Molecules containing actinide–nitrogen multiple bonds are of current interest as simple models for new actinide nitride nuclear fuels, and for their potential for the catalytic activation of inert ...hydrocarbon C–H bonds. Complexes with up to three uranium–nitrogen double bonds are now being widely studied, yet those with one thorium–nitrogen double bond are rare, and those with two are unknown. A new, simple mono(imido) thorium complex and the first bis(imido) thorium complex, KTh(NAr)N″3 and K2Th(NAr)2N″2, are readily made from insertion reactions (Ar = aryl, N″ = N(SiMe3)2) into the Th–C bond of the cyclometalated thorium amides ThN″2(N(SiMe3)(SiMe2CH2)) and KThN″(N(SiMe3)(SiMe2CH2))2. X-ray and computational structural analyses show a “transition-metal-like” cis-bis(imido) geometry and polarized ThN bonds with twice the Wiberg bond order of the formally single Th–N bond in the same molecule.
Design of experiments (DOE) is a key method for optimizing physical processes by altering multiple variables at once to assess their effect. In chemistry, DOE explores a wider parameter space than ...the dominant “One Factor at a Time” (OFAT) method providing greater opportunity to explore the factors that can be used to optimize yield, purity, and to explore chemical space for new compounds. One area of chemistry that suffers from low yields and poor reproducibility but is full of hard to predict and interesting materials is polyoxometalate cluster science. Herein, we developed a DOE analysis methodology to explore the parameter space of polyoxometalate cluster formation to explore the subtle input effects that are known to have an impact on the product discovery, purity, and stability under the preparation conditions. Using a Plackett–Burman screening design, we analyzed the effect of six synthetic parameters in only 12 experiments, following up with a full factorial analysis of the three most significant factors to identify the key parameters in the successful synthesis of each. Based on this, we provide a useful template that produces the input data for automated synthesis based on DOE on other synthetic procedures. In our POM test cases, redox agent stoichiometry was found in three of the four systems studied to be significant factors with pH and temperature, which also found to be commonly important. The insights derived from this analysis were applied to design optimized synthetic procedures and improve the yield of the product by on average >33% from the highest reported literature yield. Thus, the DOE methodology outlined here is shown to yield insights into reaction optimization rapidly with facile experimental design and analysis even for complex multivariate synthetic procedures.
Complexes formed between the heaviest and lightest elements in the periodic table yield the f-block hydrides, a unique class of compounds with wide-ranging utility and interest, from catalysis to ...light-responsive materials and nuclear waste storage. Recent developments in syntheses and analytics, such as exploiting low-oxidation state metal ions and improvements in X-ray diffraction tools, have transformed our ability to understand, access and manipulate these important species. This perspective brings together insights from binary metal hydrides, with molecular solution phase studies on heteroleptic complexes and gas phase investigations. It aims to provide an overview of how the f-element influences hydride formation, structure and reactivity including the sometimes-surprising power of co-ligands to tune their behaviour towards a variety of applications.
We present a chemical discovery robot for the efficient and reliable discovery of supramolecular architectures through the exploration of a huge reaction space exceeding ten billion combinations. The ...system was designed to search for areas of reactivity found through autonomous selection of the reagent types, amounts, and reaction conditions aiming for combinations that are reactive. The process consists of two parts where reagents are mixed together, choosing from one type of aldehyde, one amine and one azide (from a possible family of two amines, two aldehydes and four azides) with different volumes, ratios, reaction times, and temperatures, whereby the reagents are passed through a copper coil reactor. Next, either cobalt or iron is added, again from a large number of possible quantities. The reactivity was determined by evaluating differences in pH, UV‐Vis, and mass spectra before and after the search was started. The algorithm was focused on the exploration of interesting regions, as defined by the outputs from the sensors, and this led to the discovery of a range of 1‐benzyl‐(1,2,3‐triazol‐4‐yl)‐N‐alkyl‐(2‐pyridinemethanimine) ligands and new complexes: Fe(L1)2(ClO4)2 (1); Fe(L2)2(ClO4)2 (2); Co2(L3)2(ClO4)4 (3); Fe2(L3)2(ClO4)4 (4), which were crystallised and their structure confirmed by single‐crystal X‐ray diffraction determination, as well as a range of new supramolecular clusters discovered in solution using high‐resolution mass spectrometry.
A chemical robot was designed, assembled and utilised for the discovery of supramolecular architectures through the exploration of a chemical space exceeding 109 possible reactions. By searching for reactivity differences, a range of new 1‐benzyl‐(1,2,3‐triazol‐4‐yl)‐N‐alkyl‐(2‐pyridinemethanimine) ligands were found and four new complexes of Fe and Co were discovered, autonomously discovering the rules of self‐assembly for these systems.
The controlled manipulation of the axial oxo and equatorial halide ligands in the uranyl dipyrrin complex, UO2Cl(L), allows the uranyl reduction potential to be shifted by 1.53 V into the range ...accessible to naturally occurring reductants that are present during uranium remediation and storage processes. Abstraction of the equatorial halide ligand to form the uranyl cation causes a 780 mV positive shift in the UV/UIV reduction potential. Borane functionalization of the axial oxo groups causes the spontaneous homolysis of the equatorial U–Cl bond and a further 750 mV shift of this potential. The combined effect of chloride loss and borane coordination to the oxo groups allows reduction of UVI to UIV by H2 or other very mild reductants such as Cp*2Fe. The reduction with H2 is accompanied by a B–C bond cleavage process in the oxo-coordinated borane.
Polyoxometalate molybdenum blue (MB) 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, with the ring sizes of the MB wheels 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 inner rim, giving the general formula {Mo90Ln10}. We show three examples of this new decameric {Mo90Ln10} (Ln = La, Ce, and Pr) framework synthesized by high temperature reduction and demonstrate that later Ln ions result in {Mo92Ln9} (Ln = Nd, Sm), conserving one {Mo2} linker unit in its structure, as a consequence of the lanthanide contraction. Remarkably the {Mo90Ln10} compounds are the first examples of charge-neutral molybdate wheels as confirmed by BVS, solubility experiments, 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 utilized to selectively enrich Ln-MB wheels for effective separation of lanthanides.
Library generation experiments are a key part of the discovery of new materials, methods, and models in chemistry, but the question of how to generate high quality libraries to enable discovery is ...nontrivial. Herein, we use coordination chemistry to demonstrate the automation of many of the workflows used for library generation in automated hardware including the Chemputer. First, we explore the target-oriented synthesis of three influential coordination complexes, to validate key synthetic operations in our system; second, the generation of focused libraries in chemical and process space; and third, the development of a new workflow for prospecting library formation. This involved Bayesian optimization using a Gaussian process as surrogate model combined with a metric for novelty (or serendipity) quantification based on mass spectrometry data. In this way, we show directed exploration of a process space toward those areas with rarer observations and build a picture of the diversity in product distributions present across the space. We show that this effectively “engineers” serendipity into our search through the unexpected appearance of acetic anhydride, formed in situ, and solvent degradation products as ligands in an isolable series of three Co(III) anhydride complexes.
Eight alkene-functionalized molybdenum-based spherical Keplerate-type (inorganic fullerene) structures have been obtained
via
both direct and multistep synthetic approaches. Driven by the opportunity ...to design unique host-guest interactions within hydrophobic, π-electron rich confined environments, we have synthesised {(NH
4
)
42
Mo
132
O
372
(L)
30
(H
2
O)
72
}, where L = (
1
) acrylic acid, (
2
) crotonic acid, (
3
) methacrylic acid, (
4
) tiglic acid, (
5
) 3-butenoic acid, (
6
) 4-pentenoic acid, (
7
) 5-hexenoic acid, and (
8
) sorbic acid. The compounds, which are obtained in good yield (10-40%), contain 30 carboxylate-coordinated alkene ligands which create a central cavity with hydrophobic character. Extensive Nuclear Magnetic Resonance (NMR) spectroscopy studies contribute significantly to the complete characterisation of the structures obtained, including both 1D and 2D measurements. In addition, single-crystal X-ray crystallography and subsequently-generated electron density maps are employed to highlight the distribution in ligand tail positions. These alkene-containing structures are shown to effectively encapsulate small alkyl thiols (1-propanethiol (
A
), 2-propanethiol (
B
), 1-butanethiol (
C
), 2-butanethiol (
D
) and 2-methyl-1-propanethiol (
E
)) as guests within the central cavity in aqueous solution. The hydrophobically driven clustering of up to 6 equivalents of volatile thiol guests within the central cavity of the Keplerate-type structure results in effective thermal protection, preventing evaporation at elevated temperatures (Δ
T
25 K).
Eight alkene-functionalized molybdenum-based spherical Keplerate-type (inorganic fullerene) structures have been obtained and shown to sequester and thermally insulate volatile organics.
The assembly of nanoscale polyoxometalate (POM) clusters has been dominated by the highly reduced icosahedral {Mo132} “browns” and the toroidal {Mo154} “blues” which are 45 % and 18 % reduced, ...respectively. We hypothesised that there is space for a greater diversity of structures in this immediate reduction zone. Here we show it is possible to make highly reduced mix‐valence POMs by presenting new classes of polyoxomolybdates: MoV52MoVI12H26O20042− {Mo64} and MoV40MoVI30H30O21520− {Mo70}, 81 % and 57 % reduced, respectively. The {Mo64} cluster archetype has a super‐cube structure and is composed of five different types of building blocks, each arranged in overlayed Archimedean or Platonic polyhedra. The {Mo70} cluster comprises five tripodal {MoV6} and five tetrahedral {MoV2MoVI2} building blocks alternatively linked to form a loop with a pentagonal star topology. We also show how the reaction yielding the {Mo64} super‐cube can be used in the enrichment of lanthanides which exploit the differences in selectivity in the self‐assembly of the polyoxometalates.
Novel types of highly reduced Mo polyoxometalates, the {Mo64} cube and {Mo70} star, are obtained through near‐hydrothermal conditions with incorporations of nickel and lanthanide ions and possess a set of building blocks different to those present in Mo blues and browns. With a few of other rare structures, this group of polyoxomolybdates is redefined as Mo reds based on the major differences in building blocks and reduction degrees.
Giant polyoxomolybdates are traditionally synthesized by chemical reduction of molybdate in aqueous solutions, generating complex nanostructures such as the highly symmetrical spherical {Mo102} and ...{Mo132}, ring-shaped {Mo154} and {Mo176}, and the gigantic protein sized {Mo368}, which combines both positive and negative curvature. These complex polyoxometalates are known to be highly sensitive to reaction conditions and are often difficult to reproduce, especially {Mo368}, which is often produced in yields far below 1%, meaning further investigation has always been limited. While the electrochemical properties of these materials have been studied, their electrochemical synthesis has not been explored. Herein, we demonstrate an alternative reliable synthetic method by means of electrochemistry. By using electrochemical synthesis, we have shown the synthesis of various reported polyoxomolybdates, along with some unreported structures with unique features that have yet to be reported by traditional synthetic methods. The six different giant polyoxomolybdates that were obtained via electrochemical synthesis range from the spherical {Mo102–x Fe x } and {Mo132} to the ring-shaped {Mo148} and {Mo154–x }, as well as the largest known polyoxometalate {Mo368}, with improved yield (up to 26.1% for {Mo368}), increased reproducibility, and shorter crystallization time compared to chemical reduction methods.
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