Crystal architecture and mesophase structure of long-chain N-alkylpyridinium tetrachlorometallates

Studies of κ2- and κ3-tripyridylamine complexes of ruthenium and π-stacking by pyridyls

The reaction of tris(pyridin-2-yl)amine with [CyRuCl2]2 (Cy = p-isopropyltoluene or cymene) in refluxing diglyme led to the formation of cis-[RuCl2{κ2-(2-py)3N}2]·CHCl3 (1a) after recrystallization from chloroform/pentane, or cis-dichloridobis[tris(pyridin-2-yl)amine-κ2N,N']ruthenium(II) dichloromethane disolvate, [RuCl2(C15H12N4)2]·2CH2Cl2 or cis-[RuCl2{κ2-(2-py)3N}2]·2CH2Cl2 (1b). Treatment of 1a with one equivalent of silver(I) hexafluoridoantimonate in dichloromethane gave [RuCl{κ2-(2-py)3N}{κ3-(2-py)3N}][SbF6]·CH2Cl2 (2a). Crystallization of 2a from chloroform provided chlorido[tris(pyridin-2-yl)amine-κ2N,N'][tris(pyridin-2-yl)amine-κ3N,N',N'']ruthenium(II) hexafluoridoantimonate chloroform monosolvate, [RuCl(C15H12N4)2][SbF6]·CHCl3 or [RuCl{κ2-(2-py)3N}{κ3-(2-py)3N}][SbF6]·CHCl3 (2b). Complex 2a reacted with a further equivalent of silver(I) hexafluoridoantimonate to give [Ru{κ3-(2-py)3N}2][SbF6]2 (3). The reaction of (2-py)3N with [CyRuCl2]2 in dichloromethane followed by treatment with excess sodium hexafluoridoantimonate gave the known complex [CyRuCl{κ2-(2-py)3N}][SbF6] (4). Complex 2 is a rare example of a complex containing both κ2- and κ3-(2-py)3N. Intramolecular π-stacking interactions determine the orientation of the free pyridyl in the κ2 complexes. An interesting encapsulation of methylene chloride hydrogen-bonded tetramers was noted in one case.

On the high-temperature phase transition of a new chlorocadmate(ii) complex incorporating symmetrical Cd2Cl6 clusters: structural, optical and electrical properties

In the present investigation, a new hybrid crystal, with the formula [(C4H9)4P]2Cd2Cl6 has been synthesized by the slow evaporation method at room temperature. It was characterized by X-ray diffraction (XRD), Hirshfeld surface, differential scanning calorimetry (DSC), optical measurement and complex impedance. Single crystal X-ray diffraction structural analysis revealed that the title compound crystallizes in the triclinic system with space group P1̄ and cell parameters: a = 11.972 (1) Å, b = 15.418 (1) Å, c = 15.426 (2) Å, αa = 68.71 (2) °, β = 73.20 (3) ° and γ = 74.39 (2)°. The Hirshfeld surface analysis was conducted to investigate intermolecular interactions and associated 2D fingerprint plots, revealing quantitatively the relative contribution of these interactions in the crystal cohesion. DSC studies indicated one phase transition at about 348 K. Optical absorption spectra show that the band gap of [(C4H9)4P]2Cd2Cl6 is approximately 2.65 eV. The Nyquist plot showed only one semicircular arc, representing the grain effect in the electrical conduction. The thermal evolution of the conductivity of the grains presents an Arrhenius type behavior, demonstrating that charge carriers have to overcome different energy barriers while conducting and relaxing. Besides, the AC conductivity was analyzed by Jonscher's law and the conduction mechanism is well ensured by the correlated barrier hopping (CBH) model.

Tetrahalidometallate(II) Ionic Liquids with More than One Metal: The Effect of Bromide versus Chloride

Fifteen N-butylpyridinium salts - five monometallic [C₄ Py]₂ [MBr₄ ] and ten bimetallic [C₄ Py]₂ [M_0.5 ^a M_0.5 ^b Br₄ ] (M=Co, Cu, Mn, Ni, Zn) - were synthesized, and their structures and thermal and electrochemical properties were studied. All the compounds are ionic liquids (ILs) with melting points between 64 and 101 °C. Powder and single-crystal X-ray diffraction show that all ILs are isostructural. The electrochemical stability windows of the ILs are between 2 and 3 V. The conductivities at room temperature are between 10^-5 and 10^-6  S cm^-1 . At elevated temperatures, the conductivities reach up to 10^-4  S cm^-1 at 70 °C. The structures and properties of the current bromide-based ILs were also compared with those of previous examples using chloride ligands, which illustrated differences and similarities between the two groups of ILs.

The Coordination Behavior of Two New Complexes, [(C7H10NO2)CdCl3]n(I) and [(C7H9NO2)CuCl2] (II), Based on 2,6-Dimethanolpyridine; Elaboration of the Structure and Hirshfeld Surface, Optical, Spectroscopic and Thermal Analysis

Two novel complexes, [(C₇H₁₀NO₂)CdCl₃]_n(I) and [(C₇H₉NO₂)CuCl₂],havebeen synthesized and characterized. Single crystal X-ray diffraction revealed that in compound (I), 2,6-dimethanol pyridinium acts as a monodentate ligand through the O atom of the hydroxyl group. Contrarily, the 2,6-dimethanol pyridine ligand interacts tridentately with the Cu(II) ion via the nitrogen atoms and the two oxygen (O, O’) atoms of the two hydroxyl groups. The structure’s intermolecular interactions were studied using contact enrichment ratios and Hirshfeld surfaces. Following metal coordination, numerous hydrogen connections between entities and parallel displacement stacking interactions between pyridine rings dictate the crystal packing of both compounds. The aromatic cycles generate layers in the crystal for both substances. Powder XRD measurements confirmed the crystalline sample phase purity. SEM confirmed the surface homogeneity, whereas EDX semi-quantitative analysis corroborated the composition. IR spectroscopy identified vibrational absorption bands, while optical UV-visible absorption spectroscopy investigated optical properties. The thermal stability of the two materials was tested using TG-DTA.

Cetylpyridinium Trichlorostannate: Synthesis, Antimicrobial Properties, and Controlled-Release Properties via Electrical Resistance Tomography

Cetylpyridinium trichlorostannate (CPC-Sn), comprising cetylpyridinium chloride (CPC) and stannous chloride, was synthesized and characterized via single-crystal X-ray diffraction measurements indicating stoichiometry of C₂₁H₃₈NSnCl₃ where the molecules are arranged in a 1:1 ratio with a cetylpyridinium cation and a [SnCl₃]^- anion. CPC-Sn has shown potential for application as a broad-spectrum antimicrobial agent, to reduce bacteria-generated volatile sulfur compounds and to produce advanced functional materials. In order to investigate its controlled-release properties, electrical resistance tomography was implemented. The results demonstrate that CPC-Sn exhibits extended-release properties in an aqueous environment as opposed to the CPC counterpart.

A novel strategy to reduce the viscosity of cellulose-ionic liquid solution assisted by transition metal ions

The high viscosity of ionic liquids, even at relatively high temperatures, can greatly affect the production of cellulose fibers through the wet-spinning process. The high viscosity mainly by due to the hydrogen bond interaction between the cations and anions of ionic liquids. It is possible to reduce the viscosity by modulating the hydrogen bond interaction. In the present work, copper chloride (CuCl₂) was dissolved in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl)-cellulose solution, followed by the formation of a complex with the chloride anions by converting it to [CuCl₄]^2- anion. Through this strategy, the extrusion velocity of the solution improved, and the produced fibers obtained smoother surfaces and shrunken diameters.

Ionic Liquids with More than One Metal: Optical and Electrochemical Properties versus d-Block Metal Combinations

Thirteen N-butylpyridinium salts, including three monometallic [C4 Py]2 [MCl4 ], nine bimetallic [C4 Py]2 [M1-x a Mx b Cl4 ] and one trimetallic compound [C4 Py]2 [M1-y-z a My b Mz c Cl4 ] (M=Co, Cu, Mn; x=0.25, 0.50 or 0.75 and y=z=0.33), were synthesized and their structure and thermal and electrochemical properties were studied. All compounds are ionic liquids (ILs) with melting points between 69 and 93 °C. X-ray diffraction proves that all ILs are isostructural. The conductivity at room temperature is between 10-4 and 10-8  S cm-1 . Some Cu-based ILs reach conductivities of 10-2  S cm-1 , which is, however, probably due to IL dec. This correlates with the optical bandgap measurements indicating the formation of large bandgap semiconductors. At elevated temperatures approaching the melting points, the conductivities reach up to 1.47×10-1  S cm-1 at 70 °C. The electrochemical stability windows of the ILs are between 2.5 and 3.0 V.

Synthesis, Characterization, and Investigation of the Antimicrobial Activity of Cetylpyridinium Tetrachlorozincate

Cetylpyridinium tetrachlorozincate (referred to herein as (CP)₂ZnCl₄) was synthesized and its solid-state structure was elucidated via single-crystal X-ray diffraction (SC-XRD), revealing a stoichiometry of C₄₂H₇₆Cl₄N₂Zn with two cetylpyridinium (CP) cations per [ZnCl₄]^2- tetrahedra. Crystal structures at 100 and 298 K exhibited a zig-zag pattern with alternating alkyl chains and zinc units. The material showed potential for application as a broad-spectrum antimicrobial agent, to reduce volatile sulfur compounds (VSCs) generated by bacteria, and in the fabrication of advanced functional materials. Minimum inhibitory concentration (MIC) of (CP)₂ZnCl₄ was 60, 6, and 6 μg mL^-1 for Salmonella enterica, Staphylococcus aureus, and Streptococcus mutans, respectively. The MIC values of (CP)₂ZnCl₄ were comparable to that of pure cetylpyridinium chloride (CPC), despite the fact that approximately 16% of the bactericidal CPC is replaced with bacteriostatic ZnCl₂ in the structure. A modified layer-by-layer deposition technique was implemented to synthesize mesoporous silica (i.e., SBA-15) loaded with approximately 9.0 wt % CPC and 8.9 wt % Zn.

Long chain ionic liquid-assisted synthesis of PS/Pd beads and hierarchical porous Pd–SiO2

Long-chain ionic liquid, 1-hexadecyl-3-methylimidazolium chloride (C₁₆mimCl), was firstly used as a linking agent to construct polystyrene (PS)/C₁₆mimCl/palladium (Pd) beads. Subsequently, the PS/C₁₆mimCl/Pd beads were used as a macroporous templating agent and C₁₆mimCl was used as a mesoporous templating agent to prepare Pd-loaded hierarchical porous silica. A systematic study was carried out addressing the influence of the amount of C₁₆mimCl and the mass ratios of m(Pd)/m(PS) on the PS/C₁₆mimCl/Pd beads and the Pd-loaded hierarchical porous structures. The samples were characterized by electrophoresis experiments, SEM, TEM, small-angle XRD, and N₂ adsorption–desorption experiments. It was found that the coverage of citrate-coated Pd nanoparticles (Pd NPs) onto the PS beads can be simply tailored by changing the amount of C₁₆mimCl and the mass ratios of m(Pd)/m(PS). The resultant Pd-loaded hierarchical porous silica possessed a 3D ordered macroporous skeleton with a specific surface area of up to 967 m² g⁻¹, ordered mesoporous silica walls (SBA-3 type) and well-dispersed Pd NPs anchored on the inner walls of the spherical macroporous hollow. Importantly, the obtained Pd-loaded hierarchical porous silica exhibited an enhanced catalytic activity for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H₂O₂.

1-Hexadecyl-3-methylimidazolium chloride (C₁₆mimCl) can be used as “bridges” to prepare PS/C₁₆mimCl/Pd beads, and Pd-loaded hierarchical porous silica was synthesized using dual templates of the PS/C₁₆mimCl/Pd beads and C₁₆mimCl.

Lewis Acidic Ionic Liquids

Until very recently, the term Lewis acidic ionic liquids (ILs) was nearly synonymous with halometallate ILs, with a strong focus on chloroaluminate(III) systems. The first part of this review covers the historical context in which these were developed, speciation of a range of halometallate ionic liquids, attempts to quantify their Lewis acidity, and selected recent applications: in industrial alkylation processes, in supported systems (SILPs/SCILLs) and in inorganic synthesis. In the last decade, interesting alternatives to halometallate ILs have emerged, which can be divided into two sub-sections: (1) liquid coordination complexes (LCCs), still based on halometallate species, but less expensive and more diverse than halometallate ionic liquids, and (2) ILs with main-group Lewis acidic cations. The two following sections cover these new liquid Lewis acids, also highlighting speciation studies, Lewis acidity measurements, and applications.

Diketonylpyridinium Cations as a Support of New Ionic Liquid Crystals and Ion-Conductive Materials: Analysis of Counter-Ion Effects

Ionic liquid crystals (ILCs) allow the combination of the high ionic conductivity of ionic liquids (ILs) with the supramolecular organization of liquid crystals (LCs). ILCs salts were obtained by the assembly of long-chained diketonylpyridinium cations of the type [HOO^R(n)pyH]⁺ and BF₄⁻, ReO₄⁻, NO₃⁻, CF₃SO₃⁻, CuCl₄²⁻ counter-ions. We have studied the thermal behavior of five series of compounds by differential scanning calorimetry (DSC) and hot stage polarized light optical microscopy (POM). All materials show thermotropic mesomorphism as well as crystalline polymorphism. X-ray diffraction of the [HOO^R(12)pyH][ReO₄] crystal reveals a layered structure with alternating polar and apolar sublayers. The mesophases also exhibit a lamellar arrangement detected by variable temperature powder X-ray diffraction. The CuCl₄²⁻ salts exhibit the best LC properties followed by the ReO₄⁻ ones due to low melting temperature and wide range of existence. The conductivity was probed for the mesophases in one species each from the ReO₄⁻, and CuCl₄²⁻ families, and for the solid phase in one of the non-mesomorphic Cl⁻ salts. The highest ionic conductivity was found for the smectic mesophase of the ReO₄⁻ containing salt, whereas the solid phases of all salts were dominated by electronic contributions. The ionic conductivity may be favored by the mesophase lamellar structure.

Tetrabromidocuprates(II)-Synthesis, Structure and EPR

Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several "onium" cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g‖ and g⊥) of the tensors could be determined and information on the structural changes in the [CuBr₄](2-) anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.

Ionogels Based on Poly(methyl methacrylate) and Metal-Containing Ionic Liquids: Correlation between Structure and Mechanical and Electrical Properties

Ionogels (IGs) based on poly(methyl methacrylate) (PMMA) and the metal-containing ionic liquids (ILs) bis-1-butyl-3-methlimidazolium tetrachloridocuprate(II), tetrachloride cobaltate(II), and tetrachlorido manganate(II) have been synthesized and their mechanical and electrical properties have been correlated with their microstructure. Unlike many previous examples, the current IGs show a decreasing stability in stress-strain experiments on increasing IL fractions. The conductivities of the current IGs are lower than those observed in similar examples in the literature. Both effects are caused by a two-phase structure with micrometer-sized IL-rich domains homogeneously dispersed an IL-deficient continuous PMMA phase. This study demonstrates that the IL-polymer miscibility and the morphology of the IGs are key parameters to control the (macroscopic) properties of IGs.

Hybrid surfactants decorated with copper ions: aggregation behavior, antimicrobial activity and anti-proliferative effect

In the present study, the emphasis is laid on the self aggregation behavior and biological activity of copper based inorganic–organic hybrids in aqueous media.

Crystal structure, vibrational studies, optical properties and DFT calculations of 2-amino-5-diethyl-aminopentanium tetrachlorocadmate (II)

Single crystals of a new organic-inorganic compound (C9H24N2) CdCl4 were grown by the slow evaporation technique and characterized by X-ray diffraction, infrared absorption Raman spectroscopy scattering, optical absorption, differential scanning calorimetry (DSC) analysis and dielectric measurements. The title compound belongs to the orthorhombic space group Pbca with the following unit cell parameters: a=11.397(7), b=13.843(4), c=22.678(5)Å and Z=8. In crystal structure, the tetrachlorocadmate anion is connected to organic cations through N-H⋯Cl hydrogen bonds. Theoretical calculations were performed using density functional theory (DFT) with the B3LYP/LanL2DZ level of theory for studying the molecular structure and vibrational spectra of the title compound. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. The detailed interpretation of the vibrational modes was carried out on the basis on our DFT calculations as primary source of assignment and by comparison with spectroscopic studies of similar compounds. The optical properties were investigated by optical absorption and show three bands at 300, 329 and 513 nm.

Standard molar enthalpy of combustion and formation of quaternary ammonium tetrachlorozincate [n-CnH2n+1 N(CH3)3]2 ZnCl4

The standard molar enthalpy of combustion (Δ_cH^o_m) and formation (Δ_fH^o_m) of quaternary ammonium tetrachlorozincate [n-C_nH_2n+1N(CH₃)₃]₂ZnCl₄ have been determined for the hydrocarbon chain length from even number 8 to 18 of carbon atoms (n) by an oxygen-bomb combustion calorimeter. The results indicated that the values of Δ_cH^o_m increased and Δ_fH^o_m decreased with increasing chain length and showed a linear dependence on the number of carbon atoms, which were caused by that the order and rigidity of the hydrocarbon chain decreased with increasing the carbon atoms. The linear regression equations are -Δ_cH^o_m =1440.50n +3730.67 and -Δ_fH^o_m = −85.32n + 1688.22.

Tetrachloridocuprates(II)-synthesis and electron paramagnetic resonance (EPR) spectroscopy

Ionic liquids (ILs) on the basis of metal containing anions and/or cations are of interest for a variety of technical applications e.g., synthesis of particles, magnetic or thermochromic materials. We present the synthesis and the results of electron paramagnetic resonance (EPR) spectroscopic analyses of a series of some new potential ionic liquids based on tetrachloridocuprates(II), [CuCl₄]²⁻, with different sterically demanding cations: hexadecyltrimethylammonium 1, tetradecyltrimethylammonium 2, tetrabutylammonium 3 and benzyltriethylammonium 4. The cations in the new compounds were used to achieve a reasonable separation of the paramagnetic Cu(II) ions for EPR spectroscopy. The EPR hyperfine structure was not resolved. This is due to the exchange broadening, resulting from still incomplete separation of the paramagnetic Cu(II) centers. Nevertheless, the principal values of the electron Zeemann tensor (g_║ and g_┴) of the complexes could be determined. Even though the solid substances show slightly different colors, the UV/Vis spectra are nearly identical, indicating structural changes of the tetrachloridocuprate moieties between solid state and solution. The complexes have a promising potential e.g., as high temperature ionic liquids, as precursors for the formation of copper chloride particles or as catalytic paramagnetic ionic liquids.

Templating and Phase Behaviour of the Long Chain Ionic Liquid C16mimCl

In the light of recent studies about the favourable sol–gel templating behaviour of the long chain ionic liquids (ILs) 1-hexadecyl-3-methylimidazolium chloride and -bromide (C16mimCl and C16mimBr) the phase behaviour of these ILs is investigated in detail and compared to common surfactants such as hexadecyltrimethylammonium chloride and -bromide (CTAC and CTAB). Specially developed small angle X-ray scattering (SAXS) evaluation approaches confirm a lamellar double-layer structure for crystalline C16mimCl of the ABACAB type. Presumably, the orientation of the head groups repeats in every second head group layer. Therefore, the imidazolium head group exhibits long range interactions on packing and templating, in contrast to the ammonium head group. The lyotropic phase behaviour is investigated via SAXS, isothermal titration calorimetry (ITC) and surface tension measurements. Interestingly, the phase diagrams of C16mimCl and CTAC are quite different, especially at higher concentration of surfactant: instead of a gel phase in the phase diagram of CTAC, a lamellar-hexagonal two phase region as well as a pure lamellar phase is found in the phase diagram of C16mimCl. The critical micellar concentration (cmc) and enthalpy of micellization (Δmic H) show that the cmc for imidazolium based surfactants is slightly lower and Δmic H is more exothermic than for the ammonium type surfactants. These results are able to account for the specialties observed in the sol–gel templating behavior.

Pyrrolidinium ionic liquid crystals with pendant mesogenic groups

New ionic liquid crystals (including ionic metallomesogens) based on the pyrrolidinium core are presented. N-Methylpyrrolidine was quaternized with different mesogenic groups connected to a flexible, omega-bromosubstituted alkyl spacer. The length of the flexible alkyl spacer between the cationic head group and the rigid mesogenic group was varied. The substituted pyrrolidinium cations were combined with bromide, bis(trifluoromethylsulfonyl)imide, tetrakis(2-thenoyltrifluoroacetonato)europate(III), and tetrabromouranyl anions. The influence of the type of mesogenic unit, the lengths of the flexible spacer and terminal alkyl chain, the size of the mesogenic group, and the type of anion on the thermotropic mesomorphic behavior was investigated. Furthermore, the phase behavior was thoroughly compared with the previously reported mesomorphism of N-alkyl-N-methylpyrrolidinium salts. Low-ordered smectic A phases of the de Vries type, smectic C phases, higher-ordered smectic F/I phases, as well as crystal smectic phases (E and G, J, H, or K) were observed and investigated by polarizing optical microscopy, differential scanning calorimetry, and powder X-ray diffraction.