Functional metal-organic liquids

For decades, the study of coordination polymers (CPs) and metal-organic frameworks (MOFs) has been limited primarily to their behavior as crystalline solids. In recent years, there has been increasing evidence that they can undergo reversible crystal-to-liquid transitions. However, their "liquid" states have primarily been considered intermediate states, and their diverse properties and applications of the liquid itself have been overlooked. As we learn from organic polymers, ceramics, and metals, understanding the structures and properties of liquid states is essential for exploring new properties and functions that are not achievable in their crystalline state. This review presents state-of-the-art research on the liquid states of CPs and MOFs while discussing the fundamental concepts involved in controlling them. We consider the different types of crystal-to-liquid transitions found in CPs and MOFs while extending the interpretation toward other functional metal-organic liquids, such as metal-containing ionic liquids and porous liquids, and try to suggest the unique features of CP/MOF liquids. We highlight their potential applications and present an outlook for future opportunities.

Coordination Stoichiometry Effects on the Binding Hierarchy of Histamine and Imidazole-M2+ Complexes

Histidine-M2+ coordination bonds are a recognized bond motif in biogenic materials with high hardness and extensibility, which has led to growing interest in their use in soft materials for mechanical function. However, the effect of different metal ions on the stability of the coordination complex remains poorly understood, complicating their implementation in metal-coordinated polymer materials. Herein, rheology experiments and density functional theory calculations are used to characterize the stability of coordination complexes and establish the binding hierarchy of histamine and imidazole with Ni2+ , Cu2+ , and Zn2+ . It is found that the binding hierarchy is driven by the specific affinity of the metal ions to different coordination states, which can be macroscopically tuned by changing the metal-to-ligand stoichiometry of the metal-coordinated network. These findings facilitate the rational selection of metal ions for optimizing the mechanical properties of metal-coordinated materials.

Mixing divalent ionic liquids: effects of charge and side-chains

We have prepared novel divalent ionic liquids (ILs) based on the bis(trifluoromethylsulfonyl)imide anion where two charged imidazolium groups in the cations are either directly bound to each other or linked by a single atom. We assessed the influence of the side-chain functionality and divalency on their physical properties and on the thermodynamics of mixing. The results indicate that shortening the spacer of a divalent IL reduces its thermal stability and increases its viscosity. Mixtures of divalent and monovalent ILs show small but significant deviations from ideality upon mixing. These deviations appear to depend primarily on the (mis)match of the nature and length of the cation side-chain. The non-ideality imposed by mixing ILs with different side-chains appears to be enhanced by the increase in formal charge of the cations in the mixture.

Understanding the interactions between the bis(trifluoromethylsulfonyl)imide anion and absorbed CO2 using X-ray diffraction analysis of a soft crystal surrogate

The selective carbon dioxide (CO2) absorption properties of ionic liquids (ILs) are highly pertinent to the development of methods to capture CO2. Although it has been reported that fluorinated components give ILs enhanced CO2 solubilities, it has been challenging to gain a deep understanding of the interactions occurring between ILs and CO2. In this investigation, we have utilized the soft crystalline material [Cu(NTf2)2(bpp)2] (NTf2‒ = bis(trifluoromethylsulfonyl)imide, bpp = 1,3-bis-(4-pyridyl)propane) as a surrogate for single-crystal X-ray diffraction analysis to visualize interactions occurring between CO2 and NTf2‒, the fluorinated IL component that is responsible for high CO2 solubility. Analysis of the structure of a CO2-loaded crystal reveals that CO2 interacts with both fluorine and oxygen atoms of NTf2‒ anions in a trans rather than cis conformation about the S-N bond. Theoretical analysis of the structure of the CO2-loaded crystal indicates that dispersion and electrostatic interactions exist between CO2 and the framework. The overall results provide important insight into understanding and improving the CO2 absorption properties of ILs.

Crystal Structure of tris(tetrakis{1-vinyl-1H-imidazole-κN}copper(II)) bis[tri-μ2-bromido-tetrabromido-bis(1-vinyl-1H-imidazole-κN)tetracopper(I)], C80H96N32Cu11Br14

C80H96N32Cu11Br14, triclinic, P1̄ (no. 2), a = 11.370(2) Å, b = 14.287(3) Å, c = 17.621(3) Å, α = 85.929(2)°, β = 88.392(2)°, γ = 74.464(2)°, V = 2750.9(8) Å3, Z = 1, Rgt(F) = 0.0432, wRref(F2) = 0.0859, T = 296(2) K.

Cobalt(ii) liquid metal salts for high current density electrodeposition of cobalt

Cobalt-containing liquid metal salts were synthesized and characterized. Reversible thermochromism was observed and the electrodeposition of cobalt layers with different morphologies was investigated.

Cobalt(ii) containing liquid metal salts for electrodeposition of cobalt and electrochemical nanoparticle formation

Cobalt(ii) containing ionic liquids were used as electrolytes for the electrodeposition of cobalt thin films and cobalt nanoparticles.

Manganese-containing ionic liquids: synthesis, crystal structures and electrodeposition of manganese films and nanoparticles

Manganese(ii)-containing ionic liquids with different ligands and anions were prepared. Electrodeposition of manganese or electrosynthesis of manganese nanoparticles was observed, depending on the chemical structure of the ionic liquid.

Liquid silver tris(perfluoroethyl)trifluorophosphate salts as new media for propene/propane separation

A series of silver tris(perfluoroethyl)trifluorophosphate (Ag[FAP]) complexes with various ligands (acetonitrile ACN, chloroacetonitrile Cl-ACN, acrylonitrile acryl-CN, pyridine py, ethylenediamine en and propene C₃H₆) have been synthesized starting from Ag[NO₃] and K[FAP] using three different routes. Physicochemical properties as well as crystal structures ([Ag(ACN)_2/4][FAP], [Ag(py)₂][FAP]) were determined and the suitability of such Ag salts for propene/propane separation processes was investigated. The investigated silver complexes exhibit either low melting points or form liquid complexes when contacted with gaseous propene at 30 °C. This makes them promising separation materials for both liquid membranes and absorber fluids due to their high silver content and significant propene capacity. Single (iGSC) and mixed (NMR) gas solubilities as well as diffusion coefficients (PFG-NMR) of propene and propane were determined to predict the theoretical selectivity of solubility, membrane selectivity, capacity and transport properties of the silver salts according to the solution diffusion model. A strong influence of the number and type of ligands on chemical complexation, physicochemical properties and separation performance has been observed.

Crystal structure of di-aqua-tris-(1-ethyl-1H-imidazole-κN (3))(sulfato-κO)nickel(II)

In the title complex, [Ni(SO4)(C5H8N2)3(H2O)2], the Ni(II) ion is coordinated by three facial 1-ethyl-1H-imidazole ligands, one monodentate sulfate ligand and two water mol-ecules in a slightly distorted octa-hedral coordination environment. In the crystal, two pairs of O-H⋯O hydrogen bonds link complex mol-ecules, forming inversion dimers incorporating R 2 (4)(8), R 2 (2)(8) and R 2 (2)(12) rings. The dimeric unit also contains two symmetry-unique intra-molecular O-H⋯O hydrogen bonds. In addition, weak C-H⋯O hydrogen bonds, weak C-H⋯π inter-actions and π-π inter-actions with a centroid-centroid distance of 3.560 (2) Å combine to form a three-dimensional network. One of the ethyl groups is disordered over two sets of sites with occupancies in the ratio 0.586 (7):0.414 (7).

Synthesis and characterization of Cu(II)-halide 1-methylimidazole complexes

Three new complexes of Cu(II) halides (Cl, Br) with 1-methylimidazole (MIm), [Cu(MIm)4]Br2 (1), [Cu(MIm)4Br]Br · H2O (2), and [Cu(MIm)6]Cl2 · 2H2O (3) have been synthesized in ethanol. Their crystal structures have been determined by single-crystal X-ray diffraction. FT-IR spectroscopy, mass spectrometry, and thermal analyses were applied to characterize the compounds.

The acidity/basicity of metal-containing ionic liquids: insights from surface analysis and the Fukui function

The acidity/basicity of a series of metal-containing ionic liquids has been studied by surface analysis and the Fukui function.

Crystal structures of hydrated rare-earth bis(trifluoromethylsulfonyl)imide salts

Structural characterisation of the full range of hydrated rare-earth bis(trifluoromethylsulfonyl)imide salts showed the structures to be [Sc(H₂O)₇][Tf₂N]₃·H₂O, Ln(H₂O)₃(Tf₂N)₃, Ln(H₂O)₃(Tf₂N)₃ or [Ln(H₂O)_x][Tf₂N]₃.

Homoleptic and heteroleptic N-alkylimidazole zinc(ii)-containing ionic liquids for high current density electrodeposition

Ionic liquids with a zinc(ii) ion as an integral part of the ionic liquid cation are very useful electrolytes for the fast electrodeposition of high-quality zinc metal coatings.

Synthesis and properties of alkoxy- and alkenyl-substituted peralkylated imidazolium ionic liquids

Novel peralkylated imidazolium ionic liquids bearing alkoxy and/or alkenyl side chains have been synthesized and studied. Different synthetic routes towards the imidazoles and the ionic liquids comprising bromide, iodide, methanesulfonate, bis(trifluoromethylsulfonyl)imide ([NTf2](-)), and dicyanamide {[N(CN)2](-)} as the anion were evaluated, and this led to a library of analogues, for which the melting points, viscosities, and electrochemical windows were determined. Incorporation of alkenyl moieties hindered solidification, except for cations with high symmetry. The alkoxy-derivatized ionic liquids are often crystalline; however, room-temperature ionic liquids (RTILs) were obtained with the weakly coordinating anions [NTf2](-) and [N(CN)2](-). For the viscosities of the peralkylated RTILs, an opposite trend was found, that is, the alkoxy derivatives are less viscous than their alkenyl-substituted analogues. Of the crystalline compounds, X-ray diffraction data were recorded and related to their molecular properties. Upon alkoxy substitution, the electrochemical cathodic limit potential was found to be more positive, whereas the complete electrochemical window of the alkenyl-substituted imidazolium salts was shifted to somewhat more positive potentials.