Linear ether-based highly concentrated electrolytes for Li-sulfur batteries.

Li-S batteries have attracted attention as next-generation rechargeable batteries owing to their high theoretical capacity and cost-effectiveness. Sparingly solvating electrolytes hold promise because they suppress the dissolution and shuttling of polysulfide intermediates to increase the coulombic efficiency and extend the cycle life. This study investigated the solubility of polysulfide (Li2S8) in a range of liquid electrolytes, including organic electrolytes, highly concentrated electrolytes, and ionic liquids. The Li2S8 solubility was well correlated with the donor number (DNNMR), estimated via23Na-NMR, and was lower than 100 mM_(elemental sulfur) in electrolytes with DNNMR < 14, regardless of the type of electrolyte. Highly concentrated electrolytes comprising lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and linear chain dialkyl ethers such as methyl propyl ether (MPE), n-butyl methyl ether (BME), and ethyl propyl ether (EPE) were studied as sparingly solvating electrolytes for Li-S batteries. Monomethyl ethers, such as BME, showed more pronounced Li-ion coordination and higher ionic conductivity, whereas the steric hindrance of the longer alkyl chains in EPE lowered the solvation number, enhanced ion association, and lowered the ionic conductivity despite the solvents having similar dielectric constants. The charge-discharge rate capabilities of Li-S cells with dialkyl ether-based electrolytes were more impressive than those of cells with a localized high-concentration electrolyte using sulfolane (SL) and hydrofluoroether (HFE), [Li(SL)2][TFSA]-2HFE. The higher rate performance was attributed to the superior Li-ion transport properties of the dialkyl ether-based electrolytes. A pouch-type cell using lightweight [Li(BME)3][TFSA] demonstrated an energy density exceeding 300 W h kg-1 under lean electrolyte conditions.

Liquid Structures and Ion Dynamics of Ionic Liquids Viewed from Intermolecular Interactions.

The elucidation of the factors determining liquid structures and transport properties of ionic liquids is important for the design and development of ionic liquid electrolytes. This personal account introduces the importance of computational methods for studying ionic liquids. Molecular dynamics simulations provide detailed information on liquid structures of ionic liquid such as the structures of solvated cation complexes in equimolar mixtures of glymes and Li[TFSA] and the effects of the charges of electrode on liquid structure near the electrode. Ab initio calculations reveal that the magnitude of the attraction between ions and conformational flexibility ions play important roles in determining transport properties of ionic liquids. First principle molecular dynamics simulations elucidate why solvated cation complex is stable in the equimolar mixtures, although the Li+ -[TFSA]- interaction is greater than Li+ -glyme interaction.

Analysis of intermolecular interactions of n-perfluoroalkanes with circumcoronene using dispersion-corrected DFT calculations: comparison with those of n-alkanes.

Understanding the interactions between the adsorbate and substrate is critical in basic and advanced scientific fields, including the formation of well-organised nanoarchitectures via self-assembly on surfaces. In this study, the interactions of n-alkanes and n-perfluoroalkanes with circumcoronene were studied using dispersion-corrected density functional theory calculations as models of their adsorption on graphite. The interactions of n-perfluoroalkanes with circumcoronene were significantly weaker than those of the corresponding n-alkanes, e.g. the calculated adsorption energies of n-perfluorohexane and n-hexane were -9.05 and -13.06 kcal mol-1, respectively. The dispersion interactions were the major source of attraction between circumcoronene and the adsorbed molecules. Larger steric repulsion of n-perfluoroalkanes compared to those of n-alkanes increased their equilibrium distances from circumcoronene and decreased the dispersion interactions, resulting in weaker interactions. The interactions between two adsorbed n-perfluorohexane molecules and those of n-hexane molecules were -2.96 and -2.98 kcal mol-1, respectively, which are not negligible in the stabilisation of adsorbed molecules. The geometries of adsorbed n-perfluoroalkane dimers revealed that the equilibrium distance between two n-perfluoroalkane molecules did not match the width of the six-membered rings in circumcoronene, in contrast to that between n-alkanes. The lattice mismatch also destabilised the adsorbed n-perfluoroalkane dimers. The difference in the adsorption energy between flat-on and edge-on orientations of n-perfluorohexane was smaller than that of corresponding n-hexane.

Tuning the odd-even effect on two-dimensional assemblies of curcumin derivatives by alkyl chain substitution: a scanning tunnelling microscopy study.

Well-ordered molecular arrangement on surfaces is fundamental for fabrication of functional molecular devices which are of particular interest in nanotechnology. In addition to nano-manufacturing, the production of useful materials from natural resources has recently attracted increasing attention. Herein, we focused on the two-dimensional (2D) self-assemblies of curcumin derivatives. The effects of the number, length, and substitution of the alkyl chains on the 2D structures of curcumin derivatives were studied by scanning tunnelling microscopy at the highly oriented pyrolytic graphite/1,2,4-trichlorobenzene interface. Curcumin derivatives containing both methoxy and alkoxy chain groups and those possessing four alkoxy chains exhibit linear structures with and without interdigitation of alkoxy chains, respectively. These 2D structure formations are independent of the alkyl chain length. However, the bisdemethoxycurcumin derivatives periodically form stair-like and linear structures depending on the alkyl chain length, which indicates the existence of the odd-even effect. These results suggest that the 2D structural modulation of curcumin derivatives caused by the odd-even effect can be tuned by the number of alkyl chain substituents. The appearance and disappearance of the odd-even effect in curcumin derivatives are discussed in terms of the balance between intermolecular and molecule-substrate interactions.

On the concentration polarisation in molten Li salts and borate-based Li ionic liquids.

Electrolytes that transport only Li ions play a crucial role in improving rapid charge and discharge properties in Li secondary batteries. Single Li-ion conduction can be achieved via liquid materials such as Li ionic liquids containing Li+ as the only cations because solvent-free fused Li salts do not polarise in electrochemical cells, owing to the absence of neutral solvents that allow polarisation in the salt concentration and the inevitably homogeneous density in the cells under anion-blocking conditions. However, we found that borate-based Li ionic liquids induce concentration polarisation in a Li/Li symmetric cell, which results in their transference (transport) numbers under anion-blocking conditions (tabcLi) being well below unity. The electrochemical polarisation of the borate-based Li ionic liquids was attributed to an equilibrium shift caused by exchangeable B-O coordination bonds in the anions to generate Li salts and borate-ester solvents at the electrode/electrolyte interface. By comparing borate-based Li ionic liquids containing different ligands, the B-O bond strength and extent of ligand exchange were found to be directly linked to the tabcLi values. This study confirms that the presence of dynamic exchangeable bonds causes electrochemical polarisation and provides a reference for the rational molecular design of Li ionic liquids aimed at achieving single-ion conducting liquid electrolytes.

Halogen bond-directed self-assembly in bicomponent blends at the solid/liquid interface: effect of the alkyl chain substitution position.

The fabrication of well-organised molecular assemblies on surfaces is fundamental for the creation of functional molecular systems applicable to nanoelectronic and molecular devices. In this study, we investigated the effect of substitution positions of alkyl chains on the formation of halogen-bonded molecular networks. For this purpose, building blocks with different head groups (i.e., pyridine (Py) or tetrafluoro-iodobenzene (FI)) were substituted with hexadecyloxy chains at either the 3,4- or the 3,5-positions. The two-dimensional assembly of each compound as a single-component system was studied using scanning tunnelling microscopy (STM) at the highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface. All compounds displayed linear structures in which the alkyl chains were aligned along one of the HOPG axes. In the exceptional case of FI bearing hexadecyloxy chains at the 3,5-positions (denoted as FI-3,5), hexagonal arrays were tentatively formed owing to the triangular molecular arrangement induced by halogen bonding. A bicomponent blend of Py-3,4/FI-3,5 (1 : 1 molar ratio) enabled the formation of a honeycomb structure, whereas that of Py-3,5/FI-3,4 (1 : 1 molar ratio) produced a rectangular assembly that was periodically arranged in a zig-zag fashion. Finally, based on the observed blend ratio dependence, the formation of these different two-dimensional structures by variation in the substitution positions of the alkyl chains was discussed in terms of molecule-molecule and molecule-substrate interactions.

Thermodynamic aspect of sulfur, polysulfide anion and lithium polysulfide: plausible reaction path during discharge of lithium-sulfur battery.

The elucidation of elemental redox reactions of sulfur is important for improving the performance of lithium-sulfur batteries. The energies of stable structures of Sn, Sn˙-, Sn2-, [LiSn]- and Li2Sn (n = 1-8) were calculated at the CCSD(T)/cc-pVTZ//MP3/cc-pVDZ level. The heats of reduction reactions of S8 and Li2Sn with Li in the solid phase were estimated from the calculated energies and sublimation energies. The estimated heats of the redox reactions show that there are several redox reactions with nearly identical heats of reaction, suggesting that several reactions can proceed simultaneously at the same discharge voltage, although the discharging process was often explained by stepwise reduction reactions. The reduction reaction for the formation of Li2Sn (n = 2-6 and 8) from S8 normalized as a one electron reaction is more exothermic than that for the formation of Li2S directly from S8, while the reduction reactions for the formation of Li2S from Li2Sn are slightly less exothermic than that for the formation of Li2S directly from S8. If the reduction reactions with large exotherm occur first, these results suggest that the reduction reactions forming Li2Sn (n = 2-6 and 8) from S8 occur first, then Li2S is formed, and therefore, a two-step discharge-curve is observed.

Accuracy of intermolecular interaction energies, particularly those of hetero-atom containing molecules obtained by DFT calculations with Grimme's D2, D3 and D3BJ dispersion corrections.

Intermolecular interaction potentials for benzene, propane, perfluoromethane, furan, thiophene, selenophene, pyridine, phosphorine dimers and benzene-methane, benzene-chlorobenzene, benzene-bromobenzene complexes were calculated using the BLYP, B97 (B98), BP86, BPBE, PBE, PW91, B3LYP, B3PW91, BMK, PBE1PBE, APF, ωB97 (ωB97X), CAM-B3LYP, LC-ωPBE, B2PLYP, mPW2PLYP, TPSS, M06L, M05, M052X, M06, M062X and M06HF functionals with Grimme's dispersion correction methods of D2, D3 and D3BJ versions. The calculated potentials were compared with the CCSD(T) level potentials to evaluate the accuracy of the dispersion corrected DFT methods for calculating the intermolecular interaction energies of hydrocarbon molecules and molecules including heteroatoms (N, P, O, S, Se, F, Cl and Br). The performance of the calculations depends strongly on the choice of the functional and the dispersion correction method. None of the combinations of the functionals and the dispersion correction methods can reproduce well the CCSD(T) level interaction potentials of all the complexes. The improvement of the functionals from GGA to hybrid GGA, meta GGA or meta hybrid GGA is not essential for improving the performance. The significant functional dependence suggests that the scaling factors, which were determined for each functional by fitting, are the cause of the dependence. The performance of the calculations of hydrocarbon molecules is much better than that of the molecules including heteroatoms. A smaller number of molecules including heteroatoms were used for the reference data of the fitting compared with hydrocarbon molecules, which might be one of the causes of the worse performance of the calculations of molecules including heteroatoms.

Studies of Halogen Bonding Induced by Pentafluorosulfanyl Aryl Iodides: A Potential Group of Halogen Bond Donors in a Rational Drug Design.

The activation of halogen bonding by the substitution of the pentafluoro-λ6-sulfanyl (SF5) group was studied using a series of SF5-substituted iodobenzenes. The simulated electrostatic potential values of SF5-substituted iodobenzenes, the ab initio molecular orbital calculations of intermolecular interactions of SF5-substituted iodobenzenes with pyridine, and the 13C-NMR titration experiments of SF5-substituted iodobenzenes in the presence of pyridine or tetra (n-butyl) ammonium chloride (TBAC) indicated the obvious activation of halogen bonding, although this was highly dependent on the position of SF5-substitution on the benzene ring. It was found that 3,5-bis-SF5-iodobenzene was the most effective halogen bond donor, followed by o-SF5-substituted iodobenzene, while the m- and p-SF5 substitutions did not activate the halogen bonding of iodobenzenes. The similar ortho-effect was also confirmed by studies using a series of nitro (NO2)-substituted iodobenzenes. These observations are in good agreement with the corresponding Mulliken charge of iodine. The 2:1 halogen bonding complex of 3,5-bis-SF5-iodobenzene and 1,4-diazabicyclo[2.2.2]octane (DABCO) was also confirmed. Since SF5-containing compounds have emerged as promising novel pharmaceutical and agrochemical candidates, the 3,5-bis-SF5-iodobenzene unit may be an attractive fragment of rational drug design capable of halogen bonding with biomolecules.

Optical absorption and photoconductivity in iodine-excess ionic liquids: the case of 1-alkyl-3-methyl imidazolium iodides.

We investigated the optical absorption and photoconductivity of iodine-excess ionic liquids (ILs) based on 1-alkyl-3-methyl imidazolium iodide ([Cnmim][I]; n = 3, 4, and 6). The iodide concentration m was 2 ≦ m ≦ 8, which was determined by the molar fraction [Cnmim]+ : [Im]- = 1 : m. By adding iodine, an absorption edge shifted from 282 nm in the UV region to around 600 nm in the visible-light region. The optical bandgaps Eo decreased gradually from 2.3 eV to 1.9 eV with increasing m from 2 to 8. The alkyl-side chain lengths of the cations have little effect on the Eo. This experimental result was confirmed by ab initio molecular orbital calculations. The effects were reflected in the photoconductivity of the ILs, as expected. [C4mim][Im] exhibited greater photo-induced electron generation compared with [C3mim][Im] and [C6mim][Im]. The photoconductivity in both [C3mim][Im] and [C6mim][Im] increased slightly with increasing m. The trend of photoconductivity in [C4mim][Im] exhibited an N-shaped form. The highest photoconductivity 1.6 was observed in [C4mim][I8].

Key factor governing the physicochemical properties and extent of proton transfer in protic ionic liquids: ΔpKa or chemical structure?

In order to identify the key factor governing the transport properties and extent of proton transfer in protic ionic liquids (PILs), a series of PILs were prepared by simple neutralisation of a super-strong acid, bis(trifluoromethanesulfonyl)amide acid (H[NTf2]), with a range of amines comprising diverse structures, including secondary and tertiary amines. The bulk physicochemical properties of the resulting PILs with a wide variation in the ΔpKa values of the constituent acid and protonated bases were compared to those of previously reported PILs derived from a super-strong base, 1,8-diazabicyclo[5.4.0]-7-undecene (DBU), and different acids (M. S. Miran, H. Kinoshita, T. Yasuda, M. A. B. H. Susan and M. Watanabe, Phys. Chem. Chem. Phys., 2012, 14, 5178-5186) with emphasis on the thermal stability, vibrational spectroscopy, density, viscosity, conductivity, and ionicity characteristics. The thermal stability of all PILs, as analysed by thermogravimetric analysis (TGA), was found to linearly increase with the ΔpKa values. However, isothermal TGA measurements for an extended duration indicated that [NTf2]-based PILs exhibit higher thermal stability than [DBU]-based PILs at low ΔpKa values (<15). PILs with secondary amines showed higher viscosity and lower ionic conductivity than those with tertiary amines because of the formation of multiple hydrogen bonds. The evaluated ionicity suggested that all [NTf2]-based PILs are "good PILs", irrespective of the basicity of the amines, and have higher ionicity than [DBU]-based PILs particularly at low ΔpKa values (<15).

Magnesium bis(trifluoromethanesulfonyl)amide complexes with triglyme and asymmetric homologues: phase behavior, coordination structures and melting point reduction.

The phase behavior of binary mixtures of triglyme (G3) and Mg[TFSA]2 (TFSA: bis(trifluoromethanesulfonyl)amide) was investigated, towards the development of a Mg2+-based room-temperature solvate ionic liquid (SIL) electrolyte. In a 1 : 1 molar ratio, G3 and Mg[TFSA]2 form a thermally stable complex (decomposition temperature, Td: 240 °C) with a melting point (Tm) of 70 °C, which is considerably lower than that of the analogous tetraglyme (G4) system (137 °C). X-ray crystallography of a single crystal of [Mg(G3)][TFSA]2 revealed that a single Mg2+ cation is coordinated by a single, distorted, tetradentate G3 molecule from one side, and two monodentate [TFSA]- anions, with transoid conformation, from the reverse side to form an ion pair. Raman spectra of [Mg(G3)][TFSA]2 in the molten state revealed the presence of different coordination structures, as the liquid exhibits changes in the vibrational modes corresponding to G3 and the [TFSA]- anion compared to those observed for the solid. Investigation of the ion pair stabilization energies by DFT calculations suggests that higher stability cation complexes and ion pairs co-exist in the molten state than those observed in the crystalline state. These results imply that the coordination structures of the ion pairs play a key role in providing SILs with low Tm. To decrease the Tm further, several asymmetric homologues of G3, which have higher conformational flexibility than G3, were investigated. Notably, a 1 : 1 mixture of Mg[TFSA]2 with G3Bu (where one of the terminal methyl groups of G3 is substituted for a butyl group) formed a thermally stable complex (Td: 251 °C) without any distinct Tm and showed reasonable ionic conductivity at room-temperature, indicating partial dissociation of ions. In this electrolyte, which showed high oxidative stability, quasi-reversible Mg deposition/dissolution was achieved, indicating that Mg2+-based room-temperature SILs can be utilized as a new class of Mg electrolyte.

Molecular dynamics study of thermodynamic stability and dynamics of [Li(glyme)]+ complex in lithium-glyme solvate ionic liquids.

Equimolar mixtures of glymes and organic lithium salts are known to produce solvate ionic liquids, in which the stability of the [Li(glyme)]+ complex plays an important role in determining the ionic dynamics. Since these mixtures have attractive physicochemical properties for application as electrolytes, it is important to understand the dependence of the stability of the [Li(glyme)]+ complex on the ion dynamics. A series of microsecond molecular dynamics simulations has been conducted to investigate the dynamic properties of these solvate ionic liquids. Successful solvate ionic liquids with high stability of the [Li(glyme)]+ complex have been shown to have enhanced ion dynamics. Li-glyme pair exchange rarely occurs: its characteristic time is longer than that of ion diffusion by one or two orders of magnitude. Li-glyme pair exchange most likely occurs through cluster formation involving multiple [Li(glyme)]+ pairs. In this process, multiple exchanges likely take place in a concerted manner without the production of energetically unfavorable free glyme or free Li+ ions.

Direct N-Glycofunctionalization of Amides with Glycosyl Trichloroacetimidate by Thiourea/Halogen Bond Donor Co-Catalysis.

Using a halogen bond (XB) donor and Schreiner's thiourea as cooperative catalysts, various amides, including the asparagine residues of several peptides, were directly coupled with glycosyl trichloroacetimidates to give unique N-acylorthoamides in good yields. Synthetic applications of N-acylorthoamides, including rearrangement to the corresponding ß-N-glycoside, were also demonstrated.

Origin of attraction in p-benzoquinone complexes with benzene and p-hydroquinone.

The origin of the attraction in charge-transfer complexes (a p-hydroquinone-p-benzoquinone complex and benzene complexes with benzoquinone, tetracyanoethylene and Br2) was analyzed using distributed multipole analysis and symmetry-adapted perturbation theory. Both methods show that the dispersion interactions are the primary source of the attraction in these charge-transfer complexes followed by the electrostatic interactions. The natures of the intermolecular interactions in these complexes are close to the π/π interactions of neutral aromatic molecules. The electrostatic interactions play important roles in determining the magnitude of the attraction. The contribution of charge-transfer interactions to the attraction is not large compared with the dispersion interactions in these complexes.

Odd-even effect in two dimensions induced by the bicomponent blends of isobutenyl compounds.

Scanning tunneling microscopy (STM) investigation was performed for the blends of isobutenyl compounds, in which the long alkyl chains were connected with ester or carbamoyl linkages. Each component by itself did not show the odd-even effect of alkyl chain length, whereas after blending them, the 2D structures drastically changed and modulated to exhibit odd-even effect. Star, lozenge, twist-like, and linear structures were found, dependent on the blend ratio and alkyl chain length. The blend ratio dependence of 2D structures was explained in terms of homogeneous and heterogeneous dimerization due to the interdigitation of alkyl chains.

Effect of the cation on the stability of cation-glyme complexes and their interactions with the [TFSA]- anion.

The interactions of glymes with alkali or alkaline earth metal cations depend strongly on the metal cations. For example, the stabilization energies (Eform) calculated for the formation of cation-triglyme (G3) complexes with Li+, Na+, K+, Mg2+, and Ca2+ at the MP2/6-311G** level were -95.6, -66.4, -52.5, -255.0, and -185.0 kcal mol-1, respectively, and those for the cation-tetraglyme (G4) complexes were -107.7, -76.3, -60.9, -288.3 and -215.0 kcal mol-1, respectively. The electrostatic and induction interactions are the major source of the attraction in the complexes; the contribution of the induction interactions to the attraction is especially significant in the divalent cation-glyme complexes. The binding energies of the cation-G3 complexes with Li+, Na+, K+, Mg2+, and Ca2+ and the bis(trifluoromethylsulfonyl)amide anion ([TFSA]-) were -83.9, -86.6, -80.0, -196.1, and -189.5 kcal mol-1, respectively, and they are larger than the binding energies of the corresponding cation-G4 complexes (-73.6, -75.0, -77.4, -172.1, and -177.2 kcal mol-1, respectively). The binding energies and conformational flexibility of the cation-glyme complexes also affect the melting points of equimolar mixtures of glyme and TFSA salts. Furthermore, the interactions of the metal cations with the oxygen atoms of glymes significantly decrease the HOMO energy levels of glymes. The HOMO energy levels of glymes in the cation-glyme-TFSA complexes are lower than those of isolated glymes, although they are higher than those of the cation-glyme complexes.

Electrophilic Activation of Iodonium Ylides by Halogen-Bond-Donor Catalysis for Cross-Enolate Coupling.

The umpolung alkylation of silyl enol ethers with an iodonium(III) ylide proceeds under mild conditions to afford various 1,4-dicarbonyl compounds in high yields in the presence of a halogen-bonding catalyst. Unlike typical transition-metal activation processes of such ylide precursors, which tend to proceed via carbenoid intermediates, experimental and computational studies indicate that halogen bonding (XB) between the XB donor catalyst and the iodonium ylide plays a crucial role in promoting the reaction. The identification of a compatible Bronsted base catalyst enabled the extension of this method to enols generated in situ to give the corresponding adducts in good yields.

Room-Temperature Phosphorescence of Crystalline Metal-Free Organoboron Complex.

The photoluminescence (PL) properties of a metal-free organoboron complex, bis(4-iodobenzoyl)methanatoboron difluoride (1BF2 ), were elucidated. At room temperature, 1BF2 emits blue fluorescence (FL) in nBuCl upon photoexcitation. In contrast, crystals of 1BF2 emit green PL comprised of FL and phosphorescence (PH). The room-temperature PH of crystalline 1BF2 is a consequence of 1) suppression of thermal deactivation of the S1 and T1 excited states and 2) enhancement of intersystem crossing (ISC) from the S1 to T2 or T1 . The results of X-ray crystallographic and theoretical studies supported the proposal that the former (1) is a result of intermolecular interactions caused by π-stacking in the rigid crystal packing structure of 1BF2 . The latter (2) is an effect of not only the heavy-atom effect of iodine, but also the continuous π-stacking alignment of 1BF2 molecules in crystals, which leads to a forbidden S1 →S0 transition and a small energy gap between the S1 and T2 or T1 .

Synthesis, Ion Recognition Ability, and Metal-Assisted Aggregation Behavior of Dinuclear Metallohosts Having a Bis(Saloph) Macrocyclic Ligand.

Macrocyclic molecule 1 that has two saloph coordination sites was designed and synthesized. The macrocycle 1 was easily converted into the corresponding metallohosts 2 and 3 by the reaction with nickel(II) and palladium(II), respectively. As expected from the molecular structure of these metallohosts having an 18-crown-6-like cavity, the nickel(II) metallohost 2 showed excellent binding affinity toward Na(+), Ca(2+), and Sr(2+) to give 1:1 host-guest complexes. Preorganization effect due to the extremely rigid metal-containing macrocycle was suggested to be a major factor for the strong binding. Larger cations such as K(+), Rb(+), Cs(+), and Ba(2+) gave higher aggregated host-guest complexes such as 22M, 23M2, and 24M3. Density functional theory calculations revealed that smaller metal ions do not occupy the center of each macrocycle in the sandwich structures 22M, while larger Cs(+) simultaneously interacts with all the 12 oxygen donor atoms. On the basis of the interaction energy calculations, the preference for 2·Na over 22Na can be explained by destabilization of 22Na due to the elongated Na-O bonds and repulsive three-body interactions. When the ionic radius of the guest ion increases (K(+), Rb(+), Cs(+)), this destabilization becomes less significant and the formation of sandwich complexes 22M is favored. Such aggregation would significantly affect the physical and chemical properties of the metal complexes due to the interplane interactions between the metal centers.