Soluble metal-hydroxide clusters of Group 13 metals are popular in both materials chemistry and geochemistry. In geochemistry these clusters are used as experimental models for clay-like minerals. In materials chemistry these clusters are the precursors for useful thin films. However, little is known about the formation mechanisms and solution dynamics of these species or how they compare to monomer ions. In this study we use 1H-NMR spectroscopy to estimate the exchange rates of protons on sites in the Ga13(μ3-OH)6(μ2-OH)18(H2O)24(NO3)15 (Ga13) and Ga7In6(μ3-OH)6(μ2-OH)18(H2O)24(NO3)15 (Ga7In6) cluster species. To date, these clusters provide the best molecular-scale models for the surface chemistry of thin films and layered minerals. Trivalent metal-hydroxide minerals are environmentally important, because of the rich acid-base chemistry that exists in the pH regions of most soils. Our data suggest millisecond timescales for the exchange of protons on the μ2-OH bridges with bulk water in Group 13 metal-hydroxide minerals, such as tsumgallite and diaspore.

Metal-oxide thin films are used extensively in electronic and energy applications. Solution processing offers a potentially scalable and inexpensive deposition method to expand the applications of metal-oxide films and to complement vacuum-deposition techniques. Among precursors for solution deposition, metal nitrates stand out for their ability to form high-quality metal-oxide thin films. This review focuses on unique aspects of metal-nitrate chemistry that have been exploited to advance the development of solution-processed thin films. We discuss the solid-state bulk, solution, and thin-film chemical reactions involving metal nitrates and illustrate how the resulting metal-oxide thin-film properties depend on the entire reaction pathway. To conclude, we offer perspective as to how understanding the chemistry of film formation from metal-nitrate precursors is useful for addressing the primary drivers for industrial manufacturing of solution-processed metal-oxide thin films.

The measurement of a deuterium equilibrium isotope effect (EIE) for the aryl CH···Cl^- interaction of anion receptor 1H/1D is reported. Computations corroborate the results of solution measurements for a small, normal EIE in the full complex (K_a^H/K_a^D = 1.019 ± 0.010). Interestingly, isotope effects involving fragments of the anion receptor (urea, aryl ring, etc.) are predicted to produce an inverse effect. This points to an unusual and subtle structural organization effect of the anion receptor complex that changes the nature of the combined interactions to a normal isotope effect. The reversal of EIE values suggests that overall architecture of the anion receptor can dramatically impact the nature of bonding in these complexes.

Solution deposition is a scalable method to fabricate transparent conducting and semiconducting oxide films that could enable low-cost large-area optoelectronic devices, including solar cells and electrochromic windows. However, high temperatures (>500 C) are typically required to remove excess counterions and ligands from solution-deposited films. We report the synthesis of reactive F-modified tin(II) hydroxide nitrate nanoscale cluster precursors from the controlled dissolution of SnO and SnF2 in minimal nitric acid (∼1.6 mol HNO3 per mol Sn). After spin-casting to form films, heating at temperatures < 100 C consumes the nitrate counterions likely by oxidation of the tin(II) precursor to form amorphous F:SnO 2. The optical, electrical, structural, and morphological properties of F-doped and undoped SnO2 thin films are reported as a function of annealing temperature on both glass and polyimide (Kapton) substrates. Electron microscopy and X-ray reflectivity results show that the films are uniform and crack-free with <10% thickness reduction after annealing at temperatures up to 450 C. X-ray diffraction shows the formation of crystalline SnO2 at >300 C. Quartz-crystal microbalance, X-ray photoelectron spectroscopy, and infrared spectroscopy show near-complete removal of nitrate counterions and hydroxide/water by 200 C, leading to an approximate 30% mass loss from the as-deposited film. Secondary-ion mass spectrometry shows that the F concentration in the annealed films scales with the concentration in the precursor solution. The F-doped films are conductive when annealed at ≥250 C in H2/N2 gas and at ≥350 C in air. The lowest electrical resistivity (ρ) of 1.5 × 10^-4 Ω·m was obtained from 10 atom % F-doped SnO2 films annealed at 600 C in air. These films had a Hall mobility of 4.2 cm² V^-1 s ^-1 and a carrier concentration of 9.5 × 10¹⁹ cm ^-3. Films deposited directly on polyimide sheets were crack-free after annealing at temperatures below 350 C. The films exhibited ρ ≈ 10^-2 Ω·m after H2/N2 annealing and were stable to more than 200 bending cycles at angles up to 90, demonstrating flexibility. © 2013 American Chemical Society.

Hydrogen sulfide (H2 S) has emerged as a crucial biomolecule in physiology and cellular signaling. Key challenges associated with developing new chemical tools for understanding the biological roles of H2 S include developing platforms that enable reversible binding of this important biomolecule. The first synthetic small molecule receptor for the hydrosulfide anion, HS(-) , using only reversible, hydrogen-bonding interactions in a series of bis(ethynylaniline) derivatives, is reported. Binding constants of up to 90 300±8700 m(-1) were obtained in MeCN. The fundamental science of reversible sulfide binding, in this case featuring a key CH⋅⋅⋅S hydrogen bond, will expand the possibility for discovery of sulfide protein targets and molecular recognition agents.

Large aqueous ions are interesting because they are useful in materials science (for example to generate thin films) but also because they serve as molecular models for the oxide-aqueous mineral interface where spectroscopy is difficult. Here we show that new clusters of the type M[(μ-OH)₂ Co(NH₃ )₄ ]₃ (NO₃ )₆ (M=Al, Ga) can be synthesized using Werner's century-old cluster as a substitutable framework. We substituted Group 13 metals into the hexol Co[(μ-OH)₂ Co(NH₃ )₄ ]₃⁶⁺ ion to make diamagnetic heterometallic ions. The solid-state structure of the hexol-type derivatives were determined by single-crystal XRD and NMR spectroscopy and confirmed that the solid-state structure persists in solution after dissolution into either D₂ O or [D₆ ]DMSO. Other compositions besides these diamagnetic ions can undoubtedly be made using a similar approach, which considerably expands the number of stable aqueous heteronuclear ions.

Metal-oxide thin films find many uses in (opto)electronic and renewable energy technologies. Their deposition by solution methods aims to reduce manufacturing costs relative to vacuum deposition while achieving comparable electronic properties. Solution deposition on temperature-sensitive substrates (e.g., plastics), however, remains difficult due to the need to produce dense films with minimal thermal input. Here, we investigate combustion thin-film deposition, which has been proposed to produce high-quality metal-oxide films with little externally applied heat, thereby enabling low-Temperature fabrication. We compare chemical composition, chemical structure, and evolved species from reactions of several metal nitrate [In(NO3)3, Y(NO3)3, and Mg(NO3)2] and fuel additive (acetylacetone and glycine) mixtures in bulk and thin-film forms. We observe combustion in bulk materials but not in films. It appears acetylacetone is removed from the films before the nitrates, whereas glycine persists in the film beyond the annealing temperatures required for ignition in the bulk system. From analysis of X-ray photoelectron spectra, the oxide and nitrate content as a function of temperature are also inconsistent with combustion reactions occurring in the films. In(NO3)3 decomposes alone at low temperature (â200-250 °C) without fuel, and Y(NO3)3 and Mg(NO3)2 do not decompose fully until high temperature even in the presence of fuel when used to make thin films. This study therefore distinguishes bulk and thin-film reactivity for several model oxidizer-fuel systems, and we propose ways in which fuel additives may alter the film formation reaction pathway.

This Perspective article highlights some of the traditional and non-traditional analytical tools that are presently used to characterize aqueous inorganic nanoscale clusters and polyoxometalate ions. The techniques discussed in this article include nuclear magnetic resonance spectroscopy (NMR), small angle X-ray scattering (SAXS), dynamic and phase analysis light scattering (DLS and PALS), Raman spectroscopy, and quantum mechanical computations (QMC). For each method we briefly describe how it functions and illustrate how these techniques are used to study cluster species in the solid state and in solution through several representative case studies. In addition to highlighting the utility of these techniques, we also discuss limitations of each approach and measures that can be applied to circumvent such limits as it pertains to aqueous inorganic cluster characterization.