Halometallate complexes of germanium(II) and (IV): probing the role of cation, oxidation state and halide on the structural and electrochemical properties

Effect of the cation structure on the properties of homobaric imidazolium ionic liquids

In this work we investigate the structure-property relationships in a series of alkylimidazolium ionic liquids with almost identical molecular weight. Using a combination of theoretical calculations and experimental measurements, we have shown that re-arranging the alkyl side chain or adding functional groups results in quite distinct features in the resultant ILs. The synthesised ILs, although structurally very similar, cover a wide spectrum of properties ranging from highly fluid, glass forming liquids to high melting point crystalline salts. Theoretical ab initio calculations provide insight on minimum energy orientations for the cations, which then are compared to experimental X-ray crystallography measurements to extract information on hydrogen bonding and to verify our understanding of the studied structures. Molecular dynamics simulations of the simplest (core) ionic liquids are used in order to help us interpret our experimental results and understand better why methylation of C² position of the imidazolium ring results in ILs with such different properties compared to their non-methylated analogues.

Electrochemical Behavior of Graphene in a Deep Eutectic Solvent

Graphene electrodes and deep eutectic solvents (DESs) are two emerging material systems that have individually shown highly promising properties in electrochemical applications. To date, however, it has not been tested whether the combination of graphene and DESs can yield synergistic effects in electrochemistry. We therefore study the electrochemical behavior of a defined graphene monolayer of centimeter-scale, which was produced by chemical vapor deposition and transferred onto insulating SiO₂/Si supports, in the common DES choline chloride/ethylene glycol (12CE) under typical electrochemical conditions. We measure the graphene potential window in 12CE and estimate the apparent electron transfer kinetics of an outer-sphere redox couple. We further explore the applicability of the 12CE electrolyte to fabricate nanostructured metal (Zn) and metalloid (Ge) hybrids with graphene by electrodeposition. By comparing our graphene electrodes with common bulk glassy carbon electrodes, a key finding we make is that the two-dimensional nature of the graphene electrodes has a clear impact on DES-based electrochemistry. Thereby, we provide a first framework toward rational optimization of graphene-DES systems for electrochemical applications.

Versatile Platform of Ion Conducting 2D Anionic Germanate Covalent Organic Frameworks with Potential for Capturing Toxic Acidic Gases

Anionic covalent organic framework is an emerging class of functional materials in which included ionic species of the opposite charges play an important role in the ion conduction and selective gas adsorption. Herein, we reported a facile method to construct a series of germanate-based anionic COFs (Ge-COFs) by reticulating dianionic hexa-coordinated GeO₆ nodes with anthracene building blocks adopting a hcb topology in an extended 2D framework. A systematic change of pore properties in Ge-COFs was observed through the incorporation of three different alkali metal cations: Li⁺, Na⁺, and K⁺. The intrinsically negatively charged backbone provides a host matrix with a homogeneous distribution of counter cations and poses variable and exciting features for gas adsorption and ionic conduction. Among the series, K⁺-based Ge-COF-K with a surface area of 1252 m²/g and pore volume of 0.84 cm³/g shows a maximum CO₂ uptake of 126 cm³/g (247.4 mg/g) at 273 K and 1 bar, an IAST selectivity of 140 over N₂. Ge-COF-K also exhibits a high SO₂ kinetic breakthrough capacity of 154 mg/g at low ppm of SO₂ concentration under ambient conditions among recently reported porous materials. Moreover, reasonably high lithium, sodium, and potassium ionic conductivities were observed with the values of 1.2 × 10^-4, 3.4 × 10^-5, and 2.2 × 10^-5 S/cm for propylene carbonate infiltrated Ge-COF-Li, Ge-COF-Na, and Ge-COF-K at 100 °C, respectively.

Exploring six-coordinate germanium(IV)-diketonate complexes as anticancer agents

Cancer remains one of the leading causes of death worldwide and despite several attempts using chemotherapy to combat the deadly disease, toxic side effects and drug resistance temper efficacy [1]. Thus, drugs with potentially new mechanisms and lower toxicity to normal cells are needed. Metalloids such as arsenic compounds have been clinically beneficial in fighting cancer, but germanium is yet to gain such prominence [2,3]. We report the synthesis of four octahedral germanium(IV) complexes bearing acetylacetonato ligand, [GeIV(acac)3)]+, with different anions (3 - 6) using a streamlined synthetic approach. The compounds were structurally and electrochemically characterized using NMR, MS, X-ray crystallography, and cyclic voltammetry. The cyclic voltammogram of 3-5 revealed distinct irreversible peaks in the range of -0.9 to -1.9 V, corresponding to Ge(IV)/ Ge(II) or Ge(II)/Ge(0) couple in DMSO. We explored the anticancer activity of the complexes against a panel of cancer cell lines with IC50 values in the sub-micromolar range (9-15 μM). The compounds display ~3-fold selectivity in cancer cells over normal epithelial cells. In addition to the promising anticancer activity, the compounds display high complex stability in biological media, induces G1 arrest, reactive oxygen stress (ROS) accumulation, and mitochondria membrane depolarization in cancer cells. Furthermore, the compounds induce significant apoptosis.

Crystal structure, magneto-structural correlation, thermal and electrical studies of an imidazolium halometallate molten salt: (trimim)[FeCl4]

A novel imidazolium halometallate molten salt with formula (trimim)[FeCl4] (trimim: 1,2,3-trimethylimidazolium) was synthetized and studied with structural and physico-chemical characterization. Variable-temperature synchrotron X-ray powder diffraction (SXPD) from 100 to 400 K revealed two structural transitions at 200 and 300 K. Three different crystal structures were determined combining single crystal X-ray diffraction (SCXD), neutron powder diffraction (NPD), and SXPD. From 100 to 200 K, the compound exhibits a monoclinic crystal structure with space group P21/c. At 200 K, the former crystal system and space group are retained, but a disorder in the organic cations is introduced. Above 300 K, the structure transits to the orthorhombic space group Pbcn, retaining the crystallinity up to 400 K. The study of the thermal expansion process in this temperature range showed anisotropically evolving cell parameters with an axial negative thermal expansion. Such an induction occurs immediately after the crystal phase transition due to the translational and reorientational dynamic displacements of the imidazolium cation within the crystal building. Electrochemical impedance spectroscopy (EIS) demonstrated that this motion implies a high and stable solid-state ionic conduction (range from 4 × 10-6 S cm-1 at room temperature to 5.5 × 10-5 S cm-1 at 400 K). In addition, magnetization and heat capacity measurements proved the presence of a three-dimensional antiferromagnetic ordering below 3 K. The magnetic structure, determined by neutron powder diffraction, corresponds to ferromagnetic chains along the a-axis, which are antiferromagnetically coupled to the nearest neighboring chains through an intricate network of superexchange pathways, in agreement with the magnetometry measurements.

Towards a 3D GeSbTe phase change memory with integrated selector by non-aqueous electrodeposition

We have recently reported a new method for the electrodeposition of thin film and nanostructured phase change memory (PCM) devices from a single, highly tuneable, non-aqueous electrolyte. The quality of the material was confirmed by phase cycling via electrical pulsed switching of both 100 nm nano-cells and thin film devices. This method potentially allows deposition into extremely small confined cells down to less than 5 nm, 3D lay-outs that require non-line-of-sight techniques, and seamless integration of selector devices. As electrodeposition requires a conducting substrate, the key condition for electronic applications based on this method is the use of patterned metal lines as the working electrode during the electrodeposition process. In this paper, we show the design and fabrication of a 2D passive memory matrix in which the word lines act as the working electrode and nucleation site for the growth of confined cells of Ge-Sb-Te. We will discuss the precursor requirement for deposition from non-aqueous, weakly coordinating solvents, show the transmission electron microscopy analysis of the electrodeposition growth process and elemental distribution in the deposits, and show the fabrication and characterisation of the Ge-Sb-Te memory matrix.

Crystallographic Insights into the Behavior of Highly Acidic Metal Cations in Ionic Liquids from Reactions of Titanium Tetrachloride with [1-Butyl-3-Methylimidazolium][X] Ionic Liquids (X = Chloride, Bromide, Tetrafluoroborate)

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.

Imidazolium-based ionic liquids with large weakly coordinating anions

An investigation into the intramolecular interactions in a series of imidazolium salts with weakly coordinating anions reveals that it is possible to control the strength and location of hydrogen bonding by varying the substituents on the imidazolium cation.

Surface modification and porosimetry of vertically aligned hexagonal mesoporous silica films

Grafting vertically aligned mesoporous silica films with small organosilane precursors increases pore hydrophobicity, whereas larger reagents change only the film surfaces.

Haloplumbate salts as reagents for the non-aqueous electrodeposition of lead

Cyclic voltammetry experiments on the Pb(ii) salts, [PPh₄][PbX₃] (X = Cl, Br, I) in CH₂Cl₂ solution ([PPh₄]X supporting electrolyte) at Pt electrodes show reproducible nucleation and stripping features consistent with reduction to elemental Pb.

Hexahalometallate salts of trivalent scandium, yttrium and lanthanum: cation–anion association in the solid state and in solution

The hydrogen bonding of hexahalometallate anions with various organic cations is explored via crystallographic and solution NMR studies.

Cationic aza-macrocyclic complexes of germanium(II) and silicon(IV)

[GeCl2(dioxane)] reacts with the neutral aza-macrocyclic ligands L, L = Me3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane), Me4cyclen (1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) or Me4cyclam (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and two mol. equiv. of Me3SiO3SCF3 in thf solution to yield the unusual and hydrolytically very sensitive [Ge(L)][O3SCF3]2 as white solids in moderate yield. Using shorter reaction times [Ge(Me3tacn)]Cl2 and [Ge(Me3tacn)]Cl[O3SCF3] were also isolated; the preparation of [Ge(Me4cyclen)][GeCl3]2 is also described. The structures of the Me3tacn complexes show κ(3)-coordination of the macrocycle, with the anions interacting only weakly to produce very distorted five- or six-coordination at germanium. In contrast, the structure of [Ge(Me4cyclen)][O3SCF3]2 shows no anion interactions, and a distorted square planar geometry at germanium from coordination to the tetra-aza macrocycle. Crystal structures of the Si(iv) complexes, [SiCl3(Me3tacn)]Y (Y = O3SCF3, BAr(F); [B{3,5-(CF3)2C6H3}4]) and [SiHCl2(Me3tacn)][BAr(F)], obtained from reaction of SiCl4 or SiHCl3 with Me3tacn, followed by addition of either Me3SiO3SCF3 or Na[BAr(F)], contain distorted octahedral cations, with facialκ(3)-coordinated Me3tacn. The open-chain triamine, Me2NCH2CH2N(Me)CH2CH2NMe2 (pmdta), forms [SiCl3(pmdta)][BAr(F)] and [SiBr3(pmdta)][BAr(F)] under similar conditions, containing mer-octahedral cations.

The preparation and structure of Ge3F8 - a new mixed-valence fluoride of germanium, a convenient source of GeF2

The new binary mixed-valence fluoride of germanium, Ge3F8, has been obtained by heating GeF4 with powdered Ge in an autoclave (390 K/4 bar/48 h). The structure contains pyramidal Ge(II)F3 and octahedral Ge(IV)F6 units, linked by fluoride bridges. The new compound is the missing member of the series (GeF2)n·GeF4 (n = 2, 4, or 6). Sublimation of (GeF2)n·GeF4in vacuo provides a convenient source of GeF2 in ca. 30% overall yield.