两个四硫富瓦烯分子正离子自由基TTF·^＋之间的共价吸引作用

使用MP2／6-311G方法得到了四硫富瓦烯自由基正离子二聚体（TTF·^＋ -TTF·^＋）能量极小点的结构．这显示这种正离子间的吸引作用存在．这种新的吸引作用是望远镜形状的20中心2电子分子间共价π/π键．这种共价π/π键的键能约为-21kcal·mol^-1,它被正离子间的库伦排斥作用掩盖．有负离子围绕的四硫富瓦烯自由基正离子二聚体（TTF·^＋ -TTF·^＋）体系是稳定的．     

Intermolecular covalent pi-pi bonding interaction indicated by bond distances, energy bands, and magnetism in biphenalenyl biradicaloid molecular crystal

Density-functional theory (DFT) calculations were performed for energy band structure and geometry optimizations on the stepped pi-chain, the isolated molecule and (di)cations of the chain, and various related molecules of a neutral biphenalenyl biradicaloid (BPBR) organic semiconductor 2. The dependence of the geometries on crystal packing provides indirect evidence for the intermolecular covalent pi-pi bonding interaction through space between neighboring pi-stacked phenalenyl units along the chain. The two phenalenyl electrons on each molecule, occupying the singly occupied molecular orbitals (SOMOs), are participating in the intermolecular covalent pi-pi bonding making them partially localized on the phenalenyl units and less available for intramolecular delocalization. The band structure shows a relatively large bandwidth and small band gap indicative of good pi-pi overlap and delocalization between neighboring pi-stacked phenalenyl units. A new interpretation is presented for the magnetism of the stepped pi-chain of 2 using an alternating Heisenberg chain model, which is consistent with DFT total energy calculations for 2 and prevails against the previous interpretation using a Bleaney-Bowers dimer model. The obtained transfer integrals and the magnetic exchange parameters fit well into the framework of a Hubbard model. All presented analyses on molecular geometries, energy bands, and magnetism provide a coherent picture for 2 pointing toward an alternating chain with significant intermolecular through-space covalent pi-pi bonding interactions in the molecular crystal. Surprisingly, both the intermolecular transfer integrals and exchange parameters are larger than the intramolecular through-bond values indicating the effectiveness of the intermolecular overlap of the phenalenyl SOMO electrons.     

Theoretical analysis of intermolecular covalent pi-pi bonding and magnetic properties of phenalenyl and spiro-biphenalenyl radical pi-dimers

Singlet-triplet splittings DeltaEST and intermolecular covalent pi-pi bonding characteristics of the prototypical phenalenyl pi-dimer and eight spiro-biphenalenyl radical pi-dimer structures are analyzed with the aid of restricted and unrestricted density functional theory calculations and paramagnetic susceptibility data fitted using the Bleaney-Bowers dimer model and the Curie-Weiss model. Single determinant approximations for DeltaEST as a function of transfer integrals and on-site Coulomb repulsion energy are presented for the two-electron two-site pi-dimers of phenalenyls and the two-electron four-site pi-dimers of spiro-biphenalenyl radicals. Within the range of intermolecular separation of 3.12相似文献   

A covalent attraction between two molecular cation TTF·+

The optimized structure of the tetrathiafulvalence radical-cation dimer (TTF·⁺-TTF·⁺) with all-real frequencies is obtained at MP2/6-311G level, which exhibits the attraction between two molecular cation TTF·⁺. The new attraction interaction is a 20-center-2-electron intermolecular covalent π/π bonding with a telescope shape. The covalent π/π bonding has the bonding energy of about ?21 kcal·mol^?1 and is concealed by the Coulombic repulsion between two TTF·⁺ cations. This intermolecular covalent attraction also influences the structure of the TTF·⁺ subunit, i.e., its molecular plane is bent by an angle θ = 5.6°. This work provides new knowledge on intermolecular interaction.

     

A covalent attraction between two molecular cation TTF·+

The optimized structure of the tetrathiafulvalence radical-cation dimer (TTF·⁺-TTF·⁺) with all-real frequencies is obtained at MP2/6-311G level, which exhibits the attraction between two molecular cation TTF·⁺. The new attraction interaction is a 20-center-2-electron intermolecular covalent π/π bonding with a telescope shape. The covalent π/π bonding has the bonding energy of about −21 kcal·mol⁻¹ and is concealed by the Coulombic repulsion between two TTF·⁺ cations. This intermolecular covalent attraction also influences the structure of the TTF·⁺ subunit, i.e., its molecular plane is bent by an angle θ = 5.6°. This work provides new knowledge on intermolecular interaction.     

The maximin principle of pi-radical packings

A two-term model is proposed for hydrocarbon and N-containing pi-radicals which are in close contact with one another. The first term is attractive (due to partially occupied frontier pi-orbitals), and the second, repulsive (due to hard-core repulsion between close-lying atoms). This model is applied to dimers where intermolecular contacts are closer than <0.95 x the sum of the atomic van der Waals radii. The maximin principle is proposed. The maximin principle states that the lowest energy conformation maximizes overlap of the frontier orbitals while simultaneously minimizing intermolecular contacts. A Hückel Hamiltonian, the mu(2)-Hamiltonian, which contains the above attractive and repulsive terms, is applied. The interaction surfaces of two pi-hydrocarbon radical cations were calculated for the three systems known crystallographically to contain cations in close contact: naphthalene, fluoranthene, and pyrene. The global minima of these surfaces correspond to the experimentally determined structures. The mu(2)-Hamiltonian energy surfaces of the naphthalene cation dimer are qualitatively similar to those calculated at the RHF/6-311G(d,p) and MP2/6-311G(d,p) levels. The maximin principle is applied to N-containing pi-radicals. Except in the case of tetracyanoethene, the maximin principle correctly predicts the most common dimer crystal packing. (MgPc)(NO(3)).0.5THF and (MgPc)(ReO(4)).1.5THF (Pc = phthalocyanine) were prepared: both new crystal structures follow the maximin principle. The maximin principle is used to suggest the dimer cation ground state of oligoacenes, cations important as organic hole-based semiconductors.     

镁铝水滑石层板与层间阴离子相互作用的理论研究

本文采用以ASED-MO(含原子对排斥的EHMO法)为基础的结构自动优化的EHTOPT程序,对镁铝水滑石(LDHs)层板与层间阴离子相互作用进行了理论研究.以Mg6Al2(OH)16X@H2O为分子结构单元,计算并分析了与不同层间阴离子形成稳定结构的能量变化、成键状况及电荷转移情况,揭示了层间作用力的本质.结果表明,LDHs层板与层间阴离子间存在静电吸引、氢键等非共价键弱相互作用,且氢键作用为主,其强弱与阴离子电荷分布、空间排布方式密切相关;层间阴离子电荷分布同时还影响着层板酸碱性的变化.     

When Like Charged Ions Attract in Ionic Liquids: Controlling the Formation of Cationic Clusters by the Interaction Strength of the Counterions

The properties of ionic liquids are described by a subtle balance between Coulomb interaction, hydrogen bonding, and dispersion forces. We show that lowering the attractive Coulomb interaction by choosing weakly coordinating anions leads to the formation of cationic clusters. These clusters of like‐charged ions are stabilized by cooperative hydrogen bonding and controlled by the interaction potential of the anion. IR and NMR spectroscopy combined with computational methods are used to detect and characterize these unusual, counter‐intuitively formed clusters. They can be only observed for weakly coordinating anions. When cationic clusters are formed, cyclic tetramers are particularly stable. Therein, cooperative hydrogen‐bond attraction can compete with like‐charge repulsion. We present a simple but effective spectroscopic scale for the possibility of like‐charge attraction in ionic liquids, based on IR and NMR signatures.     

Anion receptors composed of hydrogen- and halogen-bond donor groups: modulating selectivity with combinations of distinct noncovalent interactions

Studies of a series of urea-based anion receptors designed to probe the potential for anion recognition through combinations of hydrogen and halogen bonding are presented. Proton- and fluorine-NMR spectroscopy indicates that the two interactions act in concert to achieve binding of certain anions, a conclusion supported by computational studies. Replacement of the halogen-bond donating iodine substituent by fluorine (which does not participate in halogen bonding) enables estimation of the contribution of this interaction to the free energy of anion binding. Evidence for attractive contacts between anions and electron-deficient arenes arising from the use of perfluoroarene-functionalized ureas as control receptors is also discussed. The magnitude of the free energy contribution of halogen bonding depends both on the geometric features of the group linking the hydrogen- and halogen-bond donor groups and on the identity of the bound anion. The results are interpreted in relation to fundamental features of the halogen-bonding interaction, including its directionality and unusual preference for halides over oxoanions. Cooperation between two distinct noncovalent interactions leads to unusual effects on receptor selectivity, a result of fundamental differences in the interactions of halogen- and hydrogen-bond donor groups with anions.     

Halogen Bonding Between Anions: Association of Anion Radicals of Tetraiodo‐p‐benzoquinone with Iodide Anions

Halogen bonding between two negatively charged species, tetraiodo‐p‐benzoquinone anion radicals (I₄Q^?.) and iodide anions, was observed and characterized for the first time. X‐ray structural and EPR/UV–Vis spectral studies revealed that the anion–anion bonding led to the formation of crystals comprising 2D layers of I₄Q^?. anion radicals linked by iodides and separated by Et₄N⁺ counter‐ions. Computational analysis suggested that the seemingly antielectrostatic halogen bonds in these systems were formed via a combination of several factors. First, an attenuation of the interionic repulsion by the solvent facilitated close approach of the anions leading to their mutual polarization. This resulted in the appearance of positively charged areas (σ‐holes) on the surface of the iodine substituents in I₄Q^?. responsible for the attractive interaction. Finally, the solid‐state associations were also stabilized by multicenter (4:4) halogen bonding between I₄Q^?. and iodide.     

Halogen Bonding Between Anions: Association of Anion Radicals of Tetraiodo-p-benzoquinone with Iodide Anions

Halogen bonding between two negatively charged species, tetraiodo-p-benzoquinone anion radicals (I₄Q^−.) and iodide anions, was observed and characterized for the first time. X-ray structural and EPR/UV–Vis spectral studies revealed that the anion–anion bonding led to the formation of crystals comprising 2D layers of I₄Q^−. anion radicals linked by iodides and separated by Et₄N⁺ counter-ions. Computational analysis suggested that the seemingly antielectrostatic halogen bonds in these systems were formed via a combination of several factors. First, an attenuation of the interionic repulsion by the solvent facilitated close approach of the anions leading to their mutual polarization. This resulted in the appearance of positively charged areas (σ-holes) on the surface of the iodine substituents in I₄Q^−. responsible for the attractive interaction. Finally, the solid-state associations were also stabilized by multicenter (4:4) halogen bonding between I₄Q^−. and iodide.     

Conformational disorder in 4‐(5,5′‐dibromo‐2′‐chloro‐4,4′‐bipyridyl‐2‐yl)benzaldehyde: role of π–π and halogen interactions

The crystal packing of the title compound, C₁₇H₉Br₂ClN₂O, is governed by strong π–π stacking, where molecules are tightly bound within infinite (100) planes; these planes interact mainly through non‐optimal π–π stacking where arene rings are noticeably displaced from perfect overlap, and also through halogen–halogen interactions. The aldehyde group shows conformational disorder, with a significant population difference between the two conformers; this difference is rationalized by the energetic analysis of the crystal packing using the PIXEL method, which also allows a decomposition of intermolecular interaction energy into Coulombic, polarization, dispersion and repulsion contributions. Using such an analysis, it is found that the main reason for this unequal population of the two conformers in the crystal is two hydrogen bonds that are present only for the major conformer.     

Energetic analysis of the molecular packing of 5,5′‐dibromo‐2,2′‐bis[4‐(methylsulfanyl)phenyl]‐4,4′‐bipyridine: the role of π–π and halogen interactions

The crystal packing of the title compound, C₂₄H₁₈Br₂N₂S₂, is rationalized using the PIXEL method, which allows a separation of the intermolecular interaction energy into Coulombic, polarization, dispersion and repulsion contributions. Infinite (01) molecular planes are formed through π–π stacking and other minor interactions, including a Br...S contact, with the σ hole of the Br atom pointing towards the S‐atom lone pair. The title compound has crystallographically imposed twofold symmetry, with the twofold axis at the mid‐point of the central C—C bond.     

Binding of acetylcholine and tetramethylammonium to a cyclophane receptor: anion's contribution to the cation-pi interaction

The interaction of the lipophilic cyclophane 1 with several acetylcholine (ACh) and tetramethylammonium (TMA) salts has been investigated in deuteriochloroform to ascertain the influence of the counterion on the cation-pi interaction. Reliable association constants have been measured for 17 salts of commonly used anions; corresponding binding free energies -DeltaG degrees ranged from over 8 kJ mol(-1) down to the limit of detection. The dramatic dependence of the binding energy on the anion showed that the latter takes part in the process with a passive and adverse contribution, which inhibits cation binding even to complete suppression in unfavorable cases. Thermodynamic parameters for the association of 1 with TMA picrate demonstrate that binding is enthalpic in origin, showing a substantial enthalpy gain (DeltaH degrees = -16.7 kJ mol(-1)) and an adverse entropic contribution (DeltaS degrees = -27.9 J mol(-1) K(-1)). A correlation has been found between the "goodness" of anions as binding partners and the solubility of their salts. Conversion of the anion into a more charge-dispersed species, for example, conversion of chloride into dialkyltrichlorostannate, improves cation binding substantially, indicating that charge dispersion is a main factor determining the influence of the anion on the cation-pi interaction. DFT computational studies show that the variation of the binding free energy of TMA with the counterion is closely accounted for by the electrostatic potential (EP) of the ion pair: guest binding appears to respond to the cation's charge density exposed to the receptor, which is determined by the anion's charge density through a polarization mechanism. A value of -DeltaG degrees = 38.6 kJ mol(-1) has been extrapolated for the free energy of binding of TMA to 1 in chloroform but in the absence of a counterion. The transmission of electrostatic effects from the ion pair to the cation-pi interaction demonstrates that host-guest association is governed by Coulombic attraction, as long as factors (steric, entropic, solvation, etc.) other than pure electrostatics are not prevalent.     

Attraction between electrophilic caps: A counterintuitive case of noncovalent interactions

Intermolecular attractive interaction between electrophilic sites is a counterintuitive phenomenon, as the electrostatic interaction therein is repulsive and destabilizing. Here, we confirm this phenomenon in four representative complexes, using state-of-the-art quantum mechanical methods. By employing the block-localized wavefunction (BLW) method, which can turn off intermolecular charge transfer interactions, we profoundly demonstrated the significance of charge transfer interactions in these seemingly counterintuitive complexes. Indeed, after being “turned off” the intermolecular charge transfer interaction in, for example, the FNSi···BrF complex, the originally attractive intermolecular interaction turns to be repulsive. The energy decomposition approach based on the BLW method (BLW-ED) can partition the overall stability gained on the formation of intermolecular noncovalent interaction into several physically meaningful components. According to the BLW-ED analysis, the electrostatic repulsion in these counterintuitive cases is overwhelmed by the stabilizing polarization, dispersion interaction, and most importantly, the charge transfer interaction, resulting in the eventual counterintuitive overall attraction. The present study suggests that, predicting bonding sites of noncovalent interactions using only the “hole” concept may be not universally sufficient, because other significant stabilizing factors will contribute to the stability and sometimes, play even bigger roles than the electrostatic interaction and consequently govern the complex structures. © 2018 Wiley Periodicals, Inc.     

Stable (long-bonded) dimers via the quantitative self-association of different cationic, anionic, and uncharged pi-radicals: structures, energetics, and optical transitions

Unusual dimers with wide interplanar separations, that is, very long bonds with d(D) approximately 3.05 A, are common to the spontaneous self-association of various organic pi-radicals in solution and in the crystalline solid state, independent of whether they are derived from negatively charged anion radicals of planar electron acceptors (TCNE-*, TCNQ-*, DDQ-*, CA-*), positively charged biphenylene cation-radical (OMB+*), or neutral phenalene radical (PHEN*). All dimeric species are characterized by intense absorption bands in the near-IR region that are diagnostic of the charge-transfer transitions previously identified with intermolecular associations of various electron-donor/acceptor dyads. The extensive delocalizations of a pair of pi-electrons accord with the sizable values of (i) the enthalpies (-Delta H(D)) and entropies (-Delta S(D)) of pi-dimerization measured by quantitative UV-vis/EPR spectroscopies and (ii) the electronic coupling element H(ab) evaluated from the strongly allowed optical transitions, irrespective of whether the diamagnetic dimeric species bear a double-negative charge as in (TCNE)(2)(2-), (TCNQ)(2)(2-), (DDQ)(2)(2-), (CA)(2)(2-) or a double-positive charge as in (OMB)(2)(2+) or are uncharged as in (PHEN)(2). These long-bonded dimers persist in solution as well as in the solid state and suffer only minor perturbations with Delta d(D) < 10% from extra-dimer forces that may be imposed by counterion electrostatics, crystal packing, and so forth. The characteristic optical transitions in such diamagnetic two-electron dimers are shown to be related to those in the corresponding paramagnetic one-electron pimers of the same pi-radicals with their parent acceptor, both in general accord with Mulliken theory.     

Interanionic (-)O-H...O(-) interactions: a solid-state and computational study of the ring and chain motifs

The (-)O-H...O(-) interaction formed by the anions HCO3-, HCO4, HC4O4 and HC5O5- (HA-), obtained upon monodeprotonation of the corresponding carbonic, oxalic, squaric and croconic acids (H2A), has been investigated theoretically and experimentally. The ring (RING) and chain (CHAIN) hydrogen bond motifs established between these anions have been analysed in terms of geometry and energy and their occurrence in crystalline salts investigated by searching the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD). It has been shown that hydrogen carbonates form RINGs, with the notable exception of NaHCO3, while only CHAINs are known for hydrogen oxalates. Hydrogen squarates and hydrogen croconates can form both RINGs and CHAINs. The structures of Rb- and Cs- hydrogen croconates, which present the two alternative motifs, have been discussed together with that of the hydrated salt NaHC5O5.H2O. The relationship between RING and CHAIN has been examined in the light of ab initio calculations. A rigorous quantum chemical study of the nature of the interanionic (-)O-H...O(-) interaction in both vacuum and condensed phase has shown that the interaction energy is dominated by the electrostatic component which becomes attractive at short O...O distances (less than 2.5 A) if the net ionic charge on the anion is delocalised away from the -OH group. It has been demonstrated that the RING motif is slightly metastable with respect to dissociation in the gas phase, but becomes stable in the crystal owing to the influence of the Madelung field. However, the CHAIN motif is unstable both in the gas phase and in the crystal. It is argued that interanionic (-)O-H...O(-) interactions ought to be regarded as stabilising bonding interactions rather than proper intermolecular hydrogen bonds because the RING and CHAIN aggregates are not energetically stable on an absolute scale of bonding energy (i.e., in the absence of counterions). The presence of very short non-hydrogen-bridged O...O contacts resulting from charge compression of polyatomic anions bridged by alkali cations is also discussed.     

Magnetic susceptibility of alkali-tetracyanoquinodimethane salts and extended Hubbard models with bond order and charge density wave phases

The molar spin susceptibilities χ(T) of Na-tetracyanoquinodimethane (TCNQ), K-TCNQ, and Rb-TCNQ(II) are fit quantitatively to 450 K in terms of half-filled bands of three one-dimensional Hubbard models with extended interactions using exact results for finite systems. All three models have bond order wave (BOW) and charge density wave (CDW) phases with boundary V = V(c)(U) for nearest-neighbor interaction V and on-site repulsion U. At high T, all three salts have regular stacks of TCNQ(-) anion radicals. The χ(T) fits place Na and K in the CDW phase and Rb(II) in the BOW phase with V ≈ V(c). The Na and K salts have dimerized stacks at T < T(d) while Rb(II) has regular stacks at 100 K. The χ(T) analysis extends to dimerized stacks and to dimerization fluctuations in Rb(II). The three models yield consistent values of U, V, and transfer integrals t for closely related TCNQ(-) stacks. Model parameters based on χ(T) are smaller than those from optical data that in turn are considerably reduced by electronic polarization from quantum chemical calculation of U, V, and t of adjacent TCNQ(-) ions. The χ(T) analysis shows that fully relaxed states have reduced model parameters compared to optical or vibration spectra of dimerized or regular TCNQ(-) stacks.     

Morphology controlled self-assembled nanostructures of sandwich mixed (phthalocyaninato)(porphyrinato) europium triple-deckers. Effect of hydrogen bonding on tuning the intermolecular interaction

A series of five novel sandwich-type mixed (phthalocyaninato)(porphyrinato) europium triple-decker complexes with different numbers of hydroxyl groups at the meso-substituted phenyl groups of porphyrin ligand 1-5 have been designed, synthesized, and characterized. Their self-assembly properties, in particular the effects of the number and positions of hydroxyl groups on the morphology of self-assembled nanostructures of these triple-decker complexes, have been comparatively and systematically studied. Competition and cooperation between the intermolecular pi-pi interaction and hydrogen bonding in the direction perpendicular to the pi-pi interaction direction for different compounds were revealed to result in nanostructures with a different morphology from nanoleafs for 1, nanoribbons for 2, nanosheets for 3, and curved nanosheets for 4 and to spherical shapes for 5. The IR and X-ray diffraction (XRD) results reveal that, in the nanostructures of triple-decker 2 as well as 3-5, a dimeric supramolecular structure was formed through an intermolecular hydrogen bond between two triple-decker molecules, which as the building block self-assembles into the target nanostructures. Electronic absorption spectroscopic results on the self-assembled nanostructures reveal the H-aggregate nature in the nanoleafs and nanoribbons formed from triple-deckers 1 and 2 due to the dominant pi-pi intermolecular interaction between triple-decker molecules, but the J-aggregate nature in the curved nanosheets and spherical shapes of 4 and 5 depending on the dominant hydrogen bonding interaction in cooperation with pi-pi interaction among the triple-decker molecules. Electronic absorption and XRD investigation clearly reveal the decrease in the pi-pi interaction and increase in the hydrogen bonding interaction among triple-decker molecules in the nanostructures along with the increase of hydroxyl number in the order of 1-5. The present result appears to represent the first effort toward realization of controlling and tuning the morphology of self-assembled nanostructures of sandwich tetrapyrrole rare earth complexes through molecular design and synthesis.     

The nature of intermolecular CuI...CuI interactions: a combined theoretical and structural database analysis

The nature of intermolecular interactions between dicoordinate Cu(I) ions is analyzed by means of combined theoretical and structural database studies. Energetically stable Cu(I).Cu(I) interactions are only found when the two monomers involved in the interaction are neutral or carry opposite charges, thus allowing us to speak of bonding between the components of the bimolecular aggregate. A perturbative evaluation of the components of the intermolecular interaction energies, by means the IMPT scheme of Stone, indicates that both the Coulombic and dispersion forces are important in determining the Cu(I).Cu(I) bonding interactions, because only a small part of that energy is attributable to Cu.Cu interactions, while a large component results from Cu.ligand interactions. The electrostatic component is the dominant one by far in the interaction between charged monomers, while in the interaction between neutral complexes, the electrostatic component is found to be of the same order of magnitude as the dispersion term. Bimolecular aggregates that have like charges are repulsive by themselves, and their presence in the solid state results from anion.cation interactions with ions external to this aggregate. In these cases, the short-contact Cu.Cu interactions here should be more properly called counterion-mediated Cu.Cu bonds.