Resonance Character of Copper/Silver/Gold Bonding in Small Molecule⋅⋅⋅MX (X=F,Cl, Br,CH3, CF3) Complexes

The resonance character of Cu/Ag/Au bonding is investigated in B???M?X (M=Cu, Ag, Au; X=F, Cl, Br, CH₃, CF₃; B=CO, H₂O, H₂S, C₂H₂, C₂H₄) complexes. The natural bond orbital/natural resonance theory results strongly support the general resonance‐type three‐center/four‐electron (3c/4e) picture of Cu/Ag/Au bonding, B:M?X?B⁺?M:X^?, which mainly arises from hyperconjugation interactions. On the basis of such resonance‐type bonding mechanisms, the ligand effects in the more strongly bound OC???M?X series are analyzed, and distinct competition between CO and the axial ligand X is observed. This competitive bonding picture directly explains why CO in OC???Au?CF₃ can be readily replaced by a number of other ligands. Additionally, conservation of the bond order indicates that the idealized relationship b_B???M+b_MX=1 should be suitably generalized for intermolecular bonding, especially if there is additional partial multiple bonding at one end of the 3c/4e hyperbonded triad.     

Dipole‐bound anions supported by charge–transfer interaction: Anionic states of HnF3−nN → BH3 and H3N → BHnF3−n (n = 0, 1, 2, 3)

The possibility of electron binding to five molecules (i.e., F₃N → BH₃, H₂FN → BH₃, HF₂N → BH₃, H₃N → BH₂F, H₃N → BHF₂) was studied at the coupled cluster level of theory with single, double, and noniterative triple excitations and compared to earlier results for H₃N → BH₃ and H₃N → BF₃. All these neutral complexes involve dative bonds that are responsible for significant polarization of these species that generates large dipole moments. As a consequence, all of the neutral systems studied, except F₃N → BH₃, support electronically stable dipole‐bound anionic states whose calculated vertical electron detachment energies are 648 cm^?1 ([H₂FN → BH₃]^?), 234 cm^?1 ([HF₂N → BH₃]^?), 1207 cm^?1 ([H₃N → BH₂F]^?), and 1484 cm^?1 ([H₃N → BHF₂]^?). In addition, we present numerical results for a model designed to mimic charge–transfer (CT) and show that the electron binding energy correlates with the magnitude of the charge flow in the CT complex. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Interface configuration effects on excitation,exciton dissociation,and charge recombination in organic photovoltaic heterojunction

The morphology of donor-acceptor heterojunction interface significantly affects the electron/hole processes in organic solar cells, including charge transfer (CT), exciton dissociation (ED), and charge recombination (CR). Here, to investigate interface molecular configuration effects, the donor-acceptor complexes with face-on, edge-on, and end-on configurations were constructed as model systems for the p-SIDT(FBTTh₂)₂/C₆₀ heterojunction. The geometries, electronic structures, and excitation properties of monomers and the complexes with three configurations were studied based on density functional theory (DFT) and time-dependent DFT calculations with optimally tuned range separation parameters and solid polarization effects. In terms of Marcus theory, the rate constants of ED and CR processes were analyzed. The results show that most of the excited states for p-SIDT(FBTTh₂)₂ exhibit an intramolecular CT character, and the similarity of the excitation characters (CT and local excitation) and energies among three complexes with different configurations indicate that the electronic structure and excitation properties are insensitive to the interfacial molecular configurations. However, the rates of ED and CR processes heavily depend on it. These results underline the importance of controlling molecular configuration and then the morphology at the heterojunction interface in organic solar cells.     

Peculiarity of Hexamethylenetetratellurafulvalene (HMTTeF) Charge Transfer Complexes of Donor-Acceptor (D-A) Type

The complex formation of hexamethylenetetratellurafulvalene (HMTTeF) with 28 kinds of organic electron acceptors yielded 31 charge transfer (CT) complexes. The infrared and ultra-violet-visible-near-infrared spectra of the complexes were examined to study the ionicity of their ground states in solid. A plot of CT transition energies and the difference of redox potentials; ΔE(DA) of donor (D) and acceptor (A) molecules indicated that four complexes have a neutral ground state. Four other complexes exhibit characteristic features of a fully ionic ground state based on the vibrational spectra. Notably, the HCBD, F₄TCNQ and DDQ complexes indicate both a relatively low first CT band and high conductivity in a solid in spite of the fully ionic character being very plausible. Twenty-three complexes having a partially ionic ground state have a CT band below 4×10 cm⁻¹ and are highly conductive. The preparation of good single crystals of the HMTTeF complexes for structural analysis was only successful with Et₂TCNQ and BTDA-TCNQ, which have the structure of DA alternately stacking. These two complexes indicate high conductivities in spite of their disadvantageous packing manner. The intermolecular interactions are found to be strongly enhanced by both the bulky molecular orbital of HMTTeF and the decreased on-site Coulomb repulsion in the HMTTeF complexes. These two factors in particular seem to prevent both the fully ionic and the DA alternating HMTTeF complexes from becoming insulators, even though the redox parameters and the crystal structures predict them to be insulating.     

Anionic CH⋅⋅⋅X− Hydrogen Bonds: Origin of Their Strength,Geometry, and Other Properties

CF₃H as a proton donor was paired with a variety of anions, and its properties were assessed by MP2/aug‐cc‐pVDZ calculations. The binding energy of monoanions halide, NO₃^?, formate, acetate, HSO₄^?, and H₂PO₄^? lie in the 12–17 kcal mol^?1 range, although F^? is more strongly bound, by 26 kcal mol^?1. Dianions SO₄^2? and HPO₄^2? are bound by 27 kcal mol^?1, and trianion PO₄^3? by 45 kcal mol^?1. When two O atoms are available on the anion, the CH???O^? H‐bond (HB) is usually bifurcated, although asymmetrically. The CH bond is elongated and its stretching frequency redshifted in these ionic HBs, but the shift is reduced in the bifurcated structures. Slightly more than half of the binding energy is attributed to Coulombic attraction, with smaller contributions from induction and dispersion. The amount of charge transfer from the anions to the σ*(CH) orbital correlates with many of the other indicators of bond strength, such as binding energy, CH bond stretch, CH redshift, downfield NMR spectroscopic chemical shift of the bridging proton, and density at bond critical points.     

Cooperativity between the Dihydrogen Bond and the N⋅⋅⋅HC Hydrogen Bond in LiH–(HCN)n Complexes

The cooperativity between the dihydrogen bond and the N???HC hydrogen bond in LiH–(HCN)_n (n=2 and 3) complexes is investigated at the MP2 level of theory. The bond lengths, dipole moments, and energies are analyzed. It is demonstrated that synergetic effects are present in the complexes. The cooperativity contribution of the dihydrogen bond is smaller than that of the N???HC hydrogen bond. The three‐body energy in systems involving different types of hydrogen bonds is larger than that in the same hydrogen‐bonded systems. NBO analyses indicate that orbital interaction, charge transfer, and bond polarization are mainly responsible for the cooperativity between the two types of hydrogen bonds.     

Influence of the Li⋅⋅⋅π Interaction on the H/X⋅⋅⋅π Interactions in HOLi⋅⋅⋅C6H6⋅⋅⋅HOX/XOH (X=F,Cl, Br,I) Complexes

The influences of the Li???π interaction of C₆H₆???LiOH on the H???π interaction of C₆H₆???HOX (X=F, Cl, Br, I) and the X???π interaction of C₆H₆???XOH (X=Cl, Br, I) are investigated by means of full electronic second‐order Møller–Plesset perturbation theory calculations and “quantum theory of atoms in molecules” (QTAIM) studies. The binding energies, binding distances, infrared vibrational frequencies, and electron densities at the bond critical points (BCPs) of the hydrogen bonds and halogen bonds prove that the addition of the Li???π interaction to benzene weakens the H???π and X???π interactions. The influences of the Li???π interaction on H???π interactions are greater than those on X???π interactions; the influences of the H???π interactions on the Li???π interaction are greater than X???π interactions on Li???π interaction. The greater the influence of Li???π interaction on H/X???π interactions, the greater the influences of H/X???π interactions on Li???π interaction. QTAIM studies show that the intermolecular interactions of C₆H₆???HOX and C₆H₆???XOH are mainly of the π type. The electron densities at the BCPs of hydrogen bonds and halogen bonds decrease on going from bimolecular complexes to termolecular complexes, and the π‐electron densities at the BCPs show the same pattern. Natural bond orbital analyses show that the Li???π interaction reduces electron transfer from C₆H₆ to HOX and XOH.     

K⋅⋅⋅F/O Interactions Bridge Copper(I) Fluorinated Alkoxide Complexes and Facilitate Dioxygen Activation

Seven E[Cu(OR)₂] copper(I) complexes (E=K⁺, {K(18C6)}⁺ (18C6=[18]crown‐6), or Ph₄P⁺; R=C₄F₉, CPhMe^F₂, and CMeMe^F₂) have been prepared and their reactivity with O₂ studied. The K[Cu(OR)₂] species react with O₂ in a copper‐concentration‐dependent manner such that 2:1 and 3:1 Cu/O₂ adducts are observed manometrically at ?78 °C. Analogous reactivity with O₂ is not observed with the {K(18C6)}⁺ or Ph₄P⁺ derivatives. Solution conductivity data demonstrate that these K[Cu(OR)₂] complexes do not behave as 1:1 electrolytes in solution. The K⁺ ions induce aggregation of multiple [Cu(OR)₂]^? units through K???F/O interactions and thereby effect irreversible O₂ reduction by multiple Cu centers. Bond valence analyses for the potassium cations confirm the dominance of the fluorine interactions in the coordination spheres of K⁺ ions. Intramolecular hydroxylation of ligand aryl and alkyl C? H bonds is observed. Nucleophilic reactivity with CO₂ is observed for the oxygenated Cu complexes and a Cu^II carbonate has been isolated and characterized.     

Cooperativity between the Halogen Bond and the Hydrogen Bond in H3N⋅⋅⋅XY⋅⋅⋅HF Complexes (X,Y=F,Cl, Br)

Ab initio calculations are used to provide information on H₃N???XY???HF triads (X, Y=F, Cl, Br) each having a halogen bond and a hydrogen bond. The investigated triads include H₃N???Br₂‐HF, H₃N???Cl₂???HF, H₃N???BrCI???HF, H₃N???BrF???HF, and H₃N???ClF???HF. To understand the properties of the systems better, the corresponding dyads are also investigated. Molecular geometries, binding energies, and infrared spectra of monomers, dyads, and triads are studied at the MP2 level of theory with the 6‐311++G(d,p) basis set. Because the primary aim of this study is to examine cooperative effects, particular attention is given to parameters such as cooperative energies, many‐body interaction energies, and cooperativity factors. The cooperative energy ranges from ?1.45 to ?4.64 kcal mol^?1, the three‐body interaction energy from ?2.17 to ?6.71 kcal mol^?1, and the cooperativity factor from 1.27 to 4.35. These results indicate significant cooperativity between the halogen and hydrogen bonds in these complexes. This cooperativity is much greater than that between hydrogen bonds. The effect of a halogen bond on a hydrogen bond is more pronounced than that of a hydrogen bond on a halogen bond.     

Boron as an Electron‐Pair Donor for B⋅⋅⋅Cl Halogen Bonds

MP2/aug′‐cc‐pVTZ calculations were performed to investigate boron as an electron‐pair donor in halogen‐bonded complexes (CO)₂(HB):ClX and (N₂)₂(HB):ClX, for X=F, Cl, OH, NC, CN, CCH, CH₃, and H. Equilibrium halogen‐bonded complexes with boron as the electron‐pair donor are found on all of the potential surfaces, except for (CO)₂(HB):ClCH₃ and (N₂)₂(HB):ClF. The majority of these complexes are stabilized by traditional halogen bonds, except for (CO)₂(HB):ClF, (CO)₂(HB):ClCl, (N₂)₂(HB):ClCl, and (N₂)₂(HB):ClOH, which are stabilized by chlorine‐shared halogen bonds. These complexes have increased binding energies and shorter B?Cl distances. Charge transfer stabilizes all complexes and occurs from the B lone pair to the σ* Cl?A orbital of ClX, in which A is the atom of X directly bonded to Cl. A second reduced charge‐transfer interaction occurs in (CO)₂(HB):ClX complexes from the Cl lone pair to the π* C≡O orbitals. Equation‐of‐motion coupled cluster singles and doubles (EOM‐CCSD) spin–spin coupling constants, ^1xJ(B‐Cl), across the halogen bonds are also indicative of the changing nature of this bond. ^1xJ(B‐Cl) values for both series of complexes are positive at long distances, increase as the distance decreases, and then decrease as the halogen bonds change from traditional to chlorine‐shared bonds, and begin to approach the values for the covalent bonds in the corresponding ions [(CO)₂(HB)?Cl]⁺ and [(N₂)₂(HB)?Cl]⁺. Changes in ¹¹B chemical shieldings upon complexation correlate with changes in the charges on B.     

Using (FH)2 and (FH)3 to Bridge the σ‐Hole and the Lone Pair at P in Complexes with H2XP,for X=CH3, OH,H, CCH,F, Cl,NC, and CN

Ab initio MP2/aug′‐cc‐pVTZ calculations are used to investigate the binary complexes H₂XP:HF, the ternary complexes H₂XP:(FH)₂, and the quaternary complexes H₂XP:(FH)₃, for X=CH₃, OH, H, CCH, F, Cl, NC, and CN. Hydrogen‐bonded (HB) binary complexes are formed between all H₂XP molecules and FH, but only H₂FP, H₂ClP, and H₂(NC)P form pnicogen‐bonded (ZB) complexes with FH. Ternary complexes with (FH)₂ are stabilized by F?H???P and F?H???F hydrogen bonds and F???P pnicogen bonds, except for H₂(CH₃)P:(FH)₂ and H₃P:(FH)₂, which do not have pnicogen bonds. All quaternary complexes H₂XP:(FH)₃ are stabilized by both F?H???P and F?H???F hydrogen bonds and P???F pnicogen bonds. Thus, (FH)₂ with two exceptions, and (FH)₃ can bridge the σ‐hole and the lone pair at P in these complexes. The binding energies of H₂XP:(FH)₃ complexes are significantly greater than the binding energies of H₂XP:(FH)₂ complexes, and nonadditivities are synergistic in both series. Charge transfer occurs across all intermolecular bonds from the lone‐pair donor atom to an antibonding σ* orbital of the acceptor molecule, and stabilizes these complexes. Charge‐transfer energies across the pnicogen bond correlate with the intermolecular P?F distance, while charge‐transfer energies across F?H???P and F?H???F hydrogen bonds correlate with the distance between the lone‐pair donor atom and the hydrogen‐bonded H atom. In binary and quaternary complexes, charge transfer energies also correlate with the distance between the electron‐donor atom and the hydrogen‐bonded F atom. EOM‐CCSD spin‐spin coupling constants ^2hJ(F–P) across F?H???P hydrogen bonds, and ^1pJ(P–F) across pnicogen bonds in binary, ternary, and quaternary complexes exhibit strong correlations with the corresponding intermolecular distances. Hydrogen bonds are better transmitters of F–P coupling data than pnicogen bonds, despite the longer F???P distances in F?H???P hydrogen bonds compared to P???F pnicogen bonds. There is a correlation between the two bond coupling constants ^2hJ(F–F) in the quaternary complexes and the corresponding intermolecular distances, but not in the ternary complexes, a reflection of the distorted geometries of the bridging dimers in ternary complexes.     

Substituent effects in donor-acceptor complexes with D→A coordination bonds (D = N, O, S; A = B, Al, Ga, Sn, Sb) and related systems

The effect of substituent on the enthalpy ΔH ⁰ and free energy ΔG ⁰ of complexation, on the dipole moments of complexes μ_C and coordination bonds μ_DA, and on the degree of charge transfer Δq was analyzed for 20 series of complexes with D→A coordination bonds (D = N, O, S; A = B, Al, Ga, Sn, Sb), hydrogen bonds, and charge transfer. It was found that ΔH ⁰, ΔG ⁰, μ_C, μ_DA, and Δq depend not only on the inductive and resonance effects, but also on the polarization effect of substituents; its contribution varies in a wide range and can exceed 50%.     

Magnitude and origin of the attraction and directionality of the halogen bonds of the complexes of C6F5X and C6H5X (X = I, Br, Cl and F) with pyridine

The geometries and interaction energies of complexes of pyridine with C₆F₅X, C₆H₅X (X=I, Br, Cl, F and H) and R_FI (R_F=CF₃, C₂F₅ and C₃F₇) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (E_int) for the C₆F₅X–pyridine (X=I, Br, Cl, F and H) complexes at the basis set limit were estimated to be ?5.59, ?4.06, ?2.78, ?0.19 and ?4.37 kcal mol^?1, respectively, whereas the E_int values for the C₆H₅X–pyridine (X=I, Br, Cl and H) complexes were estimated to be ?3.27, ?2.17, ?1.23 and ?1.78 kcal mol^?1, respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C₆F₅X. The values of E_int estimated for the R_FI–pyridine (R_F=CF₃, C₂F₅ and C₃F₇) complexes (?5.14, ?5.38 and ?5.44 kcal mol^?1, respectively) are close to that for the C₆F₅I–pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short‐range (charge‐transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C₆F₅I– and C₂F₅I–pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water–formaldehyde complex. The calculations suggest that the C? I and C? Br halogen bonds play an important role in controlling the structures of molecular assemblies, that the C? Cl bonds play a less important role and that C? F bonds have a negligible impact.     

Experimental and Theoretical Evidence of the Existence of Gold(I)⋅⋅⋅Mercury(II) Interactions in Solution through Fluorescence‐Quenching Measurements

Heteronuclear complexes {[Hg(R)₂][Au(R′)(PMe₃)]₂}_n (R=R′=C₆Cl₂F₃ ( 3 ); R=R′=C₆F₅ ( 4 ); R=C₆Cl₂F₃, R′=C₆F₅ ( 5 ); R=C₆F₅, R′=C₆Cl₂F₃ ( 6 )) were prepared by the treatment of the corresponding organomercury compounds, [Hg(C₆X₅)₂], with two equivalents of [Au(C₆X₅)(PMe₃)]. Their crystal structures, as determined by using X‐ray diffraction methods, display Au???Hg interactions. Although only compound 4 and 5 show luminescence in the solid state, all of these compounds quench the fluorescence of naphthalene in solution. Solution studies of these derivatives suggest a cooperative effect of the gold(I) center in switching on the quenching capabilities of the [Hg(C₆X₅)₂] synthon with naphthalene. Theoretical studies confirmed the quenching ability of the organomercury species in the presence of gold.     

Visible‐Light‐Promoted Dearomative Fluoroalkylation of β‐Naphthols through Intermolecular Charge Transfer

The first visible‐light‐promoted dearomative fluoroalkylation of β‐naphthols was realized without the assistance of any transition‐metal catalysts or external photosensitizers. Inexpensive fluoroalkyl iodides were directly used as efficient fluoroalkylation reagents under very mild reaction conditions. The scope of this process was found to be general and broad, and both trifluoromethyl and perfluoroalkyl groups (‐C₄F₉, ‐C₆F₁₃, and ‐C₈F₁₇) were installed in excellent yields. Preliminary mechanistic studies suggest that visible‐light‐promoted intermolecular charge transfer within the naphtholate–fluoroalkyl iodide electron donor–acceptor (EDA) complex induces a single electron transfer in the absence of photocatalysts.     

Synthesis and Characterization of Acetylene‐Linked Bisphenalenyl and Metallic‐Like Behavior in Its Charge‐Transfer Complex

We prepared and isolated a phenalenyl‐based neutral hydrocarbon ( 1 b ) with a biradical index of 14 %, as well as its charge‐transfer (CT) complex 1 b –F₄‐TCNQ. The crystal structure and the small HOMO–LUMO gap assessed by electrochemical and optical methods support the singlet‐biradical contribution to the ground state of the neutral 1 b . This biradical character suggests that 1 b has the electronic structure of phenalenyl radicals coupled weakly through an acetylene linker, that is, some independence of the two phenalenyl moieties. The monocationic species 1 b^{. +} was obtained by reaction with the organic electron acceptor F₄‐TCNQ. The cationic species has a small disproportionation energy ΔE for the reaction 2× 1 b^{. +}? 1 b + 1 b ²⁺, which presumably originates from the independence of the phenalenyl moieties. The small ΔE led to a small on‐site Coulombic repulsion U_eff=0.61 eV in the CT complex. Moreover, a very effective orbital overlap of the phenalenyl rings between molecules afforded a relatively large transfer integral t=0.09 eV. The small U_eff/4t ratio (=1.7) resulted in a metallic‐like conductive behavior at around room temperature. Below 280 K, the CT complex showed a transition into a semiconductive state as a result of bond formation between phenalenyl and F₄‐TCNQ carbon atoms.     

Density functional study of lanthanide complexes (η-C5H5)2LnX·OC4H8 (Ln=La-Lu; X=F, Cl, Br and I)

Density functional calculations were performed on a series of mixed-ligand organolanthanide complexes, (η⁵-C₅H₅)₂LnX·OC₄H₈ (η⁵-C₅H₅=Cp; Ln=La-Lu; X=F, Cl, Br and I; OC₄H₈=THF). The calculated geometrical parameters are in reasonable agreement with the experimental data. The distances between Ln and ligands follow linearity along the ionic radius of lanthanide metal, as the same as that observed in experiment. In the mixed-ligand complexes, Ln-Cp and Ln-THF bonds are more covalent compared to Ln-X. The lanthanide contraction of various bond and the metal-ligand interaction energy followed the order of Ln-X>Ln-Cp>Ln-OC₄H₈. The orbital population and dipole moment were also discussed.     

Hydrogen sulphide H2S and noble gases (Ng = He,Ne, Ar,Kr, Xe,Rn) complexes: A theoretical study of their dynamics,spectroscopy, and interactions

In this work, some basic features of the intermolecular bond in gas phase H₂S-Ng complexes (Ng = He, Ne, Ar, Kr, Xe, and Rn) have been investigated in detail, coupling information from scattering experiments with results of quantum chemical calculations at the CCSD(T)/aug-cc-pVTZ level. Spectroscopic constants, rotovibrational energies, and lifetime as a function of temperature have been evaluated for the complete family of H₂S-Ng systems, and an extensive study of involved intermolecular interactions has been performed. In particular, their nature has been characterized by exploiting Atoms-In-Molecules (AIM), Non-Covalent Interactions (NCI), Symmetry-Adapted Perturbation Theory (SAPT), and Charge Displacement (CD) methods, and it was found that all complexes are bound essentially by near-isotropic van der Waals forces, perturbed by weak-stabilizing charge (electron) transfer contributions. Obtained results also show that these additional contributions increase from He up to Rn, providing an appreciable chemical-stabilizing effect of the noncovalent intermolecular bond for H₂S-heavier Ng systems.     

Charge‐transfer character of halogen bonding: Molecular structures and electronic spectroscopy of carbon tetrabromide and bromoform complexes with organic σ‐ and π‐donors

Carbon tetrabromide and bromoform are employed as prototypical electron acceptors to demonstrate the charge‐transfer nature of various intermolecular complexes with three different structural types of electron donors represented by (1) halide and pseudohalide anions, (2) aromatic (π‐bonding) hydrocarbons, and (3) aromatics with (n‐bonding) oxygen or nitrogen centers. UV–Vis spectroscopy identifies the electronic transition inherent to such [1:1] complexes; and their Mulliken correlation with the donor/acceptor strength verifies the relevant charge‐transfer character. X‐ray crystallography of CBr₄/HCBr₃ complexes with different types of donors establishes the principal structural features of halogen bonding. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:449–459, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20264