Π-arene Interactions Research Articles

Low coordinate Zn(II) organocations bearing extremely bulky NHC ligands: structural features, air-/water-tolerance and use in hydrosilylation and hydrogenation catalysis.

This work details the synthesis and characterization of low-coordinate Zn(II)-based organocations [(NHC)Zn(R)]+ incorporating extremely bulky NHCs [ITr] and [IAd] ([ITr] = ([ITr] = [(HCNCPh3)2C:]; [IAd] = [(HCNAd)2C:], Ad = adamantyl)). Their structural features and particularities are thoroughly assessed as well as their air and water tolerance. Neutral ITr and IAd adducts [(ITr)Zn(R)2] (1, R = Me; 2, R = Et) and [(IAd)Zn(R)2] (3, R = Me; 4, R = Et) were synthesized by reaction of carbene [ITr] or [IAd] with a stoichiometric amount of [ZnR2] and isolated in good yields. Despite the steric bulk of [ITr] and [IAd], neutral compounds 1-4 are robust and the solid state structure of adduct 3 was established through X-ray crystallographic studies as a trigonal monomer Zn(II) species. Adducts 1-4 may readily be ionized by [Ph3C][B(C6F5)4] to afford two-coordinate Zn(II) alkyl cations [(ITr)Zn(Me)]+ ([5]+) and [(ITr)Zn(Et)]+ ([6]+), [(IAd)Zn(Me)]+ ([7]+) and [(IAd)Zn(Me)]+ ([8]+), all isolated in high yields (>80%) as [B(C6F5)4]- salts, which were fully characterized. Remarkably, cation [(ITr)Zn(C6F5)]+ ([9]+), prepared by reaction of [5][B(C6F5)4] with [B(C6F5)3], features π-arene interactions with the electrophilic Zn(II), as deduced from solid state data and further completed by DFT-estimated non-covalent interactions (NCI), indicating that [ITr] may provide substantial steric and electrostatic stabilization. The latter certainly explains the remarkable stability of [(ITr)Zn(C6F5)]+ ([9]+) towards hydrolysis at RT, as it only coordinates H2O to afford an unprecedented stable Zn-OH2 organocation [10]+. Also noteworthy, H2O coordination is reversible allowing recovery of [(ITr)Zn(C6F5)]+ cation, even after prolonged air exposure. Yet, controlled hydrolysis of [(ITr)Zn(C6F5)]+ may occur upon heating with selective protonolysis of the Zn-C6F5 bond to afford structurally characterized dication [(ITr)Zn(OH)]22+ [11]2+. Interestingly, despite steric hindrance, the air-/water-tolerant cation [(ITr)Zn(C6F5)]+ is an effective CO2 hydrosilylation catalyst, and was also shown to mediate imine hydrogenation catalysis.

Heavy Alkali Metal Manganate Complexes: Synthesis, Structures and Solvent-Induced Dissociation Effects.

Rare examples of heavier alkali metal manganates [{(AM)Mn(CH2 SiMe3 )(N'Ar )2 }∞ ] (AM=K, Rb, or Cs) [N'Ar =N(SiMe3 )(Dipp), where Dipp=2,6-iPr2 -C6 H3 ] have been synthesised with the Rb and Cs examples crystallographically characterised. These heaviest manganates crystallise as polymeric zig-zag chains propagated by AM⋅⋅⋅π-arene interactions. Key to their preparation is to avoid Lewis base donor solvents. In contrast, using multidentate nitrogen donors encourages ligand scrambling leading to redistribution of these bimetallic manganate compounds into their corresponding homometallic species as witnessed for the complete Li - Cs series. Adding to the few known crystallographically characterised unsolvated and solvated rubidium and caesium s-block metal amides, six new derivatives ([{AM(N'Ar )}∞ ], [{AM(N'Ar )⋅TMEDA}∞ ], and [{AM(N'Ar )⋅PMDETA}∞ ] where AM=Rb or Cs) have been structurally authenticated. Utilising monodentate diethyl ether as a donor, it was also possible to isolate and crystallographically characterise sodium manganate [(Et2 O)2 Na(n Bu)Mn[(N'Ar )2 ], a monomeric, dinuclear structure prevented from aggregating by two blocking ether ligands bound to sodium.

Structural Snapshots of π-Arene Bonding in a Gold Germylene Cation.

Heavier group 14 element cations exhibit a remarkable reactivity that has typically hampered their isolation. For the few available examples, the role of π‐arene interactions is crucial to provide kinetic stabilization, but dynamic and structural information on those contacts is yet limited. In this study we have accessed the metalogermylenium cation [(PMe2ArDipp2)AuGe(ArDipp2)Cl]+ (4+) (ArDipp2=C6H3‐2,6‐(C6H3‐2,6‐iPr2)2) that has been structurally characterized with three different non‐coordinating counter anions. These studies provide for the first time dynamic information about the conformational rearrangement that characterizes π‐arene bonding thorough a series of X‐ray diffraction structural snapshots. Computational studies reveal the weak character of the π‐arene bonding (ca. 2 kcal mol−1) that can be described as the donation from a πC=C bond toward the empty p valence orbital of germanium.

Intramolecular Metal⋅⋅⋅π-Arene Interactions in Neutral and Cationic Main Group Compounds.

The role of intramolecular metal⋅⋅⋅π-arene interactions has been investigated in the solid-state structures of a series of main group compounds supported by the bulky amide ligands, [N(tBu Ar≠ )(SiR3 )]- (tBu Ar≠ =2,6-(CHPh2 )2 -4-tBuC6 H2 , R=Me, Ph). The lithium and potassium amide salts showed different patterns of solvation and demonstrated that the SiPh3 substituent is able to be involved in stabilizing the electrophilic metal. These group 1 metal compounds served as ligand transfer reagents to access a series of bismuth(III) halides. Chloride extraction from Bi(N{tBu Ar≠ }{SiPh3 })Cl2 using AlCl3 afforded the 1:1 salt [Bi(N{tBu Ar≠ }{SiPh3 })Cl][AlCl4 ]. This was accompanied by a significant rearrangement of the stabilizing π-arene contacts in the solid-state. Attempted preparation of the corresponding tetraphenylborate salt resulted in phenyl-transfer and generation of the neutral Bi(N{tBu Ar≠ }{SiPh3 })(Ph)Cl.

Ligation-Enhanced π-Hole···π Interactions Involving Isocyanides: Effect of π-Hole···π Noncovalent Bonding on Conformational Stabilization of Acyclic Diaminocarbene Ligands.

The reaction of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with the aminoazoles [1 H-imidazol-2-amine (1), 4 H-1,2,4-triazol-3-amine (2), 1 H-tetrazol-5-amine (3), 1 H-benzimidazol-2-amine (4), 1-alkyl-1 H-benzimidazol-2-amines, where alkyl = Me (5), Et (6)] in a 2:1 ratio in the presence of a base in CHCl3 at RT proceeds regioselectively and leads to the binuclear diaminocarbene complexes [(ClPdCNXyl)2{μ-C(N-azolyl)N(Xyl)C═NXyl}] (7-12; 73-91%). Compounds 7-12 were characterized by C, H, N elemental analyses, high-resolution ESI+-MS, Fourier transform infrared spectroscopy, 1D (1H, 13C) and 2D (1H,1H-COSY, 1H,1H-NOESY, 1H,13C-HSQC, 1H,13C-HMBC) NMR spectroscopies, and X-ray diffraction (XRDn). Inspection of the XRDn data and results of the Hirshfeld surface analysis suggest the presence in all six structures of intramolecular π-holeisocyanide···πarene interactions between the electrophilic C atom of the isocyanide moiety and the neighboring arene ring. These interactions also result in distortion of the Pd-C≡N-Xyl fragment from the linearity. Results of density functional theory calculations [M06/MWB28 (Pd) and 6-31G* (other atoms) level of theory] for model structures of 7-9 followed by the topological analysis of the electron density distribution within the framework of Bader's theory (QTAIM method) reveal the presence of these weak interactions also in a CHCl3 solution, and their calculated strength is 1.9-2.2 kcal/mol. The natural bond orbital analysis of 7-9 revealed that π(C-C)Xyl → π*(C-N)isocyanide charge transfer (CT) takes place along with the intramolecular π-holeisocyanide···πarene interactions. The observed π(C-C)Xyl → π*(C-N)isocyanide CT is due to ligation of the isocyanide to the metal center, whereas in the cases of the uncomplexed p-CNC6H4NC and CNXyl species, the effects of CT are negligible. Available CCDC data were processed from the perspective of isocyanide-involving π-hole···π interactions, disclosed the role of metal coordination in the π-hole donor ability of isocyanides, and verified the π-holeisocyanide···πarene interaction effect on the stabilization of the in-conformation in metal-bound acyclic diaminocarbenes.

On the molecular and supramolecular properties of N,N′-disubstituted iminoisoindolines: Synthesis, spectroscopy, X-ray structure and Hirshfeld surface analyses, and DFT calculations of two (E)-N,N′-bis(aryl)iminoisoindolines (aryl = 2-tert-butylphenyl or perfluorophenyl)

Supramolecular studies of iminoisoindoline-derived compounds have been prompted by their biological and photophysical properties. In this article, we report the synthesis, spectroscopy, X-ray structural characterization, and DFT study of two N,N′-(aryl)-disubstituted 1-iminoisoindolines, namely (E)-N,N′-bis(2-tert-butylphenyl)iminoisoindoline (2-t-BuPhimiso) and (E)-N,N′-bis(perfluorophenyl)iminoisoindoline (F5Phimiso). Our X-ray structural analyses have shown that the isoindoline N2 atom of 2-t-BuPhimiso is slightly pyramidalized whereas the respective atom of F5Phimiso displays the expected trigonal planar geometry. The supramolecular arrangement of 2-t-BuPhimiso comprises one-dimensional chains along the [101] direction formed by CH···πarene interactions, in which the isoindoline ring behaves as a hydrogen-bond donor. For 2-t-BuPhimiso, DFT calculations at the B97-D3/6-311G** level have shown that the dimer formed by this CH···πarene contact displays a binding energy of −12.83 kcal mol−1. Product F5Phimiso assembles in the crystal state through type-I F3 synthons in addition to CH⋯F, C–Fδ–···πF+, and πarene/F–πarene/F stacking interactions. Accordingly, our DFT-D3 calculations have confirmed that these interactions synergistically play a dominating role in the crystal packing of F5Phimiso. Finally, the relative stability of the (Z) and (E) isomers of each product has been evaluated at the DFT level of theory. Our calculations have shown that the (E) forms are the most stable ones.

Changing the Charge: Electrostatic Effects in Pd-Catalyzed Cross-Coupling

A stable dianionic 14-electron Pd(0) complex supported by monoanionic carboranyl phosphines is reported. This complex rapidly undergoes the oxidative addition of Cl-C6H5 at room temperature and is a competent catalyst for Kumada cross-coupling. The isosteric PdL2 complex, supported by neutral o-carboranyl phosphines, does not display the same reactivity. The high reactivity of the dianionic Pd(0) complex toward chloroarenes can be explained by electrostatic effects that promote both formation of monophosphine-ligated LPd0 and stabilization of the transition state during oxidative addition. This mode of stabilization is distinct from the well-known π-arene interactions of biaryl phosphines, in that it occurs both on and off cycle.

Synthesis and Crystal Structure of a “FeBi” Cluster Compound with Noncovalent Low-Valent Bi···πArene Interactions

We describe the synthesis and structural characterization of the unprecedented [Bi4Fe3(CO)9] cluster, the low-valent Bi atoms of which are involved in the types of previously not identified intermolecular Bi···π(arene) and ΔBi···π(arene)interactions. Different coordination modes of arene rings bound to Bi atoms were determined.

Delocalized π-electrons in 2-oxazoline rings resulting in negatively charged nitrogen atoms: revealing the selectivity during the initiation of cationic ring-opening polymerizations

The inventory of the single-crystal X-ray structures of aliphatic and aromatic 2-oxazolines, namely 2-nonyl-2-oxazoline, 2,2′-tetramethylenebis(2-oxazoline) and 2-phenyl-2-oxazoline, reveals significant delocalization of π-electrons along the NCO segment. The delocalization of π-electrons is stabilized by inductive and resonance contributions of the side-chains; in 2-phenyl-2-oxazoline, also π-arene interactions between the benzene ring and the CN and the CO bond stabilize the crystalline phase. This delocalization gives a partial negative charge to the nitrogen atom and a partial positive charge to the oxygen atom. The partial negative charge of the nitrogen atom makes this atom the exclusive reaction partner also for highly reactive non-selective cations, which explains the regioselectivity of electrophilic attacks in cationic ring-opening polymerizations. Copyright © 2011 Society of Chemical Industry

Rubidium-Mediated Birch-Type Reduction of 1,2-Diphenylbenzene in Tetrahydrofuran

The reaction of 1,2-diphenylbenzene with rubidium metal in THF yields extremely sensitive and pyrophoric [η(5)-{1,2-diphenyl-2,5-cyclohexadienyl}rubidium](∞) (1). Compound 1 characterizes a possible intermediate in a Birch-type reaction and represents a very rare example of a fully characterized organorubidium complex as well as an open main-group metal pentadienide as part of a six-membered ring. In the solid state the rubidium atoms interact with the cyclohexadienyl moiety, whereas the coordination sphere of the soft cation is additionally stabilized exclusively by several metal π-arene interactions despite the presence of strongly coordinating donors. The bonding situation was elucidated by MP2/def2-TZVPP calculations including population analysis.

Synthesis of bismuth and antimony complexes of the “larger” calix[n]arenes (n = 6–8); from mononuclear to tetranuclear complexes

A series of calix[n]arene (n=6-8) bismuth and antimony complexes were synthesized and fully characterized by NMR, X-ray, IR, UV-Vis and elemental analysis. The monobismuth calix[6]arene complex [Bi{tBuC6(H)3}]2 1 was prepared by the reaction of para-tert-butylcalix[6]arene (tBuC6(H)6) with one equivalent of Bi[N(SiMe3)2]3. Complex 1 featured a Bi2(micro-O)2 central core similar to other bismuth calixarene complexes prepared by our group. Reaction of calix[6]arene (HC6(H)6) with two equivalents of Bi(OtBu)3 yielded different outcomes depending on the reaction solvent. If THF was used, complex [Bi{HC6(H)3}] 2 was obtained in 72% yield; however, when toluene was used, complexes 2 and [Bi2{HC6}] 3 were isolated in 23 and 57% yields, respectively. Mononuclear complexes 1 and 2 displayed dimeric structures in the solid state with cone-like conformations for the calixarene ligands. The 1H NMR spectrum of complex 2 displays patterns for an asymmetric structure with two signals in a 2:1 ratio for the unreacted OH groups. Treatment of calix[6]arenes RC6(H)6 (R=H, tBu) with two equivalents of SbR3 (R=OtBu, NMe2) produced dinuclear complexes [Sb2{HC6}] 4, and [Sb2{tBuC6}] 5, respectively. The 1H NMR spectra for the dinuclear complexes 3, 4, and 5 showed the characteristic calixarene pattern for a 1,2,3-alternate conformer. In the process of recrystallization of complex 4 an unexpected trimetallic complex with composition [Sb3O2{HC6(H)}] 4a was obtained in low yield. Treatment of para-tert-butylcalix[7]arene (tBuC7(H)7) with two equivalents of Bi(OtBu)3 produced the bimetallic complex [Bi2O{tBuC7(H)3}]2 6. Complex 6 contains an overall Bi4O2(OAr)8 core system with a structural resemblance to other bimetallic bismuth calixarene complexes reported by our group. The larger para-benzylcalix[8]arene (BnC8(H)8) and calix[8]arene (HC8(H)8) reacted with excess Bi(OtBu)3 to produce the tetranuclear complexes [Bi4O2{HC8}] 7 and [Bi4O2{BnC8}] 8, respectively. The solid state structure of complex 8 featured a dimeric unit with the calixarene ligands in pinched-cone conformation and displaying an overall Bi8O4(OAr)16.H2O core. No metal pi-arene interactions were observed.

High temperature synthesis of some strontium and barium 2,6-dibenzylphenolates

Direct treatment of HOdbp (= 2,6-dibenzylphenol) with strontium or barium metal in the absence of solvent at high temperature provides the corresponding phenolates Sr(Odbp) 2 and Ba(Odbp) 2. Recrystallisation of Ba(Odbp) 2 from THF gave a good yield of the crystalline dimer [Ba(Odbp) 2(THF)] 2 · 2THF. Attempted recrystallisation of Sr(Odbp) 2 from THF mostly yielded microcrystalline material characterized as [Sr(Odbp) 2] n but on one occasion gave a small crop of crystalline [Sr 9(Odbp) 8(O 2SiMe 2) 4(OH) 2(THF) 6(OH 2) 2] · 6THF derived from the adventitious reaction of Sr(Odbp) 2 with dimethylsilicone grease ({OSiMe 2} ∞). In the solid-state [Ba(Odbp) 2(THF)] 2 · 2THF displays significant intramolecular Ba⋯π-arene interactions with the pendant benzyl substituents. [Sr 9(Odbp) 8(O 2SiMe 2) 4(OH) 2(THF) 6(OH 2) 2] · 6THF features a square prismatic [Sr(O 2SiMe 2) 4] 6− core capped by two inverse crown-like square [Sr 4(Odbp) 4(OH)(L) 4] 3+ units, where L = OH 2 or THF, that are staggered with respect to the cuboidal core.

Gas-Phase Assembling of Dirhodium Units into a Novel Organometallic Ladder: Structural and DFT Study

A hydrocarbon that has three separate aromatic rings, namely 1,4-bis(p-tolylethyl)benzene (C24H26), has been structurally characterized for the first time and tested as an elongated aromatic π-donor in assembling reactions under solvent-free conditions. Its gas-phase interaction with the electrophilic dimetal complex, [Rh2(O2CCF3)4], affords single crystals of a novel organometallic complex, [Rh2(O2CCF3)4]2·(C24H26). The product has a ladder type structure built on weak but directional rhodium(II)−π-arene interactions. In the above framework, each C24H26 exhibits a tetradentate-bridging coordination having four rhodium(II) centers attached to the opposite sides of the two peripheral benzene rings. The underlying reasons for such coordination defining the formation of the title product have been discussed based on the results of density functional theory, namely the orbital interaction analysis of the reacting partners.

The First Example of a μ2-Imido Functionality Bound to a Lanthanide Metal Center: X-ray Crystal Structure and DFT Study of [(μ-ArN)Sm(μ-NHAr)(μ-Me)AlMe2]2 (Ar = 2,6-iPr2C6H3)1

Reaction of 3 equiv of 2,6-diisopropylaniline with Sm[N(SiMe3)2]3 affords the dimeric species [Sm(NHAr)3]2 (1). X-ray crystallography illustrates that each metal center in 1 engages in an η6-arene interaction with the aryl ring of an amide ligand attached to an adjacent samarium. IR spectroscopy indicates that the π-arene interactions are maintained in solution. Reaction of 1 with 4 equiv of trimethylaluminum leads to formation of the bis(μ2-imido) complex [(μ-ArN)Sm(μ-NHAr)(μ-Me)AlMe2]2 (2). The molecular structure of 2 contains a unique central Sm2N2 core which displays extremely short bridging Sm−N distances of 2.152(8) and 2.271(7) A, characteristic of an imido complex. Density functional theory (DFT) calculations have been carried out in order to gain a better understanding of the nature of the bonding interactions within complex 2 and indicate that the 5d metal acceptor orbitals play a significant role in stabilizing π-donation from the imido groups to the samarium centers within the Sm2N2 core.

A solvated ytterbium diaryl: bis(1,1′:3′,1′′-terphenyl-C2′)bis(tetrahydrofuran-O)ytterbium(II)

The title compound, [Yb(Dpp)2(thf)2] [Dpp = 2,6-Ph2C6H3 (m-ter­phenyl), C18H13, and thf = tetra­hydro­furan, C4H8O], is the first example of a structurally characterized YbII di­aryl. The Yb atom shows a strongly distorted tetrahedral environment formed by the C atoms of two aryl groups (average Yb—C = 2.520 Å) and the O atoms of two tetra­hydro­furan ligands (average Yb—O = 2.412 Å). In addition, there are two weak η1–π-arene interactions (average Yb⋯C = 3.138 Å) involving ortho-C atoms of the m-ter­phenyl phenyl groups.

Intermolecular interactions in the chiral and racemic forms of 3-hydroxy-2-(1-oxoisoindolin-2-yl)butanoic acid derived from threonine.

The title compounds, C12H13NO4, are derived from l-threonine and dl-threonine, respectively. Hydro­gen bonding in the chiral derivative, (2S/3R)-3-hydroxy-2-(1-oxoisoindolin-2-yl)­butanoic acid, consists of O—Hacid⋯Oalkyl—H⋯O=Cindole chains [O⋯O 2.659 (3) and 2.718 (3) Å], Csp3—H⋯O and three C—H⋯πarene interactions. In the (2R,3S/2S,3R) racemate, conventional carboxylic acid hydrogen bonding as cyclical (O—H⋯O=C)2 [graph set R22(8)] is present, with Oalkyl—H⋯O=Cindole, Csp3—H⋯O and C—H⋯πarene interactions. The COOH group geometry differs between the two forms, with C—O, C=O, C—C—O and C—C=O bond lengths and angles of 1.322 (3) and 1.193 (3) Å, and 109.7 (2) and 125.4 (3)°, respectively, in the chiral structure, and 1.2961 (17) and 1.2210 (18) Å, and 113.29 (12) and 122.63 (13)°, respectively, in the racemate structure. The O—C=O angles of 124.9 (3) and 124.05 (14)° are similar. The differences arise from the contrasting COOH hydrogen-bonding environments in the two structures.

Intermolecular interactions in the chiral and racemic forms of 3-hydroxy-2-(1-oxoisoindolin-2-yl)butanoic acid derived from threonine

The title compounds, C12H13NO4, are derived from l-threonine and dl-threonine, respectively. Hydro­gen bonding in the chiral derivative, (2S/3R)-3-hydroxy-2-(1-oxoisoindolin-2-yl)­butanoic acid, consists of O—Hacid⋯Oalkyl—H⋯O=Cindole chains [O⋯O 2.659 (3) and 2.718 (3) Å], Csp3—H⋯O and three C—H⋯πarene interactions. In the (2R,3S/2S,3R) racemate, conventional carboxylic acid hydrogen bonding as cyclical (O—H⋯O=C)2 [graph set R22(8)] is present, with Oalkyl—H⋯O=Cindole, Csp3—H⋯O and C—H⋯πarene interactions. The COOH group geometry differs between the two forms, with C—O, C=O, C—C—O and C—C=O bond lengths and angles of 1.322 (3) and 1.193 (3) Å, and 109.7 (2) and 125.4 (3)°, respectively, in the chiral structure, and 1.2961 (17) and 1.2210 (18) Å, and 113.29 (12) and 122.63 (13)°, respectively, in the racemate structure. The O—C=O angles of 124.9 (3) and 124.05 (14)° are similar. The differences arise from the contrasting COOH hydrogen-bonding environments in the two structures.

1-deoxy-1-(4-fluorophenyl)-beta-D-ribofuranose, its hemihydrate, and 1-deoxy-1-(2,4-difluorophenyl)-beta-D-ribofuranose: structural evidence for intermolecular C-H...F-C interactions

The structures of 1-deoxy-1-(4-fluoro­phenyl)-β-d-ribo­furan­ose in two crystal forms, (Ia) and (Ib) (C11H13FO4), 1-deoxy-1-(4-fluoro­phenyl)-β-d-ribo­furan­ose hemihydrate, (Ic) (C11H13­FO4·0.5H2O) and 1-deoxy-1-(2,4-di­fluoro­phenyl)-β-d-ribo­furan­ose, (II) (C11H12F2O4), show two-dimensional networks of intermolecular hydrogen bonds between the hydroxyl groups. Weak intermolecular C—H⋯F—C and C—H⋯πarene interactions complete the packing in the third dimension. The ribo­furan­ose ring has a conformation intermediate between a C1′-exo,C2′-endo twist and a C2′-endo envelope for (Ia) and (Ic), a conformation intermediate between a C2′-endo,C3′-exo twist and a C2′-endo envelope for (Ib) and an unsymmetrical C2′-exo,C3′-endo twist conformation for (II).

Unusual Two-Dimensional Sheet Structure of the Solvent-Free Cesium Aryloxide Complex CsO-2,6-i-Pr(2)C(6)H(3).

The solvent-free cesium aryloxide complex Cs(O-2,6-i-Pr2C6H3) (1) has been isolated and structurally characterized. In the solid state, 1 consists of Cs(O-2,6-i-Pr2C6H3) units held in pseudo-one-dimensional infinite chains by both Cs−O and Cs−π-arene interactions with the neighboring unit. The chains are cross-linked into two-dimensional sheets by Cs−C interactions between a carbon atom in the para position of the arene ring and a cesium cation from an adjacent chain.