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Energy density in nonaqueous redox flow batteries (RFBs) is often limited by the modest solubility of the redox-active organic molecules (ROMs). In addition, the lack of a separator that prevents ROMs from crossing between anolyte and catholyte solutions necessitates the use of 1:1 mixtures of two ROMs in both the anolyte and catholyte solutions in symmetric RFBs, further limiting concentrations. We show that permanently cationic oligomers of viologen, tris(dialkylamino)cyclopropenium, and phenothiazine molecules have high solubility in acetonitrile and cross over an anion exchange membrane at slow to undetectable rates, enabling the creation of asymmetric RFBs with low crossover. No added supporting electrolyte is necessary, with only the PF

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

This report describes the development of a photochemical method for C(sp

This Article describes the development of 1,2-bis(diisopropylamino)-3-cyclopropenylium-functionalized (DAC-functionalized) benzene derivatives as high-potential catholytes for non-aqueous redox flow batteries. Density functional theory (DFT) calculations predict that the oxidation potentials (in CH3CN) of various DAC-benzene derivatives will range from +0.96 to +1.64 V vs Fc+/0, depending upon the substituents on the benzene ring. To test these predictions, a set of eight DAC-arene derivatives were synthesized and evaluated electrochemically. The molecule 1-DAC-4-tert-butyl-2-methoxy-5-pentafluoropropoxybenzene was found to offer the optimal balance of high redox potential (E1/2 = +1.19 V vs Fc+/0) and charge-discharge cycling stability (with 92% capacity retention over 116 h of cycling at 0.3 M concentration in a symmetrical flow cell). This optimal derivative was successfully deployed as a catholyte in a non-aqueous redox flow cell with butyl viologen as the anolyte to yield a 2.0 V battery.

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.

This report describes the design of diaminocyclopropenium-phenothiazine hybrid catholytes for non-aqueous redox flow batteries. The molecules are synthesized in a rapid and modular fashion by appending a diaminocyclopropenium (DAC) substituent to the nitrogen of the phenothiazine. Combining a versatile C-N coupling protocol (which provides access to diverse derivatives) with computation and structure-property analysis enabled the identification of a catholyte that displays stable two-electron cycling at potentials of 0.64 and 1.00 V vs. Fc/Fc+ as well as high solubility in all oxidation states (≥0.45 M in TBAPF6 /MeCN). This catholyte was deployed in a high energy density two-electron RFB, exhibiting >90 % capacity retention over 266 hours of flow cell cycling at >0.5 M electron concentration.

High redox potential, two-electron organic catholytes for nonaqueous redox flow batteries were developed by appending diaminocyclopropenium (DAC) substituents to phenazine and phenothiazine cores. The parent heterocycles exhibit two partially reversible oxidations at moderate potentials [both at lower than 0.7 V vs ferrocene/ferrocenium (Fc/Fc+)]. The incorporation of DAC substituents has a dual effect on these systems. The DAC groups increase the redox potential of both couples by ∼300 mV while simultaneously rendering the second oxidation (which occurs at 1.20 V vs Fc/Fc+ in the phenothiazine derivative) reversible. The electron-withdrawing nature of the DAC unit is responsible for the increase in redox potential, while the DAC substituents stabilize oxidized forms of the molecules through resonance delocalization of charge and unpaired spin density. These new catholytes were deployed in two-electron redox flow batteries that exhibit voltages of up to 2.0 V and no detectable crossover over 250 cycles.

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

A highly reducing diquat-type molecule was explored as a negative electrolyte for nonaqueous redox flow batteries. The molecule displays a highly negative 2+/0 reduction potential of −1.67 V (vs. ferrocene), a low mass per electron transferred, and good solubility in CH3CN in both redox states. Moderate capacity retention is observed during electrochemical charge–discharge cycling. A pathway for decomposition during electrochemical cycling is elucidated, and this provides a clear path forward for enhancing stability.

Porous frameworks consisting of functionalized imidazolate ligands and zinc nodes are employed as hosts for the oxidant tetranitromethane to produce energetic composite materials. This new class of energetic materials are achieved through the facile strategy of oxidant adsorption wherein fuel and oxidant are intimately mixed yielding a material that responds violently to thermal and impact stimuli.

While the loading of liquid or solid materials in the pores of metal–organic frameworks (MOFs) can yield composite materials with novel and useful emergent properties, the loading of solids, and ionic solids in particular, can be challenging. We report the loading of the salts NH4NO3 and LiNO3 in the MOF UiO-66. The relatively low-melting NH4NO3 is loaded in UiO-66 in a solvent-free method, and loading is complete in 8 h at 75 °C, far below the melting point of NH4NO3. The higher-melting LiNO3 requires a small amount of solvent (water) for loading, and active removal of water assists in loading of the salt to form a composite that is 38% by mass LiNO3. These and similar salt–MOF composites are of interest for applications such as solid-ion conductors and energetic materials.

We report the electrochemical characterization of a polythianthrene ladder polymer as a promising positive electrode active material for organic polymer batteries. Polythianthrene was synthesized as a distribution of relatively short oligomers (n = 3 to ∼20) by the condensation of diphenylsulfide catalyzed by AlCl3, and its likely solid-state structure was determined by molecular modeling in combination with X-ray powder diffraction. Polythianthrene functions as the active material in an anion-insertion positive battery electrode with a highly positive potential of +0.87 V vs. ferrocene+/0, or approximately 4.1 V vs. Li/Li+. It has a specific capacity of 71 mAh/g, which may be improved toward a theoretical capacity of 194 mAh/g for one-electron redox per repeat unit. The polythianthrene ladder polymer thus has both a high capacity and high voltage relative to other organic materials, and is a promising material for use as a positive electrode in a “dual-ion” battery.

A synthesis is reported for 9,10-dimethyl-2,3,6,7-anthracenetetra(thioacetate), an anthracenetetrathiol derivative that may find use in molecular electronics and conducting metal-organic frameworks (MOFs). The easily accessible 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene was treated with 2-(4-pyridyl)ethanethiol in molten p-toluenesulfonic acid to yield the tetra(thioether), which was methylated and then deprotected with triethylamine in the presence of acetic anhydride to yield 9,10-dimethyl-2,3,6,7-anthracenetetra(thioacetate), a protected form of the tetrathiol. Separately, the first synthesis of benzenepentathiol and streamlined syntheses of 1,2,4,5-benzenetetra(thioacetate) and benzenehexathiol are reported.

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).

When immersed in 1-methylimidazole, the metals copper, zinc, and cobalt will react with ambient dioxygen and carbon dioxide to yield the blue-green molecular complex Cu(CO

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.

A detailed plane-wave density functional theory investigation of the solid-state properties of the extended organometallic system Pb{sub 3}C{sub 6}X{sub 6} for X = O, S, Se, and Te has been performed. Initial geometry parameters for the Pb-X and C-X bond distances were obtained from optimized calculations on molecular fragment models. The Pb{sub 3}C{sub 6}X{sub 6} extended solid molecular structures were constructed in the space group P6/mmm on the basis of the known structure for X = S. Ground-state geometries, band gap energies, densities of states, and charge densities were calculated with the PBE-generalized gradient exchange-correlation functional and the HSE06 hybrid exchange-correlation functional. The PBE band gap energies were found to be lower than the HSE06 values by >0.7 eV. The band energies at points of high symmetry along the first Brillouin zone in the crystal were larger than the overall band gap of the system. Pb{sub 3}C{sub 6}O{sub 6} was predicted to be a direct semiconductor ({Lambda} point) with a PBE band gap of 0.28 eV and an HSE06 band gap of 1.06 eV. Pb{sub 3}C{sub 6}S{sub 6} and Pb{sub 3}C{sub 6}Se{sub 6} were predicted to have indirect band gaps. The PBE band gap for Pb{sub 3}C{sub 6}S{sub 6} wasmore » 0.98 eV, and the HSE06 band gap was 1.91 eV. The HSE06 value is in good agreement with the experimentally observed band gap of 1.7 eV. Pb{sub 3}C{sub 6}Se{sub 6} has a PBE band gap of 0.56 eV and a HSE06 band gap of 1.41 eV. Pb{sub 3}C{sub 6}Te{sub 6} was predicted to be metallic with both of the PBE and HSE06 functionals. A detailed analysis of the PBE band structure and partial density of states at two points before and after the metallic behavior reveals a change in orbital character indicative of band crossing in Pb{sub 3}C{sub 6}Te{sub 6}. These results show that the band gap energies can be fine-tuned by changing the substituent X atom.« less

The reaction of Hg(OAc)(2) with 1,4-benzenedithiol in ethylenediamine at 80 °C yields [Hg(SC(6)H(4)S)(en)](n), while the reaction of Pb(OAc)(2) with 1,4-benzenedithiol in diethylenetriamine at 130 °C yields [Pb(SC(6)H(4)S)(dien)](n). Both products are crystalline materials, and structure determination by synchrotron X-ray powder diffraction revealed that both are essentially one-dimensional metal-organic polymers with -M-SC(6)H(4)S- repeat units. Diffuse reflectance UV-visible spectroscopy indicates band gaps of 2.89 eV for [Hg(SC(6)H(4)S)(en)](n) and 2.54 eV for [Pb(SC(6)H(4)S)(dien)](n), while density functional theory (DFT) band structure calculations yielded band gaps of 2.24 and 2.10 eV, respectively. The two compounds are both infinite polymers of metal atoms linked by 1,4-benzenedithiolate, the prototypical molecule for single-molecule conductivity studies, yet neither compound has significant electrical conductivity as a pressed pellet. In the case of [Pb(SC(6)H(4)S)(dien)](n) calculations indicate fairly flat bands and therefore low carrier mobilities, while the conduction band of [Hg(SC(6)H(4)S)(en)](n) does have moderate dispersion and a calculated electron effective mass of 0.29·m(e). Hybridization of the empty Hg 6s orbital with SC(6)H(4)S orbitals in the conduction band leads to the band dispersion, and suggests that similar hybrid materials with smaller band gaps will be good semiconductors.

The crystal structures of the isostructural title compounds poly[(μ-benzene-1,4-dithiolato)dithallium], Tl2(SC6H4S), and poly[(μ-benzene-1,4-diselenolato)dithallium], Tl2(SeC6H4Se), were solved by simulated annealing from high-resolution synchrotron X-ray powder diffraction. Rietveld refinements of an initial structure with one formula unit per triclinic cell gave satisfactory agreement with the data, but led to a structure with impossibly close non-bonded contacts. A disordered model was proposed to alleviate this problem, but an alternative supercell structure leads to slightly improved agreement with the data. The isostructural superlattice structures were confirmed for both compounds through additional data collection, with substantially better counting statistics, which revealed the presence of very weak superlattice peaks not previously seen. Overall, each structure contains Tl—S or Tl—Se two-dimensional networks, connected by phenylene bridges. The sulfur (or selenium) coordination sphere around each thallium is a highly distorted square pyramid or a `see-saw' shape, depending upon how many Tl—S or Tl—Se interactions are considered to be bonds. In addition, the two compounds contain pairs of TlIions that interact through a closed-shell `thallophilic' interaction: in the sulfur compound there are two inequivalent pairs of Tl atoms with Tl—Tl distances of 3.49 and 3.58 Å, while in the selenium compound those Tl—Tl interactions are at 3.54 and 3.63 Å.

The molecule (C═C)TTP (TTP = tetra-p-tolylporphyrin) and the triflate salt of its dication, [(C═C)TTP][OTf](2), have been synthesized and characterized. NMR spectroscopy, nucleus-independent chemical shift calculations, and the crystal structure of (C═C)TTP indicate that (C═C)TTP is antiaromatic and (C═C)TTP(2+) is aromatic.

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 reaction of vanadium(III) acetylacetonate with HBF4 in acetonitrile yields [(CH3CN)5V-O-V(CH3CN)5][BF4]4, a material that serves as a convenient precursor to other [V-O-V]4+ species such as [(bipy)2(CH3CN)V-O-V(CH3CN)(bipy)2][BF4]4 (bipy=2,2'-bipyridine). Single-crystal X-ray diffraction shows that the V-O-V linkage of [(CH3CN)5V-O-V(CH3CN)5]4+ is linear. An Evans method measurement of the solution-phase magnetic susceptibility indicates strong ferromagnetic coupling between the vanadium centers. Magnetic susceptibility (chi) and magnetization (M(H)) data for a powdered sample and for a single crystal oriented with its V-O-V axis parallel to the applied field were measured over 1.8-300 K. The results suggest that the V(III) centers are ferromagnetically coupled with J approximately 72 K (approximately 50 cm(-1)) yielding a ground state with a total spin Stotal=2. Theoretical fit to the M(H) plot for the single crystal yielded g||=2.01+/-0.01 and the zero-field splitting parameter D=0.60+/-0.04 K (0.42+/-0.03 cm(-1)). EPR measurements at 34 and 101.6 GHz are consistent with the Stotal=2 ground state and yield g||=1.9825, g perpendicular=1.9725 and D=0.57+/-0.03 K.

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.

Dopants for organic molecular semiconductors that yield immobile dopant ions are necessary for the creation of stable molecular semiconductor p–n junctions, the basis for almost all traditional inorganic semiconductor devices. We present evidence for the substitutional cocrystallization of tris(4-nitrophenyl)methyl radical (1) with small amounts of tris[4-(dimethylamino)phenyl]methyl radical (2), resulting in n-doped 1 with immobile 2+ counterions. Cyclic voltammetry indicates that electron transfer from 2 to 1 is favored by 0.51 eV. The powder X-ray diffraction patterns of pure 1 and 1 doped with 2 are very similar, indicating substitutional cocrystallization. The electrical conductivity of doped 1 increases with increasing concentration of 2, and the conductivity is constant over time. Variable-temperature conductivity measurements of 1 doped with 2% and 5% 2 indicate that the activation energy of conduction is 0.32 eV at both dopant concentrations.

[reaction: see text] Oxidation of dilithium tetraphenylporphyrin, Li(2)(TPP), yields the doubly oxidized porphyrin complex [Li(TPP)][BF(4)]. Free TPP appears to be unstable. The crystal structure of [Li(TPP)][BF(4)] reveals that the 16-atom C-N inner ring of the porphyrin consists of alternating single and double bonds. NMR spectroscopy and nucleus-independent chemical shift (NICS) calculations, in addition to the distortion from planarity observed in the crystal structure, indicate that the 16 pi-electron inner C-N ring of the porphyrin is antiaromatic.

A lithium phthalocyanine radical and the analogous aluminum phthalocyanine radical were synthesized as part of an investigation of isostructural dopants. An improved synthesis of the free base of octa(pentoxy)phthalocyanine (H2Pc*) involves the reduction of 1,2-dicyano-4,5-dipentoxybenzene with hydroquinone. Deprotonation with lithium bis(trimethylsilyl)amide leads to the dilithium derivative Li2Pc* and subsequent oxidation with ferrocenium yields the radical LiPc*. Treatment of H2Pc* with Et2AlCl gives ClAlPc* and reduction with sodium amalgam yields AlPc*, the first reported aluminum phthalocyanine radical. In the solid state LiPc* and AlPc* are electrical conductors with pressed-pellet conductivities of 8 × 10−11 Ω−1 cm−1 and 5 × 10−7 Ω−1 cm−1, respectively.

The molecule 4,4''''-di-n-octyl-p-quaterphenyl was synthesized in one step by a nickel-catalyzed cross-coupling reaction. Powder X-ray diffraction shows that it crystallizes in a layered structure with the long axis of the molecule nearly perpendicular to the layer plane. Differential scanning calorimetry indicates a transition to a liquid-crystalline phase at 81 degrees C. Reaction of 4,4'-bis(4-pyridyl)biphenyl with 1-bromooctane yields the dication 2(2+) 2Br-, an "extended viologen" isostructural with 4,4''''-di-n-octyl-p-quaterphenyl. Reduction of 2(2+) 2Br- with sodium amalgam in DMF yields 2, the first neutral extended viologen to be isolated. The molecule 2 is, to the best of our knowledge, the most reducing neutral organic molecule that has been synthesized. Single-crystal X-ray diffraction shows that a diradical form, either singlet or triplet, makes an important contribution to the electronic structure of 2. The broadened 1H NMR spectrum of 2 indicates the presence of a triplet, but it has not been possible to observe the triplet by ESR spectroscopy. The electronic structure of 2 appears to be closely related to that of a classic molecule, Chichibabin's hydrocarbon.

Alcoholysis of W(OMe)6 afforded (p-PhCH2OC6H4O)6W (1-OCH2Ph), which could be hydrogenated (10% Pd/C, 1 atm H2) to prepare (p-HOC6H4O)6W (1-OH). Related alcoholyses of WCl6 with HOC6H4-p-X provided the hexaphenoxides (p-XC6H4O)6W (1-X, X = H, CH3, OCH3, Cl, Br) through minor modifications of literature procedures. Acid catalyzed treatment of 1-X with p-HOC6H4OCH2Ph provided a mixture of substitution products (p-XC6H4O)6−xW(OC6H4OCH2Ph)x (x = 1, 5-X) that could be hydrogenated (10% Pd/C, 1 atm H2) to a mixture of hydroxylated products. Chromatography permitted isolation of (p-XC6H4O)5W(OC6H4OH) (6-X, X = H, 19%; Me, 29%; OCH3, 19%; Cl, 12%; Br, 11%) in modest yields. Hexaphenoxides 1-X and 6-X manifested two electrochemical reduction waves whose positions were a function of para-substituent. When oxidized, 6-X and 1-OH were proposed to behave as W(V)quinone mimics, albeit at potentials capable of oxidizing hydrocarbons as shown via a thermochemical cycle. If the proposed transients (p-XC6H4O)5W(OC6H4O) (7-X) were generated, degradation was apparently competitive with CH bond activation. The structure of oligomeric {K[(p-ClC6H4O)6W]}∞ (8-Cl) is addressed, and comments on the nature of radical CH bond activation in this and related systems are presented.

The synthesis and characterization of the 9,10-diphenylacridyl radical (2), the isostructural n-dopant for 9,10-diphenylantracene (1), are described. Crystals of 1 doped with up to 10% 2 are grown from tetrahydrofuran−heptane solutions and are single phase and isomorphous with crystals of pure 1 grown from the same solvent system. The doped crystals do not have significant room-temperature electrical conductivity, and solution-phase electrochemical measurements demonstrate why this is so. Investigations of 2 reveal that it is monomeric with one unpaired electron in solution, displays unusual magnetic behavior in the solid state, and is a modest electrical conductor as a pressed pellet. The solution-phase ESR and NMR spectra of 2 are presented and interpreted.

An array of 20 compositionally different carbon black−polymer composite chemiresistor vapor detectors was challenged under laboratory conditions to discriminate between a pair of extremely similar pure analytes (H_(2)O and D_(2)O), compositionally similar mixtures of pairs of compounds, and low concentrations of vapors of similar chemicals. Several discriminant algorithms were utilized, including k nearest neighbors (kNN, with k = 1), linear discriminant analysis (LDA, or Fisher's linear discriminant), quadratic discriminant analysis (QDA), regularized discriminant analysis (RDA, a hybrid of LDA and QDA), partial least squares, and soft independent modeling of class analogy (SIMCA). H_(2)O and D_(2)O were perfectly classified by most of the discriminants when a separate training and test set was used. As expected, discrimination performance decreased as the analyte concentration decreased, and performance decreased as the composition of the analyte mixtures became more similar. RDA was the overall best-performing discriminant, and LDA was the best-performing discriminant that did not require several cross-validations for optimization.

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.

Treatment of M(OiPr)4 (M = Ti, V) and [Zr(OEt)4]4 with excess 1,4-HOC6H4OH in THF afforded [M(OC6H4O)a(OC6H4OH)3.34-1.83a(OiPr)0.66-0.17a(THF)0.2]n (M = Ti, 1-Ti; V, 1-V, 0.91or = aor = 1.82) and [Zr(1,4-OC6H4O)2-x(OEt)2x]n (1-Zr, x = 0.9). The combination of of 1-M (M = Ti, V, Zr) or M(OiPr)4 (M = Ti, V), excess 1,4- or 1,3-HOC6H4OH, and pyridine or 4-phenylpyridine at 100 degrees C for 1 d to 2 weeks afforded various 2-dimensional covalent metal-organic networks: [cis-M(mu 1,4-OC6H4O)2py2] infinity (2-M, M = Ti, Zr), [trans-M(mu 1,4-OC6H4O)2py2.py] infinity (3-M, M = Ti, V), solid solutions [trans-TixV1-x(mu 1,4-OC6H4O)2py2.py] infinity (3-TixV1-x, x approximately 0.4, 0.6, 0.9), [trans-M(mu 1,4-OC6H4O)2(4-Ph-py)2] infinity (4-M, M = Ti, V), [trans-Ti(mu 1,3-OC6H4O)2py2] infinity (5-Ti), and [trans-Ti(mu 1,3-OC6H4O)2(4-Ph-py)2] infinity (6-Ti). Single-crystal X-ray diffraction experiments confirmed the pleated sheet structure of 2-Ti, the flat sheet structure of 3-Ti, and the rippled sheet structures of 4-Ti, 5-Ti, and 6-Ti. Through protolytic quenching studies and by correspondence of powder XRD patterns with known titanium species, the remaining complexes were structurally assigned. With py or 4-Ph-py present, aggregation of titanium centers is disrupted, relegating the building block to the cis- or trans-(ArO)4Tipy2 core. The sheet structure types are determined by the size of the metal and the interpenetration of the layers, which occurs primarily through the pyridine residues and inhibits intercalation chemistry.

A quantitative structure–activity relationship (QSAR) has been formulated to describe the inhibitory action of a series of alcohols on the cytochrome P-450 catalyzed p -hydroxylation of aniline. The descriptors used in the QSAR are the responses of individual sensors in a polymer-based electronic nose, and are all easily generated experimental values. If the various electronic nose sensor response patterns for the family of test alcohols reflect differences in the chemical properties that are involved in the cytochrome P-450 inhibition process, it ought to be possible to correlate the differences in the electronic nose signals of these analytes with the differences in the cytochrome P-450 inhibition by these species. To evaluate this possibility, multiple linear regression was performed on data obtained from exposure of a series of test alcohols to 19 sensors of a conducting polymer composite electronic nose array. A genetic algorithm was then used to select the optimal set of sensors that best described the inhibitory activity of these alcohols within a linear regression model. The regression equation fit the inhibition data of 20 of the alcohols with an R of 0.995. This fit compares favorably with previously published QSARs on this system that have used log P ( P octanol–water partition coefficient) along with steric parameters of the alcohols, and also compares favorably to QSARs formulated using theoretically calculated parameters.

The reaction of GeCl2(dioxane) with K2Pc(DMF)4 yields germanium phthalocyanine, GePc. GePc dissolves in pyridine to form GePc(py)2. The 1H NMR spectrum of GePc(py)2 and nucleus-independent chemical shift (NICS) calculations on GePc(NMe3)2 both show the presence of a strong paratropic ring current. That ring current, along with the bond-length alternation in the crystal structure of GePc(tBuPy)2, indicates the presence of an antiaromatic pi-electron circuit in GePc(py)2. SiPc(py)2 was synthesized, and its electronic structure is similar to that of GePc(py)2.

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 ...

A statistical metric, based on the magnitude and standard deviations along linear projections of clustered array response data, was utilized to facilitate an evaluation of the performance of detector arrays in various vapor classification tasks. This approach allowed quantification of the ability of a 14-element array of carbon black−insulating polymer composite chemiresistors to distinguish between members of a set of 19 solvent vapors, some of which vary widely in chemical properties (e.g., methanol and benzene) and others of which are very similar (e.g., n-pentane and n-heptane). The data also facilitated evaluation of questions such as the optimal number of detectors required for a specific task, whether improved performance is obtained by increasing the number of detectors in a detector array, and how to assess statistically the diversity of a collection of detectors in order to understand more fully which properties are underrepresented in a particular set of array elements. In addition, the resolvi...

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.

Treatment of tetraphenylporphyrinato(aluminum) chloride, Al(TPP)Cl, with Na/Hg in THF yields the stable radical Al(TPP)(THF)2. Similarly, treatment of aluminum phthalocyanine chloride, Al(Pc)Cl, with Na/Hg in THF yields the stable radical Al(Pc)(THF)2. Solution-phase magnetic susceptibility measurements show that both are monomeric radicals in solution, and ESR spectroscopy and density functional theory (DFT) calculations indicate that in both molecules the unpaired electron is delocalized throughout the ring system. While DFT calculations indicate that both molecules should undergo a Jahn-Teller distortion, only the porphyrin complex exhibits the predicted C-C bond length alternation in its X-ray crystal structure. That distortion of the ring system has precedent only in the similar reduced porphyrin complex Si(TPP)(THF)2.

The electronic structure and photophysical properties of (C=C)TTP(2+) (TTP = tetra-p-tolylporphyrin) were scrutinized by using quantum mechanical calculations and transient absorption spectroscopic measurements. When compared to a metalloporphyrin, the presence of the C=C unit in (C=C)TTP(2+) causes a splitting of the degenerate LUMO and a large decrease in the HOMO-LUMO gap, while the 2+ charge and tolyl groups lead to additional charge-transfer-like transitions in the visible absorption spectrum. The small HOMO-LUMO gap and ruffled structure lead to a very short excited-state lifetime of 10 ± 0.3 ps.

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/NH3 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.

Metal-organic frameworks based on metal-sulfur or metal-selenium bonds are relatively rare; herein we describe the synthesis and structural characterization of several examples, including, for example, [Cd(en)3][Cd(SC6H4S)2], which contains the anionic two-dimensional square-grid network [Cd(SC6H4S)2]n(2n-).