Cyano(fluoro)borate and cyano(hydrido)borate ionic liquids: low-viscosity ionic media for electrochemical applications

The synthesis and detailed characterization of low-viscosity room-temperature ionic liquids (RTILs) and [BnPh₃P]⁺ salts with the cyano(fluoro)borate anions [BF(CN)₃]^- (MFB), [BF₂(CN)₂]^- (DFB), and [BF₃(CN)]^- as well as the new mixed-substituted anion [BFH(CN)₂]^- (FHB) is described. The RTILs with [EMIm]⁺ or [BMPL]⁺ as countercations were obtained in yields of up to 98% from readily available alkali metal salts and in high purities that allow application in electrochemical devices. Trends in thermal stability, melting and freezing behavior, density, electrochemical stability, dynamic viscosity, specific conductivity and ion diffusivity have been assessed and compared to those of the related tetracyanoborate- and cyano(hydrido)borate-RTILs. The crystal structure analysis of the [BnPh₃P]⁺ salts of [BF_n(CN)_4-n]^- (n = 0-4), [BH_n(CN)_4-n]^- (n = 1-3) and [BFH(CN)₂]^- provided experimental access to anion volumina that together with ion molecular mass, electrostatic potential, shape and chemical stability have been correlated to physicochemical properties. In addition, the cytotoxicity of the [EMIm]⁺-ILs and potassium or sodium salts was studied.

Main group cyanides: from hydrogen cyanide to cyanido-complexes

Homoleptic cyanide compounds exist of almost all main group elements. While the alkali metals and alkaline earth metals form cyanide salts, the cyanides of the lighter main group elements occur mainly as covalent compounds. This review gives an overview of the status quo of main group element cyanides and cyanido complexes. Information about syntheses are included as well as applications, special substance properties, bond lengths, spectroscopic characteristics and computations. Cyanide chemistry is presented mainly from the field of inorganic chemistry, but aspects of chemical biology and astrophysics are also discussed in relation to cyano compounds.

Innovative Syntheses of Cyano(fluoro)borates: Catalytic Cyanation, Electrochemical and Electrophilic Fluorination

Different types of high-yield, easily scalable syntheses for cyano(fluoro)borates Kt[BFn (CN)4-n ] (n=0-2) (Kt=cation), which are versatile building blocks for materials applications and chemical synthesis, have been developed. Tetrafluoroborates react with trimethylsilyl cyanide in the presence of metal-free Brønsted or Lewis acid catalysts under unprecedentedly mild conditions to give tricyanofluoroborates or tetracyanoborates. Analogously, pentafluoroethyltrifluoroborates are converted into pentafluoroethyltricyanoborates. Boron trifluoride etherate, alkali metal salts, and trimethylsilyl cyanide selectively yield dicyanodifluoroborates or tricyanofluoroborates. Fluorination of cyanohydridoborates is the third reaction type that includes direct fluorination with, for example, elemental fluorine, stepwise halogenation/fluorination reactions, and electrochemical fluorination (ECF) according to the Simons process. In addition, fluorination of [BH(CN)2 {OC(O)Et}]- to result in [BF(CN)2 {OC(O)Et}]- is described.

Retarding Ion Exchange between Conducting Polymers and Ionic Liquids for Printable Top Electrodes in Semitransparent Organic Solar Cells

Semitransparent organic solar cells (ST-OSCs) are considered to be an influential tool for aesthetic and economic building-integrated photovoltaics, which can be fabricated by the printing technology. A poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and ionic liquid (IL) composite has been considered as an electrode for ST-OSCs because of its high electrical conductivity, high transparency, and printability. However, we found that the introduction of IL into the PEDOT:PSS solution for enhancing its electrical conductivity results in (1) nonreliable printing of PEDOT:PSS/IL composite films because of gradual gelation of the mixture solution and (2) the production of chemically reactive ion pairs during ion exchange between PSS and IL, which induces the oxidation of the underlying organic semiconductors during printing. To solve these problems, we developed a sequential printing method using pristine PEDOT:PSS and IL solutions to retard ion exchange, thus preventing chemical doping of organic semiconductors by newly generated ion pairs. Finally, by using only solution processes, we demonstrate efficient ST-OSCs with a printed PEDOT:PSS/IL composite as the top electrode, exhibiting a power conversion efficiency of 6.32% at an average visible transmittance of 35.4%.

Manifestations of Weak O-H···F Hydrogen Bonding in M(H2O) n(B12F12) Salt Hydrates: Unusually Sharp Fourier Transform Infrared ν(OH) Bands and Latent Porosity (M = Mg-Ba, Co, Ni, Zn)

Eight M(H₂O) _n(Z) salt hydrates were characterized by single-crystal X-ray diffraction (Z^2- = B₁₂F₁₂^2-): M = Ca, Sr, n = 7; M = Mg, Co, Ni, Zn, n = 6; M = Ba, n = 4, 5. Weak O-H···F hydrogen bonding between the M(H₂O) _n²⁺ cations and Z^2- resulted in room-temperature Fourier transform infrared (FTIR) spectra having sharp ν(OH) bands, with full widths at half max of 10-30 cm^-1, which are much more narrow than ν(OH) bands in room temperature FTIR spectra of most salt hydrates. Clearly resolved ν_asym(OH/OD) and ν_sym(OH/OD) bands with Δν(OH) as small as 17 cm^-1 and Δν(OD) as small as 11 cm^-1 were observed (Δν(OX) = ν_asym(OX) - ν_sym(OX)). The isomorphic hexahydrates ( R3̅) have two fac-(H₂O)₃ sets of H₂O ligands and nearly octahedral coordination spheres. They exhibited four resolvable ν(OH) bands, one ν_asym(OH)/ν_sym(OH) pair for H₂O ligands with longer O(H)···F distances and one ν_asym(OH)/ν_sym(OH) pair for H₂O ligands with shorter O(H)···F distances. The ν(OH) bands for the three H₂O molecules with shorter, slightly stronger O(H)···F hydrogen bonds were broader, more intense, and red-shifted by ca. 25 cm^-1 relative to the bands for the three other H₂O molecules, the first time that such small differences in relatively weak O(H)···F hydrogen bonds in the same crystalline hexahydrate have resulted in observable IR spectroscopic differences at room temperature. For the first time room temperature ν(OH) values for salt hexahydrates showed the monotonic progression Mg²⁺ > Co²⁺ > Ni²⁺ > Zn²⁺, essentially the same progression as the p K_a values for these metal ions in aqueous solution. A further manifestation of the weak O-H···F hydrogen bonding in these hydrates is the latent porosity exhibited by Ba(H₂O)_5,8(Z), Sr(H₂O) _n,m(Z), and Ca(H₂O)_4,6(Z). Finally, the H₂O/D₂O exchange reaction Co(D₂O)₆(Z) → Co(H₂O)₆(Z) was ca. 50% complete in 1 h at 50 °C in N₂/17 Torr H₂O( g).

On the relationship between the structural and volumetric properties of solvated metal ions in O-donor solvents using new structural data in amide solvents

The structures of the N,N-dimethylformamide (dmf), N,N-dimethylacetamide (dma), and N,N-dimethylpropionamide (dmp) solvated strontium and barium ions have been determined in solution using large angle X-ray scattering and EXAFS spectroscopy. The strontium ion has a mean coordination number (CN) between 6.2 and 6.8, and the barium ion has a mean CN between 7.1 and 7.8 in these amide solvents. The non-integer numbers indicates that equilibria between different coordination numbers and geometries exist in these systems. Structural information of the alkali, alkaline earth, and selected transition metal and lanthanoid(iii) ions, and the halide ions in water, methanol, ethanol, dimethylsulfoxide, formamide, dmf and dma has been combined with previously reported standard partial molar volumes, V0. The ionic radii and charge densities (charge/ionic volume), and corresponding V0 values have been used to gain information on the relationship between structural and volumetric properties. For the structure-breaking ions, i.e. the alkali metal and halide ions, there is an almost linear relationship between the ionic radius and V0. On the other hand, for the structure-making ions, here the alkaline earth, transition metal and lanthanoid(iii) ions, a linear relationship is observed between the charge density and V0. Solvents with a well-defined bulk structure through hydrogen bonding, specifically, water, methanol and ethanol, will be more contracted through solvation than aprotic solvents, as the space between the solvent molecules is lost as a result of the hydrogen bonding. In this respect, methanol stands out as the most compressed solvent participating in solvation compared to its bulk structure.

Structural diversity in the alkaline earth metal compounds of tetra and pentacyanocyclopentadienide

The reaction of the alkaline earth dihalides MCl₂·nH₂O (M = Mg, Ca, Sr, Ba) with the silver salts of cyanocyclopentadienides [C₅(CN)₄X]^- (X = H, CN) yields the corresponding alkaline earth biscyclopentadienides. The pentacyanocyclopentadienides of Mg and Ca and the tetracyanocyclopentadienides of Ca, Sr and Ba were studied by X-ray diffraction. The Mg compound 1a' shows only coordination by water molecules, but numerous hydrogen bridges between coordinated water molecules and pentacyanocyclopentadienide anions and further guest water molecules create a three-dimensional network. The structure of the calcium pentacyanocyclopentadienide 1b shows two inequivalent anions, one uncoordinated and one coordinating via three nitrile groups to three different metal ions. Ca²⁺ and [C₅(CN)₅]^- ions together form a rhombohedral grid structure, in which the voids are filled by the uncoordinated [C₅(CN)₅]^- ion and guest water molecules, all taking part in a hydrogen bond network too. The isostructural Ca and Sr tetracyanocyclopentadienides exhibit eightfold coordinated metal ions, in which both [C₅(CN)₄H]^- anions coordinate to the metals by one cyano group each, and each anion bridging two metal ions. Thus, one-dimensional ribbons of {Ca[C₅(CN)₄H]_4/2}_x are formed, which are interconnected via hydrogen bridges from and to coordinated water molecules to build a three-dimensional network. The barium tetracyanocyclopentadienide contains a ninefold coordinated metal with the anion using three of its nitrile functions for coordination to three different metals. A complicated network is formed by four interpenetrating {Ba[C₅(CN)₄H]₂} helices that are interconnected via the remaining third nitrile function, while the fourth nitrile group always remains uncoordinated. Although all coordinated water molecules are involved in hydrogen bridges, these are not contributing to the formation of the network.