Complex Formation In Solvents Research Articles

(Best Student Presentation) A Calorimetric and Potentiometric Titration Method to Elucidate Ca2+ Solvation Thermodynamics

Calcium metal batteries are a promising long-term sustainable alternative to lithium metal batteries due to calcium’s high natural abundance and low electrochemical redox potential. Learning how to control Ca2+ coordination chemistry is essential in enabling high performance and stable calcium batteries. While several spectroscopic and computational studies of Ca2+ coordination have been conducted, they are limited by their qualitative nature and/or require experimental validation. This work introduces a novel methodology using a combination of calorimetric and potentiometric titration techniques, to quantitatively probe electrolyte coordination shell composition, as well as previously unattainable experimental coordination enthalpy, Gibbs free energy, and entropy. To establish the effectiveness of the method, here we investigate the coordination shell thermodynamics in simpler, highly dissociating LiPF6 electrolytes. Starting with a weakly solvated electrolyte, we titrate in a strong solvent—which preferentially coordinates to Li+—and measure the associated heat release/absorption and Li+ potential change with each injection. Fitting both sets of data to a mathematical binding model allows for the extraction of the change in enthalpy (ΔHi), Gibbs free energy (ΔGi), and entropy (ΔSi) associated with each Li+-solvent complex formation. Several weak solvent and strong solvents are investigated to build a dataset of ΔHi, ΔGi, and ΔSi. These thermodynamic values are used to calculate the average coordination number of each solvent in the Li+ coordination shell which agree well with literature. Raman and NMR spectroscopy confirm salt dissociation and solvent displacement during titration. This method unlocks a precise description of the chemical environment around Li+ and enables prediction of the Li+ coordination shell in new electrolytes by rationalizing the hierarchy of solvent binding. Given that this method extends to relevant calcium electrolytes, it is a powerful tool to engineer effective electrolytes for use with a calcium metal anode.

A comprehensive understanding of carbon-carbon bond formation by alkyne migratory insertion into manganacycles.

Migratory insertion (MI) is one of the most important processes underpinning the transition metal-catalysed formation of C–C and C–X bonds. In this work, a comprehensive model of MI is presented, based on the direct observation of the states involved in the coupling of alkynes with cyclometallated ligands, augmented with insight from computational chemistry. Time-resolved spectroscopy demonstrates that photolysis of complexes [Mn(C^N)(CO)4] (C^N = cyclometalated ligand) results in ultra-fast dissociation of a CO ligand. Performing the experiment in a toluene solution of an alkyne results in the initial formation of a solvent complex fac-[Mn(C^N)(toluene)(CO)3]. Solvent substitution gives an η2-alkyne complex fac-[Mn(C^N)(η2-R1C2R2)(CO)3] which undergoes MI of the unsaturated ligand into the Mn–C bond. These data allowed for the dependence of second order rate constants for solvent substitution and first order rate constants for C–C bond formation to be determined. A systematic investigation into the influence of the alkyne and C^N ligand on this process is reported. The experimental data enabled the development of a computational model for the MI reaction which demonstrated that a synergic interaction between the metal and the nascent C–C bond controls both the rate and regiochemical outcome of the reaction. The time-resolved spectroscopic method enabled the observation of a multi-step reaction occurring over 8 orders of magnitude in time, including the formation of solvent complexes, ligand substitution and two sequential C–C bond formation steps.

Fixing Transient Iodine on Developed Latent Fingermarks.

In the present study, a simple and novel fume-mist technique is described which can be used efficiently to fix the latent fingermarks developed using iodine. It is well known that the residues left over in the fingermarks interact with iodine to give transient brown impressions which disappear in a short time. Also, iodine forms colored complexes with various organic solvents. Based on iodine-fingermark interaction and iodine-solvent complex formation, latent fingermarks were developed on paper surface using iodine fumes which were subsequently fixed by spraying polar and nonpolar solvents. The fingermarks developed with this technique were not only clear but also permanent in nature. The interaction of fingermark residue, iodine, and solvent forming a ternary structure is believed to be a possible reason for the stability of iodine-developed fingermarks. Ease of method, availability of chemicals, and minimum training make the method adaptable in routine development of forensic fingermarks present on paper surface.

Enhanced Charge Transport in Hybrid Perovskite Field‐Effect Transistors via Microstructure Control

AbstractHybrid organic–inorganic perovskites have recently gained immense attention due to their unique optical and electronic properties and low production cost, which make them promising candidates for a wide range of optoelectronic devices. But unlike most other technologies, the breakthroughs witnessed in hybrid perovskite optoelectronics have outgrown the basic understanding of the fundamental material properties. For example, the effectiveness of charge transport in relation to film microstructure and processing has remained elusive. In this study, field‐effect transistors are fabricated and evaluated in order to probe the nature and dynamics of charge transport in thin films of methylammonium lead iodide. A dramatic improvement is shown in the electrical properties upon solvent vapor annealing. The resulting devices exhibit ambipolar transport, with room‐temperature hole and electron mobilities exceeding 10 cm2 V−1 s−1. The remarkable enhancement in charge carrier mobility is attributed to the increase in the grain size and passivation of grain boundaries via the formation of solvent complexes.

Dimethylformamide-free processing of halide perovskite solar cells from electrodeposited PbI2 precursor films

A novel DMF-free perovskite solar cell fabrication protocol, based on electrodeposited PbI2 films from ionic liquid and subsequent conversion into perovskite is presented. Hexane is proposed to be used as an efficient co-solvent in the conversion solution, to affect the film morphology in a controlled way. The effect of the hexane in the [CH3NH3-PbI2]solvent complex formation and the impact of the complexes in the PbI2 to CH3NH3PbI3 conversion is discussed. Close-packing density nanocrystalline perovskite films from open-packed PbI2 films platelets are successfully obtained after dipping during 10minutes in isopropanol:hexane 90:10v:v conversion solutions. Solar cells based on the obtained perovskite films exhibit a power conversion efficiency of 9%. This finding points out the viability of the reported process in the DMF-free fabrication of perovskite solar cells.

Solvent-dependent Photoisomerization Quantum Yield of 2-Phenylazo-1-alkyl-3-methylimidazolium Cations in Ionic Liquids under S1(n, π*) Excitation

Abstract Photoisomerization quantum yields (ΦE–Z) of phenylazo-substituted imidazolium cations, which are counterparts of recently developed photochromic ionic liquids, were measured under S1(n, π*) excitation. The ΦE–Z values are lower in imidazolium-type ionic liquids than those in conventional solvents and in tert-alkylammonium-type ionic liquids. This observation was argued based on solute–solvent complex formation at imidazolium rings.

Mechanistic Insights into Amplification of Specific Ion Effect in Water–Nonaqueous Solvent Mixtures

Ethylene glycol (EG) and hydrogen peroxide (H2O2) can act as both hydrogen-bond donors and acceptors in the formation of solvent complexes with water molecules. In the present work, we have systematically investigated the ion-specific lower critical solution temperature (LCST) behavior of poly(N-isopropylacrylamide) (PNIPAM) in H2O–EG and H2O–H2O2 mixtures. The results obtained from turbidity measurements show that the specific anion effect is amplified with the increasing molar fraction of EG (x(EG)) but is independent of the molar fraction of H2O2 (x(H2O2)). The studies of Raman spectra and differential scanning calorimetry indicate that the discrepancy in amplification of specific anion effect between H2O–EG and H2O–H2O2 mixtures is due to the difference in the anion–solvent complex interactions rather than the anion–polymer or solvent–polymer interactions. On the other hand, the specific cation effect can also be amplified with the increasing x(EG) but changes only slightly with the x(H2O2). The discrepancy in amplification of specific cation effect between the two types of solvent mixtures is attributed to the difference in the solvent–polymer interactions.

Conductivity enhancement via chemical modification of chitosan based green polymer electrolyte

The potential of carboxymethyl chitosan as a green polymer electrolyte has been explored. Chitosan produced from partial deacetylation of chitin was reacted with monochloroacetic acid to form carboxymethyl chitosan. A green polymer electrolyte based chitosan and carboxymethyl chitosan was prepared by solution-casting technique. The powder and films were characterized by reflection Fourier transform infrared (ATR-FTIR) spectroscopy, 1H nuclear magnetic resonance, elemental analysis and X-ray diffraction, electrochemical impedance spectroscopy, and scanning electron microscopy. The shift of wavenumber that represents hydroxyl and amine stretching confirmed the polymer solvent complex formation. The XRD spectra results show that chemical modification of chitosan has improved amorphous properties of chitosan. The ionic conductivity was found to increase by two magnitudes higher with the chemical modification of chitosan. The highest conductivity achieved was 3.6×10−6Scm−1 for carboxymethyl chitosan at room temperature and 3.7×10−4Scm−1 at 60°C.

Chemical interaction and conductivity of carboxymethyl κ-carrageenan based green polymer electrolyte

The potential of κ-carrageenan derivatives as a green polymer electrolyte has been explored. κ-Carrageenan extracted from marine red algae was reacted with monochloacetic acid to form carboxymethyl κ-carrageenan. The powders were characterized by reflection fourier transform infrared (ATR-FTIR) spectroscopy,13C nuclear magnetic resonance, 1H nuclear magnetic resonance, X-ray diffraction and elemental analysis to confirm the structural, crystallinity and the degrees of substitution. A green polymer electrolyte of κ-carrageenan and carboxymethyl κ-carrageenan were prepared by solution-casting technique. The films were characterized by reflection fourier transform infrared (ATR-FTIR) spectroscopy and electrochemical impedance spectroscopy to determine the chemical interaction and ionic conductivity. The decrease in intensity of hydroxyl, carbonyl, sulfate and ether band confirmed the polymer solvent complex formation. XRD spectra show that chemical modification of κ-carrageenan does not change its amorphous properties. The ionic conductivity was found to increase by three magnitudes higher with the chemical modification of κ-carrageenan. The conductivity achieved was 2.0×10−4Scm−1 for carboxymethyl κ-carrageenan in comparison to 5.3×10−7Scm−1 for κ-carrageenan.

Inhibition of Bubble Coalescence by Electrolytes in Binary Mixtures of Dimethyl Sulfoxide and Propylene Carbonate

We have investigated the effect of solvent composition on inhibition of bubble coalescence by electrolytes in binary mixtures of dimethyl sulfoxide (DMSO) and propylene carbonate (PC). Unlike most mixtures, combinations of DMSO and PC exhibit minimal foaming over all compositions (with the strongest effect being at 25% PC by volume); thus, the influence of electrolytes can be investigated. Both LiBr and KSCN at moderate concentrations inhibit bubble coalescence at all solvent compositions. However, the concentration of electrolyte required to inhibit coalescence was in both cases a minimum at the PC(v/v) of 25%. The surface tension of electrolyte solutions in the mixed solvents indicates that the gradient in surface tension is not correlated with coalescence inhibition and therefore inhibition cannot be attributed to surface elasticity. We have also studied the inhibition of bubble coalescence by HCl at different solvent compositions. HCl is strongly inhibitory in DMSO but only weakly so in PC. We have found that HCl exhibits strong inhibition behavior at all mixtures studied. All electrolytes studied were most effective at inhibiting bubble coalescence at the PC(v/v) of 25%, indicating that the interactions between solvent molecules strongly determine the influence of electrolyte on coalescence inhibition. We propose that the formation of solvent complexes between DMSO and PC results in an increase in surface viscosity and the presence of electrolytes further amplifies this effect.

Modeling Preferential Solvation in Ternary Solvent Systems

The theoretical solvent exchange model of Bosch and Rosés for binary solvents was extended to ternary solvent mixtures. The model was applied to ENT values for the mixture methanol/1-propanol/acetonitrile, in terms of 48 new values in a total of 79, measured at 25 degrees C over the whole range of solvent compositions. It was also applied to the mixture methanollethanol/acetone at the same temperature using 93 E(N)T values obtained from literature. Very good fits between experimental and calculated values, substantiated by external validation methods, were achieved for both sets of data. The use of the developed extended model allowed the interpretation of measured solvatochromic shifts in terms of solute-solvent and solvent-solvent interactions in the local environment of the solute's dye for the two ternary systems and the underlying binary mixtures. It also provided the identification of various complex solvent entities and the quantification of their relative concentrations in the probe's cybotactic region, thus leading to new and significant physicochemical insights at a molecular level, regardless of the nonconsideration of the formation of solvent complexes in the bulk. Results clearly showed a different solvent composition in the vicinity of the solute. The further extension of the model to four and five components is also presented.

Time-Resolved Infrared Dynamics of C−F Bond Activation by a Tungsten Metal−Carbonyl

Chemical reactions that break, or activate, C-H and C-F are of tremendous synthetic interest. The intramolecular C-F bond activation of a tungsten carbonyl system has been studied by time-resolved infrared spectroscopy. The formation of solvent complexes and the final product are monitored using time-resolved infrared spectroscopy of the CO stretches. The rate of the reaction is shown to be limited by the formation of an intermolecular complex between the tungsten metal center and a solvent molecule. Comparison with DFT calculations shows that in the absence of solvent molecules the intramolecular complex with the tethered perfluorobenzene ring is energetically favorable, but is not the primary kinetic product because of the initial geometry of the complex.

Thermodynamic and Structural Investigation of Thermoreversible Poly(3-dodecyl thiophene) Gels in the Three Isomers of Xylene

Poly(3-dodecyl thiophene) (P3DDT) produces thermoreversible gels in o-, m-, and p-xylene (Xy). All of these gels have fibrillar network morphology and exhibit reversible first-order phase transitions. The enthalpy changes related to the polymer part of P3DDT−p-Xy gels indicate polymer−solvent complex formation having stoichiometry of P3DDT monomeric unit/p-Xy = 2:3. In P3DDT−o-Xy and P3DDT−m-Xy gels, the enthalpy changes also indicate similar polymer−solvent complexation of 2:3 type. In our experimental condition, only p-Xy crystallizes, and analysis of its enthalpy changes indicate the formation of a polymer−solvent complex of stoichiometry P3DDT monomeric unit/p-Xy = 3:1. In the phase diagrams, there are main chain melting and side chain melting boundaries; the latter encompasses the whole composition region. In the P3DDT−p-Xy system, there is an additional solvent melting boundary. The phase diagram nature suggests that the 2:3 complex is singular type. The solvent-subtracted Fourier-transform infrared...

Test cells for plating

A novel DMF-free perovskite solar cell fabrication protocol, based on electrodeposited PbI2 films from ionic liquid and subsequent conversion into perovskite is presented. Hexane is proposed to be used as an efficient co-solvent in the conversion solution, to affect the film morphology in a controlled way. The effect of the hexane in the [CH3NH3-PbI2]solvent complex formation and the impact of the complexes in the PbI2 to CH3NH3PbI3 conversion is discussed. Close-packing density nanocrystalline perovskite films from open-packed PbI2 films platelets are successfully obtained after dipping during 10 minutes in isopropanol:hexane 90:10 v:v conversion solutions. Solar cells based on the obtained perovskite films exhibit a power conversion efficiency of 9%. This finding points out the viability of the reported process in the DMF-free fabrication of perovskite solar cells.

Ab Initio Electronic Structure Calculations on Chlorocarbene−Ethylene and Chlorocarbene−Benzene Complexes

Interaction energies for carbene−solvent complex formation have been computed at the MP2/6-311+G**//MP2/6-31G* level, including full counterpoise corrections. Our results indicate that chlorocarbenes do not form stable complexes with ethylene at ambient temperatures and react with tetramethylethylene to form cyclopropanes without an activation energy barrier. Chlorocarbenes and benzene form weakly interacting but thermally stable 1:1 and 1:2 π-type complexes. Two π-type complexes and a hydrogen-bonded ylidic structure were obtained for the 1:1 methylchlorocarbene−anisole system. The formation of carbene−solvent complexes might modulate carbenic reactivity in aromatic solvents.

Thermoreversible Gelation of Poly(vinylidene flouride) in Diethyl Adipate: A Concerted Mechanism

Poly(vinylidene flouride) (PVF2) gels in diethyl adipate (DEA) with fibrillar morphology. The gels are transparent. The Wide-angle X-ray scattering pattern and FT-IR spectra of the gel indicate the presence of solvated α-phase PVF2 crystallites in the gel. The intensities of the X-ray diffraction peaks of the gel are mostly different than those of the melt-crystallized sample. The plots of enthalpy of gel fusion and enthalpy of gel formation with a weight fraction of PVF2 (WPVF2) indicate a positive deviation from linearity. Analysis of these results indicates polymer−solvent complex formation in the molar ratio of 1:2 for the DEA and PVF2 repeating unit, respectively. The phase diagram also supports polymer−solvent complex formation with an incongruent melting point. The gelation kinetics is studied by the test tube tilting method. Analysis of the concentration function of the gelation rate supports the theory that this gelation process obeys the three-dimensional percolation mechanism. The temperature coefficient analysis is done both by the Flory and Weaver theory of coil-to-helix transtion and by the growth rate theory of fibrillar crystallization extended to the polymer−diluent system. A comparison of energy barrier values of both the processes indicates that the gelation is a concerted process of conformational ordering and crystallization.

A Thermodynamic Study on the Thermoreversible Poly(vinylidene fluoride) Gels in Acetophenone, Ethyl Benzoate, and Glyceryl Tributyrate

The gel melting temperatures of poly(vinylidene fluoride) (PVF2) gels in acetophenone (ACTP), ethyl benzoate (EB), and glyceryl tributyrate (GTB) are measured by differential scanning calorimetry (DSC) at high PVF2 concentration (WPVF2 ≥ 0.1) and visually for very low PVF2 concentration (WPVF2 ≤ 0.1). The gelation temperatures are also measured in DSC by dynamic cooling method. The enthalpy of gelation and enthalpy of gel fusion vs weight fraction of PVF2 (WPVF2) plots exhibit different nature in the three solvents. It is linear for the PVF2/ACTP gels but the PVF2 gels in the other two solvents exhibit positive deviation from linearity. A thermodynamic analysis of the enthalpy values in PVF2/EB and PVF2/GTB systems indicates the polymer−solvent complex formation in both the systems. The stoichiometry of the PVF2−EB compound is 1:1 molar ratio and that of PVF2−GTB compound is 3:1 molar ratio with respect to PVF2 monomeric unit and the solvent molecule, respectively. The phase diagram of the PVF2/ACTP system is linear, that of PVF2/EB system exhibits compound formation with incongruent melting point, and that of PVF2/GTB system exhibits compound formation with singular point. The spheroidal morphology of the PVF2/ACTP gels has been attributed to the chain folding process, whereas the fibrillar morphology of PVF2/GTB gels is due to polymer−solvent complex formation. The reason for the mixed morphology of PVF2/EB gels is not clear and is probably due to the comparable rates of the polymer−solvent compound formation and the chain-folding processes.

Photoinduced Formation of [fac-Re(bpy)(CO)3CN] from [fac-Re(bpy)(CO)3(4-CNpy)]+ (bpy = 2,2′-bipyridine, py = pyridine): CN Group Rearrangement of a Cyanopyridine Ligand onto Central Metal

Abstract [fac-Re(bpy)(CO)3CN] was photochemically formed from [fac-Re(bpy)(CO)3(4-CNpy)]+ with a 53% yield using 365 nm irradiation in the presence of triethanolamine (TEOA). This rearrangement proceeds via formation of solvent complexes [fac-Re(bpy)(CO)3(DMF)]+ and [fac-Re(bpy)(CO)3(TEOA)]+.

Semiclassical Theory of the Effects of Internal Motions on the Linewidths in Electron Spin Resonance Spectra

A number of classical dynamical models are developed for describing the effects of internal rotational motions and solvent-complex formation on the ESR hyperfine linewidths of free radicals in solution. These dynamical processes can lead to linewidth effects because they cause time-dependent modulations of the isotropic hyperfine interactions of the different magnetic nuclei. An alternating linewidth effect, which has been observed in a number of recent studies, is predicted to result when there is an out-of-phase correlation between the hyperfine splittings ai(t) of equivalent nuclei. By equivalent nuclei here are meant those for which the time-average splittings 〈ai(t) 〉Av are equal, and an out-of-phase correlation is one in which an increase in the instantaneous splitting from Nucleus i, ai(t), is correlated with a decrease in the splitting aj(t) from nucleus j. This out-of-phase correlation can result from a coupling of the mechanical motions of different rotating groups and also from the effects that changes in orientations of uncorrelated rotors may have on redistributing electron spin density in the molecule. Continuous motion cases are treated by Brownian-motion theory using coupled and uncoupled internal rotors and torsional oscillators. Random jump models between discrete states are also considered. It is shown that all these models can give rise to an alternating linewidth effect provided that certain definite relationships of the proper type exist for the coupling of the motions or the variations of the spin densities. For many of these models the correlation a1(t)=a2(t) for all t, or complete equivalence of both nuclei, may also result when different relationships exist. The correlation of the splittings of more than two groups of completely equivalent nuclei will, in general, lead to more complex linewidth effects.

Intermolecular forces and solvent effects, II. Band intensities

The intensities and shapes of vibration bands of the H —C and D — C groups in HCN, DCN and propargyl chloride, and of the C≡N group in these and other nitriles have been measured in a number of solvents. The results have been discussed in relation to Buckingham’s theory of solvent effects. The relative significance of bulk dielectric effect and intermolecular interaction varies in different cases. A marked contrast in the effect of solvent has been found between CH 3 CN and CCl 3 CN used as solutes, which suggests that in the formation of solvent complexes the dipole derivative of the C ≡ N group may change sign. Further data have been obtained about the band shapes which suggest that the Lorentz function is rarely satisfactory, and in different solvents a given vibration band may have very different contour.