Mixed cation (Li+, Na+ and K+) and anion (F?, Cl?, Br?) complexes of the aromatic π‐surfaces (top and bottom) are studied by using dispersion‐corrected density functional theory. The selectivity of the aromatic surface to interact with a cation or an anion can be tuned and even reversed by the electron‐donating/electron‐accepting nature of the side groups. The presence of a methyl group in the ? OCH3, ? SCH3, ? OC2H5 in the side groups of the aromatic ring leads to further cooperative stabilization of the otherwise unstable/weakly stable anion???π complexes by bending of the side groups towards the anion to facilitate C? H???anion interactions. The cooperativity among the interactions is found to be as large as 100 kcal mol?1 quantified by dissection of the three individual forces from the total interaction energy. The crystal structures of the fluoride binding tripodal and hexapodal ligands provide experimental evidence for such cooperative interactions. 相似文献
Spectroscopic evidence for C? H ??? O hydrogen bonding in chloroform ??? acetone [Cl3CH ??? O?C(CH3)2] mixtures was obtained from vibrational inelastic neutron scattering (INS) spectra. Comparison between the INS spectra of pure samples and their binary mixtures reveals the presence of new bands at about 82, 130 and 170 cm?1. Assignment of the 82 cm?1 band to the νO ??? H anti‐translational mode is considered and discussed. In addition, the βC? H mode of CHCl3 at 1242 cm?1 is split in the spectra of the mixtures, and the high‐wavenumber component is assigned to the hydrogen‐bonded complex. The plot of the integrated intensity of this component shows a maximum for x=0.5, in agreement with the 1:1 stoichiometry of the chloroform ??? acetone complex, with a calculated complexation constant of 0.15 dm3 mol?1. Results also show that the complex behaves as an independent entity, that is, despite being weak, such interactions play a key role in supramolecular chemistry. 相似文献
The 1H NMR chemical shifts of the C(α)? H protons of arylmethyl triphenylphosphonium ions in CD2Cl2 solution strongly depend on the counteranions X?. The values for the benzhydryl derivatives Ph2CH? PPh3+ X?, for example, range from δH=8.25 (X?=Cl?) over 6.23 (X?=BF4?) to 5.72 ppm (X?=BPh4?). Similar, albeit weaker, counterion‐induced shifts are observed for the ortho‐protons of all aryl groups. Concentration‐dependent NMR studies show that the large shifts result from the deshielding of the protons by the anions, which decreases in the order Cl? > Br? ? BF4? > SbF6?. For the less bulky derivatives PhCH2? PPh3+ X?, we also find C? H???Ph interactions between C(α)? H and a phenyl group of the BPh4? anion, which result in upfield NMR chemical shifts of the C(α)? H protons. These interactions could also be observed in crystals of (p‐CF3‐C6H4)CH2? PPh3+ BPh4?. However, the dominant effects causing the counterion‐induced shifts in the NMR spectra are the C? H???X? hydrogen bonds between the phosphonium ion and anions, in particular Cl? or Br?. This observation contradicts earlier interpretations which assigned these shifts predominantly to the ring current of the BPh4? anions. The concentration dependence of the 1H NMR chemical shifts allowed us to determine the dissociation constants of the phosphonium salts in CD2Cl2 solution. The cation–anion interactions increase with the acidity of the C(α)? H protons and the basicity of the anion. The existence of C? H???X? hydrogen bonds between the cations and anions is confirmed by quantum chemical calculations of the ion pair structures, as well as by X‐ray analyses of the crystals. The IR spectra of the Cl? and Br? salts in CD2Cl2 solution show strong red‐shifts of the C? H stretch bands. The C? H stretch bands of the tetrafluoroborate salt PhCH2? PPh3+ BF4? in CD2Cl2, however, show a blue‐shift compared to the corresponding BPh4? salt. 相似文献
This theoretical study suggests that CH???π stacking interactions between monomeric units can be used to design novel single‐chain magnets (SCMs), as the sign of coupling is predictable and such chains inherently yield negative axial anisotropy, a condition often difficult to achieve in conventional SCMs. 相似文献
Charge transport in organic semiconductors is strongly dependent on their molecular packing modes in the solid state. Therefore, understanding the relationship between molecular packing and charge transport is imperative, both experimentally and theoretically. However, so far, the fundamental effects of solid‐state packing and molecular interactions (e.g. N? H ??? π) on charge transport need further elucidation. Herein, indolo[3,2‐b]carbazole (ICZ) and a derivative thereof are used as examples to approach this scientific target. An interesting insight obtained thereby is that N? H ??? π interactions among ICZ molecules facilitate charge transport for higher mobility. Subtle changes in the of N? H ??? π interactions can significantly influence both the molecular packing and the charge‐transport properties. Therefore, a method for exploiting intermolecular N? H ??? π interactions would yield novel molecular systems with designable characteristics.相似文献
Catalyst–substrate hydrogen bonds in artificial catalysts usually occur in aprotic solvents, but not in protic solvents, in contrast to enzymatic catalysis. We report a case in which ligand–substrate hydrogen‐bonding interactions cooperate with a transition‐metal center in alcoholic solvents for enantioselective catalysis. Copper(I) complexes with prolinol‐based hydroxy amino phosphane chiral ligands catalytically promoted the direct alkynylation of aldehydes with terminal alkynes in alcoholic solvents to afford nonracemic secondary propargylic alcohols with high enantioselectivities. Quantum‐mechanical calculations of enantiodiscriminating transition states show the occurrence of a nonclassical sp3‐C? H???O hydrogen bond as a secondary interaction between the ligand and substrate, which results in highly directional catalyst–substrate two‐point hydrogen bonding. 相似文献
A family of PdII/PtII dinuclear receptors, designed to give a smooth increase in their cavity lengths (from 7.46–13.78 Å), is presented. Their inclusion complexes with a representative set of polycyclic aromatic substrates (naphthalene, carbazol, pyrene, and benzo[a]pyrene), were characterized and studied in aqueous solution and the solid state. By taking into account the dimensions of both receptors and substrates, an excellent complementarity was found between the size of the receptors and their ability to complex a given substrate. Furthermore, this dimensional matching results in specific binding modes depending on the ability of the guest to establish stabilizing [C? H???π] interactions with the host. 相似文献
Cooperativity between weak hydrogen bonds can be revealed in molecular clusters isolated in the gas phase. Here we examine the structure, internal dynamics, and origin of the weak intermolecular forces between sevoflurane and a benzene molecule, using multi‐isotopic broadband rotational spectra. This heterodimer is held together by a primary C H⋅⋅⋅π hydrogen bond, assisted by multiple weak C H⋅⋅⋅F interactions. The multiple nonbonding forces hinder the internal rotation of benzene around the isopropyl C H bond in sevoflurane, producing detectable quantum tunneling effects in the rotational spectrum. 相似文献
The formation of weakly bound molecular complexes between dimethyl ether (DME) and the trifluoromethyl halides CF3Cl, CF3Br and CF3I dissolved in liquid argon and in liquid krypton is investigated, using Raman and FTIR spectroscopy. For all halides evidence is found for the formation of C? X???O halogen‐bonded 1:1 complexes. At higher concentrations of CF3Br, a weak absorption due to a 1:2 complex is also observed. Using spectra recorded at temperatures between 87 and 125 K, the complexation enthalpies for the complexes are determined to be ?6.8(3) kJ mol?1 (DME?CF3Cl), ?10.2(1) kJ mol?1 (DME?CF3Br), ?15.5(1) kJ mol?1 (DME?CF3I), and ?17.8(5) kJ mol?1 [DME(?CF3Br)2]. Structural and spectral information on the complexes is obtained from ab initio calculations at the MP2/ 6‐311++G(d,p) and MP2/6‐311++G(d,p)+LanL2DZ* levels. By applying Monte Carlo free energy perturbation calculations to account for the solvent influences, and statistical thermodynamics to estimate the zero‐point vibrational and thermal influences, the ab initio complexation energies are converted into complexation enthalpies for the solutions in liquid argon. The resulting values are compared with the experimental data deduced from the cryosolutions.相似文献
The factors governing the stability and the reactivity towards cyclic esters of heteroleptic complexes of the large alkaline earth metals (Ae) have been probed. The synthesis and stability of a family of heteroleptic silylamido and alkoxide complexes of calcium [{LOi}Ca? Nu(thf)n] supported by mono‐anionic amino ether phenolate ligands (i=1, {LO1}?=4‐(tert‐butyl)‐2,6‐bis(morpholinomethyl)phenolate, Nu?=N(SiMe2H)2?, n=0, 4 ; i=2, {LO2}?=2,4‐di‐tert‐butyl‐6‐{[2‐(methoxymethyl)pyrrolidin‐1‐yl]methyl}phenolate, Nu?=N(SiMe2H)2?, n=0, 5 ; i=4, {LO4}?=2‐{[bis(2‐methoxyethyl)amino]methyl}‐4,6‐di‐tert‐butylphenolate, Nu?=N(SiMe2H)2?, n=1, 6 ; Nu?=HC?CCH2O?, n=0, 7 ) and those of the related [{LO3}Ae? N(SiMe2H)2] ({LO3}?=2‐[(1,4,7,10‐tetraoxa‐13‐azacyclopentadecan‐13‐yl)methyl]‐4,6‐di‐tert‐butylphenolate Ae=Ca, 1 ; Sr, 2 ; Ba, 3 ) have been investigated. The molecular structures of 1 , 2 , [( 4 )2], 6 , and [( 7 )2] have been determined by X‐ray diffraction. These highlight Ae???H? Si internal β‐agostic interactions, which play a key role in the stabilization of [{LOi}Ae? N(SiMe2H)2] complexes against ligand redistribution reactions, in contrast to regular [{LOi}Ae? N(SiMe3)2]. Pulse‐gradient spin‐echo (PGSE) NMR measurements showed that 1 , 4 , 6 , and 7 are monomeric in solution. Complexes 1 – 7 mediate the ring‐opening polymerization (ROP) of L ‐lactide highly efficiently, converting up to 5000 equivalents of monomer at 25 °C in a controlled fashion. In the immortal ROP performed with up to 100 equivalents of exogenous 9‐anthracenylmethanol or benzyl or propargyl alcohols as a transfer agent, the activity of the catalyst increased with the size of the metal ( 1 < 2 < 3 ). For Ca‐based complexes, the enhanced electron‐donating ability of the ancillary ligand favored catalyst activity ( 1 > 6 > 4 ≈ 5 ). The nature of the alcohol had little effect over the activity of the binary catalyst system 1 /ROH; in all cases, both the control and end‐group fidelity were excellent. In the living ROP of L ‐LA, the HC?CCH2O? initiating group (as in 7 ) proved superior to N(SiMe2H)2? or N(SiMe3)2? (as in 6 or [{LO4}Ca? N(SiMe3)2] ( B ), respectively). 相似文献
Research on structure–property relationships in distyrylarylene derivatives is far behind their wide applications in optoelectronic devices due to the absence of crystal structure information. Herein, the single crystals of 4,4′‐bis(2‐thienylvinyl)biphenyl ( 1 ) and 4,4′‐bis(2‐thieno[3,2‐b]thienylvinyl)biphenyl ( 2 ) were successfully grown by the vapor transport method. Both molecules adopt the typical herringbone packing motif. However, the intermolecular C? H???π interaction in compound 2 is much stronger than that in compound 1 . The correlations of interchain interaction with film morphology, optical and electronic properties were studied. Compound 2 formed higher crystalline films with (001) and (111) orientations. The organic field‐effect transistor properties of both materials were investigated. Compound 2 showed better performance with a hole mobility higher than 0.01 cm2 V?1 s?1 and an on/off current ratio over 106. These results reveal that the intensity of C? H???π interactions can exert dramatic influences on the optical and electronic properties of distyrylarylene‐based materials. 相似文献
Attractive chlorine : Noncovalent interactions between chlorine or bromine atoms and aromatic rings in proteins open up a new method for the manipulation of molecular recognition. Substitution at distinct positions of two factor Xa inhibitors improves the free energy of binding by interaction with a tyrosine unit. The generality of this motif was underscored by multiple crystal structures as well as high‐level quantum chemical calculations (see picture).
Attraktives Chlor : Nichtkovalente Wechselwirkungen zwischen Chlor‐ oder Brom‐Atomen und aromatischen Ringen in Proteinen bieten einen neuen Ansatzpunkt für die Beeinflussung der molekularen Erkennung. Die Einführung dieser Substituenten an spezifischen Positionen zweier Faktor‐Xa‐Inhibitoren erhöht deren freie Bindungsenergie durch die Wechselwirkung mit einer Tyrosineinheit. Das allgemeine Vorkommen dieses Strukturmotivs wird anhand zahlreicher Kristallstukturen und quantenchemischer Rechnungen belegt (siehe Bild).
The crystal structure of fluorobenzene is compared with isomorphous crystal structures of molecules of roughly similar shape. The lowest-energy fluorobenzene dimers are identified by theoretical calculations. Molecular pair analysis of the crystal structure of fluorobenzene and of an isomorphous virtual low-energy polymorph of benzene suggests that the important intermolecular interactions in the two structures are closely similar. In particular, the intermolecular C-H...F interactions in the fluorobenzene crystal have approximately the same structure-directing ability and influence on the intermolecular energy as the corresponding C-H...H interactions in benzene. Molecular pair analysis of the isomorphous crystal structures of benzonitrile, alloxan, and cyclopentene-1,2,3-trione indicates that essentially the same crystal structure can be adopted with quite different patterns of pair energies and atom-atom interactions. The question as to whether the packing radius of organic fluorine is larger or smaller than that of hydrogen, is addressed, but not answered. 相似文献
Relativity matters: Calculations of NMR shielding tensors and spin–spin coupling constants transmitted through Ir? H???H? N dihydrogen bonds are presented. The picture shows one of the simplified models employed. It is shown that the spin–orbit relativistic effects influence the NMR shielding constants far more than the spin–spin coupling constants.
Full structural characterisation and complete synthetic procedures for three monohalogenated cobaltacarborane compounds closo-[3-Co(eta5-C5H5)-8-X-1,2-C2B9H10] (X=Cl (1), Br (2), I (3)) and the dibromo derivative closo-[3-Co(eta5-C5H5)-8,9-Br2-1,2-C2B9H9] (4) are reported. The supramolecular structures of 1, 3, and 4 reveal the existence of intermolecular C--HX--B interactions. The role of these interactions has been investigated through a CSD search and subsequent analysis of the reported crystalline compounds. The results show that halogens become reasonably good hydrogen-bond acceptors when bonded to boron and, in this respect, are comparable in strength to metal-bound halogens. 相似文献