C-H?Br, C-Br?Br, and C-Br?π interactions in the crystal structures of mesitylene- and dimesitylmethane-derived compounds bearing bromomethyl units

X-ray structure determinations of mesitylene- and dimesitylmethane-derived compounds bearing bromomethyl units (compounds 1-3) show that the crystal packing of the molecules is characterized by the presence of C-H?Br interactions, such as BrCH₂?Br, CH₃?Br, and C_PhH?Br. In addition, C-Br?Br and C-Br?π interactions determine the crystal packing. The bromomethyl groups play a major role in the packing of 1-3.     

New triorganotin(IV) complexes of polyfunctional S,N,O-ligands: Supramolecular structures based on π?π and/or C-H?π interactions

A series of new triorganotin(IV) complexes with 4-hydroxy-2-mercapto-6-methylpyrimidine (L¹H₂), 4-hydroxy-2-mercapto-pyrimidine (L²H₂), 2,4(1H,3H)-pyrimidinedithione (L³H₂) (Scheme 1) of the type R₃SnLSnR₃ (R = Me 1, 4, 7; R = Ph 2, 5, 8; R = PhCH₂3, 6, 9) have been synthesized by reactions of triorganotin(IV) chloride and corresponding ligands. All complexes are characterized by elemental analyses, IR spectra and NMR spectra analyses. Among them, complexes 2, 5 and 8 are also characterized by X-ray crystallography diffraction analyses. Significant π?π stacking, C-H?π interactions and intramolecular hydrogen bonds stabilize these structures.     

On the weakly C-H···π hydrogen bonded complexes of sevoflurane and benzene

A vibrational assignment of the anaesthetic sevoflurane, (CF(3))(2)CHOCH(2)F, is proposed and its interaction with the aromatic model compound benzene is studied using vibrational spectroscopy of supersonic jet expansions and of cryosolutions in liquid xenon. Ab initio calculations, at the MP2/cc-pVDZ and MP2/aug-cc-pVDZ levels, predict two isomers for the 1?:?1 complex, one in which the near-cis, gauche conformer of sevoflurane is hydrogen bonded through its isopropyl-hydrogen atom, the other in which the same conformer is bonded through a bifurcated hydrogen bond with the fluoromethyl hydrogen atoms. From the experiments it is shown that the two isomers are formed, however with a strong population dominance of the isopropyl-bonded species, both in the jet and liquid phase spectra. The experimental complexation enthalpy in liquid xenon, ΔH(o)(LXe), of this species equals -10.9(2) kJ mol(-1), as derived from the temperature dependent behaviour of the cryosolution spectra. Theoretical complexation enthalpies in liquid xenon were obtained by combining the complete basis set extrapolated complexation energies at the MP2/aug-cc-pVXZ (X = D,T) level with corrections derived from statistical thermodynamics and Monte Carlo Free Energy Perturbation calculations, resulting in a complexation enthalpy of -11.2(3) kJ mol(-1) for the isopropyl-bonded complex, in very good agreement with the experimental value, and of -11.4(4) kJ mol(-1), for the fluoromethyl-bonded complex. The Monte Carlo calculations show that the solvation entropy of the isopropyl-bonded species is considerably higher than that of the fluoromethyl-bonded complex, which assists in explaining its dominance in the liquid phase spectra.     

Strong phenyl-perfluorophenyl π-π stacking and C-H?F-C hydrogen bonding interactions in the crystals of the corresponding aromatic aldimines

The X-ray diffraction analysis of two co-crystals, 1·2 (aldimines 1 and 2) and 3·4 (aldimines 3 and 4), reveals that there are strong phenyl-perfluorophenyl π-π stacking and intermolecular hydrogen bonding interactions. The new perfluoroaryl-aryl face-to-face interaction of the crystalline aldimines provides a design motif for a new class of self-assembling system.     

C-H…O Hydrogen Bonds and π…π Interaction and the Crystal and Molecular Structures of 3-Nitro-benzylideneaniline-methyl-2’

The title compound (C14H12N2O2,Mr=240.26) crystallizes in the monoclinic system,space group P21/a with a=7.394(1),b=21.334(3),c=7.423(1)A,β=89.82(1)A°,V=1170.8(3)A3,Z=4,Dc=1.363 g/cm3,μ(MoKα)=0.93 cm-1 and F(000)=504.00.The final R and wR are 0.0440 and 0.1370 for 2153 observed reflections (I>2σ(I)),respectively.The dihedral angle between the two phenyl rings is 52.9°and that between the NO2 group and its attached ring is 3.0°.In the crystal,molecules are stacked along [100] throughπ…πinteractions.The C-H…O hydrogen bond (3.403 A,120.4°) laterally connects the stacks along [010] to form networks (001) which are further anti-parallelly connected by C-H…O(3.382 A,142.9°) andπ…πinteractions extending along [001].Also presented here is a brief study on the C-H…O hydrogen bonds in nitro-substituted benzyl-ideneanilines which can be classified into five types,namely,R12(5)R21(4),R22(8),R12(6),andR22(7),with the first three occurring more often.     

An Extended Cu(Ⅱ) Complex Structure Sustained by Hydrogen Bonding and C-H…π Interactions

The title complex [Cu(L1)(L2)(H2O)]·H2O(1,HL1 = N-(imino(pyridin-2-yl)me-thyl)picolinamidine),HL2 = salicylic acid) has been obtained by volatilization method with L1 prepared from 2,4,6-tripyridyl-1,3,5-triazine in situ.1 was fully characterized by single-crystal X-ray diffraction,elemental analysis and FT-IR.This complex exhibits a three-dimensional frame-work constructed through hydrogen bonding and C-H···π stacking interactions.The cyclic voltametric behavior of complex 1 was also investigated.1 belongs to the monoclinic system,space group P21/c with a = 15.112(5),b = 7.115(2),c = 19.899(6) ,β = 112.32°,V = 1979.4(11) 3,Mr = 460.94,Dc = 1.540 g/cm3,F(000) = 948,μ = 1.146 mm-1,Z = 4,the final R = 0.0612 and wR = 0.1813 for 2510 observed reflections with I 2σ(I).     

1D and 2D supramolecular structures of silver carborane dicyclohexylphosphine complexes constructed by C-H?H-B dihydrogen bonding interactions

Five new carborane dicyclohexylphosphine complexes, [Ag₂(μ-I)₂{1,2-(P Cy₂)₂-1,2-C₂B₁₀H₁₀}₂] (1), [Ag₂(SCN)₂{1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}₂]_n·CH₂Cl₂ (2), [Ag(ClO₄){1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}]·CH₂Cl₂ (3), [Ag₂(μ-NO₃)₂{1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}₂]·CH₂Cl₂ (4) and [Ag(SC₆H₄COOH){1,2-(PCy₂)₂-1,2-C₂B₁₀H₁₀}₂]·CH₂Cl₂ (5), have been synthesized by the reactions of 1,2-bis(dicyclohexylphosphino)-1,2-dicarba-closo-dodecaborane with AgX (X = I, SCN, ClO_4, NO₃ and SC₆H₄COOH) in CH₂Cl₂. The structures of the five complexes were characterized by elemental analysis, FT-IR, ¹H, ¹³C, ¹¹B and ³¹P NMR spectroscopy. X-ray structure analysis revealed that the structures of the complexes can be classified into three types. Complexes 1 and 4 are di-μ-X-bridged structures and complexes 3 and 5 are mononuclear structures, while complex 2 is a chain-like polymer. Complexes 1 and 2 form 2D supramolecular networks and complexes 3, 4 and 5 form 1D chains via C-H?H-B dihydrogen bonding interactions.     

First homo- and hetero-nuclear complexes of a chemical messenger-histamine: Cu(II) complex being a supramolecular assembly based on hydrogen bond, Ni(II)?π and C-H?π non-covalent interactions

In this study, the first homo- and hetero-nuclear cyanocomplexes of histamine (His), namely, [Cu(His)₂][Ni(CN)₄], [Ni(His)₂Ni(CN)₄]_n and [Cd(His)Ni(CN)₄]_n are investigated by X-ray diffraction (XRD) technique, electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy. Besides being the first hetero-nuclear complex of histamine, [Cu(His)₂][Ni(CN)₄] complex has an interesting property as being a supramolecular structure constructed by three different non-covalent interactions as hydrogen bond, Ni(II)?π and C-H?π interactions. In [Cu(His)₂][Ni(CN)₄] complex histamine exists in gauche conformation and N^τ-H tautomeric form, and plays an important role in supramolecular structure formation by participating in non-covalent interactions through its aminoethyl side chain and imidazole group. The shifts and splittings in the stretching vibrations of cyano groups show that [Ni(His)₂Ni(CN)₄]_n and [Cd(His)Ni(CN)₄]_n complexes are one-dimensional and three-dimensional coordination polymers, respectively. In [Ni(His)₂Ni(CN)₄]_n complex, histamine acts as a chelating ligand by adopting gauche conformation. In [Cd(His)Ni(CN)₄]_n complex, Cd(II) ions and [Ni(CN)₄]²⁻ anions form two-dimensional layered structure and histamine has a novel bonding mode as a bridging ligand between these layered structures. It is concluded that histamine may have trans conformation and Nπ-H tautomer as a bridging ligand in [Cd(His)Ni(CN)₄]_n complex, which has not been reported so far for the solid structures of bidentate histamine. EPR studies on [Cu(His)₂][Ni(CN)₄] and Cu²⁺-doped [Cd(His)Ni(CN)₄]_n complexes show that the ground state of the unpaired electron in both complexes is dominantly d_x²-y².     

Combined cation-π and anion-π interactions for zwitterion recognition

Brothers and enemies: Anion-π and cation-π interactions act in a synergistic way when gathered in the molecular cavity of a hemicryptophane host, affording an efficient contribution (-170?kJ?mol(-1)) in zwitterion recognition. NMR titration experiments and calculations reveal the positioning of the guest in the cavity of the heteroditopic receptor. This study emphasizes the importance of anion-π bonds in host-guest chemistry.     

Self-assembly of Bis[2-(2-hydroxyphenyl)-pyridine]Copper(Ⅱ) Induced by C-H…π and π…π Stacking Interaction

Introduction The control of molecular assembly in the solid state is an important theme of modern chemistry.It is in this regard that there is an activity in the area of supramolecular structures at present.The self-assembly of molecules can form well-defined supramolecular structures under the influence of drive forces such as hydrogen bonds[1-3],metal-ligand coordination bonds[4-6] and π…π stacking interactions[7-10].Word et al.have described the co-ordination chemistry of polydentate chelating ligands which contain mixed pyridine-phenol donor sets[11].Some unusual structures of transition metal pyridine-phenol complexes have been established in which non-covalent interactions such as hydrogen bonding and π…π stacking appear to play a dominant part.These observations suggest that it might be possible to construct supramolecular structures with a metal pyridine-phenol system.To explore this idea we have begun to investigate the self-assembly properties of metal pyridine-phenol complexes.Herein we present the self-assembly properties of Cu(pp)2[pp=2-(2-hydroxyphenol)-pyridine] under different conditions.     

Functionally Important Aromatic-Aromatic and Sulfur-π Interactions in the D2 Dopamine Receptor

The recently published crystal structure of the D3 dopamine receptor shows a tightly packed region of aromatic residues on helices 5 and 6 in the space bridging the binding site and what is thought to be the origin of intracellular helical motion. This highly conserved region also makes contacts with residues on helix 3, and here we use double mutant cycle analysis and unnatural amino acid mutagenesis to probe the functional role of several residues in this region of the closely related D2 dopamine receptor. Of the eight mutant pairs examined, all show significant functional coupling (Ω > 2), with the largest coupling coefficients observed between residues on different helices, C3.36/W6.48, T3.37/S5.46, and F5.47/F6.52. Additionally, three aromatic residues examined, F5.47, Y5.48, and F5.51, show consistent trends upon progressive fluorination of the aromatic side chain. These trends are indicative of a functionally important electrostatic interaction with the face of the aromatic residue examined, which is likely attributed to aromatic-aromatic interactions between residues in this microdomain. We also propose that the previously determined fluorination trend at W6.48 is likely due to a sulfur-π interaction with the side chain of C3.36. We conclude that these residues form a tightly packed structural microdomain that connects helices 3, 5, and 6, thus forming a barrier that prevents dopamine from binding further toward the intracellular surface. Upon activation, these residues likely do not change their relative conformation, but rather act to translate agonist binding at the extracellular surface into the large intracellular movements that characterize receptor activation.     

Self-assembly of organooxotin(IV) clusters with Schiff-base-containing-triazole from hydrolysis or solvothermal synthesis: Crystal structures, hydrogen bonds, C-H?π stacking and S?S interaction

Eight new organostannoxane-based multiredox assemblies containing-Schiff-base-triazole ligand peripheries have been readily synthesized by hydrolysis or solvothermal synthetic routes. The reactions of the diorganotin dichloride with the Schiff-base-containing-triazole ligand afford the following types: [(Me₂Sn)₂O₂(Ln)]₂ (n = 1, for 1) [(Me₂Sn)₂O(RO)(Ln)]₂ (R = Et, n = 2, for 2; R = Me, n = 3, for 3), [(n-Bu₂Sn)₂O₂(Ln)]₂ (n = 1, for 4; n = 2, for 5; n = 3, for 6) and [(Me₂Sn)₂Ln₂O]₂ · L (n = 2; L = H₂O for 7, L = CH₃OH for 8). All the complexes were characterized by elemental analysis, IR, ¹H, ¹³C and ¹¹⁹Sn spectra analyses. Except for complexes 4 and 6, the other complexes are also characterized by X-ray crystallography diffraction analyses. Complexes 1-3 and 5 show similar structures containing a Sn₄O₄ ladder-shaped skeleton in which the N atom from a corresponding thione-form deprotonated Schiff base coordinated to the exo tin atoms in monodentate chelating agent. Complex 7 and 8 show a novel framework containing a Sn₂O₂ symmetrical core with two N atoms from triazole moiety coordinated to tin atoms. Weak but significant intermolecular hydrogen bondings, C-H?π stacking or non-bonded S?S interaction lead to aggregation and self-assembly of these complexes into 1D, 2D or 3D supramolecular frameworks.     

Novel Intermolecular C-H…π Interactions from a One-dimensional Chain:Synthesis and Crystal Structure of a Ladder Dibenzyl Tin Carboxylate

The title ladder organotin carboxylate,{[(C6H5CH2)2Sn]4(p-NH2C6H4-COO)2O2(OCH3)2}·0.5H2O 1,has been synthesized and structurally characterized by elemental analyses,IR and single-crystal X-ray diffraction analysis.Complex 1 is located across on an inversion center and displays a Sn4O4 ladder-like structure with a one-dimensional supramolecular chain through C-H…π interactions.In the asymmetric unit two Sn(Ⅳ) atoms assume similar trigonal bipyramidal coordination geometry.Two aminobenzoate groups coordinate to the terminal Sn(Ⅳ) atoms.The deprotonated methanol molecule bridges two independent Sn(Ⅳ) atoms.A half of lattice water molecule is disorderly filled in the cavity formed by Sn(Ⅳ) complexes.     

C-X···π halogen and C-H···π hydrogen bonding: interactions of CF3X (X = Cl, Br, I or H) with ethene and propene

Using FTIR and Raman spectroscopy, the formation of halogen bonded complexes of the trifluorohalomethanes CF(3)Cl, CF(3)Br and CF(3)I with ethene and propene dissolved in liquid argon has been investigated. For CF(3)Br and CF(3)I, evidence was found for the formation of C-X···π halogen bonded 1:1 complexes. At a higher ratio of CF(3)I/propene, weak absorptions due to a 2:1 complex were also observed. Using spectra recorded at different temperatures, the complexation enthalpies for the complexes were determined to be -5.3(2) kJ mol(-1) for CF(3)Br·ethene, -7.5(2) kJ mol(-1) for CF(3)I·ethene, -5.6(1) kJ mol(-1) for CF(3)Br·propene, -8.8(1) kJ mol(-1) for CF(3)I·propene and -16.5(6) kJ mol(-1) for (CF(3)I·)(2)propene. The complexation enthalpies of the hydrogen bonded counterparts, with CF(3)H as the Lewis acid, were determined to be -4.6(4) kJ mol(-1) for CF(3)H·ethene and -5.1(2) kJ mol(-1) for CF(3)H·propene. For both hydrogen bonded complexes, a blue shift, by +4.8 and +4.0 cm(-1), respectively, was observed for the C-H stretching mode. The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level.     

C-H⋯O, O-H⋯C, and C-H⋯C interactions in complexes of carbocations and carboanions

Molecular complexes formed by different forms of carbocations (carbenium ions) and carboanions with water, acetylene, and methane molecules have been calculated by the MP2/6-311++G(2df,2pd) method. In complexes with water where the carbon atom of the carbocation (carboanion) acts as the proton donor (acceptor), the energies of the C-H?O and O-H?C hydrogen bonds turn out to be approximately the same being 13–20 kcal/mol for carbocation (carboanion) species differing in the valence state of the carbon atom. Two types of C-H?C interactions have been revealed depending on the charge at the bridging hydrogen atom, which is determined by the hybridization of the donor carbon atom. The C-H?C interaction energy in molecular complexes with the positively charged hydrogen atom (carboanion complexes with acetylene) is an order of magnitude higher than in the complexes where the bridging hydrogen atom has an excess of electron density (carbocation complexes with methane). In all the complexes under consideration, the covalent C-H bond involved in interaction is elongated, and the negative charge is transferred from the acceptor to the donor.     

Quantification of binding affinities of essential sugars with a tryptophan analogue and the ubiquitous role of C-H···π interactions

The role of noncovalent interactions in carbohydrate recognition by aromatic amino acids has long been reported. To develop a molecular understanding of noncovalent interactions in the recognition process, we have examined a series of binary complexes between 3-methylindole (3-MeIn) and sugars. In particular, the geometries and binding affinities of 3-MeIn with α/β-D-glucose, β-D-galactose, α-D-mannose and α/β-L-fucose are obtained using the MP2(full)/6-31G(d,p) and the M06/TZV2D//MP2/6-31G(d,p) level of theories. The conventional hydrogen bonding such as N-H···O and C-H···O as well as nonconventional O-H···π and C-H···π type of interactions is, in general, identified as responsible for the moderately strong interaction energies. Large variations in the position-orientations of 3-MeIn with respect to saccharide are noticed, within the same sugar family, as well as across different sugar series. Furthermore, complexes with large differences in their geometries are recognized as capable of exhibiting very similar interaction energies, underscoring the significance of exhaustive conformation sampling, as carried out in the present study. These observations are readily attributed to the differences in the efficiency of the type of interactions enlisted above. The highest and lowest interaction energies, upon inclusion of 50% BSSE correction, are found to be -16.02 and -6.22 kcal mol(-1), respectively, for α-D-glucose (1a) and α-L-fucose (5j). While more number of prominent conventional hydrogen bonding contacts remains as a characteristic feature of the strongly bound complexes, the lower end of the interaction energy spectrum is dominated by multiple C-H···π interactions. The complexes exhibiting as many as four C-H···π contacts are identified in the case of α/β-D-glucose, β-D-galactose, and α/β-L-fucose with an interaction energy hovering around -8 kcal mol(-1). The presence of effective C-H···π interactions is found to be dependent on the saccharide configuration as well as the area of the apolar patch constituted by the C-H groups. The study offers a comprehensive set of binary complexes, across different saccharides, which serves as an illustration of the significance and ubiquitous nature of C-H···π interactions in carbohydrate binding in saccharide-protein complexes.     

Ring currents that survive bond alternation in constrained 8π and 6π monocycles

Current density maps are computed at the ipsocentric CTOCD-DZ/6-31G^**//RHF/6-31G^** level for angle-constrained planar 1,3,5,7-cyclooctatetraenes (COT) and benzene. Constraint of α(CCH) angles to 90° in D_4h COT (3b) leads to endo-4 and exo-4 valence isomers. The exo structure, with CH bonds perpendicular to long sides of the octagon, is lower in energy by 202 kJ/mol and has stronger bond alternation (ΔR 0.265 Å). However, endo-4, exo-4 and COT 3b at its best planar geometry all sustain intense paratropic ring currents, attributed to the rotational character of the HOMO–LUMO transition, and consistent, mutatis mutandis, with the diatropic current in D_3h benzene 5.     

Synthesis, X-ray crystallographic, and dynamic H NMR studies of crown-tetrathia[3.3.3.3]metacyclophanes—conformational control by cooperative intramolecular C-H?π interaction both in solid state and in solution

Crown-tetrathia[3.3.3.3]metacyclophanes 3a-c were synthesized via intermolcular coupling reaction in 22-30% yields. X-ray crystal analysis of 3b revealed that it adopted a perpendicular conformation (3b-B or 3b-C) in which two aromatic rings were inclined to be perpendicular to the opposite aromatic rings, driving two internal methyl groups into the π-cloud of the corresponding benzene rings. Furthermore, this perpendicular structural feature led to benzylic protons of thia-bridges being in close proximity to the adjacent aromatic rings. As a result, the induced upfield shifts for the two internal methyl protons and four benzylic protons were clearly observed in dynamic ¹H NMR spectra at low temperature, indicating that the intramolecular C-H?π interaction became increasingly important at low temperature. The energy barrier for inter-conversion between 3b-B and 3b-C was estimated to be 12.1 kcal mol⁻¹ by using a coalescence method. The total stabilization enthalpy of the C-H?π interactions was quantitatively calculated to be 7.9±0.8 kcal mol⁻¹ by the dynamic NMR spectroscopy. In contrast, 3a showed two non-interconvertible conformers at room temperature, which tended to interconvert at elevated temperature, however, many conformers co-existed at low temperature.     

Intramolecular MLOH/π and MLNH/π interactions in crystal structures of metal complexes

Intramolecular metal-ligand OH/π (MLOH/π) and metal-ligand NH/π (MLNH/π) interactions in transition metal complexes between aqua or ammine ligand and ligand containing a C6-aromatic ring were investigated in crystal structures deposited in the Cambridge Structural Database (CSD). These intramolecular interactions appear in 38 structures with aqua ligand as the hydrogen atom donor and in 10 structures with ammine ligand as the hydrogen atom donor. Among all these complexes only one is negatively charged, 14 are positively charged and 33 are neutral indicating that the overall charge of the molecule has an influence on the XH/π (X = O or N) interactions. Energy estimated by DFT calculations is approximately 19 kJ mol⁻¹ for the MLOH/π interactions and approximately 15 kJ mol⁻¹ for the MLNH/π interactions. Dedicated to Professor Milan Melník on the occasion of his 70th birthday