because the systematic approach required for an experimental search is limited when the number of parameters in a chemical space becomes too large, restricting both exploration and reproducibility. Herein, we present a synthetic strategy to systematically search a very large set of potential reactions, using an inexpensive, high-throughput platform that is modular in terms of both hardware and software and is capable of running multiple reactions with in-line analysis, for the automation of inorganic and materials chemistry. The platform has been used to explore several inorganic chemical spaces to discover new and reproduce known tungsten-based, mixed transition-metal polyoxometalate clusters, giving a digital code that allows the easy repeat synthesis of the clusters. Among the many species identified in this work, the most significant is the discovery of a novel, purely inorganic W24FeIII–superoxide cluster formed under ambient conditions. The modular wheel platform was employed to undertake two chemical space explorations, producing compounds 1–4: (C2H8N)10Na2[H6Fe(O2)W24O82] (1, {W24Fe}), (C2H8N)72Na16[H16Co8W200O660(H2O)40] (2, {W200Co8}), (C2H8N)72Na16[H16Ni8W200O660(H2O)40] (3, {W200Ni8}), and (C2H8N)14[H26W34V4O130] (4, {W34V4}), along with many other known species, such as simple Keggin clusters and 1D {W11M2+} chains.

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Abstract: A spin-flip from a triplet to a singlet excited state, that is, reverse intersystem crossing (RISC), is an attractive route for improving light emission in organic light-emitting diodes, as shown by devices using thermally activated delayed fluorescence (TADF). However, device stability and efficiency roll-off remain challenging issues that originate from a slow RISC rate (kRISC). Here, we report a TADF molecule with multiple donor units that form charge-resonance-type hybrid triplet states leading to a small singlet–triplet energy splitting, large spin–orbit couplings, and a dense manifold of triplet states energetically close to the singlets. The kRISC in our TADF molecule is as fast as 1.5 × 107 s−1, a value some two orders of magnitude higher than typical TADF emitters. Organic light-emitting diodes based on this molecule exhibit good stability (estimated T90 about 600 h for 1,000 cd m−2), high maximum external quantum efficiency (>29.3%) and low efficiency roll-off (<2.3% at 1,000 cd m−2).

Open Access

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Abstract: The self-assembly of Pd4L2 metallocylcic and Pd6L3 trigonal prismatic assemblies are described. The selction of one species over the other has been achieved by carfeul choice of ancilliary ligands, which switch the dynamics of the Pd-N bonds such that a highly unusual and distorted smaller assembly can be kinetically trapped en route to the more energetically favourable larger species. Both assemblies provide promise as easy to access multicavity reaction vessels.

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Abstract: Due to ever increasing pressure for pharmaceutical companies to characterise and patent the polymorph landscape of new APIs, it is important that as many forms as possible are identified in the early stages of drug development. Novel polymorph screening techniques are required to expand the scope of traditional solution-phase methods, and access highly metastable or difficult to nucleate solid forms. This work exemplifies a modern polymorph screen, using a wide variety of experimental and computational methods to comprehensively characterise the polymorph landscape of mexiletine hydrochloride. Instead of the six forms described in previous literature, this screen revealed seven: an enantiotropic pair of anhydrous polymorphs that are stable at different temperatures, one anhydrous metastable form, three families of isostructural channel solvates, and a fourth solvate of unknown structure. Two new channel solvates, and new routes to three known forms were discovered by crystallising mexiletine within drug-mimetic supramolecular gels. As gelation was often turned off when a new polymorph crystallised within the gel, these changes in solid form are likely driven by strong interactions between the drug and gelator. The crystallisation of high temperature stable Form 2 from a gel at room temperature is a particularly striking example of the powerful stabilising effect of these tailored supramolecular gels. A complementary study into the gel-phase crystallisation of diatrizoic acid showed that the drug followed the same two-step crystallisation regime as the gelator, leading to the formation of two novel drug-gelator salt solvates. These results suggest that the polymorph landscape of the gelator has influenced the drug crystallisation, which may provide a new avenue of inquiry for the design of supramolecular gelators for pharmaceutical crystallisation. From this work, it is clear that supramolecular gels are a valuable tool for pharmaceutical polymorph screening.