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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.

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.

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.

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 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.

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.

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.

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 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.

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.

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.

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-).

Ti((i)OPr)(4) was treated with 2.58 equiv of hydroquinone in THF to yield a red-orange powder formulated as [Ti(OC(6)H(4)O)(a)()(OC(6)H(4)OH)(3.34)(-)(1.83)(a)()(O(i)Pr)(0.66)(-)(0.17)(a)() (THF)(0.2)](n)() (1, (0.91/= a/= 1.82)) based upon D(2)O/DCl quenching studies. Treatment of 1 with an excess of hydroquinone in Et(2)O or DME afforded burgundy [Ti(2)(mgr;(1,4)-OC(6)H(4)O)(2)(mgr;(1,4)-OC(6)H(4)OH)(2)(mgr;-OC(6)H(4)OH)(2)](infinity) (2). Burgundy [Ti(2)(mgr;(1,4)-OC(6)H(4)O)(2)(mgr;(1,4):eta(2),eta(1)-OC(6)H(4)O)(2)(OH(2))(2).(H(2)O)(2).(H-OC(6)H(4)OH).(MeCN)](infinity) (4) was prepared from 1 and excess wet hydroquinone in CH(3)CN. The acetonitrile in 4 can be exchanged for THF or DME. Treatment of Ti(O(i)Pr)(4) with approximately 4 equiv of 2,7-dihydroxynaphthalene in Et(2)O at 100 degrees C (2 days) in a sealed tube yielded orange crystals of [Ti(2)(mgr;(1,7)-OC(10)H(6)O)(2)(mgr;(1,7):eta(2),eta(1)-OC(10)H(6)OH)(2)(O(i)Pr)(2)](infinity) (5). Diffraction studies were conducted at the Cornell High Energy Synchrotron Source (CHESS) because of the small crystal sizes. 2 (C(18)H(14)O(6)Ti, monoclinic, P2(1)/n, a = 9.624 (2), b = 11.283 (2), c = 14.916 (3), beta = 90.47(3) degrees, Z = 4), 4 (C(32)H(33)NO(14)Ti(2), monoclinic, P2(1)/n, a = 16.137 (3), b = 10.762 (2), c = 20.368 (4), beta = 111.65(3) degrees, Z = 4), and 5 (C(23)H(20)O(5)Ti, orthorhombic, Pbca, a = 11.095 (2), b = 17.970 (4), c = 19.484 (4), Z = 8) are 3-dimensional materials based on diaryloxide connectivity between geometrically similar edge shared (i.e., Ti(2)(mgr;-OAr)(2)) bioctahedral dititanium building blocks. While 2 and 5 possess a roughly body-centered arrangement of dititanium units, 4 has a hexagonal secondary structural motif. The nature of crystallization through alcoholysis is also discussed.