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The cocrystals (CH3)3As·C6F5I (1) and (CH3)3Sb·C6F5I (2) were generated in situ from equimolar mixtures of their components. 1 and 2 show very close I⋯As and I⋯Sb directional intermolecular interactions. They are 0.5 and 0.7 Å shorter than the sums of van der Waals radii, respectively, and are the shortest C–I⋯As and C–I⋯Sb halogen bonds of this type found for experimentally characterized molecular (co)crystals. Comparisons of the packing motifs and contacts in 1 and 2 with those in (CH3)3As (3), (CH3)3Sb (4) and C6F5I (5) illustrate the occurrence and hierarchy of the specific interactions. The heteromolecular components in 1 and 2 are assembled by I⋯As, I⋯Sb and F⋯H interactions. There are no significant intermolecular As⋯As contacts in 3, but Sb⋯Sb interactions in 4. Molecules in 5 are mainly associated by I⋯F, F⋯F and F⋯C contacts. The intermolecular interactions observed in the (co)crystals correspond to the calculated electrostatic potentials.

This work shows a detailed study of the synthesis, structural characterization, electrical, thermal, and mechanical luminescent behavior of one-dimensional coordination polymer formed by a Cu(I)-I double chain, using 2-amino-4 chloropyrimidine as ligand. The asymmetric structure of double chain type [Cu(L)I]n, (L= 2-amino-4-chloropyrimidine (aCLpym)) with Cu-Cu distances shorter than the sum of the van der Waals radii of two copper atoms, and the substantial flexibility of this structure are crucial to understanding its optoelectronic behavior. The electrical conductivity values at 295 K are in agreement with a possible semiconductor behavior. Additionally, the luminescence properties of this coordination polymer (CP) are characterized at ambient conditions (ambient pressure (AP) and 295 K) by a non-symmetric High Energy (HE) band centered at 465 nm, tentatively assigned to a mixed 3(I+M)LCT. The intensity of the emission increase lowering the temperature. A structural contraction can explain this behaviour, clearly observed when solving the structures employing single-crystal X-ray diffraction of the compound at 296 K and 110 K. A strong mechanochromic behavior was observed when hydrostatic pressure is applied, with the appearance of an additional Low Energy (LE) band around 650 nm, which for this kind of CuI CPs is typically associated with transitions in the CuI cluster-core, involving 3IMCT and clustered centered 3d10→3d94s1 (3MCC) states. This latter because of the shortening with the pressure of the Cu-Cu distances below the Van der Waals limit. Moreover, the study of the mechanochromic behavior versus pressure exerted by grinding shows a decrease in the intensity of the emission due to the increase in the number of defects and decrease in the particle size

Sub-nanometer armchair graphene nanoribbons (GNRs) with moderate band gap have great potential towards novel nanodevices. GNRs can be synthesized in the confined tubular space of single-walled carbon nanotubes (SWCNTs), in which precursor molecules have been specifically designed to form the GNRs with certain width and edge. However, it is still unexplored how the diameter and metallicity of SWCNTs influence the synthesis of the GNRs. Herein, we applied a series of SWCNTs with different average diameters to study the diameter-dependent synthesis of GNRs. By using Raman spectroscopy and transmission electron microscopy, we found that the width of the GNRs can be tailored by the diameter of the SWCNTs. Especially, the SWCNTs with average diameter of 1.3 nm produced 6 and 7 armchair GNRs with the highest yield, which can be well explained by considering the width of the GNRs and van der Waals radius of hydrogen and carbon atoms. In addition, semiconducting and metallic SWCNTs produced GNRs with different yields, which could attribute to different diameter distributions and density of defects. These results enable the possibility of a high-yield production of certain armchair graphene nanoribbons in large scale, which would benefit future applications as semiconductor with sub-nanometer in width.

The transition from weak (noncovalent) interactions to fully developed covalent bonds is examined using the quantum theory of atoms in molecules in a series of halogen-bonded (XB) complexes of bromosubstituted electrophiles, RBr, with 1,4-diazabicyclo[2.2.2]octane (DABCO) and Cl– and Br– anions. The gradual decrease in the XB lengths in these associations, dBr···Y (where Y = Cl–, Br–, or N), was accompanied by the exponential increase in the binding energies and charge transfer, as well as electron densities and magnitudes of the kinetic and potential energy densities at the bond critical points (BCPs) on the Br···Y bond path. These indices, as well as characteristics of the adjacent bonds in the XB donor, followed remarkably close trend lines when plotted against the normalized XB length RBrY = dBr···Y/(rBr + rY) (where rBr and rY are the van der Waals radii) regardless of the methods [MP2/6-311+G(d,p) or M062X/6-311+G(d,p)], media (gas phase or dichloromethane), and nucleophiles (Cl–, Br–, or DABCO). In the systems with an RBrY higher than about 0.78, the energy densities H(r) at BCPs at the Br···Y bond path were small and positive, and XBs did not substantially affect the characteristics of the adjacent R–Br covalent bond in the XB donor. Accordingly, the XB can be identified as noncovalent in this range. In the complexes with RBrY values between about 0.67 and 0.78, energy densities H(r) at Br···Y BCPs were negative, and their magnitudes increased with the decrease in the Br···Y separation. In this range, formation of XBs was accompanied by the increase in the R–Br bond length in the XB donor and the decrease in the magnitude of the (negative) H(r) values at the BCPs of the R–Br bonds. XBs can be classified as partially covalent in this RBrY range. At an RBrY less than about 0.67, electron densities were larger, and energy densities were more negative at BCPs of the Br···Y bond than those at BCPs of the R–Br bond in the XB donor. This indicates that Br···Y bonds were stronger than R–Br bonds, and these (Br···Y) XBs can be regarded as essentially covalent. The synchronous change of a variety of (R–Br and Br···Y) bonding characteristics with RBrY suggests that the normalized XB bond length can be used as a basic parameter in the identification of the type of intermolecular interaction. A continuity of these characteristics suggests an inherent relationship between limiting (covalent and noncovalent) types of XBs and thus an onset of molecular–orbital interactions in the weaker bonds.

Iako se u školi uče iznosi ionskih, van der Waalsovih i kovalentnih radijusa, ne uči se što oni zapravo jesu – školske definicije prikrivaju njihovu pravu, kvantnomehaničku prirodu. U radu je ispitano značenje definicija veličine atoma te opisan njihov izvod: iz elektronske gustoće (povezane s funkcijom koju zovemo atomskom orbitalom), iz duljine kovalentne veze i položaja jezgara, iz prvog virijalnog koeficijenta jednadžbe realnog plina te Lennard-Jonesova potencijala (van der Waalsov radijus). Iz navedenog se vidi da se veličina atoma ne može jednoznačno definirati ili, točnije, da se ne može govoriti o veličini atoma na isti način na koji se govori o veličini makroskopskih objekata. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., Despite the fact that atomic, i.e. Van der Waals, ionic, and covalent radii are commonplace in chemical textbooks, their real, quantum-mechanical nature is blurred by simplified scholar definitions. The size of an atom may be defined, and calculated, in many ways (from atomic orbital density, bond lengths, microwave spectra, virial coefficient, Lennard-Jones potential), but whatever is calculated, or defined, the obtained value cannot be properly compared to the size of a macroscopic object. This paper stresses the need that students understand the real nature of quantum-chemical models, and not confuse various representations of molecular structure (molecular models) with the real atoms and molecules. This work is licensed under a Creative Commons Attribution 4.0 International License.

Cone and distance-cone corrected statistical analyses have been performed on X-C⋅⋅⋅O (X=H, B, C, N, O and F; the C atom is sp2 and sp3 hybridized) tetrel bonds. The sp3 -C and sp2 -C prefer to form the interactions through σ-hole (∠XCO≈180°) and π-hole (∠XCO≈90°), respectively. With the increase in electronegativity of X, the preference for the particular angles of the respective geometries increases and the C⋅⋅⋅O distance becomes shorter. The angular preference is found to be more prominent in the cases of π-hole interactions than that in the σ-hole interactions. A similar distance-cone corrected statistical analysis on O=C⋅⋅⋅O interaction also suggests that the preferred ∠OCO angle is ∼90° and the preferred C⋅⋅⋅O distance is around the sum of van der Waals radii (3.22 A) of the C and O atoms. However, a cone-corrected statistical analysis on X-Si⋅⋅⋅O interactions suggests that the preference for linearity in this case is much higher than that for the X-C⋅⋅⋅O σ-hole interactions.

Alloying elements can pronouncedly change the mechanical properties of intermetallic compounds. However, the effect mechanism of this in Mg2Si alloys is not clear yet. In this paper, systematic first-principles calculations were performed to investigate the effect of alloying elements on the ductility of Mg-Si alloys. It was found that some alloying elements such as In, Cu, Pd, etc. could improve the ductility of Mg2Si alloys. Moreover, the interatomic bonding mechanisms were analyzed through the electron localization functional. Simultaneously, the machine-learning method was employed to help identify the most important features associated with the toughening mechanisms. It shows that the ground state atomic volume (VGS) is strongly related to the stacking fault energy (γus) of Mg2Si alloys. Interestingly, the alloying elements with appropriate VGS and higher Allred-Rochow electronegativity (En) would reduce the γus in the Mg-Si-X system and yield a better ductility. This work demonstrates how a fundamental theoretical understanding at the atomic and electronic levels can rationalize the mechanical properties of Mg2Si alloys at a macroscopic scale.

Halogen bonding is a flourishing field of research, but has for long been little recognized. The same goes for its scientific hero, Odd Hassel, who laid the foundations for all current developments. The crystallographic observation of halogen−oxygen interatomic distances shorter than the sum of the van der Waals radii of the involved atoms, and the interpretation of this phenomenon as a charge-transfer interaction, have been ground-breaking. Today, charge-transfer to a polarized halogen is not any longer seen as “odd”, but is commonly referred to as halogen bonding, and is widely exploited in chemistry. Despite the recognition of Hassel's work with a Nobel prize in 1969, surprisingly little appreciation is given to date to the devoted scientist, who established a world-leading laboratory during one of the darkest eras of history. Herein, we wish to revive the legacy and highlight the impact of Odd Hassel's ground-breaking discoveries.

Circularly polarized luminescence (CPL) enables promising applications in asymmetric photonics. However, the performances of CPL molecules do not yet meet the requirements of these applications. The shortcoming originates from the trade-off in CPL between the photoluminescence quantum yield (PLQY) and the photoluminescence dissymmetry factor (gPL). In this study, we developed a molecular strategy to circumvent this trade-off. Our approach takes advantage of the strong propensity of [Pt(N^C^N)Cl], where the N^C^N ligand is 1-(2-oxazoline)-3-(2-pyridyl)phenylate, to form face-to-face stacks. We introduced chiral substituents, including (S)-methyl, (R)- and (S)-isopropyl, and (S)-indanyl groups, into the ligand framework. This asymmetric control induces torsional displacements that give homohelical stacks of the Pt(II) complexes. X-ray single-crystal structure analyses for the (S)-isopropyl Pt(II) complex reveal the formation of a homohelical dimer with a Pt···Pt distance of 3.48 A, which is less than the sum of the van der Waals radii of Pt. This helical stack elicits the metal-metal-to-ligand charge-transfer (MMLCT) transition that exhibits strong chiroptical activity due to the electric transition moment making an acute angle to the magnetic transition moment. The PLQY and gPL values of the MMLCT phosphorescence emission of the (S)-isopropyl Pt(II) complex are 0.49 and 8.4 × 10-4, which are improved by factors of ca. 6 and 4, respectively, relative to the values of the unimolecular emission (PLQY, 0.078; gPL, 2.4 × 10-4). Our photophysical measurements for the systematically controlled Pt(II) complexes reveal that the CPL amplifications depend on the chiral substituent. Our investigations also indicate that excimers are not responsible for the enhanced chiroptical activity. To demonstrate the effectiveness of our approach, organic electroluminescence devices were fabricated. The MMLCT emission devices were found to exhibit simultaneous enhancements in the external quantum efficiency (EQE, 9.7%) and the electroluminescence dissymmetry factor (gEL, 1.2 × 10-4) over the unimolecular emission devices (EQE, 5.8%; gEL, 0.3 × 10-4). These results demonstrate the usefulness of using the chiroptically active MMLCT emission for achieving an amplified CPL.

The conformational properties of 2'-fluoro-substituted acetophenone derivatives were elucidated based on Hα-F and Cα-F through-space spin-spin couplings (TS-couplings), which occur between two atoms constrained at a distance smaller than the sum of their van der Waals radii. This study revealed that 2'-fluoro-substituted acetophenone derivatives in solutions form exclusively s-trans conformers by analyzing their NMR spectra focused on the TS-couplings. The magnitudes of the coupling constants 5J (Hα, F) and 4J (Cα, F) correlate linearly with the value of the dielectric constant of the solvents. Furthermore, s-trans conformations of the two derivatives were confirmed by X-ray crystallographic analysis. These conformational preferences were consistent with the DFT calculations. The s-cis conformer, in which fluorine and oxygen atoms lie in a syn-periplanar mode, may be subject to strong repulsion between the two polar atoms and become unstable. The s-trans preference of the 2'-fluoro-substituted acetophenone derivatives may be utilized in drug design.

High-pressure X-ray and neutron diffraction analyses of an ambient-pressure phase (AP) and two high-pressure phases (HP1 and HP2) of ammonia borane (i.e., NH3BH3 and ND3BD3) were conducted to investigate the relationship between their crystal structures and dihydrogen bonds. It was confirmed that the hydrogen atoms in AP formed dihydrogen bonds between adjacent molecules, and the H-H distance between the hydrogen atoms forming this interaction was shorter than 2.4 A, which was nearly 2 times larger than the van der Waals radius of hydrogen. In the case of half of the hydrogen bonds, a phase transition from AP to the first high-pressure phase (HP1) at ∼1.2 GPa resulted in an increase in the H-H distances, which suggested that the dihydrogen bonds were broken. However, when HP1 was further pressurized to ∼4 GPa, all of the H-H distances became shorter than 2.4 A again, which implied the occurrence of pressure-induced re-formation of the dihydrogen bonds. It was speculated that the re-formation was consistent with a second-order phase transition suggested in previous studies by Raman spectroscopy and X-ray diffraction measurement. Furthermore, at ∼11 GPa, HP1 transformed to the second high-pressure phase (HP2), and its structure was determined to be P21 (Z = 2). In this phase transition, the inclination of the molecule axis became larger, and the number of types of dihydrogen bonds increased from 6 to 11. At 18.9 GPa, which was close to the upper pressure limit of HP2, the shortest dihydrogen bond decreased to ∼1.65 A. Additionally, the X-ray diffraction results suggested another phase transition to the third high-pressure phase (HP3) at ∼20 GPa. The outcomes of this study confirmed experimentally for the first time that the structural change under pressure causes the breakage and re-formation of the dihydrogen bonds of NH3BH3.

Reactions of (η4-benzylideneacetone)Fe(CO)3 and the α,ω-diphosphines Ar2P(CH2)nPAr2 afford the trigonal bipyramidal diiron tetraphosphorus complexes trans,trans-(CO)3Fe[Ar2P(CH2)nPAr2]2Fe(CO)3 (n/Ar = 3/Ph 3, 4/Ph 4a, 4/p-tol 4b; 56-19%). Crystal structures establish essentially parallel P-Fe-P axes, iron-iron distances of 5.894(9)-5.782(1) A (3) and 6.403(1)-6.466(1) A (4a,b), and van der Waals radii of 4.45 A for the Fe(CO)3 rotators, the planes of which are offset by 0.029-1.665 A. Analogous reactions of Ph2P(CH2)6PPh2 yield the square pyramidal monoiron complex trans-(CO)3Fe[Ph2P(CH2)6PPh2] (6', 31%), a rare case where a diphosphine spans trans basal positions (∠P-Fe-P 147.4(2)°). Both 3 and 6' exhibit two CO 13C NMR signals at room temperature, indicating slow exchange on the NMR time scale, which in the former could entail Fe(CO)3/Fe(CO)3 gearing. Under analogous conditions, 4a,b exhibit one signal. Previously reported adducts of Fe(CO)3 and Ph2P(CH2)nPPh2 are surveyed (1:1, n = 1-5; 2:2, n = 5), and the IR νC≡O band patterns and energies of all complexes analyzed with the aid of DFT calculations. The diiron complexes are preferred thermodynamically. Attention is given to limiting types of Fe(CO)3/Fe(CO)3 interactions in the diiron complexes.

A widely used criterion for the existence of a noncovalent interaction is that the interatomic separation be less than the sum of the van der Waals radii of the respective atoms. However, this criterion should not be applied rigidly, but rather with considerable caution and flexibility, for several reasons. First, there is considerable uncertainty in the values assigned as van der Waals radii. Second, because of the manner in which they are assigned, their sums will necessarily miss a significant number of noncovalent interactions. Finally, not all interactions are between atoms; sometimes, instead of an atom, it is a region of positive or negative electrostatic potential that is involved.

The chirality feature of C1 and C3 boron subphthalocyanines (BsubPcs) is an attractive property in material science and supramolecular chemistry. Normally in the field, enantiomeric mixtures are separated through a standard process. The goal of this study was to determine if the mixture of BsubPc enantiomers could form a mixed alloyed composition in the solid state, which is very relevant to their potential application in the organic electronic field. We present the synthesis and physical characteristics of a selection of four chiral BsubPc mixtures. These BsubPcs are specifically trichlorinated and trifluorinated in the periphery, such as Cl-βF3BsubPc, Cl-αF3BsubPc, Cl-βCl3BsubPc and Cl-αCl3BsubPc. The isomeric (C1/C3) ratios of each BsubPc were determined by NMR. Single-crystal XRD of all four BsubPc mixtures showed that the C1 and C3 isomers co-crystallized within their respective lattices forming solid-state mixed alloyed compositions. The structures of Cl-αF3BsubPc and Cl-βF3BsubPc crystallized in the same lattice as Cl-BsubPc, with some expansion of the unit cell volume, while the trichlorinated BsubPcs did not due to the large van der Waals radii of the chlorine atoms. This set of mixed alloyed BsubPcs was also integrated into organic solar cells/photovoltaics (OSCs/OPVs) as both non-fullerene electron acceptors and as electron donors. It was confirmed that these BsubPc isomers/enantiomers are applicable in OPVs as mixed alloyed compositions, with more promising functionality as non-fullerene electron acceptors given their significant contribution to the EQE spectra. Further molecular engineering of these materials will be made to enhance their OPV performance and to explore their bifunctional charge carrier mobility roles.

4-(Tetradecyloxy)phenacyl thiocyanate NCS—CH2—C(O)—C6H4—OC14H29 was studied by differential scanning calorimetry (DSC) and X-ray diffraction. According to the DSC analysis, this compound does not form a mesophase upon melting or cooling of the isotropic melt. The crystal-I—crystal-II phase transition with a small enthalpy, which is not accompanied by mechanical degradation of the crystal, occurs at 68.8 °C prior to the melting of the crystals (82.5 °C). The crystal and molecular structure of the compound was studied by X-ray diffraction at temperatures below (22 °C) and above (73 °C) the temperature of the phase transition in the crystal. Both crystalline phases have nearly identical structures. The crystal packing consists of alternating loosely packed aliphatic and closely packed aromatic regions, which is typical of crystals of mesomorphic compounds. In the aromatic regions of the crystal packing, there are intermolecular S…S contacts. In the low-temperature phase crystal-I, the S…S distances equal to 3.458 A correspond to a non-covalent interaction, through which the molecules are linked into centrosymmetric dimers. In the high-temperature phase, the S…S distances are increased to 3.623 A, which corresponds to twice the van der Waals radius of sulfur. The absence of mesomorphism in the compound is attributed to the fact that, upon heating, the crystal undergoes a transition to another phase, which contains no structural elements responsible for the structuring of the melt.

To access the applications of a conformationally flexible molecule, thorough understanding of even the weak contributors to a particular conformation is necessary. We have synthesized and X-ray characterized a series of six diaryl-substituted heteroarenes in order to analyze the role of unconventional intramolecular CAr–H⋯N/O vs. conventional H-bonds on the preferred planar geometry of such molecules. The distance well below the sum of van der Waals radii in their solid state structures indicated the existence of intramolecular CAr–H⋯N/O interactions. Consequently, the theoretical study was carried out to analyze the energies associated to each of these bonds using the quantum theory of “atoms-in-molecules” (QTAIM) and also the NCI plot. The results indicate that the unconventional C–H⋯O H-bonds involving aromatic H-atoms and the O-atoms of o-methoxy or o-hydroxy substituents in 2, 3a and 3b despite being weaker (dissociation energies around 3–5 kcal mol−1) are relevant and contributing to their planar geometry along with various other factors. However, the electronic repulsion between the lone pair of the nitrogen/oxygen atoms and the neighboring π cloud in these molecules likely contributes more to their preferred planar conformation.

In the present investigation, we compare the host and selectivity behaviour of two compounds, namely α,α-diphenyl-9,10-dihydro-9,10-ethanoanthracene-11-methanol H1 and α,α-bis(p-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11-methanol H2, when recrystallized from both singular and mixed isomers comprising the xylenes (o-Xy, m-Xy and p-Xy) and ethylbenzene (EB) as potential guest solvents. H1 formed a complex with o-Xy alone in the single solvent experiments, while H2 included all four of these aromatic compounds. In equimolar guest competition experiments, H1 only crystallized from binary mixtures where o-Xy was present, and high selectivities for this guest were observed in these instances (84.5–93.7%). The other binary mixtures ultimately presented as gels, and H1 therefore failed to crystallize from these. In fact, this was true also for all ternary and quaternary experiments with H1, even when o-Xy was present. H2, on the other hand, consistently formed mixed complexes from all of the solutions employed. However, its selectivity for any particular guest was unremarkable. Guest/guest competition experiments using both equimolar and non-equimolar mixtures revealed that H1 may be employed to purify o-Xy/m-Xy, o-Xy/p-Xy and o-Xy/EB binary mixtures, especially when these solutions comprised 50% or more o-Xy (these experiments all favoured o-Xy). SCXRD analyses were employed to understand the moderate preference of H2 for o-Xy: only this guest was involved in contacts with the host compound, two in number, that measured significantly less than the sum of the van der Waals radii of the atoms involved. Additionally, Hirshfeld surface investigations showed that H2, through its chlorine atoms, was involved in the greater number of contacts with the preferred o-Xy guest compound. Thermal analyses, however, proved less useful in understanding these selectivity data.

A hexacationic cage 36+ was synthesized via hydrazone condensation in aqueous acid. Cage 36+ bears three biscationic arms, each of which contains four relatively acidic protons, including one NH and three CH protons. These hydrogen bond donors, as well as its intrinsic cationic nature, enable cage 36+ to encapsulate two anions concurrently within its cavity. The axial asymmetrical nature of the biscationic arms allow the cage to recognize two different anions in a selective manner, to encompass bound heteroanion dimers, such as Cl-·NO3- and Cl-·Br-. Single crystal X-ray diffraction analyses reveal that in the solid state the two anions are constrained in ultraclose proximity within the cage; e.g., the Cl-···Cl- and Cl-···Br- distances are 3.2 and 2.9 A, respectively, which are shorter than the sum of their van der Waals radii. Evidence consistent with the sequential binding of two identical or disparate anions in CD3CN is also presented.

Weakly or "partially" bonded molecules are an important link between the chemical and van der Waals interactions. Molecular structures of six new SbBr3-Py complexes in the solid state have been determined by single-crystal X-ray diffraction analysis. In all complexes all Sb atoms adopt a pseudo-octahedral coordination geometry which is completed by additional Sb center dot center dot center dot Br contacts shorter than the sum of the van der Waals radii, with Br-Sb center dot center dot center dot Br angles close to 180 degrees. To reveal the nature of Sb-Br and Sb-N interactions, the DFT calculations were performed followed by the analysis of the electrostatic potentials, the orbital interactions and the topological analysis. Based on Natural Bond Orbital (NBO) analysis, the Sb-Br interactions range from the covalent bonds to the pnictogen bonds. A simple structural parameter, non-covalence criterion (NCC) is defined as a ratio of the atom-atom distance to the linear combination of sums of covalent and van der Waals radii. NCC correlates with E(2) values for Sb-N, Sb-Cl and Sb-Br bonds, and appears to be useful criterion for a preliminary evaluation of the bonding situation.

The phosphino‐stibine ligands (o‐PPh2C6H4)2SbR [R = o‐PPh2C6H4 (L1), Ph (L2), Cl (L3)] were incorporated into tungsten and molybdenum carbonyl complexes leading to the formation of cis‐[W(CO)4{(o‐PPh2C6H4)2SbR}] [R = o‐PPh2C6H4 (1), Ph (2), Cl (3)], fac‐[W(CO)3{(o‐PPh2C6H4)3Sb}] (4), fac‐[W(CO)3{(o‐PPh2C6H4)2SbCl}] (5), fac‐[(W(CO)3{(o‐PPh2C6H4)2Sb})2] (6), fac‐[Mo(CO)3{(o‐PPh2C6H4)2SbR}] [R = o‐PPh2C6H4 (7), Ph (8), Cl (9)]. Compounds 1 and 4 were allowed to react with MX salts with M = Cu, Ag, Au and X = Cl–, [PF6]–, respectively. These reactions yielded cis‐[W(CO)4{(o‐PPh2C6H4)3Sb}{MCl}] [M = Cu (10), Ag (11)], cis‐[W(CO)4{(o‐PPh2C6H4)2Sb}{AuCl(o‐PPh2C6H4)}{AuCl}] (12) cis‐[(W(CO)4{(o‐PPh2C6H4)2Sb})2AuCl] (13), cis‐[W(CO)3(μ‐CO){(o‐PPh2C6H4)3Sb}{Cu}][PF6] (14), cis‐[W(CO)4{(o‐PPh2C6H4)3Sb}{AgMeCN}][PF6] (15), cis‐[W(CO)4{(o‐PPh2C6H4)3Sb}{Au}][PF6] (16) cis‐[W(CO)2(μ‐CO){(o‐PPh2C6H4)3Sb}{Cu2(μ‐Cl)2}] (17), fac‐[W(CO)3{(o‐PPh2C6H4)3Sb}{AuCl}] (18), and fac‐[W(CO)2(μ‐CO){(o‐PPh2C6H4)3Sb}{ML}][PF6] [M = Cu, L = MeCN (19), M = Ag, L = MeCN (20), M = Au (21)]. Complexes 10–21 all show metal‐metal distances below the sum of the corresponding van der Waals radii. The proximity of the two metal centers is especially significant in 19–21, indicating the presence of metal‐metal bonding.

A method has been proposed for calculating the lattice parameter of binary substitutional solid solutions, which takes into account the presence of pressure (p) in alloys. The method has been applied to SiGe and CuAu alloys. It has been shown that, at p = 0, the deviation from Vegard’s law (Δl) results from the difference in compressibility and atomic volume between the pure constituent components of the alloys. With increasing pressure, Δl increases. According to our calculations, the Δl(p) of SiGe becomes positive at p0 = 0.685 GPa.

The hardening and embrittlement of reactor pressure vessel steels source from the formation of Cu-enriched precipitates (CRPs) and Mn-Ni-Si precipitates (MNSPs). Recent studies of atom probe tomography indicated that the formation of CRPs and MNSPs may have similar mechanisms, and the major difference may be the nucleation site. Cu clusters and Cu-vacancy complexes may act as the nucleation sites for CRPs, whereas the nucleation sites for MNSPs are unknown. In this work, vacancy clusters of different sizes were analyzed by first-principles calculations for their possibility to act as the nucleation sites for MNSPs. The results were compared with that of Cu clusters and Cu-vacancy complexes in CRPs. Cluster size effects were also discussed. It has been found that Ni was attracted by both Cu cluster and vacancy cluster. Si was not much attracted by Cu cluster but was highly attracted by vacancy cluster, and it was the vacancy in Cu-V complex that attracted Si. In all the configurations calculated, the Mn atoms in antiferromagnetic state would stabilize the configurations and lead to positive binding energy with the clusters. The magnetic state of Mn could be correlated with its atomic volume in bcc-Fe.

International audience; The selective ring-opening reaction of fluoroalkylidene-oxetanes was directed by the presence of the fluorine atom, enabling a two-step access to tetrasubstituted fluoroalkenes with excellent geometry control. Despite its small van der Waals radii electronic, rather than steric influences of the fluorine atom governed the ring-opening reaction with bromide ions, even in the presence of bulky sub-stituents. 1936

Nucleobase pair–metal dimer/dinuclear metal cation interactions play an important role in biological applications because of their highly symmetrical structures and high stabilities. In this work, we have selected five adenine–adenine hydrogen bonding, adenine–thymine (AT), adenine–uracil, adenine–adenine stacking pairs, and Watson–Crick AT stacking pairs and studied their interaction with the coinage metal dimer M2 and M22+ metal cations, where M = Ag, Au, and Cu. Quantum chemical calculations have been carried out with density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Electronic structures were analyzed by the partial density of states method. During interactions, we find that M–M distances are shorter than the sum of van der Waals radii of the corresponding two homocoinage metal atoms, which show the existence of significant metallophilic interactions. Results indicated that nucleobase–M22+ complexes are stronger as compared to nucleobase–M2 complexes. Also, the replacement of the hydrogen bond by the dinuclear metal cation-coordinated bond forms more stable alternative metallo-DNA sequences in AAST base pairs. TDDFT calculations reveal that nucleobase–Cu2 complexes and nucleobase–Ag22+/Au22+ complexes can be used for fluorescent markers and logic gate applications. Atom-in-molecules analysis predicted the noncovalent interaction in these complexes.

Matrix isolation studies in solid argon and neon at 4.2 K reveal that iodoacetic acid initially only exists as its ground state (c,x) conformer with an almost perpendicular I-C-C═O dihedral angle, but UV irradiation in the 240-255 nm range leads to population of the 0.8 kcal mol-1 less stable (c,c) isomer. The latter structure exhibits a close 3.23 A contact of the iodine and carbonyl oxygen atoms decidedly below the sum of their van der Waals radii (3.50 A). Increasing the matrix temperature by only a few Kelvin triggers the thermal back reaction of (c,c) to (c,x) and leads to an estimated upper limit of 0.38 kcal mol-1 for the associated torsional barrier. While wave function methods including completely uncorrelated Hartree-Fock theory have no problem to identify (c,c) as a proper minimum, many popular density functionals fail to describe the C-C torsional potential in cis-iodoacetic acid qualitatively correct. We assessed the performance of 12 density functionals of different levels of sophistication, namely, the BLYP, PBE, TPSS, B3LYP, BHandHLYP, PBE0, M06-2X, CAM-B3LYP, ωB97X-D3, B2-PLYP, B2GP-PLYP, and DSD-PBEP86 methods, against accurate extrapolated CCSD(T)/CBS(T-Q)//MP2/def2-TZVPP energies and found that almost all of them yield acceptable relative energies. Still, even some of the best performers fail to find a reasonably deep minimum in the region of the (c,c) conformer, and addition of the empirical D3-dispersion correction does not remedy the qualitative shortcoming. Instead, inclusion of a sufficient amount of (long-range) exact exchange and likely a proper treatment of medium-range correlation effects all along the torsional coordinate play an important role in the proper description of the sub-van der Waals iodine-oxygen contact. More modern, recommended functionals do not suffer from the described shortcoming.

In this work, the density of biofuel is estimated using four intelligent models: a Least Square Support Vector Machine (LSSVM), a Radial Basis Function Artificial Neural Network (RBF-ANN), a Multi-layer Perceptron Artificial Neural Network (MLP-ANN), and an Adaptive Network-based Fuzzy Inference System (ANFIS). These models are used to estimate the density of biofuel based on intermolecular interactions and the van der Waals radii of the atoms. Various statistical analyses are performed on the original (experimental) and estimated data. It is found that the LSSVM model can provide more accurate predictions than the other three models. The R-squared value (R2) and the mean absolute relative error (MARE) for the LSSVM, RBF-ANN, MLP-ANN and ANFIS models are 0.847 & 0.056, 52.067 & 0.379, 57.385 & 0.371 and 65.096 & 0.678, respectively. This study shows that the LSSVM model is a promising tool for estimating the density of biofuel, offering an alternative to classic thermodynamic models.

The elastic properties of oxyfluoride tellurite glasses in the ternary system ZnF2-WO3 -TeO2 were analyzed and their changes when ZnF2 was replaced with TeO2 or WO3 were predicted. The most significant structural and compositional parameters were evaluated on the basis of the well known models and approaches existing in the field and correlated with both elastic moduli and Poisson's ratio. It has been found that the molar volume, fractal bond connectivity, first-order stretching force constant of the Te–O and W–O covalent bonds and dissociation energy per unit volume of the constituent components play an important role in determining and predicting of elastic moduli. The semi-empirical formula of Abd El-Moneim and Alfifi, which correlates bulk modulus with the ratio between packing density and mean atomic volume, appears to be valid for the investigated oxyfluoride tellurite glasses. On the basis of Makishima-Mackenzie's theory, the agreement between the theoretically calculated and experimentally measured values is excellent for shear and Young's moduli and satisfactory for Poisson's ratio as well as bulk and longitudinal moduli. The slight divergence between the theoretical and experimental values was interpreted in terms of the basic structural units that constituting the glass network.

The properties of graphdiyne (GDY), such as energy gap, morphology, and affinity to alkali metals, can be adjusted by including electron-withdrawing/donating groups. The push-pull electron ability and size differences of groups play a key role on the partial property adjusting of GDY derivatives MeGDY, HGDY, and CNGDY. Cyano groups (electron-withdrawing) and methyl groups (electron-donating) decrease the band gap and increase the conductivity of the GDY network. The cyano and methyl groups affects the aggregation of GDY, providing a higher number of micropores and specific surface area. These groups also endow the original GDY additional advantages: the stronger electronegativity of cyano groups increase the affinity of GDY frameworks to lithium atoms, and the larger atomic volume of methyl groups increases the interlayer distance and provides more storage space and diffusion tunnels.

The element Vanadium (V) appears unique among alloying elements for providing high strengthening in both the fcc Co-Cr-Fe-Mn-Ni-V and bcc Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr high-entropy alloy families. The origin of Vanadium's special role is its atomic volume: large in the fcc alloys and small in the bcc alloys, and thus having a large misfit volume in both crystalline structures. A parameter-free theory applicable to both fcc and bcc HEAs rationalizes this finding, with predictions of strength across a range of fcc and bcc alloys in quantitative and qualitative agreement with experiments. In the fcc class, the analysis demonstrates why the newly-discovered NiCoV and Ni0.632V0.368 alloys have far higher strength than any other fcc alloy and are predicted to be the highest attainable. In the bcc class, the analysis demonstrates that the addition of V always increases the strength relative to the same alloys without V. The optimization of complex alloys for high strength should thus center around the inclusion of V as a primary element at concentration levels of around 25 at.% (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Exploring isotropic negative thermal expansion (NTE) compounds is interesting, but remains challenging. Here, a new concept of "average atomic volume" is proposed to find new NTE open-framework materials. According to this guidance, two NTE compounds, AgB(CN)4 and CuB(CN)4, have been discovered, of which AgB(CN)4 exhibits a large NTE over a wide temperature range (αv = -40 × 10-6 K-1, 100-600 K). The analysis by extended X-ray absorption fine structure spectroscopy and first-principles calculation indicate that (i) the NTE driving force comes from the transverse vibrations of bridge chain atoms of C and N, corresponding to the low-frequency phonon modes; and (ii) the same transverse vibration direction of C and N atoms is a key factor for the occurrence of strong NTE in AgB(CN)4. The present concept of "average atomic volume" can be a simple parameter to explore new NTE compounds especially in those open-framework materials.

Many glasses exhibit fractional power law (FPL) between the mean atomic volume va and the first diffraction peak position q1, i.e. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v_{\mathrm{a}} \propto q_1^{ - d}$$\end{document}va∝q1−d with d ≃ 2.5 deviating from the space dimension D = 3, under compression or composition change. What structural change causes such FPL and whether the FPL and d are universal remain controversial. Here our simulations show that the FPL holds in both two- and three-dimensional glasses under compression when the particle interaction has two length scales which can induce nonuniform local deformations. The exponent d is not universal, but varies linearly with the deformable part of soft particles. In particular, we reveal an unexpected crossover regime with d > D from crystal behavior (d = D) to glass behavior (d, A puzzle in metallic glass research is the existence of the fractional power law in reciprocal space, whilst its origin remains controversial. Zhang et al. show that nonuniform local deformations under compression induce this phenomenon and quantify the power law exponent at both two and three dimensions.

Tetraarylantimony carboxylates Ph4SbOC(O)R (R = CF2Br (I), CF2CF2CF3 (II)), (4‑MeC6Н4)4SbOC(O)CF2CF3 (III), and (4-MeC6Н4)4SbOC(O)CF2CF2CF3 (IV) have been synthesized by the reaction between pentaarylantimony Ar5Sb (Ar = Ph, 4-MeC6H4) and fluorine-containing carboxylic acids. Despite an excess amount of carboxylic acid in the reaction mixture, it does not form any solvates Ar4SbOC(O)R ⋅ HOC(O)R with tetraarylantimony carboxylates. X-ray diffraction shows that the Sb atoms in complexes I–IV have differently distorted trigonal bipyramidal coordination. Crystals of complexes III and IV contain two types of crystallographically independent molecules. The axial СSbO angles in complexes I, II, III, and IV are 175.32(14)°, 178.87(8)°, 178.56(13)° and 178.33(10)°, 178.16(13)°, and 179.58(15)°, respectively. The Sb–O and Sb–С bond lengths are 2.333(3) and 2.106(4)–2.151(5) A in I, 2.340(2) and 2.101(2)–2.154(3) A in II, 2.364(3), 2.411(3), and 2.096(4)–2.159(4) A in III, and 2.376(3), 2.367(3), and 2.105(4)–2.161(4) A in IV. The intramolecular Sb⋅⋅⋅O distances with the carbonyl oxygen atom are 3.506(4) A (I), 3.517(6) A (II), 3.565(6) A (III), and 3.527(6) A (IV), being ~0.2 A smaller than the sum of Sb and O van der Waals radii. The second carbonyl oxygen atoms in crystals of complexes III and IV do not participate in the coordination with the central metal atom.

Crystalline powder boron carbide samples are subjected to explosive loading by 2-μs shock waves with an amplitude of 38 GPa and shock heating to 700 K and to subsequent conservation. The samples recovered after shock-wave loading are studied by X-ray diffraction, and new effects of shock-wave loading on boron carbide are revealed. The explosive treatment is shown to shift the X-ray diffraction reflections of initial boron carbide toward high angles, which is attributed to an increase in the boron carbide density at the level of atomic volume in the unit cell of boron carbide. The X-ray diffraction reflections are found to broaden, which is interpreted as an increase in the coherent scattering region in the crystalline boron carbide subjected to the explosive treatment.

AgInCd alloy is widely used as neutron absorber in nuclear reactors. However, the AgInCd control rods may fail during service due to the irradiation swelling. In the present study, a calculational method is proposed to calculate the composition change of the AgInCd absorber. Calculated results show that neutron fluence has significant impact on the chemical compositions. Ag and In contents gradually decrease while Cd and Sn conversely increases from the center to the rim of AgInCd absorber due to the depression of neutron flux. The composition change at the surface is higher almost two times than that at the center. Based on the calculated compositions, six simulated AgInCdSn alloys were prepared and examined. With the increase of Cd and Sn, the simulated AgInCdSn alloys transform from a single fcc phase into the mixed fcc and hcp phases, and finally into the single hcp phase. The atomic volume of the hcp phase is obviously larger than the fcc phase. The fcc-hcp transformation results in considerable volume swelling of the AgInCd absorber. Moreover, the lattice parameters of the fcc and hcp phases gradually increase with Cd and Sn contents, which also can induce small volume swelling. Keywords: AgInCd absorber, Chemical composition, Microstructure, Phase, Swelling

The results of a search for correlations between the crystal-geometry parameters and structural-phase states in the alloys based on Ag–Me (Me = Co, Rh, Ir, Ni, Pd, Pt, Cu, Au) are presented. The limits of numerical values of the crystal-geometry and thermodynamic factors are identified, within which inorganic regions of solid solutions are formed in the state diagrams of binary systems or monotectic reactions take place in the systems due to a limited solubility of the system components in liquid states. It is shown that an approach relying on the analysis of state diagrams, including the crystal-geometry and thermodynamic factors of the alloy-forming elements into consideration, is promising in searching for common patterns of structural-phase states in the Ag-based alloys; it is found out that an Ag–Pt system is the most attractive binary system in this respect. A slight deviation of the experimental concentration dependences of the atomic volume in the solid solutions of the Ag–Pd and Ag–Au systems from the Zen relation is observed in intermetallic compounds in the alloys of the Ag–Pt system.

Using the methods of X-ray diffraction and density measurement (in the short- and middle-order scale), the influence of the chemical composition on the parameters of the local structure and the physical properties of chalcogenide glassy semiconductors (CGS) of the As–Ge–Se system is studied. The changes occurring in the numerical values of the correlation length and quasi-period in the middle-order region, as well as the packing coefficient, compactness, average atomic volume, and the number of constraints, are interpreted within the cluster-void model and the theory of topological constraints by the existence of the chemical percolation threshold.

Grain boundaries have been shown to dramatically influence the behavior of relatively simple materials such as monatomic metals and binary alloys. The increased chemical complexity associated with multiprincipal element alloys is hypothesized to lead to unique grain boundary phenomena. To explore the relationship between grain boundary structure and chemistry in these materials, hybrid molecular dynamics/Monte Carlo simulations of a faceted $\mathrm{\ensuremath{\Sigma}}11$ $\ensuremath{\langle}110\ensuremath{\rangle}$ tilt boundary, chosen to sample both high- and low-energy boundary configurations, are performed in face-centered cubic (fcc) CrFeCoNiCu and CrFeCoNi equiatomic alloys. Unexpected enrichment of Fe is discovered in the fcc regions adjacent to the interface and found to be correlated with a structurally distinct region of reduced atomic volume. Comparison with the boundary of the same type in monatomic Cu demonstrates that altered near-boundary regions exist in simpler systems as well, with the chemical complexity of the multiprincipal element alloys highlighting its existence and importance.

This manuscript reports the synthesis, X-ray characterization and DFT study of three new [M(bipy)3]2[Au(CN)2]3(X) (M = Fe, Co, and Ni; bipy = 2,2′-bipyridine; X = anion) ionic compounds. These salts are composed of [M(bipy)3]2+ dications and [Au(CN)2]− anions in a 2 : 3 ratio. The positive charge is compensated by X = Cl− anions in compounds 1 (M = Fe) and 2 (M = Co) and X = OH− in 3 (M = Ni). The three tridentate bipyridine ligands define the coordination of the M2+ cation, resulting in a nearly octahedral coordination sphere. The linear dicyanoaurate(I) anions are completely surrounded by a cradle of aromatic rings with Au-ring centroid distances below the sum of van der Waals radii, evidencing the existence of a specific Au⋯π attraction. This interaction has been analyzed in terms of the role of the Au-atom (Lewis acid or Lewis base) using DFT calculations combined with the quantum theory of atoms in molecules (QTAIM), noncovalent interaction plot index (NCIplot) and natural bond orbital (NBO) computational tools. The NBO suggests that the Au⋯π interaction is an example of a coinage bond in spite of the anionic nature of the acceptor and the cationic nature of the donor.

A model is proposed to calculate the melting points of nanoparticles based on the Lennard-Jones (L-J) potential function. The effects of the size, the shape, and the atomic volume and surface packing of the nanoparticles are considered in the model. The model, based on the L-J potential function for spherical nanoparticles, agrees with the experimental values of gold (Au) and lead (Pb) nanoparticles. The model, based on the L-J potential function, is consistent with Qi and Wang’s model that predicts the Gibbs-Thompson relation. Moreover, the model based on the non-integer L-J potential function can be used to predict the melting points Tm of nanoparticles.

This paper presents a molecular dynamics study of how the localization and transfer of excess atomic volume by structural defects affects the evolution and self-healing of nanosized cracks in bcc iron single crystals under different mechanical loading conditions at room temperature. It is shown that deformation is initially accompanied by a local growth of the atomic volume at the crack tips. The crack growth behavior depends on whether the excess atomic volume can be transferred by structural defects from the crack tips to the free surface or other interfaces. If an edge crack is oriented with respect to the loading direction so that dislocations are not emitted from its tip or only twins are emitted, then the sample undergoes a brittle-ductile fracture. The transfer of the excess atomic volume by dislocations from the crack tips prevents the opening of edge cracks and is an effective healing mechanism for nanocracks in a mechanically loaded material.

In this work we assess and extend strategies for calculating surface tension of complex liquids from molecular dynamics simulations: the mechanical route and the instantaneous liquid interface (ILI) approach. The former employs the connection between stress tensor and surface tension, whereas the latter involves computation of instantaneous density field. Whereas the mechanical route is general, the ILI method involves system-dependent parameters restricting its original application to liquid water only. Here we generalize the approach to complex molecular liquids using atomic van der Waals radii. The performance of the approaches is evaluated on two liquid systems: acetonitrile and water–methanol mixture. In addition, we compare the effect of the computational models for interaction potentials based on semi-empirical electronic structure theory and classical force fields on the estimate of the surface tension within both stress tensor and ILI approaches.

In this manuscript, three examples retrieved from the PDB are selected to demonstrate the existence and relevance of spodium bonding (SpB) in biological systems. SpB is defined as an attractive noncovalent interaction between elements of group 12 of the periodic table acting as a Lewis acid and any atom or group of atoms acting as an electron donor. The utilization of this term (SpB) is convenient to differentiate classical coordination bonds from noncovalent interactions. In the latter, the distance between the electron rich and the spodium atoms is longer than the sum of the covalent radii but shorter than the sum of the van der Waals radii. In most Zn-dependent metalloenzymes, the spodium atom is bonded to three imidazole moieties belonging to the side chains of histidine amino-acids. Herein, in addition to the investigation of the SpB in the active site of three exemplifying enzymes, theoretical models where the Zn(II) atom is bonded either to three imidazole or triazole ligands are used in order to investigate the strength of the SpB and its competition with hydrogen bonding. A series of Lewis bases and anions have been used as SpB acceptors combined with six SpB donors (receptors) of general formula [ZnY3X]+ (Y = imidazole and triazole and X = Cl, N3 and SCH3). In addition to the investigation of the energetic and geometric features of the complexes, the SpB interactions have been further characterized using the natural bond orbital (NBO) method, quantum theory of “atoms-in-molecules” and the noncovalent interaction plot (NCI plot).

A new amorphous alloy system $(TiZrNbCu)_{1-x}Co_x$ covering a broad composition range from the high-entropy (HEA) to Co rich alloys (x$\leqslant$ 0.43) has been fabricated, characterized and investigated. A comprehensive study of the chemical compositions, homogeneity, thermal stability, electronic structure and magnetic and mechanical properties has been performed. All properties change their variations with x within the HEA range. In particular, the average atomic volume deviates from the Vegard's law for x$\ge 0.2$, where also the average atomic packing fraction suddenly changes. The valence band structure, studied with ultraviolet photoemission spectroscopy, shows a split-band shape with 3d-states of Co approaching the Fermi level on increasing x. Due to onset of magnetic correlations magnetic susceptibility rapidly increases for x$\ge 0.25$. Very high microhardness increases rapidly with x. The results are compared with those for similar binary and quinary metallic glasses and with those for Cantor type of crystalline alloys., 29 pages, 10 figures

X-band electron paramagnetic resonance (EPR) spectroscopy has been used to investigate the rotational diffusion of a stable, positively charged nitroxide 4-trimethylammonium-2, 2, 6, 6- tetramethylpiperidine-1-oxyl iodide (Cat-1) in a series of 1-alkyl-3-methylimidazolium tetrafluoroborate room temperature ionic liquids (RTILs) having alkyl chain lengths from two to eight carbons. The rotation of Cat-1 is anisotropic with the preferential axis of rotation along the NO˙ moiety. The Stokes−Einstein−Debye (SED) law describes the mean rotational correlation time of Cat-1, assuming that the hydrodynamic radius is smaller than the van der Waals radius of the probe. This implies the probe rotates freely, experiencing slip boundary condition, which is solvent dependent. The rotational correlation time of Cat-1 in RTILs can very well be fitted to a power-law functionality with a singular temperature, which suggests that the apparent activation energy of rotation exhibits non-Arrhenius behavior. Compared to the rotation of perdeuterated 2, 2, 6, 6-tetramethyl-4-oxopiperidine-1-oxyl (pDTO), which is neutral, the rotation of Cat-1 is several times slower. The rotational anisotropy, the ratio of the rotational times of pDTO and Cat-1, and the apparent activation energy indicate the transition from a homogeneously globular structure to a sponge-like structure when the alkyl chain has four carbons, which is also observed in molecular dynamics (MD) computational studies. For the first time, we have been able to show that the rotational correlation time of a solute molecule can be analyzed in terms of the Cohen– Turnbull free volume theory. The Cohen-Turnbull theory fully describes the rotation of Cat-1 in all the ionic liquids in the measured temperature range.