Solvent Coordination Research Articles

Dynamics in condensed phase for systems involving phase functions obeying Gaussian statistics

The study of non-equilibrium processes in condensed phase has been fascinating and has attracted considerable attention of experimentalists as well as theoreticians during the last few decades. Since the theoretical treatment using Liouville equation involves multi-dimensional phase space functions, it is very difficult to visualize and also to obtain analytical expressions for the time-dependent distribution functions in Liouville space, which has led to formulation of various reduced space descriptions. The bottleneck in describing the non-equilibrium processes in the reduced space lies in the appearance of coupled velocity and position correlation functions in the equations, which are difficult to evaluate in general. In this work, we have developed a scheme to decouple the complicated multi-point coupled correlation function into two-point velocity and position correlation functions for situations characterized by a time-dependent phase function obeying Gaussian distribution, by making use of the Novikov's theorem. As an illustrative application, we have investigated the problem of optically controlled solvation dynamics and obtained exact expressions for the non-equilibrium solvation time correlation functions showing explicit dependence on the excitation frequency, as observed experimentally. We have shown that the linear response theory result is valid as long as the energy gap obeys the Gaussian distribution, rescuing the linear response theory based result from the domain of validity for small fluctuations in solvation coordinate.

Effects of Axial Solvent Coordination to Dirhodium Complexes on the Reactivity and Selectivity in C–H Insertion Reactions: A Computational Study

Effects of Axial Solvent Coordination to Dirhodium Complexes on the Reactivity and Selectivity in C–H Insertion Reactions: A Computational Study

A highly sensitive fluorescent sensor for Al3+ detection based on luminescent Eu(III)-β-dicetonate complexes

The structure of the Eu(III) complexes were determined by single-crystal X-ray diffraction. The results showed that these complexes exist as a heteronuclear of Eu(III)-Na(I) in which ion Eu3+ is coordinated through eight oxygen atoms of four β-dixetone ligands. The authors found that the monomeric europium-sodium complex displays a very strong red emission with a quantum yield up to 47.5% at λex=370 nm. The authors have successfully designed a simple process to put the Eu(III) complexes on anion exchange resin to create Resin-EuTFNB and Resin-EuTFPB materials. The products have a luminescent intensity that is stronger than that of the precursor complexes due to the removal of the coordination solvents in these complexes. Initially, using these materials to test the ability to recognise Al3+ ion at low concentrations, Resin-EuTFNB and Resin-EuTFPB played a role as a sensing chemosensor based on turn-off mechanism. In the future, they are expected to detect Al3+ion in the biological system.

Beyond Continuum Solvent Models in Computational Homogeneous Catalysis

In homogeneous catalysis solvent is an inherent part of the catalytic system. As such, it must be considered in the computational modeling. The most common approach to include solvent effects in quantum mechanical calculations is by means of continuum solvent models. When they are properly used, average solvent effects are efficiently captured, mainly those related with solvent polarity. However, neglecting atomistic description of solvent molecules has its limitations, and continuum solvent models all alone cannot be applied to whatever situation. In many cases, inclusion of explicit solvent molecules in the quantum mechanical description of the system is mandatory. The purpose of this article is to highlight through selected examples what are the reasons that urge to go beyond the continuum models to the employment of micro-solvated (cluster-continuum) of fully explicit solvent models, in this way setting the limits of continuum solvent models in computational homogeneous catalysis. These examples showcase that inclusion of solvent molecules in the calculation not only can improve the description of already known mechanisms but can yield new mechanistic views of a reaction. With the aim of systematizing the use of explicit solvent models, after discussing the success and limitations of continuum solvent models, issues related with solvent coordination and solvent dynamics, solvent effects in reactions involving small, charged species, as well as reactions in protic solvents and the role of solvent as reagent itself are successively considered.

The many roles of solvent in homogeneous catalysis - The reductive amination showcase

In the global effort to fight climate change, the design and development of novel procedures for complex chemical multi-step reactions is essential for the transformation of chemical industry. The transformation of chemical production processes from petrochemicals towards renewable, sustainable feedstock and the identification of green solvent candidates require a careful assessment of the effects of solvent on thermodynamics and kinetics. As a prime example for the many roles of solvent in chemical catalysis, the reaction mechanism of the homogeneous rhodium-catalyzed reductive amination of 1-undecanal from plant oils with diethylamine forming the long-chain tertiary N,N-diethylundecylamine is investigated. The many roles of solvent during the course of a chemical reactions become apparent when direct substrate-solvent and catalyst-solvent interactions are considered and their polarization effects. Hydrogen bond forming solvent molecules promote the enamine intermediate formation in terms of thermodynamics and kinetics by actively participating as proton transfer agents but a de-solvation penalty for polar groups compromises the overall pathway. The sophisticated bidentate phosphine (SulfoXantPhos)RhH reducing catalyst controls the regioselectivity of the reaction by dedicated ligand-substrate interactions. Its activity is critically dependent on the strength of solvent coordination. The effect of solvent on the reaction rate becomes apparent from a solvent screening of the transition state of the rate-determining step and give a perspective on solvent control of rate constants in this complex multi-step reaction. Only in presence of an appropriate solvent, the calculated Gibbs free potential energy surface becomes shallow and flat and delivers thermodynamic and kinetic parameters in good agreement with experiment.

Anion-Assisted Delivery of Multivalent Cations to Inert Electrodes

In the quest for molecular-scale details of electrochemically induced desolvation, we employed free energy sampling techniques to reveal the preferred solvent and anion coordination of divalent Mg cations at the interface between an ether-based electrolyte (MgTFSI2/THF) and a model, inert electrode (graphene). Surprisingly, we find that anion solvophobicity drives a high population of anion-containing complexes to the interface, even when the electrode is negatively charged, and this facilitates the desolvation of Mg cations. We propose anion solvophobicity as a key factor for increasing the efficiency of electrochemical processes in electrolytes limited by multivalent cation desolvation.

Solvent Effects on the Electrochemistry of Nickel (II) Diethyldithiocarbamate

Multielectron molecular redox couples have been used both as anolytes and catholytes in redox flow batteries (RFBs). The energy stored in an RFB is proportional to the number of electrons transferred per molecule. Thus, increasing the number of electrons transferred per molecule can enhance the amount of stored energy. Previous works in this field mostly looked for molecules containing multiple 1e- redox couples. The advantage of a single 2e- redox couple over multiple 1e- redox couples is that both electrons are stored and released at the same potential. Nickel (II) diethyldithiocarbamate, NiII(Et2dtc)2 undergoes 2e- oxidation at a single potential to form [NiIV(Et2dtc)3]+.1 In different nonaqueous solvents NiII(Et2dtc)2 can offer divergent redox behavior based on their coordination properties.2 This divergent redox behavior means significant changes on the electrochemistry of the complex during oxidation and reduction. Pyridine, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetonitrile (MeCN), methanol (MeOH), acetone, and dichloromethane (DCM) have been studied in this work as they have dissimilar donor numbers with different coordination abilities towards the Ni center. Both cyclic voltammetry and spectroscopic data in the above-mentioned solvents show distinct behavior which is expected as solvent coordination ability varies. Due to its highest coordination ability among the solvents used in this study, pyridine hinders the Ni (II) to Ni (IV) oxidation by coordinating strongly to the Ni (III) center to form [NiIII(Et2dtc)2(Py)2]+. On the contrary, noncoordinating DCM allows oxidation to Ni (IV) albeit through two distinguishable 1e- oxidation processes. MeCN and acetone allow Ni (II)→(IV) oxidation at a single potential. DMSO, DMF, and MeOH show intermediate redox behavior between 1e- and 2e- transfer reactions. These studies point to the ability of solvent to aid or hinder multielectron redox strategies which use Ligand Coupled Electron Transfer where changes in coordination environment are necessary.3 Mazumder, M. M.; Burton, A.; Richburg, C.; Saha, S.; Cronin, B.; Duin, E.; Farnum, B., Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate. Inorganic Chemistry 2021.Islam, R.; Mazumder, M. M. R.; Farnum, B. H., Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage, ECS Meeting s, IOP Publishing: 2021; p 54. Saha, S.; Sahil, S. T.; Mazumder, M. M. R.; Stephens, A. M.; Cronin, B.; Duin, E. C.; Jurss, J. W.; Farnum, B. H., Synthesis, characterization, and electrocatalytic activity of bis (pyridylimino) isoindoline Cu (II) and Ni (II) complexes. J Dalton Transactions 2021, 50 (3), 926-935. Figure 1

Structure and Reactivity of NO/NO+/NO−Pincer and Porphyrin Complexes

AbstractThis review covers recent progress in the field of nitrosyl pincer and porphyrinate complexes, and how their reactivity depends on the redox state of the NO ligand. Synthetic methods, and the most significant structural information, spectroelectrochemical studies, and different reactivities of nitrosyl pincer complexes are presented. These include selective activation and functionalization of carbon‐halogen bonds, catalysis for a variety of specific organic reactions, mediation of NO disproportionation and reversible coordination of solvents and weakly‐coordinating anions. Regarding the porphyrinate complexes, the focus is on biorelevant nitroxyl (NO−/HNO) complexes, discussing pioneering studies along with preparation and common characterization methods. Their relative stability in different conditions is compared, and possible decomposition mechanisms are discussed in terms of their ability to act as biomimetic models for enzymatic systems.

Electron Flow Characterization of Charge Transfer for Carbonic Acid to Strong Base Proton Transfer in Aqueous Solution.

Protonation of the strong base methylamine CH3NH2 by carbonic acid H2CO3 in aqueous solution, HOCOOH···NH2CH3 → HOCOO-···+HNH2CH3, has been previously studied ( J. Phys. Chem. B 2016, 109, 2271-2280; J. Phys. Chem. B 2016, 109, 2281-2290) via Car-Parinnello molecular dynamics. This proton transfer (PT) reaction within a hydrogen (H)-bonded complex was found to be barrierless and very rapid, with key reaction coordinates comprising the proton coordinate, the H-bond separation RON, and a solvent coordinate, reflecting the water solvent rearrangement involved in the neutral to ion pair conversion. In the present work, the reaction's charge flow aspects are analyzed in detail, especially a description via Mulliken charge transfer for PT (MCTPT). A natural bond orbital analysis and some extensions of them are employed for the complex's electronic structure during the reaction trajectories. Results demonstrate that consistent with the MCTPT picture, the charge transfer (CT) occurs from a methylamine base nonbonding orbital to a carbonic acid antibonding orbital. A complementary MCTPT reaction product perspective of CT from the antibonding orbital of the HN+ moiety to the nonbonding orbital of the oxygen in the H-bond complex is also presented. σOH and σHN+ bond order expressions show this CT to occur within the H-bond OHN triad, an aspect key for simultaneous bond-breaking and -forming in the PT reaction.

Influence of solvent and axial coordination on self-assembly of a heteroditopic porphyrin derivative

A novel heteroditopic porphyrin and its zinc complex with four long aliphatic chains on the same side of the porphyrin ring were synthesized and used for controllable self-assembly. A variety of aggregation morphologies, including nanosheets, nanospheres, films, leaves, trunks, nanorods, and disks, were furnished by using different pyridyl ligands to coordinate with the Zn-porphyrin or selecting different solvents.

Iodide vs Chloride: The Impact of Different Lead Halides on the Solution Chemistry of Perovskite Precursors

Controlled perovskite growth from solution is crucial for efficient optoelectronic applications and requires a deep understanding of the perovskite precursor chemistry. The so-called “chlorine route” to lead–iodide perovskite, using PbCl2 or MACl additive as a precursor, is frequently employed to form homogeneous perovskite layers by retarding perovskite crystallization. To understand the role of chlorine-containing lead precursors in solution, we analyze the chemical interaction of PbCl2 and PbI2 precursors with commonly employed solvents (γ-butyrolactone (GBL), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO)) by combining first-principles simulations and experimental UV–vis spectroscopy in diluted precursor solutions. Ab initio molecular dynamics simulations reveal reduced solvation and an increased free energy barrier of lead-halide bond dissociation of PbCl2 compared to PbI2 with chlorine acting as a stronger ligand, which, in turn, limits the solvent coordination. In contrast to PbI2, PbCl2 absorption spectra lack signatures of high-valent [PbCln]2–n complexes and show low sensitivity on the employed solvent, as confirmed by combined UV–vis and excited-state time-dependent density functional theory (TD-DFT) analysis. Altogether, our data suggest the presence of residual chlorine coordinated to Pb even in the presence of high iodine excess, which may retard the perovskite growth and could also lead to chlorine incorporation within the lead–iodide perovskite crystal.

Solvation Structure around Li+ Ions in Organic Carbonate Electrolytes: Spacer-Free Thin Cell IR Spectroscopy.

Organic carbonate electrolytes are widely used materials for lithium-ion batteries. However, detailed solvation structures and solvent coordination numbers (CNs) of lithium cations in such solutions have not been accurately described nor determined yet. Because transmission-type IR spectroscopy is not of use for measuring the carbonyl stretch modes of electrolytes due to their absorption saturation problem, we here show that simple spacer-free thin cell IR spectroscopy can provide quantitative information on the number of solvating carbonate molecules around each lithium ion. We could estimate the solvent (carbonate) CNs of lithium ions in dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, and butylene carbonate over a wide range of lithium salt concentrations accurately, and they are compared with the previous results obtained with attenuated total reflection IR spectroscopy technique. We anticipate that our spacer-free thin cell approach will potentially be used to investigate the solvation dynamics, chemical exchange process, and vibrational energy transfers between solvating carbonate molecules in lithium salt electrolytes when combined with time-resolved IR spectroscopy.

Ligand and solvent effects on the kinetics of the electrochemical reduction of Ni(II) complexes: Experiment and quantum chemical modeling

The two-electron reduction of some Ni(II) complexes with α-diimine ligands ([Ni(bpy)3]2+ and [Ni(pybox)2]2+) at a platinum electrode from acetonitrile (AN) and dimethylformamide (DMF) solutions is investigated by cyclic voltammetry (CV). Digisim simulations are employed to determine kinetic parameters. For [Ni(bpy)3]2+ in AN the first electron transfer (ET) step was found to be rate-controlling. The rate constants of the first and second steps (k1 and k2) are practically the same in the DMF solution. In contrast, the second ET step is rate controlling for the [Ni(pybox)2]2+ complex in AN, while the difference between k1 and k2 for this complex reactant in DMF becomes less noticeable. Molecular modeling based on the quantum mechanical theory of electron transfer and on density functional theory (DFT) calculations is performed for the first time to predict the activation barriers of the two-step heterogeneous redox processes and to elucidate the role of the ligands and solvents in the kinetics of these processes. Three-dimensional reaction free energy surfaces are constructed along the solvent and intramolecular coordinates. The electronic transmission coefficients are estimated as well. The results of model calculations are in qualitative agreement with the experimental data.

Formation of Lead Halide Perovskite Precursors in Solution: Insight from Electronic‐Structure Theory

Understanding the formation of lead halide (LH) perovskite solution precursors is crucial to gain insight into the evolution of these materials to thin films for solar cells. Using density functional theory in conjunction with the polarizable continuum model, 18 complexes with chemical formula are investigated, where X = Cl, Br, I, and M are common solvent molecules. Through the analysis of structural properties, binding energies, and charge distributions, the role of halogen species and solvent molecules in the formation of LH perovskite precursors is clarified. It is found that interatomic distances are critically affected by the halogen species, whereas the energetic stability is driven by the solvent coordination to the backbones. Regardless of the solvent, lead iodide complexes are more strongly bound than the others. Based on the charge distribution analysis, it is found that all solvent molecules bind covalently with the LH backbones and that PbI and PbBr bonds lose ionicity in solution. The results contribute to clarify the physical properties of LH perovskite solution precursors and offer a valuable starting point for further investigations on their crystalline intermediates.

Solvation coordination compounds of scandium chloride from the dehydration of scandium chloride hexahydrate

Attempts to dehydrate [Sc(H2O)6]3[Cl]•(H2O) using simple organic solvents led to the isolation of [ScCl3(THF)3] (1) from the addition of thionyl chloride (O = SCl2) to the hydrate, slurried in tetrahydrofuran (THF). Modification of 1 by a variety of solvents yielded the crystallographically characterized compounds: [ScCl3(MeCN)3]•MeCN (2), [ScCl3(py)3]•py (3), [ScCl2(MeOH)4][X] (X = Cl 4; X = Br 4a), and [ScCl2(HOPri)4][Cl] (5) (where MeCN = acetonitrile; py = pyridine; MeOH = methanol, HOPri = isopropanol). The heating of 3 resulted in the formation of [py-H-py][ScCl4(py)2]•(py)1/2 referred to as 6•py1/2. Attempts to dehydrate [Sc(H2O)6]3[Cl]•(H2O) with the same set of organic solvents did not lead to full exchange; however, direct dehydration was readily observed for Zwitterionic species, including: triphenylphosphine oxide (O=PPh3), diphenylsulfoxide (O=SPh2), urea (O=C(NH2)2), dimethylformamide (OC(H)N(Me)2), diphenylformamide (O=C(H)N(Ph)2) which formed [ScCl2(O=PPh3)4][Cl]•2HOEt (7), [ScCl3(O=SPh2)3] (8), [Sc(OC(NH2)2)6]3[Cl] (9), [ScCl3(O=C(H)N(Me)2)3] (10), [ScCl3(OC(H)N(Ph)2)3] (11), respectively. Interestingly, the use of propylene carbonate (PC) resulted in the reduction of the modifier forming [Sc(κ2(O,O’)PD)(μ, κ 2(O,O’)H-PD)(H2O)2]22[Cl] (12) where H2-PD = propane-1,2 diol. All compounds were identified using single crystal X-ray and solution 45Sc NMR.

Potentiometric MRI of a Superconcentrated Lithium Electrolyte: Testing the Irreversible Thermodynamics Approach

Superconcentrated electrolytes, being highly thermodynamically nonideal, provide a stringent proving ground for continuum transport theories. Herein, we test an ostensibly complete model of LiPF6 in ethyl-methyl carbonate (EMC) based on the Onsager–Stefan–Maxwell theory from irreversible thermodynamics. We perform synchronous magnetic resonance imaging (MRI) and chronopotentiometry to examine how superconcentrated LiPF6:EMC responds to galvanostatic polarization and open-circuit relaxation. We simulate this experiment using an independently parametrized model with six composition-dependent electrolyte properties, quantified up to saturation. Spectroscopy reveals increasing ion association and solvent coordination with salt concentration. The potentiometric MRI data agree closely with the predicted ion distributions and overpotentials, providing a completely independent validation of the theory. Superconcentrated electrolytes exhibit strong cation–anion interactions and extreme solute-volume effects that mimic elevated lithium transference. Our simulations allow surface overpotentials to be extracted from cell-voltage data to track lithium interfaces. Potentiometric MRI is a powerful tool to illuminate electrolytic transport phenomena.

Reversible Switching of Single-Molecule Magnetic Behaviour by Desorption/Adsorption of Solvent Ligand in a New Dy(III)-Based Metal Organic Framework.

Two metal-organic frameworks (MOFs), [Dy(BDC)(NO3)(DMF)2]n (1, H2BDC = terephthalic acid) and [Dy(BDC)(NO3)]n (1a), were synthesized. The structures of MOFs 1 and 1a are easy to be reversibly transformed into each other by the desorption or adsorption of coordination solvent molecules. Accordingly, their magnetic properties can also be changed reversibly, which realizes our goals of manipulating on/off single-molecule magnet behaviour. MOF 1 behaves as a single-molecule magnet either with or without DC field. Contrarily, no slow magnetic relaxation was observed in 1a both under zero field and applied field.

XAS Diagnostic of the Photoactive State in Co(II) Azobenzene Complex in Organic Solvents

AbstractX‐ray absorption spectroscopy (XAS) was used to characterize the structure of the photoactive Co(II) azobenzene complex. Optical absorption spectra show that photoinduced changes occur only in dimethylformamide (DMF) solvent, while in acetonitrile, this complex is photochemically inactive. Co K‐edge XAS spectra indicate 6‐coordinated species in acetonitrile with a structure similar to one in the crystalline form of the complex. However, in DMF, an activation process occurs related to the decrease of coordination number, bond shortening and absorption edge shift to the higher energies. Quantitative analysis indicates that observed spectral changes are related to the high spin ‐ low spin transition in the Co complex accompanied by the bond dissociation and solvent coordination.

Deciphering the Mechanistic Details of Manganese-Catalyzed Formic Acid Dehydrogenation: Insights from DFT Calculations.

A comprehensive density functional theory investigation has been carried out to unravel the complete mechanistic landscape of aqueous-phase formic acid dehydrogenation (FAD) catalyzed by a pyridyl-imidazoline-based Mn(I) catalyst [Mn(PY-NHIM)(CO)3Br], which was recently reported by Beller and co-workers. The computed free energy profiles show that for the production of a Mn-formate intermediate [Mn(HCO2-)], a stepwise mechanism is both kinetically and thermodynamically favorable compared to the concerted mechanism. This stepwise mechanism involves the dissociation of a Br- ion from a Mn-bromide complex [Mn(Br)] to create a vacant site and coordination of water solvent to this vacant site, followed by the dissociative exchange of the aqua ligand with the formate ion to form Mn(HCO2-). Non-covalent interaction analysis revealed that the steric hindrance at the transition state is the cardinal reason for the preference to a stepwise mechanism. The β-hydride elimination process was estimated to be the rate-determining step with a barrier of 19.0 kcal/mol. This confirms the experimental observation. The generation of a dihydrogen-bound complex was found to occur through the protonation of Mn-hydride by a hydronium ion instead of formic acid. The mechanistic details and insights presented in this work would promote future catalytic designing and exploration of earth-abundant Mn-based catalytic systems for potential applications toward FAD.

Synthesis and characterization of the dinuclear cobalt(III) complex: [(C2F5)3Co(μ-F)]22−

Reaction of the versatile tris(perfluoroethyl) cobalt(III) precursor [fac-(MeCN)3Co(C2F5)3] with [NMe4]F and [PPh4]Cl in THF formed the unexpected cobalt(III) bridging fluoride dimer [(C2F5)3Co(μ-F)]22−. The new fluoro-organometallic cobalt(III) complex was characterized by NMR and UV-vis spectroscopies, X-ray crystallography, cyclic voltammetry, and by computational methods. In the strongly coordinating solvent MeCN, [(C2F5)3Co(μ-F)]22− exhibits dynamic processes on the NMR timescale which are consistent with solvent coordination. However, in the weakly coordinating solvent CH2Cl2, a more static structure is observed suggesting that the dimer retains its structure in solution state. An electrochemical analysis of [(C2F5)3Co(μ-F)]22− was performed, and the data are compared to previously reported cobalt(III) perfluoroethyl complexes.