Matthew E. Carnes

Single Nanoscale Cluster Species Revealed by 1H NMR Diffusion‐Ordered Spectroscopy and Small‐Angle X‐ray Scattering

A solved structure: The hydrated Ga(13) cluster, [Ga(13)(μ(3)-OH)(6)(μ-OH)(18)(H(2)O)(24)](NO(3))(15)], persists as a discrete nanoscale structure in an aqueous polar solvent at millimolar concentration. SAXS data confirm the presence of Ga(13) in dimethyl sulfoxide (DMSO). In aqueous [D(6)]DMSO (1)H NMR signals for the hydroxo and aquo ligands of Ga(13) were detected, thus showing a cluster with a hydrodynamic radius of (11.2±0.8) Å (see picture).

Electrochemical synthesis of flat-[Ga13−xInx(μ3-OH)6(μ-OH)18(H2O)24(NO3)15] clusters as aqueous precursors for solution-processed semiconductors

Flat-[Ga13(μ3-OH)6(μ-OH)18(H2O)24](NO3)15 (Ga13) and heterometallic [Ga13−xInx(μ3-OH)6(μ-OH)18(H2O)24](NO3)15 (x = 5, 4) clusters were synthesized by the electrolysis of metal nitrate salt solutions to directly form, without purification, aqueous precursor inks for InxGa13−xOy semiconducting films in <2 h. Raman spectroscopy and 1H-NMR spectroscopy confirm the presence of [Ga13−xInx(μ3-OH)6(μ-OH)18(H2O)24(NO3)15] clusters. Bottom-gate thin-film transistors were fabricated using ∼15 nm-thick Ga13−xInxOy films as the active channel layer, displaying turn-on voltages of −2 V, and on/off current ratios greater than 106. The average channel mobility of the transistors fabricated from the cluster solutions generated by electrolysis was ∼5 cm−2 V−1s−1 which was more than twice that of transistors fabricated from control solutions with the simple nitrate salt precursors of ∼2 cm−2 V−1s−1. Electrochemical cluster synthesis thus provides a simple and direct route to aqueous precursors for solution-processed inorganic electronics.

Identifying Nanoscale M13 Clusters in the Solid State and Aqueous Solution: Vibrational Spectroscopy and Theoretical Studies

Raman spectroscopy, infrared spectroscopy, and quantum mechanical computations were used to characterize and assign observed spectral features, highlight structural characteristics, and investigate the bonding environments of [M13(μ3-OH)6(μ2-OH)18(H2O)24](NO3)15 (M = Al or Ga) nanoscale clusters in the solid phase and aqueous solution. Solid-phase Raman spectroscopy was used to reveal that the metal-oxygen (M-O) symmetric stretch (breathing mode) for the Al13 cluster is observed at 478 cm(-1), whereas this same mode is seen at 464 cm(-1) in the Ga13 cluster. The hydroxide bridges in each cluster are weakly Raman active but show slightly stronger infrared activity. The breathing modes associated with the clusters in the solid state are not clearly visible in aqueous solution. This change in behavior in the solution phase may indicate a symmetry breaking of the cluster or exchange events between protons on the ligands and the protic solvent. Overall, each cluster has several unique vibrational modes in the low wavenumber region (<1500 cm(-1)) that are distinct from the parent nitrate salt and other polymeric species with similar structure, which allows for unambiguous identification of the cluster in solution and solid phases.

Exploring anion-induced conformational flexibility and molecular switching in a series of heteroaryl-urea receptors

Anion-induced conformational switching provides insight into binding selectivity in a series of heteroaryl-urea receptors.

A facile route to old and new cyclophanes via self-assembly and capture

Cyclophanes are a venerable class of macrocyclic and/or cage compounds that often feature high strain, unusual conformations and quite surprising properties, many of which are legendary in physical organic chemistry. However, the discovery of new, diverse cyclophanes and derivatives has been hindered by syntheses that are traditionally low-yielding, requiring long reaction times, laborious purification steps and often extreme conditions. Herein, we demonstrate a new self-assembly route to a variety of discrete cyclic and caged disulfide structures, which can then be kinetically captured upon sulfur extrusion at room temperature to give a diversity of new thioether (hetera)cyclophanes in high yield. In addition to the synthesis of novel macrocycles (dimers through hexamers), this process provides an improved route to a known macrobicyclic trithiacyclophane. This technique also enables the facile isolation of a tetrahedral macrotricyclic tetrathiacyclophane in two steps at an ambient temperature.

Solution structural characterization of an array of nanoscale aqueous inorganic Ga₁₃₋[subscript]xIn[subscript]x (0 ≤ x ≤ 6) clusters by ¹H-NMR and QM computations

NMR spectroscopy is the go-to technique for determining the solution structures of organic, organometallic, and even macromolecular species. However, structure determination of nanoscale aqueous inorganic clusters by NMR spectroscopy remains an unexplored territory. The few hydroxo-bridged inorganic species well characterized by 1H Nuclear Magnetic Resonance spectroscopy (1H-NMR) do not provide enough information for signal assignment and prediction of new samples. 1H-NMR and quantum mechanical (QM) computations were used to characterize the NMR spectra of the entire array of inorganic flat-Ga13-x In x (0 ≤ x ≤ 6) nanoscale clusters in solution. A brief review of the known signals for μ2-OH and μ3-OH bridges gives expected ranges for certain types of protons, but does not give enough information for exact peak assignment. Integration values and NOESY data were used to assign the peaks of several cluster species with simple 1H-NMR spectra. Computations agree with these hydroxide signal assignments and allow for assignment of the complex spectra arising from the remaining cluster species. This work shows that 1H-NMR spectroscopy provides a variety of information about the solution behavior of inorganic species previously thought to be inaccessible by NMR due to fast ligand and/or proton exchange in wet solvents.Complete structural determination by 1H NMR spectroscopy and QM computations reveals a series of heterometallic Ga13–xInx(μ3-OH)6(μ2-OH)18(H2O)24](NO3)15 clusters persist in solution and can exist as an isomeric mixture.