Electron Solvation in Liquid Ammonia: Lithium, Sodium, Magnesium, and Calcium as Electron Sources

A two-electron reducing reaction of CO2 to an oxalate anion: a theoretical study of delocalized (presolvated) electrons in Al(CH3)n(NH3)m, n = 0-2 and m = 1-6, clusters

Presolvated electron possibility in three oxidation states of aluminum - Al(0), Al(I), and Al(II) - has been theoretically investigated for the Al + 6NH3, Al(CH3) + 5NH3, and Al(CH3)2 + 4NH3 reactions. It has been shown that the metal center adopts a tetrahedral shape for its most stable geometric structure, irrespective of the degree of Al oxidation states. Using different analysis techniques (highest occupied molecular orbital shapes, spin density distributions, and electron delocalization ranges), we showed that presolvated (delocalized) electrons are only formed in the Al(CH3)2(NH3)p coordination complexes when 2 ≤ p ≤ 4. It has also been evidenced that these delocalized electrons being powerful reducing agents allowed two CO2 molecules to be captured and form an oxalate ion in close contact with the [Al2(CH3)2(CH2)2(NH3)4]2+ dication core.

A fresh perspective on metal ammonia molecular complexes and expanded metals: opportunities in catalysis and quantum information

Recent advances in our comprehension of the electronic structure of metal ammonia complexes have opened avenues for novel materials with diffuse electrons. These complexes in their ground state can host peripheral "Rydberg" electrons which populate a hydrogenic-type shell model imitating atoms. Aggregates of such complexes form the so-called expanded or liquid metals. Expanded metals composed of d- and f-block metal ammonia complexes offer properties, such as magnetic moments and larger numbers of diffuse electrons, not present for alkali and alkaline earth (s-block) metals. In addition, tethering metal ammonia complexes via hydrocarbon chains (replacement of ammonia ligands with diamines) yields materials that can be used for redox catalysis and quantum computing, sensing, and optics. This perspective summarizes the recent findings for gas-phase isolated metal ammonia complexes and projects the obtained knowledge to the condensed phase regime. Possible applications for the newly introduced expanded metals and linked solvated electrons precursors are discussed and future directions are proposed.

Fragments-in-fragments method for efficient and reliable estimates of individual hydrogen bond energies in large molecular clusters

The knowledge of individual hydrogen bond (HB) strength in molecular clusters is indispensable to get insights into the bulk properties of condensed systems. Recently, we have developed the molecular tailoring approach based (MTA-based) method for the estimation of individual HB energy in molecular clusters. However, the direct use of this MTA-based method to large molecular clusters becomes progressively difficult with the increase in the size of a cluster. To overcome this caveat, herein, we propose the use of linear scaling method (such as the original MTA method) for the estimation of single-point (SP) energies of large-sized parent molecular cluster and their respective fragments. Because the fragments of the MTA-based method, for the estimation of HB energy, are further fragmented, this proposed strategy is called as Fragments-in-Fragments (Frags-in-Frags) method. The SP energies of fragments and parent cluster calculated by the Frags-in-Frags approach were utilized to estimate the individual HB energy. The estimated individual HB energies, in various molecular clusters, by Frags-in-Frags method are found to be in excellent linear agreement with their MTA-based counterparts (R²  = 0.9975 of 348 data points). The difference being less than 0.5 kcal/mol in most of the cases. Furthermore, RMSD is 0.43 kcal/mol, MAE is 0.33 kcal/mol, and the standard deviation is 0.44 kcal/mol. Importantly, the Frags-in-Frags method not only enables the reliable estimation of HB energy in large molecular clusters but also requires less computational time and can be possible even with off-the-shelf hardware.

Electron Presolvation in Tetrahydrofuran-Incorporated Supramolecular Sodium Entities

Alkali metal atoms can repopulate their valence electrons toward solvation due to impact from solvents or microsurroundings and provide the remaining alkali metal cations for coordinating with a variety of specific solvents, forming various electron-expanded complexes or solvated ionic pairs with special interactions. Such special solute-solvent interactions not only affect their electronic structures but also enable the formation of entirely new species. Taking Na(THF)_n (n = 1-6, THF = tetrahydrofuran) and Na₂@THF complexes as typical representatives, density functional theory calculations are carried out to explore the solvation of a sodium atom and its dimer in THF and characterize their complexes as solvent-incorporated supramolecular entities and particularly valence electron presolvation due to their interaction with solvent THF. Electron presolvation is caused by the Pauli repulsion between THF containing a coordinating O atom with a lone pair of electrons and the alkali metal Na or Na₂ containing valence electrons, and THF coordination to them forces their valence electrons to redistribute, which can be easily realized in such solvents. Compared with strongly bound valance electrons of alkali metal atoms, THF coordination enables Na or Na₂ electrons to exhibit much more active states (i.e., the presolvated states) featuring small vertical detachment energies of electrons and distorted diffuse distributions in the frames of the generally structured metal cation complexes, acting as the electron-expanded chemical entities. Furthermore, the degree of electron diffusion and the polarity of the Na-Na bond are proportional to the coordination number (n) and the coordination number difference (Δn) between two Na centers in Na₂@THF. The unique properties of such entities are also discussed. This work offers a theoretical support to the supramolecular entities formed by alkali-metal atoms or their dimers with ligands containing O or N and uncovers the unique electron presolvation phenomena and also enriches our understanding of the novel metal atom complexes.

A Tug of War between the Self- and Cross-associating Hydrogen Bonds in Neutral Ammonia-Water Clusters: Energetic Insights by Molecular Tailoring Approach

In the present work, the energies of various types of individual HBs observed in neutral (NH₃ )_m (H₂ O)_n , (m+n=2 to 7) clusters were estimated using the molecular tailoring approach (MTA)-based method. The calculated individual HB energies suggest that the O-H…N HBs are the strongest (1.21 to 12.49 kcal mol^-1 ). The next ones are the O-H…O (3.97 to 9.30 kcal mol^-1 ) HBs. The strengths of N-H…N (1.09 to 5.29 kcal mol^-1 ) and N-H…O (2.85 to 5.56 kcal mol^-1 ) HBs are the weakest. The HB energies in dimers also follow this rank ordering. However, the HB energies in dimers are much smaller than those obtained by the MTA-based method due to the loss in cooperativity contribution in the dimers. Thus, the calculated cooperativity contributions, for different types of HBs, fall in the range 0.64 to 5.73 kcal mol^-1 . We wish to emphasize based on the energetic rank ordering obtained by the MTA-based method that the O-H of water is a better HB donor than the N-H of ammonia. The reasons for the observed energetic rank ordering are two folds: (i) intrinsically stronger O-H…N HBs than the O-H…O ones as revealed by dimer energies and (ii) the higher cooperativity contribution in the former than the later ones. Indeed, the MTA-based method is useful in providing the missing energetic rank ordering of various type of HBs in neutral (NH₃ )_m (H₂ O)_n clusters, in the literature.

Intermediate Range Order in Metal-Ammonia Solutions: Pure and Na-Doped Ca-NH3

The local and intermediate range ordering in Ca-NH₃ solutions in their metallic phase is determined through H/D isotopically differenced neutron diffraction in combination with empirical potential structure refinements. For both low and high relative Ca concentrations, the Ca ions are found to be octahedrally coordinated by the NH₃ solvent, and these hexammine units are spatially correlated out to lengthscales of ∼7.4-10.3 Å depending on the concentration, leading to pronounced ordering in the bulk liquid. We further demonstrate that this liquid order can be progressively disrupted by the substitution of Ca for Na, whereby a distortion of the average ion primary solvation occurs and the intermediate range ion-ion correlations are disrupted.

Intercalated Iron Chalcogenides: Phase Separation Phenomena and Superconducting Properties

Organic molecule-intercalated layered iron-based monochalcogenides are presently the subject of intense research studies due to the linkage of their fascinating magnetic and superconducting properties to the chemical nature of guests present in the structure. Iron chalcogenides have the ability to host various organic species (i.e., solvates of alkali metals and the selected Lewis bases or long-chain alkylammonium cations) between the weakly bound inorganic layers, which opens up the possibility for fine tuning the magnetic and electrical properties of the intercalated phases by controlling both the doping level and the type/shape and orientation of the organic molecules. In recent years, significant progress has been made in the field of intercalation chemistry, expanding the gallery of intercalated superconductors with new hybrid inorganic–organic phases characterized by transition temperatures to a superconducting state as high as 46 K. A typical synthetic approach involves the low-temperature intercalation of layered precursors in the presence of liquid amines, and other methods, such as electrochemical intercalation, intercalant or ion exchange, and direct solvothermal growths from anhydrous amine-based media, are also being developed. Large organic guests, while entering a layered structure on intercalation, push off the inorganic slabs and modify the geometry of their internal building blocks (edge-sharing iron chalcogenide tetrahedrons) through chemical pressure. The chemical nature and orientation of organic molecules between the inorganic layers play an important role in structural modification and may serve as a tool for the alteration of the superconducting properties. A variety of donor species well-matched with the selected alkali metals enables the adjustment of electron doping in a host structure offering a broad range of new materials with tunable electric and magnetic properties. In this review, the main aspects of intercalation chemistry are discussed, involving the influence of the chemical and electrochemical nature of intercalating species on the crystal structure and critical issues related to the superconducting properties of the hybrid inorganic–organic phases. Mutual relations between the host and organic guests lead to a specific ordering of molecular species between the host layers, and their effect on the electronic structure of the host will be also argued. A brief description of a critical assessment of the association of the most effective chemical and electrochemical methods, which lead to the preparation of nanosized/microsized powders and single crystals of molecularly intercalated phases, with the ease of preparation of phase pure materials, crystal sizes, and the morphology of final products is given together with a discussion of the stability of the intercalated materials connected with the volatility of organic solvents and a possible degradation of host materials.

The Detosylation of Chiral 1,2-Bis(tosylamides)

The deprotection of chiral 1,2-bis(tosylamides) to their corresponding 1,2-diamines is mostly unsuccessful under standard conditions. In a new methodology, the use of Mg/MeOH with sufficient steric additions allows the facile synthesis of 1,2-diamines in 78-98% yields. These results are rationalized using density functional theory and the examination of inner and outer-sphere reduction mechanisms.

Mg(II) and Ca(II) Microsolvation by Ammonia: Born-Oppenheimer Molecular Dynamics Studies

We report the structural and energetic features of the Mg²⁺ and Ca²⁺ cations in ammonia microsolvation environments. Born-Oppenhemier molecular dynamics studies are carried out for [Mg(NH₃)_n]²⁺ and [Ca(NH₃)_n]²⁺ clusters with n = 2, 3, 4, 6, 8, 20, and 27 at 300 K based on hybrid density functional theory calculations. We determine binding energies per ammonia molecule and the metal cation solvation patterns as a function of the number of molecules. The general trend for Mg²⁺ is that the Mg-N distances increase as a function of n until the first solvation shell is populated by six ammonia molecules, and then the distances slightly decrease while CN = 6 does not change. For Ca²⁺, the first solvation shell at room temperature is populated by eight ammonia molecules for clusters with more than one solvation shell, leading to a different structure from that of [Ca(NH₃)₆]²⁺ hexamine. The evaporation of NH₃ molecules was found at 300 K only for Mg²⁺ clusters with n ≥ 10; this was not the case for Ca²⁺ clusters. Vibrational spectra are obtained for all of the clusters, and the evolution of the main features is discussed. EXAFS spectra are also presented for the [Mg(NH₃)₂₇(NH₃)₂₇]²⁺ and [Ca(NH₃)₂₇]²⁺ clusters, which yield valuable data to be compared with experimental data in the liquid phase, as previously done for the aqueous solvation of these dications.

Structure and some physicochemical and functional properties of water treated under ammonia with low-temperature low-pressure glow plasma of low frequency

Deionized, tap and two kinds of commercially available mineralized water, after supplementation with ammonia, were treated with low-pressure, low-temperature glow plasma (GP) of low frequency. Treating hard water with ammonia provided the removal of permanent and temporary water hardness already at room temperature. On such treatment, mineralized water supplemented with ammonia was partly demineralized. Precipitated rhombohedral deposit from hard water did not turn into scale even when maintained in suspension for 3 days at around 90°C. In such manner, the use of other chemicals for prevention from the scale formation and/or for the scale removal is entirely dispensable. The rate and yield of precipitation depended on the concentration of admixed ammonia and the GP treatment time. Ammonia served as a ligand of calcium, magnesium and ferric central atoms of corresponding salts constituting the hardness. Moreover, ammonia constituting the atmosphere of the treatment was arrested inside aqueous clathrates. So, stabilized ammonia solutions could potentially be utilized as an environmental-friendly nitrogen fertilizer. The precipitate could also be utilized for the same purpose.

Ab Initio Molecular Dynamics Simulations of Solvated Electrons in Ammonia Clusters

We investigated excess electron solvation dynamics in (NH₃)_n^- ammonia clusters in the n = 8-32 size range by performing finite temperature molecular dynamics simulations. In particular, we focused on three possible scenarios. The first case is designed to model electron attachment to small neutral ammonia clusters (n ≤ ∼10) that form hydrogen-bonded chains. The excess electron is bound to the clusters via dipole bound states, and persists with a VDE of ∼160 meV at 100 K for the n = 8 cluster. The coupled nuclear and electronic relaxation is fast (within ∼100 fs) and takes place predominantly by intermolecular librational motions and the intramolecular umbrella mode. The second scenario illustrates the mechanism of excess electron attachment to cold compact neutral clusters of medium size (8 ≤ n ≤ 32). The neutral clusters show increasing tendency with size to bind the excess electron on the surface of the clusters in weakly bound, diffuse, and highly delocalized states. Anionic relaxation trajectories launched from these initial states provide no indication for excess electron stabilization for sizes n < 24. Excess electrons are likely to autodetach from these clusters. The two largest investigated clusters (n = 24 and 32) can accommodate the excess electron in electronic states that are mainly localized on the surface, but they may be partly embedded in the cluster. In the last 500 fs of the simulated trajectories, the VDE of the solvated electron fluctuates around ∼200 meV for n = 24 and ∼500 meV for n = 32, consistent with the values extrapolated from the experimentally observed linear VDE-n^-1/3 trend. In the third case, we prepared neutral ammonia cluster configurations, including an n = 48 cluster, that contain possible electron localization sites within the interior of the cluster. Excess electrons added to these clusters localize in cavities with high VDEs up to 1.9 eV for n = 48. The computed VDE values for larger clusters are considerably higher than the experimentally observed photoelectric threshold energy for the solvated electron in bulk ammonia (∼1.4 eV). Molecular dynamics simulations launched from these initial cavity states strongly indicate, however, that these cavity structures exist only for ∼200 fs. During the relaxation the electron leaves the cavity and becomes delocalized, while the cluster loses its initial compactness.

Excess electron solvation in ammonia clusters

We performed a combination of quantum chemical calculations and molecular dynamics simulations to assess the stability of various size NH_{3 n} ^- ammonia cluster anions up to n = 32 monomers. In the n = 3-8 size range, cluster anions are optimized and the vertical detachment energy of the excess electron (VDE) from increasing size clusters is computed using various level methods including density functional theory, MP2, and coupled-cluster singles doubles with perturbative triples. These clusters bind the electrons in nonbranched hydrogen bonding chains in dipole bound states. The VDE increases with size from a few millielectron volt up to ∼200 meV. The electron binding energy is weaker than that in water clusters but comparable to small methanol cluster VDEs. We located the first branched hydrogen bonding cluster that binds the excess electron at n = 7. For larger (n = 8-32) clusters, we generated cold, neutral clusters by semiempirical and ab initio molecular dynamics simulations and added an extra electron to selected neutral configurations. VDE calculations on the adiabatic and the relaxed anionic structures suggest that the n = 12-32 neutral clusters weakly bind the excess electron. Electron binding energies for these clusters (∼100 meV) appear to be significantly weaker than those extrapolated from experimental data. The observed excess electron states are diffuse and localized outside the molecular frame (surface states) with minor (∼1%) penetration to the nitrogen frontier orbitals. Stable minima with excess electron states surrounded by solvent molecules (cavity states) were not found in this size regime.

Scalable and safe synthetic organic electroreduction inspired by Li-ion battery chemistry

Reductive electrosynthesis has faced long-standing challenges in applications to complex organic substrates at scale. Here, we show how decades of research in lithium-ion battery materials, electrolytes, and additives can serve as an inspiration for achieving practically scalable reductive electrosynthetic conditions for the Birch reduction. Specifically, we demonstrate that using a sacrificial anode material (magnesium or aluminum), combined with a cheap, nontoxic, and water-soluble proton source (dimethylurea), and an overcharge protectant inspired by battery technology [tris(pyrrolidino)phosphoramide] can allow for multigram-scale synthesis of pharmaceutically relevant building blocks. We show how these conditions have a very high level of functional-group tolerance relative to classical electrochemical and chemical dissolving-metal reductions. Finally, we demonstrate that the same electrochemical conditions can be applied to other dissolving metal-type reductive transformations, including McMurry couplings, reductive ketone deoxygenations, and epoxide openings.

Transition-metal solvated-electron precursors: diffuse and 3d electrons in V(NH3)0,±6

Ground and excited electronic states of V(NH₃)0,±6 complexes, investigated with ab initio electronic structure theory, consist of a V(NH₃)₆²⁺ core with up to three electrons distributed over its periphery.

Superconducting selenides intercalated with organic molecules: synthesis, crystal structure, electric and magnetic properties, superconducting properties, and phase separation in iron based-chalcogenides and hybrid organic-inorganic superconductors

Layered iron-based superconducting chalcogenides intercalated with molecular species are the subject of intensive studies, especially in the field of solid state chemistry and condensed matter physics, because of their intriguing chemistry and tunable electric and magnetic properties. Considerable progress in the research, revealing superconducting inorganic-organic hybrid materials with transition temperatures to superconducting state, T _c, up to 46 K, has been brought in recent years. These novel materials are synthesized by low-temperature intercalation of molecular species, such as solvates of alkali metals and nitrogen-containing donor compounds, into layered FeSe-type structure. Both the chemical nature as well as orientation of organic molecules between the layers of inorganic host, play an important role in structural modifications and may be used for fine tuning of superconducting properties. Furthermore, a variety of donor species compatible with alkali metals, as well as the possibility of doping also in the host structure (either on Fe or Se sites), makes this system quite flexible and gives a vast array of new materials with tunable electric and magnetic properties. In this review, the main aspects of intercalation chemistry are discussed with a particular attention paid to the influence of the unique nature of intercalating species on the crystal structure and physical properties of the hybrid inorganic-organic materials. To get a full picture of these materials, a comprehensive description of the most effective chemical and electrochemical methods, utilized for synthesis of intercalated species, with critical evaluation of their strong and weak points, related to feasibility of synthesis, phase purity, crystal size and morphology of final products, is included as well.

Overcoming Catalyst Residue Inhibition of the Functionalization of Single-Walled Carbon Nanotubes via the Billups-Birch Reduction

The Billups-Birch Reduction chemistry has been shown to functionalize single-walled carbon nanotubes (SWCNTs) without damaging the sidewalls, but has challenges in scalability. Currently published work uses a large mole ratio of Li to carbon atoms in the SWCNT (Li:C) to account for lithium amide formation, however this increases the cost and hazard of the reaction. We report here the systematic understanding of the effect of various parameters on the extent of functionalization using resonant Raman spectroscopy. Addition of 1-iodododecane yielded alkyl-functionalized SWCNTs, which were isolated by solvent extraction and evaporation, and purified by a hydrocarbon wash. The presence of SWCNT growth catalyst residue (Fe) was shown to have a strong adverse effect on SWCNT functionalization. Chlorination-based SWCNT purification reduced the amount of residual Fe, and achieve a maximum I_D/I_G ratio using a Li:C ratio of 6:1 in a reaction time of 30 min. This result is consistent with published literature requiring 20-fold mole equivalents of Li per mole SWCNT with a reaction time of over 12 h. This new understanding of the factors influencing the functionalization chemistry will help cut down material and process costs, and also increase the selectivity of the reaction toward the desired product.