Composition of Ni2+ cation solvation shell in NiCl2–methanol solution by multinuclear NMR

1H-, 2H- and 13C-NMR spectra have been used to test the Ni2+ solvation shell composition in the 1.1 molal methanol solution of NiCl2. It has been confirmed that Cl− anion takes part in the nearest environment of Ni2+ cation at all the temperatures investigated. Using 2H-NMR allowed us to detect for the first time OD-signal of methanol in the primary solvation shell of Ni2+ cation. Both 2H- and 13C-NMR spectra show that the composition of the cation solvation shell becomes more complicated at temperatures lower than 220 K

Local Structure in Terms of Nearest-Neighbor Approach in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations

Description of the local microscopic structure in ionic liquids (ILs) is a prerequisite to obtain a comprehensive understanding of the influence of the nature of ions on the properties of ILs. The local structure is mainly determined by the spatial arrangement of the nearest neighboring ions. Therefore, the main interaction patterns in ILs, such as cation–anion H-bond-like motifs, cation–cation alkyl tail aggregation, and ring stacking, were considered within the framework of the nearest-neighbor approach with respect to each particular interaction site. We employed classical molecular dynamics (MD) simulations to study in detail the spatial, radial, and orientational relative distribution of ions in a set of imidazolium-based ILs, in which the 1-butyl-3-methylimidazolium (C₄mim⁺) cation is coupled with the acetate (OAc^–), chloride (Cl^–), tetrafluoroborate (BF₄^–), hexafluorophosphate (PF₆^–), trifluoromethanesulfonate (TfO^–), or bis­(trifluoromethanesulfonyl)­amide (TFSA^–) anion. It was established that several structural properties are strongly anion-specific, while some can be treated as universally applicable to ILs, regardless of the nature of the anion. Namely, strongly basic anions, such as OAc^– and Cl^–, prefer to be located in the imidazolium ring plane next to the C–H^2/4–5 sites. By contrast, the other four bulky and weakly coordinating anions tend to occupy positions above/below the plane. Similarly, the H-bond-like interactions involving the H² site are found to be particularly enhanced in comparison with the ones at H^4–5 in the case of asymmetric and/or more basic anions (C₄mimOAc, C₄mimCl, C₄mimTfO, and C₄mimTFSA), in accordance with recent spectroscopic and theoretical findings. Other IL-specific details related to the multiple H-bond-like binding and cation stacking issues are also discussed in this paper. The secondary H-bonding of anions with the alkyl hydrogen atoms of cations as well as the cation–cation alkyl chain aggregation turned out to be poorly sensitive to the nature of the anion

Complexation of Ni(ClO₄)₂ and Mg(ClO₄)₂ with 3‑Hydroxyflavone in Acetonitrile Medium: Conductometric, Spectroscopic, and Quantum Chemical Investigation

The complex formation of Ni­(ClO₄)₂ and Mg­(ClO₄)₂ with 3-hydroxyflavone (HL, flavonol) in acetonitrile was studied using conductometric and spectroscopic methods. It was found that interaction of nickel cation with HL leads to formation of the doubly charged [Ni­(HL)]²⁺ complex, whereas in solutions of magnesium perchlorate the complex with anion [MgClO₄(HL)]⁺ is formed. Using the extended Lee–Wheaton equation, the limiting equivalent conductivities of [Ni­(HL)]²⁺ and [MgClO₄(HL)]⁺ and thermodynamic constants of their formation were obtained at 288, 298, 308, 318, and 328 K. Calculated Stoke’s radii indicate weak solvation of the formed complexes and low temperature stability of their solvation shells. On the basis of the quantum chemical calculations and noncovalent interactions analysis, it is found that in the solvated [Ni­(HL)]²⁺ and [MgClO₄(HL)]⁺ complexes interaction of the Ni²⁺ and Mg²⁺ cations with flavonol occurs via the carbonyl group of HL. Complexation with Ni²⁺ does not change the internal structure of HL greatly: in the [Ni­(HL)]²⁺ complex, flavonol shows an intramolecular H-bond between 3-hydroxyl and carbonyl groups. When a complex with [MgClO₄]⁺ is formed, the OH group turns out of the plane of the chromone moiety that leads to rupture of an intramolecular H-bond in the ligand molecule. Moreover, in the [MgClO₄(HL)]⁺ complex, perchlorate anion possesses a strong ability to interact with HL, forming an intracomplex H-bond between hydrogen of the 3-hydroxyl group and oxygen of ClO₄^–. Its strength is more pronounced than in the intramolecular one in both [Ni­(HL)]²⁺ and uncomplexed 3-hydroxyflavone

Electronic Properties of Carbon Nanotubes Intercalated with Li⁺ and Mg²⁺: Effects of Ion Charge and Ion Solvation

The influence of bare and solvated cations imbedded inside single-walled carbon nanotubes (SWCNTs) on the SWCNT electronic properties is studied by <i>ab initio</i> electronic structure calculations. The roles of ion charge and ion solvation are investigated by comparing Li⁺ vs Mg²⁺ and Li⁺ vs its solvatocomplex with two ethylene carbonate (EC) molecules, [Li(EC)₂]⁺. Two achiral nanotubes with similar radii but different electronic structure are considered, namely, the metallic, (15,15) armchair, and semiconducting, (26,0) zigzag, SWCNTs. The intercalation process is energetically favorable for both CNT topologies, with all bare cations and the solvatocomplex under investigation, with the doubly charged Mg²⁺ ion exhibiting the highest energy gain. Insertion of the bare ions into the SWCNTs increases the electronic entropy. The electronic entropy changes because the ions introduce new energy levels near the Fermi level. Those initially empty levels of the cations accept electron density and generate electronic holes in the valence band of both SWCNT topologies. As a consequence, the semiconducting (26,0) zigzag SWCNT becomes metallic, exhibiting hole conductivity. Solvation of the bare Li⁺ ion by EC molecules completely screens the influence of the ion charge on the SWCNT electronic properties, independent of the topology. The last fact validates the common practice of employing standard, nonpolarizable force field models in classical molecular dynamics simulations of electrolyte solutions interacting with CNTs. The strong dependence of the nanotube electronic properties on the presence of bare ions can be used for development of novel cation sensors for mass spectroscopy applications