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Cyanopyridines and cyanophenylpyridines were investigated as anolytes for nonaqueous redox flow batteries (RFBs). The three isomers of cyanopyridine are reduced at potentials of -2.2 V or lower vs. ferrocene

We describe the nonaqueous redox-matched flow battery (RMFB), where charge is stored on redox-active moieties covalently tethered to non-circulating, insoluble polymer beads and charge is transferred between the electrodes and the beads via soluble mediators with redox potentials matched to the active moieties on the beads. The RMFB reported herein uses ferrocene and viologen derivatives bound to crosslinked polystyrene beads. Charge storage in the beads leads to a high (approximately 1.0-1.7 M) effective concentration of active material in the reservoirs while preventing crossover of that material. The relatively low concentration of soluble mediators (15 mM) eliminates the need for high-solubility molecules to create high energy density batteries. Nernstian redox exchange between the beads and redox-matched mediators was fast relative to the cycle time of the RMFB. This approach is generalizable to many different redox-active moieties via attachment to the versatile Merrifield resin.

Highly charged metal ions are difficult to investigate in weakly coordinating ionic liquids (ILs) because of the insolubility of their solid forms, but the molecular liquid TiCl4 offers a way to react tetravalent metal ions in an IL. Reactions of TiCl4 with 1-butyl-3-methylimidazolium ([C4mim]+)-based ILs containing chloride or bromide lead to mixtures of highly metastable amorphous solids and small amounts of crystalline chlorotitanate salts including [C4mim]2[TiCl6] and two polymorphs of [C4mim]2[Ti2Cl10] in a manner not well correlated with stoichiometry or anion identity. The reaction of TiCl4 with [C4mim][BF4] yields crystals of the mixed fluoro-chloro complex [C4mim]2[Ti4F6Cl12], indicating spontaneous reaction of the IL ions to generate HF in situ. These unusual behaviors are explained in terms of the exceptionally high acidity of Ti4+ and the unusual behavior of TiCl4 among metal halides as a nonpolar molecular compound. Postprint

Two different room-temperature liquid systems were investigated, both of which conduct a DC electrical current without decomposition or net chemical transformation. DC electrical conductivity is possible in both cases because of the presence of two different oxidation states of a redox-active species. One system is a 1 : 1 molar mixture of n-butylferrocene (BuFc) and its cation bis(trifluoromethane)sulfonimide salt, [BuFc(+)][NTf2(-)], while the other is a 1 : 1 molar mixture of TEMPO and its cation bis(trifluoromethane)sulfonimide salt, [TEMPO(+)][NTf2(-)]. The TEMPO-[TEMPO(+)][NTf2(-)] system is notable in that it is an electrically conducting liquid in which the conductivity originates from an organic molecule in two different oxidation states, with no metals present. Single-crystal X-ray diffraction of [TEMPO(+)][NTf2(-)] revealed a complex structure with structurally different cation-anion interactions for cis- and trans [NTf2(-)] conformers. The electron transfer self-exchange rate constant for BuFc/BuFc(+) in CD3CN was determined by (1)H NMR spectroscopy to be 5.4 × 10(6) M(-1) s(-1). The rate constant allowed calculation of an estimated electrical conductivity of 7.6 × 10(-5)Ω(-1) cm(-1) for BuFc-[BuFc(+)][NTf2(-)], twice the measured value of 3.8 × 10(-5)Ω(-1) cm(-1). Similarly, a previously reported self-exchange rate constant for TEMPO/TEMPO(+) in CH3CN led to an estimated conductivity of 1.3 × 10(-4)Ω(-1) cm(-1) for TEMPO-[TEMPO(+)][NTf2(-)], a factor of about 3 higher than the measured value of 4.3 × 10(-5)Ω(-1) cm(-1).

Tangible models help students and researchers visualize chemical structures in three dimensions (3D). 3D printing offers a unique and straightforward approach to fabricate plastic 3D models of molecules and extended solids. In this article, we prepared a series of digital 3D design files of molecular structures that will be useful for teaching chemical education topics such as symmetry and point groups. Two main file preparation methods are discussed within this article that outlines how to prepare 3D printable chemical structures. Both methods start with either a crystallographic information file (.cif) or a protein databank (.pdb) file and are ultimately converted into a 3D stereolithography (.stl) file by using a variety of commercially and freely available software. From the series of digital 3D chemical structures prepared, 18 molecules and 7 extended solids were 3D printed. Our results show that the file preparation methods discussed within this article are both suitable routes to prepare 3D printab...

Optoelectric control of metal–organic frameworks would open up a new area of applications for hybrid materials. This article reports the calculated thermodynamic and electronic properties of a family of M3(C6X6) metal–organic frameworks (M = Mg, Ca, Zn, Cd, Hg, Ge, Sn, Pb; X = O, S, Se, Te). Herein, we present a systematic approach for studying families of hybrid compounds, and describe extended tunability of their electronic and enthalpic properties through compositional control. It was shown that the formation enthalpy is dictated by the stability of the ligand, and the band gap is tunable depending on both metal and chalcogenide selection. Five compounds were found to be candidate semiconductors as they combine thermodynamic stability with band gaps in the visible range of the electromagnetic spectrum.

Previously unknown benzenepolyselenols have been synthesized and isolated in their acetyl-protected form. The two molecules 1,3,5-tris(acetylseleno)benzene and 1,2,4,5-tetrakis(acetylseleno)benzene were synthesized by the reductive dealkylation in Na/NH(3) of 1,3,5-tris(tert-butylseleno)benzene and 1,2,4,5-tetrakis(tert-butylseleno)benzene, respectively. Hexakis(tert-butylseleno)benzene was also synthesized and structurally characterized by single-crystal X-ray diffraction, but it was not possible to isolate hexakis(acetylseleno)benzene. The synthetic methodology is likely to be useful in the synthesis of other areneselenols.

The cobalt-catalyzed cyclotrimerization of bis(4-pyridyl)acetylene affords hexakis(4-pyridyl)benzene in moderate yield. Alkylation with n-butyltriflate gives hexakis(4-(N-butylpyridylium))benzene triflate (1 6+), which can be reduced with Na/Hg in DMF to neutral 10. A single-crystal X-ray diffraction structure reveals that 1 0 has a chair-cyclohexane-like core and a [6]radialene structure. Cyclic voltammetry shows that 1 6+ is reversibly reduced to 1 2+ in one four-electron step and 1 2+ is reversibly reduced to 1 0 in one two-electron step. A reduction by four electrons at one potential is unprecedented for a molecule in which the electrochemically active centers are in electronic communication. The large structural transformation from 1 6+ to 1 0 is responsible for the "potential inversion" in the cyclic voltammetry, and DFT calculations suggest a possible structure for the stable intermediate 1 2+. A comparison is made to the electrochemistry and structural transformations in a previously prepared [4]radialene analogue of 1 0.

The contrasting photophysical properties of two silicon (IV) tetraphenylporphyrins, Si(TPP)(py)2 and Si(TPP)Cl2, have been investigated using static absorption and fluorescence spectroscopy and ultrafast transient absorption measurements. The parent Si(TPP)Cl2, in which the porphyrin macrocycle has its normal 2- oxidation state, has a fluorescence yield of 0.027, and a lifetime of 1.8 ns for the lowest excited singlet state. In marked contrast, the reduced, anti-aromatic complex Si(TPP)(py)2, with the macrocycle in the 4- oxidation state, has an extremely low fluorescence yield (or =0.0004) and a 750-fold shorter excited-state lifetime (2.4 ps) in the same solvent (pyridine). The rapid deactivation of photoexcited Si(TPP)(py)2 to the ground state is likely associated with its ruffled structure and the presence of low-energy excited states in its electronic manifold.

The reaction chemistry of H-terminated (111)-oriented Si surfaces has been explored in the presence of one-electron oxidants in alcohol solvents. Similar chemistry was observed for Si surfaces exposed to methanolic solutions of ferrocenium tetrafluoroborate or to methanolic solutions of I2, as well as for Si electrodes that were subjected to anodic electrochemical oxidation processes in methanol. Oxidation in alcohols activates the surficial Si−H bond toward nucleophilic attack, producing alkoxylated surfaces. This mechanism for Si−H activation is supported by infrared spectroscopy, temperature-programmed desorption spectroscopy, and by X-ray photoelectron spectroscopic studies of this system. These data explain a variety of observations regarding the surface chemistry and electrochemistry of Si electrodes and surfaces.

Utilization of the bulky acetylide, tBu3SiC⋮C-, enabled the synthesis of several early metal polyacetylides. Addition of NaC⋮CH to tBu3SiBr in dimethyl sulfoxide afforded tBu3SiC⋮CH, which was deprotonated to yield tBu3SiC⋮CLi. Treatment of ZrCl4, HfCl4, and TaCl5 with varying amounts of tBu3SiC⋮CLi gave {(THF)2Li(tBu3SiC⋮C)2}Zr(C⋮CSitBu3)3(THF) (1; THF = tetrahydrofuran), {(Et2O)Li(tBu3SiC⋮C)2}Hf(C⋮CSitBu3)3(OEt2) (2), {Li(tBu3SiC⋮C)3}2M (M = Zr, 6; Hf, 7), and {Li(tBu3SiC⋮C)3}Ta(C⋮CSitBu3)3 (3). Metathesis of 3 with KOTf generated KTa(C⋮CSitBu3)6 (4) and cation sequestration of 4 with crypt 2.2.2 provided [K(crypt 2.2.2)][Ta(C⋮CSitBu3)6] (5). Single-crystal X-ray structural studies determined the structures (core symmetry) of 1 (Oh), 2, (Oh), 3 (D3), 5 (D3), 6 (Oh), and 7 (Oh). The D3h to D3 twist in 3 and 5 has a steric origin, and the counterion position appears inconsequential. Origins of the structural preferences illustrated by the dichotomous twisted trigonal prismatic and octahedral cores of the ...

Relative D (Ti-R) rel have been measured previously for (silox) 2 ( t Bu 3 SiNH)TiR ( 1-R ). Pauling and Matcha equations of D (MR) that contain elements of electronegativity, D (MM), D (HH) and D (RH) were used to estimate absolute D (TiR) in 1 with minimal success. The electronegativity approaches need a variety of substituents with a wide spread in χ R , hence examination of 1-H and 1-R are heavily and incorrectly weighted by D (TiH)- D (TiR). Absolute D (TiR) generated in this manner approach those of related systems only when χX Ti = 2.9, a value shown to be irrational. Drago's ECT parameters were used in the hope that the three parameter fit would compensate for inadequacies in electronegativity-based methods. The limited set of alkyl parameters available, and a lack of distinguishing parameters that can significantly differentiate one alkyl from another, render this potentially useful method imprecise.

The chemical synthesis, isolation, and characterization of phenyl viologen (PV) as a dication, radical cation, and neutral species are described. Single-crystal X-ray diffraction of PV(2+)2Cl(-.)2H2O and PV(.+)PF(6)(-).pyridine reveals the expected differences in bond lengths and also a structural change from two coplanar central rings in PV(.+) to a twist of 36 degrees between the two central rings in PV(2+). The phenyl viologen radical cation exhibits behavior characteristic of many radical cations, including weak pi-dimerization in the solid state and reversible pi-dimerization in solution. Electrical conductivity measurements of neutral phenyl viologen, the first such measurements of a neutral viologen, reveal that it is a significantly better conductor than the radical cation. Differences in geometric relaxation during charge transfer offer a possible explanation for the higher conductivity of the neutral viologen.

The vapor classification performance of arrays of conducting polymer composite vapor detectors has been evaluated as a function of the number and type of detectors in an array. Quantitative performance comparisons were facilitated by challenging a collection of detector arrays with vapor discrimination tasks that were sufficiently difficult that at least some of the arrays did not exhibit perfect classification ability for all of the tasks of interest. For nearly all of the discrimination tasks investigated in this work, classification performance either increased or did not significantly decrease as the number of chemically different detectors in the array increased. Any given subset of the full array of detectors, selected because it yielded the best classification performance at a given array size for one particular task, was invariably outperformed by a different subset of detectors, and by the entire array, when used in at least one other vapor discrimination task. Arrays of detectors were nevertheless identified that yielded robust discrimination performance between compositionally close mixtures of 1-propanol and 2-propanol, n-hexane and n-heptane, and meta-xylene and para-xylene, attesting to the excellent analyte classification performance that can be obtained through the use of such semi-selective vapor detector arrays.

Thin films of carbon black-organic polymer composites have been deposited across two metallic leads, with swelling- induced resistance changes of the films signaling the presence of vapors. To identify and classify vapors, arrays of such vapor-sensing elements have been constructed, with each element containing a different organic polymer as the insulating phase. The differing gas-solid partition coefficients for the various polymers of the sensor array produce a pattern of resistance changes that can be used to classify vapors and vapor mixtures. This type of sensor array has been shown to resolve all organic vapors that have been analyzed, and can even resolve H_2O from D_2O. Blends of poly(vinyl acetate) and poly(methyl methacrylate) have been used to produce a series of sensor that response to vapors with a change in resistance of a magnitude that is not simply a linear combination of the responses of the pure polymers. These compatible blend composite detectors provided additional analyte discrimination information relative to a reference detector array that only contained composites formed using the pure polymer phases. Vapor signatures from chemicals used in land mine explosives, including TNT, DNT, and DNB, have been detected in air in short sampling time and discriminated from each other using these sensor arrays.