Geoffrey J. T. Cooper

Integrated 3D-printed reactionware for chemical synthesis and analysis

Three-dimensional (3D) printing has the potential to transform science and technology by creating bespoke, low-cost appliances that previously required dedicated facilities to make. An attractive, but unexplored, application is to use a 3D printer to initiate chemical reactions by printing the reagents directly into a 3D reactionware matrix, and so put reactionware design, construction and operation under digital control. Here, using a low-cost 3D printer and open-source design software we produced reactionware for organic and inorganic synthesis, which included printed-in catalysts and other architectures with printed-in components for electrochemical and spectroscopic analysis. This enabled reactions to be monitored in situ so that different reactionware architectures could be screened for their efficacy for a given process, with a digital feedback mechanism for device optimization. Furthermore, solely by modifying reactionware architecture, reaction outcomes can be altered. Taken together, this approach constitutes a relatively cheap, automated and reconfigurable chemical discovery platform that makes techniques from chemical engineering accessible to typical synthetic laboratories.

Unveiling the Transient Template in the Self-Assembly of a Molecular Oxide Nanowheel

A Hidden Template The entropic challenge inherent in forming a ring-shaped molecule generally increases considerably with the size of the ring. Assuming that a linear precursor must bind its ends together, extending its length diminishes the likelihood of the opposite ends approaching one another. In the absence of an external force, how then can a family of molybdenum oxide rings, several nanometers in diameter (quite large at the molecular scale), self-assemble? Miras et al. (p. 72, see the cover; see the Perspective by Whitmire) have now uncovered an internal template guiding the process. By carefully controlling conditions in a flow reactor, they were able to halt the assembly process partway through and characterize a smaller molybdenum oxide core cluster, around which the larger ring was forming. Ejection of this template then yielded the hollow finished product. Use of a flow reactor reveals a key intermediate in the formation of a molybdenum oxide nanostructure. Self-assembly has proven a powerful means of preparing structurally intricate nanomaterials, but the mechanism is often masked by the common one-pot mixing procedure. We employed a flow system to study the steps underlying assembly of a previously characterized molybdenum oxide wheel 3.6 nanometers in diameter. We observed crystallization of an intermediate structure in which a central {Mo36} cluster appears to template the assembly of the surrounding {Mo150} wheel. The transient nature of the template is demonstrated by its ejection after the wheel is reduced to its final electronic state. The template’s role in the self-assembly mechanism is further confirmed by the deliberate addition of the template to the reaction mixture, which greatly accelerates the assembly time of the {Mo150} wheel and increases the yield.

Spontaneous assembly and real-time growth of micrometre-scale tubular structures from polyoxometalate-based inorganic solids

We report the spontaneous and rapid growth of micrometre-scale tubes from crystals of a metal oxide-based inorganic solid when they are immersed in an aqueous solution containing a low concentration of an organic cation. A membrane immediately forms around the crystal, and this membrane then forms micrometre-scale tubes that grow with vast aspect ratios at controllable rates along the surface on which the crystal is placed. The tubes are composed of an amorphous mixture of polyoxometalate-based anions and organic cations. It is possible for liquid to flow through the tubes, and for the direction of growth and the overall tube diameter to be controlled. We demonstrate that tube growth is driven by osmotic pressure within the membrane sack around the crystal, which ruptures to release the pressure. These robust, self-growing, micrometre-scale tubes offer opportunities in many areas, including the growth of microfluidic devices and the self-assembly of metal oxide-based semipermeable membranes for diverse applications.

A Mixed‐Valence Manganese Cubane Trapped by Inequivalent Trilacunary Polyoxometalate Ligands

The title compound contains an embedded mixed-valence {Mn5O6} cubane core, which is structurally similar to the active site in photosystem II. Solid-, solution-, and gas-phase studies indicate the presence of three lacunary Keggin fragments, thereby giving insight into the complex solution chemistry of plenary POM fragments.

From Chemical Gardens to Chemobrionics

Chemical gardens in laboratory chemistries ranging from silicates to polyoxometalates, in applications ranging from corrosion products to the hydration of Portland cement, and in natural settings ranging from hydrothermal vents in the ocean depths to brinicles beneath sea ice. In many chemical-garden experiments, the structure forms as a solid seed of a soluble ionic compound dissolves in a solution containing another reactive ion. In general any alkali silicate solution can be used due to their high solubility at high pH. The cation should not precipitate with the counterion of the metal salt used as seed. A main property of seed chemical-garden experiments is that initially, when the fluid is not moving under buoyancy or osmosis, the delivery of the inner reactant is diffusion controlled. Another experimental technique that isolates one aspect of chemical-garden formation is to produce precipitation membranes between different aqueous solutions by introducing the two solutions on either side of an inert carrier matrix. Chemical gardens may be grown upon injection of solutions into a so-called Hele-Shaw cell, a quasi-two-dimensional reactor consisting in two parallel plates separated by a small gap.

Real-time direction control of self fabricating polyoxometalate-based microtubes.

Spontaneous and rapid growth of tubes occurs from crystals of a polyoxometalate upon addition of an aqueous solution containing an organic cation. Application of a potential through a multielectrode system allows the growth direction of tubes through 90 degrees or 180 degrees, and direct increase or decrease in the cation concentration reliably alters the outer diameter of the growing tube. These robust, self-growing, micrometre-scale tubes offer application opportunities in the growth of microfluidic devices and the self-assembly of metal oxide based semipermeable membranes for diverse applications.

Development of a 3D printer using scanning projection stereolithography

We have developed a system for the rapid fabrication of low cost 3D devices and systems in the laboratory with micro-scale features yet cm-scale objects. Our system is inspired by maskless lithography, where a digital micromirror device (DMD) is used to project patterns with resolution up to 10 µm onto a layer of photoresist. Large area objects can be fabricated by stitching projected images over a 5cm2 area. The addition of a z-stage allows multiple layers to be stacked to create 3D objects, removing the need for any developing or etching steps but at the same time leading to true 3D devices which are robust, configurable and scalable. We demonstrate the applications of the system by printing a range of micro-scale objects as well as a fully functioning microfluidic droplet device and test its integrity by pumping dye through the channels.

Magnetic characterization of the frustrated three-leg ladder compound [(CuCl2tachH)3Cl]Cl2

We report the magnetic features of a one-dimensional stack of antiferromagnetically coupled equilateral copper(II) triangles. High-field magnetization measurements show that the interaction between the copper triangles is of the same order of magnitude as the intratriangle exchange although only coupled via hydrogen bonds. The infinite chain turns out to be an interesting example of a frustrated cylindrical three-leg ladder with competing intra- and inter-triangle interactions. We demonstrate that the ground state is a spin singlet which is gaped from the triplet excitation.

Modular Redox‐Active Inorganic Chemical Cells: iCHELLs

Interfacial membrane formation by cation exchange of polyoxometalates produces modular inorganic chemical cells with tunable morphology, properties, and composition (see picture). These inorganic chemical cells (iCHELLs), which show redox activity, chirality, as well as selective permeability towards small molecules, can be nested within one another, potentially allowing stepwise reactions to occur in sequence within the cell.

Exploring a series of isostructural dodecanuclear mixed Ni:Co clusters: toward the control of elemental composition using pH and stoichiometry.

The compositional parameter space in the formation of polynuclear clusters is probed in the synthesis of a series of dodecanuclear coordination clusters of Ni(II) and Co(II) with isostructural D(3h)-symmetric frameworks. At the core of their construction are a carbonate template and the directing ligands cis,trans-1,3,5-triaminocyclohexane and acetate at contrasting pH values. The pH and stoichiometric dependence has been mapped, and analysis by electrospray mass spectrometry reveals the cluster cores in solution. In two specific cases, site-specific occupations are eluded to by analysis of the magnetic properties, and we discuss the possibility of controlling the molecular composition of mixed metal polynuclear clusters.