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Electronic structure calculations have the potential to predict key matter transformations for applications of strategic technological importance, from drug discovery to material science and catalysis. However, a predictive physicochemical characterization of these processes often requires accurate quantum chemical modeling of complex molecular systems with hundreds to thousands of atoms. Due to the computationally demanding nature of electronic structure calculations and the complexity of modern high-performance computing hardware, quantum chemistry software has historically failed to operate at such large molecular scales with accuracy and speed that are useful in practice. In this paper, novel algorithms and software are presented that enable extreme-scale quantum chemistry capabilities with particular emphasis on exascale calculations. This includes the development and application of the multi-Graphics Processing Unit (GPU) library LibCChem 2.0 as part of the General Atomic and Molecular Electronic Structure System package and of the standalone Extreme-scale Electronic Structure System (EXESS), designed from the ground up for scaling on thousands of GPUs to perform high-performance accurate quantum chemistry calculations at unprecedented speed and molecular scales. Among various results, we report that the EXESS implementation enables Hartree–Fock/cc-pVDZ plus RI-MP2/cc-pVDZ/cc-pVDZ-RIFIT calculations on an ionic liquid system with 623 016 electrons and 146 592 atoms in less than 45 min using 27 600 GPUs on the Summit supercomputer with a 94.6% parallel efficiency. [ABSTRACT FROM AUTHOR]

The characterization of an ionic liquid's properties based on structural information is a longstanding goal of computational chemistry, which has received much focus from ab initio and molecular dynamics calculations. This work examines kernel ridge regression models built from an experimental dataset of 2212 ionic liquid melting points consisting of diverse ion types. Structural descriptors, which have been shown to predict quantum mechanical properties of small neutral molecules within chemical accuracy, benefit from the addition of first-principles data related to the target property (molecular orbital energy, charge density profile, and interaction energy based on the geometry of a single ion pair) when predicting the melting point of ionic liquids. Out of the two chosen structural descriptors, ECFP4 circular fingerprints and the Coulomb matrix, the addition of molecular orbital energies and all quantum mechanical data to each descriptor, respectively, increases the accuracy of surrogate models for melting point prediction compared to using the structural descriptors alone. The best model, based on ECFP4 and molecular orbital energies, predicts ionic liquid melting points with an average mean absolute error of 29 K and, unlike group contribution methods, which have achieved similar results, is applicable to any type of ionic liquid. [ABSTRACT FROM AUTHOR]

Minimal understanding of the formation mechanism and structure of polydopamine (pDA) and its natural analogue, eumelanin, impedes the practical application of these versatile polymers and limits our knowledge of the origin of melanoma. The lack of conclusive structural evidence stems from the insolubility of these materials, which has spawned significantly diverse suggestions of pDA's structure in the literature. We discovered that pDA is soluble in certain ionic liquids. Using these ionic liquids (ILs) as solvents, we present an experimental methodology to solvate pDA, enabling us to identify pDA's chemical structure. The resolved pDA structure consists of self-assembled supramolecular aggregates that contribute to the increasing complexity of the polymer. The underlying molecular energetics of pDA solvation and a macroscopic picture of the disruption of the aggregates using IL solvents have been investigated, along with studies of the aggregation mechanism in water. [ABSTRACT FROM AUTHOR]

Ru-Alkylidene catalysed olefin metathesis generates metabolically stable cystine bridge peptidomimetics with defined geometry. Deleterious coordinative bonding to the catalyst by sulfur-containing functionality found in cysteine and methionine residues can be negated by in situ and reversible oxidation of thiol and thioether functionality, as disulfides and S-oxides respectively, to facilitate high yielding ring-closing and cross metathesis of bioorthogonally protected peptides. [ABSTRACT FROM AUTHOR]

Evident in many physical and chemical phenomena, thermodynamics is the study of how energy is stored, transformed and transferred in a molecule or material. However, prediction of these properties with simulation techniques is a non-trivial task as several factors such as composition and intermolecular interactions come into play. While molecular dynamics and ab initio molecular dynamics are the most common techniques for the prediction of thermodynamic properties, there exists many shortcomings associated with their use. Therefore, in this work we instead apply QCE theory to predict the thermodynamic properties of liquid water. This theory assumes that a condensed phase system can be represented as a 'mixture' of varying sized clusters rather than as a continuum. As QCE theory relies on first-principle simulations and statistical thermodynamics to determine the thermodynamic behavior of a system, appropriate selection of clusters is a crucial step towards achieving accurate predictions. In this study, we use molecular dynamics and ab initio calculations to obtain initial configurations of 400 water clusters, Wn where n = 3 to 10 and contrast their stability using two different criteria. The role of entropy towards cluster stabilization is investigated by comparing the binding (ΔEBIND/mol) and Gibbs free binding energy per molecule (ΔGBIND/mol) of various Wn at 298.15 K. Initial clustersets are constructed by exploring two-, three-, four and five-combinations of clustersets using the minimum ΔGBIND/mol structures of Wn. We also expand the ΔGBIND/mol criteria for Wn of sizes 3 to 7 to include values larger than 0.0 kJ mol−1 and smaller than 3.0 kJ mol−1 as a means of improving thermodynamic predictions. 37 of the 459 resulting clustersets predicted the correct boiling point of water and its thermodynamic properties with an accuracy of 95%. A scaled population-weighted infrared spectrum was compared to experimental results to validate the composition of the top 5 clustersets. The predicted spectra showed an exact match within the low frequency range (<1000 cm−1) with some discrepancy at the high frequency range (>3400 cm−1). This work highlights that ΔGBIND/mol is so far the best criteria to apply when determining an appropriate clusterset for QCE theory. [ABSTRACT FROM AUTHOR]

Mussel‐inspired polycatecholamine coatings and films have proven to be versatile materials for surface modification. However, the progress of chemically modified coatings with tailored properties has been slow due to the lack of definitive evidence of their polymeric structure. Polycatecholamines form aggregates during polymerization, and their formation mechanism has been a subject of debate owing to their insolubility in traditional molecular solvents. Exploiting the capability of ionic liquids (ILs) to exhibit strong electrostatic interactions, herein, the first solution‐phase polymerization approach is reported to achieve polymerization of four catecholamines – dopamine (DA), norepinephrine (NE), L‐3,4‐dihydroxyphenylalanine (L‐DOPA), and adrenaline (AD). Kinetic control over the polymerization process in the solution phase enabled it to follow the process with 1H NMR spectroscopy, revealing the formation of structural features of resulting complex heterogeneous and soluble polymers. The polymers are both covalent and associative in nature. Solution phase polymerization prevented the formation of large aggregates in the solution, thus facilitating the formation of coatings that are ultra‐smooth and have root mean square roughness of the order of sub‐nm to nm scale. [ABSTRACT FROM AUTHOR]

The prediction of physicochemical properties of ionic liquids such as conductivity and melting point would substantially aid the targeted design of ionic liquids for specific applications ranging from solvents for extraction of valuable chemicals to biowaste to electrolytes in alternative energy devices. The previously published study connecting the interaction energies of single ion pairs (1 IP) of ionic liquids to their thermodynamic and transport properties has been extended to larger systems consisting of two ion pairs (2 IPs), in which many-body and same-ion interactions are included. Routinely used cations, of the imidazolium and pyrrolidinium families, were selected in the study coupled with chloride, tetrafluoroborate, and dicyanamide. Their two ion pair clusters were subjected to extensive configuration screening to establish most stable structures. Interaction energies of these clusters were calculated at the spin-ratio scaled MP2 (SRS-MP2) level for the correlation interaction energy, and a newly developed scaled Hartree-Fock method for the rest of energetic contributions to interaction energy. A full geometry screening for each cation-anion combination resulted in 192 unique structures, whose stability was assessed using two criteria—widely used interaction energy and total electronic energy. Furthermore, the ratio of interaction energy to its dispersion component was correlated with experimentally observed melting points in 64 energetically favourable structures. These systems were also used to test the correlation of the dispersion contribution to interaction energy with measured conductivity. [ABSTRACT FROM AUTHOR]

Dinuclear silver formamidinates, [Ag2(DFForm)2(py)2] (1) (DFForm, N , N ′-bis(2,6-difluorophenyl)formamidinate, py = pyridine), [Ag2(m HForm)2(py)3] (2) and [Ag2(m HForm)2(CH3CN)2] (2a) (m HForm, N , N ′-bis(2,3,4,6-tetrafluorophenyl)formamidinate), [Ag2(p HForm)2(py)3] (3) (p HForm, N , N ′-bis(2,3,5,6-tetrafluorophenyl)formamidinate), [Ag2(PFForm)2(py)3] (4) (PFForm, N , N ′-bis(2,3,4,5,6-pentafluorophenyl)formamidinate) and [Ag2(DippForm)2]·1.25CH2Cl2 (5) (DippForm, N , N ′-bis(2,6-diisopropylphenyl)formamidinate), and polynuclear, mainly trinuclear, silver pyrazolates, [Ag3(Ph2pz)3]2 (6) (Ph2pz, 3,5-diphenylpyrazolate), [Ag(t Bu2pz)]4 (7) (t Bu2pz, 3,5-di- tert -butylpyrazolate), [Ag3(PhMepz)3] (8) (PhMepz, 3-methyl-5-phenylpyrazolate), [Ag3(Phtpz)3] (9) (Phtpz, 3-phenyl-5-(2-thienyl)pyrazolate), [Ag3(ttfpz)3] (10) (ttfpz, 3-(2-thienyl)-5-trifluoromethylpyrazolate) and [Ag2(Me2pz)(PPh3)4Cl] (11) (Me2pz, 3,5-dimethylpyrazolate) were successfully synthesized in good yield by treating silver(i) oxide with the corresponding formamidines (FormH) or pyrazoles (pzH) either in pyridine or acetonitrile. These rapid, easily handled and economical reactions are readily monitored by consumption of black silver oxide. All compounds are potential precursors in redox transmetallation reactions in the synthesis of lanthanoid and alkaline earth pyrazolate and formamidinate complexes. Dinuclear silver formamidinates and polynuclear, mainly trinuclear, silver pyrazolates were successfully synthesized in good yield by treating silver(i) oxide with the corresponding formamidines (FormH) or pyrazoles (pzH) either in pyridine or acetonitrile. [ABSTRACT FROM AUTHOR]

A study to examine the role of ionic liquids (ILs) in electrochemical devices is conducted. The ILs is used in electrochemical devices such as solar cells, high energy density batteries, fuel cells and supercapacitors for improving sustainability of energy supply.

A study is conducted to identify and benchmark reliable low-cost theoretical procedures for studying the addition-fragmentation processes in reversible-addition-fragmentation-transfer (RAFT) polymerization is presented. The addition fragmentation reaction in the RAFT polymerization process is a difficult system to model computationally, with lower cost procedures such as ROMP2 and particularly DFT, having large absolute and relative errors for the thermodynamics of some systems.

The accurate calculation of intermolecular interactions is important to our understanding of properties in large molecular systems. The high computational cost of the current "gold standard" method, coupled cluster with singles and doubles and perturbative triples (CCSD(T), limits its application to small- to medium-sized systems. Second-order Møller–Plesset perturbation (MP2) theory is a cheaper alternative for larger systems, although at the expense of its decreased accuracy, especially when treating van der Waals complexes. In this study, a new modification of the spin-component scaled MP2 method was proposed for a wide range of intermolecular complexes including two well-known datasets, S22 and S66, and a large dataset of ionic liquids consisting of 174 single ion pairs, IL174. It was found that the spin ratio, ϵΔs=EOSINT/ESSINT, calculated as the ratio of the opposite-spin component to the same-spin component of the interaction correlation energy fell in the range of 0.1 and 1.6, in contrast to the range of 3–4 usually observed for the ratio of absolute correlation energy, ϵs=EOS/ESS, in individual molecules. Scaled coefficients were found to become negative when the spin ratio fell in close proximity to 1.0, and therefore, the studied intermolecular complexes were divided into two groups: (1) complexes with ϵΔs<<1 and (2) complexes with ϵΔs≥<1. A separate set of coefficients was obtained for both groups. Exclusion of counterpoise correction during scaling was found to produce superior results due to decreased error. Among a series of Dunning's basis sets, cc-pVTZ and cc-pVQZ were found to be the best performing ones, with a mean absolute error of 1.4 kJ mol-1 and maximum errors below 6.2 kJ mol-1. The new modification, spin-ratio scaled second-order Møller–Plesset perturbation, treats both dispersion-driven and hydrogen-bonded complexes equally well, thus validating its robustness with respect to the interaction type ranging from ionic to neutral species at minimal computational cost. [ABSTRACT FROM AUTHOR]

The counterpoise (CP) correction by Boys and Bernardi has been well accepted as a reliable strategy to account for basis set superposition error (BSSE) in intermolecular complexes. The behavior of the CP correction was thoroughly studied in individual molecules of molecular complexes. This work studies the performance of the CP correction in many‐body clusters including three‐body clusters of organic compounds in the 3B‐69 dataset. Additionally, we used crystal structures of polymorphs of benzene, aspirin, and oxalyl dihydrazide (ODH) to construct a many‐body cluster dataset, abbreviated as the MBC‐36 dataset, consisting of two, four and eight molecules, and 16 molecules in the case of benzene. A series of Dunning's basis sets—cc‐pXZ and aug‐cc‐pXZ (X = D and T)—were used to predict CP‐corrected Hartree–Fock (HF) interaction energies of the 3B‐69 and MBC‐36 datasets. The CP‐corrected interaction energies were found to be basis‐set independent, whereas the non‐CP corrected interaction energies were found not to a follow a smooth exponential fitting as previously found for electronic energies of individual molecules. This observation was attributed to the presence of non‐additive induction forces in some clusters. Two 2 × 2 × 2 supercells of benzene polymorphs were constructed to explore the local nature of BSSE effects. A cut‐off radius of 10 Å was demonstrated to be sufficient to fully recover these effects. Although the behavior of CP correction was found to be non‐conventional in many‐body clusters of organic compounds, the use of a small basis set such as cc‐pVDZ showed excellent performance in the prediction of HF interaction energies. [ABSTRACT FROM AUTHOR]

The accuracy of correlation energy recovered by coupled cluster single‐, double‐, and perturbative triple‐excitations, CCSD(T), has led to the method being considered the gold standard of computational chemistry. The application of CCSD(T) has been limited to medium‐sized molecular systems due to its steep scaling with molecular size. The recent development of alternative domain‐based local pair natural orbital coupled‐cluster method, DLPNO‐CCSD(T), has significantly broadened the range of chemical systems to which CCSD(T) level calculations can be applied. Condensed systems such as ionic liquids (ILs) have a large contribution from London dispersion forces of up to 150 kJ mol−1 in large‐scale clusters. Ionic liquids show appreciable charge transfer effects that result in the increased valence orbital delocalization over the entire ionic network, raising the question whether the application of methods based on localized orbitals is reliable for these semi‐Coulombic materials. Here the performance of DLPNO‐CCSD(T) is validated for the prediction of correlation interaction energies of two data sets incorporating single‐ion pairs of protic and aprotic ILs. DLPNO‐CCSD(T) produced results within chemical accuracy with tight parameter settings and a non‐iterative treatment of triple excitations. To achieve spectroscopic accuracy of 1 kJ mol−1, especially for hydrogen‐bonded ILs and those containing halides, the DLPNO settings had to be increased by two orders of magnitude and include the iterative treatment of triple excitations, resulting in a 2.5‐fold increase in computational cost. Two new sets of parameters are put forward to produce the performance of DLPNO‐CCSD(T) within chemical and spectroscopic accuracy. [ABSTRACT FROM AUTHOR]

We test a number of dispersion corrected versatile Generalized Gradient Approximation (GGA) and meta-GGA functionals for their ability to predict the interactions of ionic liquids, and show that most can achieve energies within 1 kcal mol−1 of benchmarks. This compares favorably with an accurate dispersion corrected hybrid, ωB97X-V. Our tests also reveal that PBE (Perdew–Burke–Ernzerhof GGA) calculations using the plane-wave projector augmented wave method and Gaussian Type Orbitals (GTOs) differ by less than 0.6 kJ mol−1 for ionic liquids, despite ions being difficult to evaluate in periodic cells – thus revealing that GTO benchmarks may be used also for plane-wave codes. Finally, the relatively high success of explicit van der Waals density functionals, compared to elemental and ionic dispersion models, suggests that improvements are required for low-cost dispersion correction models of ions. [ABSTRACT FROM AUTHOR]

Suspending crystals of bis(pentafluorophenyl)mercury [Hg(C6F5)2] (1a) in a saturated n-hexane solution for a prolonged period results in transformation into the new polymorph [Hg(C6F5)2] (1 b) monoclinic P21/n, a = 11.7060(3) Å, b = 7.8531(2) Å, c = 13.5429(4) Å, β = 107.247(3)°, V = 1189.00(6) Å3. The C-Hg-C angle in 1 b is 177.10(11)° and the pentafluorophenyl rings are rotated 74.6(1)° to each other in comparison to 1a, the form known for 50+ years, which has a rotation angle of 58.0(2)°. Polymorph 1 b could also be obtained by crystallization from chloroform, or a CHCl3/n-hexane (1:1) mixture at −20 °C, or by seeding with a crystal of 1 b. Theoretical calculations suggest that the barrier to rotation is low. [ABSTRACT FROM AUTHOR]

In this study we investigate the reversibility of the reduction process of three TEMPO derivatives – TEMPOL, 4-cyano-TEMPO, and 4-oxo-TEMPO. The [C2mim][BF4] and [C4mpyr][OTf] ionic liquids (ILs) were used to perform cyclic voltammetry (CV) to analyse the redox potentials of the TEMPO derivatives. The former was previously shown to quench the aminoxy anion of TEMPO through a proton transfer reaction with the cation, whereas the latter supported the irreversibility of the TEMPO reduction process. In CV results on TEMPO derivatives, it was shown that [C4mpyr][OTf] could allow for a high degree of reversibility in the reduction of 4-cyano-TEMPO and a moderate degree of reversibility in the reduction of TEMPOL. In comparison, reduction of 4-cyano-TEMPO was predominantly irreversible in [C2mim][BF4], whilst TEMPOL showed complete irreversibility. 4-Oxo-TEMPO did not show any notable reduction reversibility in either IL tested. Reduction potentials showed little variation between the derivatives and 0.2 V variation between the ILs, with the most negative reduction potential being observed at −1.43 V vs. Fc/Fc+ for TEMPOL in [C4mpyr][OTf]. To explain the varying degrees of reversibility of the reduction process, four types of side reactions involving proton transfer to the aminoxy anion were studied using highly correlated quantum chemical methods. Proton transfer from the IL cation was shown to have the ability to quench all three aminoxy anions depending on the IL used. On average, TEMPOL was shown to be the most susceptible to proton transfer from the IL cation, having an average Gibbs free energy (GFE) of 10.5 kJ mol−1 more negative than that of 4-cyano-TEMPO, which was shown to have the highest GFE of proton transfer. Side reactions between water and aminoxy anions were also seen to have the potential to contribute to degradation of the aminoxy anions tested, with 4-oxo-TEMPO being shown to be the most reactive to degradation with water with a GFE of −12.6 kJ mol−1. 4-Oxo-TEMPO was found to be highly susceptible to self-quenching by its aminoxy anion and radical form with highly negative proton transfer GFEs of −47.9 kJ mol−1 and −57.7 kJ mol−1, respectively. Overall, 4-cyano-TEMPO is recommended as being the most stable of the aminoxy anions tested with TEMPOL, thus providing a viable alternative to improve solubility should the IL be tuned to maximize its stability. [ABSTRACT FROM AUTHOR]

We present an inexpensive and robust theoretical approach based on the fragment molecular orbital methodology and the spin‐ratio scaled second‐order Møller–Plesset perturbation theory to predict the lattice energy of benzene crystals within 2 kJ⋅mol−1. Inspired by the Harrison method to estimate the Madelung constant, the proposed approach calculates the lattice energy as a sum of two‐ and three‐body interaction energies between a reference molecule and the surrounding molecules arranged in a sphere. The lattice energy converges rapidly at a radius of 13 Å. Adding the corrections to account for a higher correlated level of theory and basis set superposition for the Hartree Fock (HF) level produced a lattice energy of −57.5 kJ⋅mol−1 for the benzene crystal structure at 138 K. This estimate is within 1.6 kJ⋅mol−1 off the best theoretical prediction of −55.9 kJ⋅mol−1. We applied this approach to calculate lattice energies of the crystal structures of phase I and phase II—polymorphs of benzene—observed at a higher temperature of 295 K. The stability of these polymorphs was correctly predicted, with phase II being energetically preferred by 3.7 kJ⋅mol−1 over phase I. The proposed approach gives a tremendous potential to predict stability of other molecular crystal polymorphs. [ABSTRACT FROM AUTHOR]

The performance and utility of the contemporary density functional theory (DFT) methods are analyzed for studying the thermodynamics of radical reactions. The results show that these DFT methods are unable to provide accurate analysis of the energetics of these reactions.

The performance of a variety of high-level composite procedures, and lower-cost density functional theory (DFT) and second-order perturbation theory (MP2) based methods, for the prediction of absolute and relative R-X bond dissociation energies was examined for RMe, Et, i-Pr and t-Bu, and X=H, CH3, OCH3, OH and F. The results indicate that the DFT methods considered can show significant systematic errors, and in number of cases fail to reproduce the correct qualitative trends.

Radical stability has been subject to continuous research due to its importance in polymerization as well as in all-organic batteries. Recently, the SOMO–HOMO conversion was identified as the main factor in controlling the stability of distonic radicals, for which the negative charge resides on the same molecule. Based on this finding, the idea of ionic liquids stabilizing radicals was hypothesized in this study. A series of ionic liquids were tested in EPR measurements of the 3-carboxy-2,2,5,5-tetramethyl-pyrroline-1-oxyl. Unusually high rotational diffusion constants (τR), 4 times larger compared to conventional media such as dichloromethane (DCM), were recorded at room temperature. This finding could only be explained by a strong interaction existing between the radical and ionic liquid ions, which was confirmed with quantum chemical calculations, with interaction energies falling between −17.1 kJ mol−1 for tetramethylphosphonium tetrafluoroborate and −85.6 kJ mol−1 for 1,3-dimethylimidazolium triflate. Elevated temperature measurements performed at 80 °C reduced the viscosity of the ionic liquids to that of DCM, while the τR values remained relatively high, thus further confirming that the rotational hindrance occurred due to radical–ionic liquid interactions. The calculated interaction energies between the radical and ionic liquids ions were also found to correlate well with experimental rotational diffusion constants, thus offering us a valuable tool in tailoring ionic liquids for enhanced stability of nitroxide radicals. The findings of this study showcase the ability of ionic liquids to reduce reactivity of nitroxides without the need for any chemical modification of the radical. [ABSTRACT FROM AUTHOR]

A series of dialkylphenylphosphines and their analogous aniline substrates have been metallated with the synergistic mixed‐metal base [(TMEDA)Na(TMP)(CH2SiMe3)Mg(TMP)] 1. Different metallation regioselectivities for the substrates were observed, with predominately lateral or meta‐magnesiated products isolated from solution. Three novel heterobimetallic complexes [(TMEDA)Na(TMP)(CH2PCH3Ph)Mg(TMP)] 2, [(TMEDA)Na(TMP)(m‐C6H4PiPr2)Mg(TMP)] 3 and [(TMEDA)Na(TMP)(m‐C6H4NEt2)Mg(TMP)]  4 and two homometallic complexes [{(TMEDA)Na(EtNC6H5)}2] 5 and [(TMEDA)Na2(TMP)(C6H5PEt)]2 6 derived from homometallic metallation have been crystallographically characterised. Complex 6 is an unprecedented sodium‐amide, sodium‐phosphide hybrid with a rare (NaNNaP)2 ladder motif. These products reveal contrasting heterobimetallic deprotonation with homometallic induced ethene elimination reactivity. Solution studies of metallation mixtures and electrophilic iodine quenching reactions confirmed the metallation sites. In an attempt to rationalise the regioselectivity of the magnesiation reactions the C−H acidities of the six substrates were determined in THF solution using DFT calculations employing the M06‐2X functional and cc‐pVTZ Dunning's basis set. Picky Pnictogen: The first synergistic bimetallic metallation of dialkylphenylphosphines show marked regioselectivity differences from those of analogous anilines, while the separated homometallic components of the bimetallic bases induce ethene elimination in metallating the diethylphenylphosphine and aniline species. [ABSTRACT FROM AUTHOR]

Experimental studies have noted the often surprising and unpredictable effect of ionic liquids as solvents on reaction kinetics for radical polymerisation. We theoretically investigate the energetic and structural effects of ionic liquids, both protic and aprotic, on radical stability, presenting stabilisation of the radical by the ionic liquid by up to −78.0 kJ mol−1. Kinetic data relating to propagating systems for several industrially viable monomers indicate that propagation rates can be increased or decreased (by up to 6 orders of magnitude) depending on the monomer and ionic liquid combination. The interplay of activation entropy and activation enthalpy, much of which depends on hydrogen bonding between the solvent and reactants, play a crucial role in controlling reaction kinetics. It is concluded that the use of cheaper protic ionic liquids as solvents may be viable for improved kinetic control over radical reactions. [ABSTRACT FROM AUTHOR]

Changing the steric bulk on amino-acid substitued naphthalenediimide ligands is shown to dramatically alter their coordination chemistry by changing the preferred conformation of the ligand and hence the structural motifs that assemble. Naphthalenediimide ligands subsituted by glycine (GlyNDI) and aminoisobutyric acid (ibaNDI) have been investigated and contrasted to previous studies using analogous NDI ligands containing chiral amino acids (ααNDIs). Whilst coordination polymers containing ααNDIs form reproducible M2L2 metallomacrocyclic motifs, the materials reported here do not, despite only a small change in the steric bulk of the α-carbon substituents. Changing from N–CHR–CO2− terminii (for ααNDIs) to N–CH2–CO2− (GlyNDI) or N–CMe2–CO2− (ibaNDI) acts to reduce or increase the steric bulk immediately around the α-carbon, respectively. Seven coordination polymers containing GlyNDI (1–7) indicate a preference for the ligands to be closely packed in a parallel manner, and three coordination polymers containing ibaNDI (8–10) show interactions occuring between the NDI cores in a more perpendicular manner; none display the same motif that is observed for the vast majority of previously reported ααNDI-based materials. The reported GlyNDI and ibaNDI coordination polymers include attempts to force formation of macrocycles by forming rotaxane or catenane motifs using co-ligands. Computational studies, and structural comparisons, show that GlyNDI, ibaNDI and ααNDIs adopt different conformations of the carboxylate groups with respect to the NDI core, with the crystallographically observed conformations matching minimised geometries. These conformational differences are a property of the molecule and are not enforced by solid-state packing, showing that small steric changes can have subtle effects on molecular geometry that are observed as pronounced effects in crystal engineering. The previously used ααNDI ligands are therefore shown to have steric demands that are neither too great nor too small, and therefore occupy a ‘Goldilocks zone’ for the formation of a macrocyclic motif. [ABSTRACT FROM AUTHOR]

A diverse range of molecular surfactants and polymers have been incorporated into aqueous graphene oxide (GO) and reduced graphene oxide (rGO) dispersions in order to understand the complex relationship between surface chemistry, surface forces and interfacial thermodynamics of these materials with typical amphiphiles. Surfactant additives were systematically varied in terms of their charge and hydrophobicity to reveal important structure–function relationships affecting adsorption and interaction with GO and rGO surfaces. Small-angle (and ultra small-angle) neutron scattering was employed to examine and monitor the interactions and self-assembly in each system. Charge was found to be the overriding factor driving adsorption, as cationic surfactants very readily adsorbed to both GO and rGO, whereas anionic surfactants gave little to no evidence of adsorption despite possessing hydrophobic tail-groups. Molecules of neutral charge such as nonionic and zwitterionic surfactants as well as neutral polymers also showed strong affinities for GO and rGO, indicating that dispersion and dipole (induction polarisation) interactions also play a significant role in adsorption with these materials. Modelling the neutron data revealed in many cases a q−2 slope in the low q and ultra low q regions, indicating that scattering was occurring from large, flat surfaces (lamellae or bilayers), suggesting an effective flattening of the sheets in dispersion. The results presented thus help to form a roadmap for the behaviour of GO and rGO with surfactants and polymers, relevant to adsorption, stabilisation, formulation and coating in aqueous environments as adsorbent and functional materials. [ABSTRACT FROM AUTHOR]

Abstract: The photodecomposition mechanism of trans,trans,trans‐[Pt(N3)2(OH)2(py)2] (1, py=pyridine), an anticancer prodrug candidate, was probed using complementary Attenuated Total Reflection Fourier Transform Infrared (ATR‐FTIR), transient electronic absorption, and UV/Vis spectroscopy. Data fitting using Principal Component Analysis (PCA) and Multi‐Curve Resolution Alternating Least Squares, suggests the formation of a trans‐[Pt(N3)(py)2(OH/H2O)] intermediate and trans‐[Pt(py)2(OH/H2O)2] as the final product upon 420 nm irradiation of 1 in water. Rapid disappearance of the hydroxido ligand stretching vibration upon irradiation is correlated with a −10 cm−1 shift to the antisymmetric azido vibration, suggesting a possible second intermediate. Experimental proof of subsequent dissociation of azido ligands from platinum is presented, in which at least one hydroxyl radical is formed in the reduction of PtIV to PtII. Additionally, the photoinduced reaction of 1 with the nucleotide 5′‐guanosine monophosphate (5′‐GMP) was comprehensively studied, and the identity of key photoproducts was assigned with the help of ATR‐FTIR spectroscopy, mass spectrometry, and density functional theory calculations. The identification of marker bands for some of these photoproducts (e.g., trans‐[Pt(N3)(py)2(5′‐GMP)] and trans‐[Pt(py)2(5′‐GMP)2]) will aid elucidation of the chemical and biological mechanism of anticancer action of 1. In general, these studies demonstrate the potential of vibrational spectroscopic techniques as promising tools for studying such metal complexes. [ABSTRACT FROM AUTHOR]

Abstract: The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal–organic framework [Cu3(cdm)4] (cdm=C(CN)2(CONH2)−) were explored in detail by using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged “lattice‐fence” mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore‐size metrics clearly illustrate the potential for temperature‐mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu3(cdm)4] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response. [ABSTRACT FROM AUTHOR]

Cellulose acetate (CA) is a resin derived from biomass. In addition to its various superior properties, CA is preferable to existing petroleum-derived resins from the viewpoint of green chemistry. Therefore, the acetylation of cellulose is one of the most important subjects in cellulose research. In this study, we found that the acetylation of cellulose could proceed in some protic ionic liquids (PILs) composed of amidine and acetic acid with ΔpKa = ca. 8.4–8.7 under mild conditions without any catalyst. The degree of substitution (DS) of the produced CA was above 1.84, and the maximum DS was 2.87 when the ΔpKa of the PIL was about 8.5. In propionate-based PILs, cellulose was not only acetylated but also propionated; however, the cellulose acetylation did not occur in formate-based PILs. It was revealed that the esterification of cellulose proceeded through the anion exchange between carboxylic anhydride and anion species of the PIL. [ABSTRACT FROM AUTHOR]

Accurate prediction of intermolecular interactions plays a pivotal role in many areas of chemistry and biology including (but not limited to) the design of pharmaceuticals, solid electrolytes and food additives. Here we present the application of the recently developed spin-ratio scaled MP2 method (termed SRS-MP2) to six different datasets covering a wide range of interaction types from strong hydrogen bonding to van der Waals dispersion and π–π stacking. The method achieves a remarkably low mean absolute error of 1.6 kJ mol−1 across all interaction types including semi-Coulombic systems such as organic ionic salts. The new SRS-MP2 method offers high level of accuracy for studying intermolecular interactions commonly found in molecular systems of chemical and biological relevance without the need for including additional terms in the formulation. This finding represents a new paradigm in the development of wavefunction-based methods for intermolecular interactions. [ABSTRACT FROM AUTHOR]

Synthesis and crystallographic and spectroscopic structural characterization, along with spectral band assignments calculated by using density functional theory (M06L/cc-pVDZ and B3LYP/6-31G(d)), are reported for Fe(OEP)picrate as a model for hemozoin (malaria pigment) and its synthetic analog β-hematin, which are spectroscopically identical. The average Fe-N distance, 2.044(12) Å, and the Raman modes indicate a high-spin five-coordinate iron(III) complex. Resonance enhancement is observed for the totally symmetric oxidation state marker band ν4 along with the characteristic bands of C β-substituted hemes in the ranges of 1621-1639 cm−1 for νas(C αC m) and 750-756 cm−1 for ν(pyr breathing) similar to β-hematin and hemozoin when using near-IR excitation wavelengths. The similarity of the resonance Raman spectral profiles for Fe(OEP)picrate and β-hematin, along with the structural results, indicates that Fe(OEP)picrate is an excellent model for understanding the stereochemistry and intermolecular interaction of β-hematin. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recent thermal runaways in lithium-ion batteries have reinforced the focus on the research of safer electrolytes based on ionic liquids. A simple switch from organic solvents to ionic liquids has been proven difficult due to the decreased efficiency of batteries caused by decreased conductivity and increased viscosity of ionic liquids upon addition of lithium salts. The new trend in replacing lithium salts with a cheaper alternative, sodium salts, has resulted in rather poor solubility of sodium salts in commonly used ionic liquids. This phenomenon has been left largely unexplained. Herein, we present a high-level quantum chemical study of the chemical bonding of lithium and sodium salts coupled with ionic liquid anions. Due to their proximity to the anion, the 1s2 electrons on the lithium cation are found to become strongly polarized by the presence of the anion such that they start participating in the bonding, making it more covalent than originally thought. In sodium salts the 2s2 orbitals are rather removed from the anion, making its influence weaker. This polarization results in 90 kJ mol−1 of difference in the interaction magnitude between lithium and sodium salts. Theoretical results have confirmed that increasing covalency in lithium salts results in their excellent solubility since these dissolve as ion-paired complexes. The downside of this ability is decreased conductivity as lithium salts are unlikely to easily dissociate in ionic liquids. Sodium salts are shown to maintain a high degree of ionicity, thus decreasing their chances of being solvated by ionic liquids as a result of their low concentration of ions per unit volume. The theoretical results are further underpinned by solubility studies of MX salts, where M = Li or Na and X = bis(trifluoromethylsulfonyl)imide (NTf2), BF4− or PF6−, conducted in six different ionic liquids. Lithium salts consisting of BF4− or PF6− exhibited significantly better solubility than their sodium analogues by at least an order of magnitude. The findings of this work will have implications on the future direction of the development of safe electrolytes for lithium and sodium-ion secondary batteries. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) has been widely used to elucidate the bulk structure of ionic liquids. In this work, we calculated 1H NMR chemical shifts of 1-ethyl-3-methylimidazolium (C2mim+) ionic liquids combined with various anions such as chloride (Cl), tetrafluoroborate (BF4), hexafluorophosphate (PF6), acetate (OAc), trifluoroacetate (TFA), and dicyanamide (DCA). The previously established level of theory, HF/6-311G+(3df,2p), was used for the accurate prediction of NMR chemical shifts both in gas phase and in solvents with varying dielectric constant such as CHCl3 and ethanol. The following factors affecting the predicted proton chemical shifts were considered. Firstly, ionic clusters consisting of 2, 8 and 16 ion pairs were optimized to model interionic interactions present in the bulk of ionic liquids. In larger clusters the distribution of the calculated chemical shifts of individual protons in the C2mim+ cation was examined with respect to the position of the cation in the cluster. We further confirmed that electronic properties of ionic liquids such as magnetic shielding had local nature, thus allowing us to accurately predict proton NMR chemical shifts of ionic liquids from relatively small-sized clusters. Secondly, solvent effects in single ion pairs as well as larger ionic clusters were accounted through a Conductor-like Polarisable Continuum Model (CPCM). Solvent effects generated through a dielectric constant of either chloroform or ethanol were found to be important in single ion pairs due to improved description of interionic distances. With increasing cluster size the difference between gas-phase and CPCM optimized structures became minimal, thus resulting in similar values for calculated 1H NMR chemical shifts. We also established that the model size that produced the best results for imidazolium ionic liquids strongly depended on the anion type. Strongly coordinating anions such as chloride and acetate require calculations of clusters consisting of at least 8 ion pairs, whereas weakly coordinating anions produce excellent accuracy for single ion pairs optimized in the presence of solvent. The polarity of the solvent was found to play a minor role. [ABSTRACT FROM AUTHOR]

The accurate prediction of physicochemical properties of condensed systems is a longstanding goal of theoretical (quantum) chemistry. Ionic liquids comprising entirely of ions provide a unique challenge in this respect due to the diverse chemical nature of available ions and the complex interplay of intermolecular interactions among them, thus resulting in the wide variability of physicochemical properties, such as thermodynamic, transport, and spectroscopic properties. It is well understood that intermolecular forces are directly linked to physicochemical properties of condensed systems, and therefore, an understanding of this relationship would greatly aid in the design and synthesis of functionalized materials with tailored properties for an application at hand. This review aims to give an overview of how electronic structure properties obtained from quantum chemical methods such as interaction/binding energy and its fundamental components, dipole moment, polarizability, and orbital energies, can help shed light on the energetic, physical, and spectroscopic properties of semi-Coulomb systems such as ionic liquids. Particular emphasis is given to the prediction of their thermodynamic, transport, spectroscopic, and solubilizing properties. [ABSTRACT FROM AUTHOR]