Characteristics of antiaromatic ring pi multi-hydrogen bonds in (H2O)n-C4H4 (n = 1, 2) complexes

By counterpoise-corrected optimization method, the six antiaromatic ring pi multi-hydrogen bond structures with diversiform shapes for (H2O)n-C4H4 (n = 1,2) have been obtained at the MP2/aug-cc-pVDZ level. At the CCSD(T)/aug-cc-pVDZ level, the interaction energy obtained mainly depends on the numbers of H2O and fold numbers of the pi multi-hydrogen bond. The interaction energy order is -2.342 (1a with pi mono-hydrogen) < -2.777 (1b with pi bi-hydrogen) < -4.683 (2a with pi bi-hydrogen) < -4.734 (2b with pi tri-hydrogen) < -4.782 (2c with pi tri-hydrogen) < -5.009 kcal/mol (2d with pi tetra-hydrogen bond). Strangely, why is the interaction energy of the pi bi-hydrogen bond in 1b close to that of the pi mono-hydrogen bond in 1a (their difference is only 15.7%)? The reason is that a pi-type H-bond (as an accompanying interaction) between two lone pairs of the O-atom and a near pair of H-atoms of C4H4 exists shoulder by shoulder in structures 1a, 2a, 2b, and 2c and contributes to the interaction energy. Another accompanying interaction, a repulsive interaction between the pi H-bond (using the H-atom(s) of H2O) and the near pair of H-atoms of C4H4, is also found. For the structures and interaction energies, the pi-type H-bond produces four effects: bending the strong pi H-bond, attracting the pair of H-atoms of C4H4 so that they deviate from the C4 ring plane, showing the interaction energy contribution, and bringing the larger electron correlation contribution. The repulsive interaction also produces four effects: pushing the pair of H-atoms of C4H4 so that they deviate from its ring plane, elongating the distance of the pi H-bond, promoting the formation of pi-type H-bond, and slightly influencing the interaction energy. In the present paper, one C=C bond with two H2O (over and below the ring plane) forms a pi H-bond link in two ways: a strong-weak pi H-bond link and a strong-strong pi H-bond link. The stability contribution of the former is more favorable than the latter. One H2O forms a pi H-bond with C4H4 in two ways. One strong pi H-bond part (over or below the ring plane) always is accompanied by another H-bond part. The accompanying part is either a weak pi H-bond or pi-type H-bond.     

Vibrational spectroscopy and structures of Ni+(C2H2)(n) (n =1-4) complexes

Nickel cation-acetylene complexes of the form Ni(+)(C(2)H(2))(n), Ni(+)(C(2)H(2))Ne, and Ni(+)(C(2)H(2))(n)Ar(m) (n = 1-4) are produced in a molecular beam by pulsed laser vaporization. These ions are size-selected and studied in a time-of-flight mass spectrometer by infrared laser photodissociation spectroscopy in the C-H stretch region. The fragmentation patterns indicate that the coordination number is 4 for this system. The n = 1-4 complexes with and without rare gas atoms are also investigated with density functional theory. The combined IR spectra and theory show that pi-complexes are formed for the n = 1-4 species, causing the C-H stretches in the acetylene ligands to shift to lower frequencies. Theory reveals that there are low-lying excited states nearly degenerate with the ground state for all the Ni(+)(C(2)H(2))(n) complexes. Although isomeric structures are identified for rare gas atom binding at different sites, the attachment of rare gas atoms results in only minor perturbations on the structures and spectra for all complexes. Experiment and theory agree that multiple acetylene binding takes place to form low-symmetry structures, presumably due to Jahn-Teller distortion and/or ligand steric effects. The fully coordinated Ni(+)(C(2)H(2))(4) complex has a near-tetrahedral structure.     

Electron scattering on OH-(H2O)n clusters (n = 0-4)

The cross sections for electron scattering on OH-(H2O)n for n = 0-4 were measured from threshold to approximately 50 eV. All detachment cross sections were found to follow the classical prediction given earlier [Phys. Rev. Lett. 74, 892 (1995)] with a threshold energy for electron-impact detachment that increased upon sequential hydration, yielding values in the range from 4.5 eV +/- 0.2 eV for OH- to 12.10 eV +/- 0.5 eV for OH-(H2O)4. For n > or = 1, we found that approximately 80% of the total reaction events lead to electron detachment plus total dissociation of the clusters into the constituent molecules of OH and H2O. Finally, we observed resonances in the cross sections for OH-(H2O)3 and for OH-(H2O)4. The resonances were located at approximately 15 eV and were ascribed to the formation of dianions in excited states.     

叠氮化合物C6H6-n(N3)n(n=1~6)的密度泛函理论研究

运用密度泛函理论, 在B3LYP/6-31G*水平上, 对叠氮化合物C6H6-n(N3)n(n=1~6)进行理论计算, 并对所得到的几何结构进行了振动频率分析. 计算结果表明, 这些化合物是热力学稳定的. 基于自然键轨道理论, 分析了稳定结构的电荷分布及成键情况. 在不破坏苯环和叠氮基的原则下, 设计等键反应计算了这些化合物的生成热, 结果表明, 标题化合物的生成热都很高, 且随着叠氮基数目的增加而线性增大.     

Theoretical study of (CH...C)- hydrogen bonds in CH(4-n)X(n) (X = F, Cl; n = 0, 1, 2) systems complexed with their homoconjugate and heteroconjugate carbanions

This work deals with a theoretical study of the (CH...C)- hydrogen bonds in CH4, CH3X, and CH2X2 (X = F, Cl) complexed with their homoconjugate and heteroconjugate carbanions. The properties of the complexes are calculated with the B3LYP method using the 6-311++G(d,p) or 6-311++G(2df,2p) basis sets. The deprotonation enthalpies (DPE) of the CH bond or the proton affinities of the carbanions (PA(C-) are calculated as well. All the systems with the exception of the CH4...CHCl2(-) one are characterized by a double minimum potential. In some of the complexes, the (CH(b)...C)- hydrogen bond is linear. In other systems, such as CH3F...CH2F- and CH3F...CHF2(-), there is a large departure from linearity, the systems being stabilized by electrostatic interactions between the nonbonded H of the neutral molecule and the F atom of the carbanion. In the transition state, the (CH(b)...C)- bond is linear, and there is a large contraction of the intermolecular C...C distance. The binding energies vary within a large range, from -1.4 to -11.1 kcal mol(-1) for the stable complexes and -8.6 to -44.1 kcal mol(-1) for the metastable complexes. The energy barriers to proton transfer are between 5 and 20 kcal mol(-1) for the heteroconjugate systems and between 3.8 and 8.3 kcal mol(-1) for the homoconjugate systems. The binding energies of the linear complexes depend exponentially on 1.5DPE - PA(C-), showing that the proton donor is more important than the proton acceptor in determining hydrogen bond strength. The NBO analysis indicates an important electronic reorganization in the two partners. The elongations of the CH bond resulting from the interaction with the carbanion depend on the occupation of the sigma*(CH(b)) antibonding orbitals and on the hybridization of the C bonded to H(b). The frequency shifts of the nu(CH)(A1) stretching vibration range between 15 and 1150 cm(-1). They are linearly correlated to the elongation of the CH(b) bond.     

Theoretical Investigations on Fluorine-Substituted Ethylene Dications C2HnF4-n 2+(n = 0–4)

The optimized geometries and energies of fluorine-substituted ethylene dications C₂H_nF_4-n ²⁺ (n = 0–4) have been investigated by means of ab initio methods. At the MP3/6-31G**//6-31G* + zero-point energy level of theory, the results predict that C₂F₄²⁺ and C₂HF₃²⁺ are planar, while C₂H₄²⁺, C₂H₃F²⁺ and 1,1—C₂H₂F₂²⁺ prefer a perpendicular geometry. For 1,2—C₂H₂F₂²⁺ an energy difference of only 0.3 kcal/mol is found between the (trans) planar and perpendicular structure. The stabilizations attributed to hyperconjugation, fluorine lone-pair donation, and (C? F) double-bond conjugation are discussed. A comparison is made for the C? C and C? F stretching frequencies determined at 6-31G*//6-31G* between the neutral and dicationic species. The theoretically determined ionization energies for the vertical process N⁺ → N²⁺ at the MP3/6-31G*//3-21G level are compared with experimental Q_min values.     

Infrared spectra of the water-nitrogen complexes (H2O)2-(N2)n(n = 1-4) in argon matrices

The infrared spectra of the water-nitrogen complexes trapped in argon matrices have been studied with Fourier transform infrared absorption spectroscopy. The absorption lines of the H20-N2 1:1, 1:2, 1:n, and 2:1 complexes have been confirmed on the basis of the concentration effects. In addition, we have observed a few lines and propose the assignments for the 2:2, 2:3, and 2:4 complexes in the nu1 symmetric stretching and nu2 bending regions of the proton-acceptor molecule, and in the bonded OH stretching region of the proton-donor molecule. The redshifts in the bonded OH stretching mode and blueshifts in the OH bending mode suggest that the hydrogen bonds in the (H2O)2-(N2)n complexes with n = 1-4 are strengthened by the cooperative effects compared to the pure H2O dimer. Two absorption bands due to the 3:n complexes are also observed near the bonded OH stretching region of the H2O trimer.     

PdS2C2(COOMe)2](6n) (n = 0, -1, -2, -3, -4): hexanuclear homoleptic palladium dithiolene complexes

Reaction of a stoichiometric equivalent of the zinc-dithiolene complex, (tmeda)ZnS2C2(COOMe)2 (tmeda = tetramethylethylenediamine), with (MeCN)2PdCl2 results in a 1:1 homoleptic dithiolene that forms the hexanuclear cluster [PdS2C2(COOMe)2]6 (1). X-ray structure analysis of 1 indicates a Pd6S12 core comprised of six face-centered palladium atoms and 12 edge-centered sulfur atoms situated on an imaginary approximate cube. Complex 1 undergoes four distinct and reversible one-electron redox steps in dichloromethane at -186, -484, -1174, and -1524 mV versus a standard calomel electrode (ferrocenium+/ferrocene redox couple 409 mV). The two-electron reduction product of 1, [Bu4N]2[(PdS2C2(COOMe)2)6] (2), has been chemically isolated and characterized.     

MP2 study of cation-(pi)n-pi interactions (n = 1-4)

Ab initio calculations at the MP2(full)/6-31++G**, RI-MP2(full)/6-31++G**, and RI-MP2(full)/6-311++G(2d,2p) levels of theory demonstrate important synergic effects between two noncovalent interactions that involve aromatic rings, that is, cation-pi and pi-pi interactions. The presence of a cation interacting with the pi cloud of an aromatic ring favors the face-to-face stacking interaction with additional aromatic rings. This effect is extended in the space up to five stacked aromatic rings.     

[Fe4S4Cl4—n（S2CNEt2）n]^2—（n=0,1,2,4）：原子簇的电子结构研究

用CNDO/2(s,p,d)方法研究了类立方烷系列Fe-S簇合物[Fe_4S_4Cl_4(?)(S_2CNEt_2)_n]~(2-)(n=0,1,2,4)的电子结构。得出[S_2CN(Et)_2]-螯合配位Fe_4S_4~(2+)簇合物中存在两类不同价态铁原子的结论;骨架Fe_4S_4~(2+)中μ_3-S电子是非定域化的,同Mssbauer谱测定结果一致。讨论了簇合物Fe—Fe之间的成键作用、螫合配体的作用和氧化还原性质。     

Water-soluble and stable dinitrogen phosphine complexes trans-[ReCl(N2)(PTA-H)n(PTA)4-n]n+ (n = 0-4), the first with 1,3,5-triaza-7-phosphaadamantane

The first dinitrogen complexes with the hydrosoluble PTA ligand, or its protonated form PTA-H, trans-[ReCl(N2)(PTA-H)n(PTA)(4-n)]n+ (n = 0-4), are prepared, shown to be soluble and stable in water, interconvertible by stepwise protonation/deprotonation and to form, upon N2 loss, the corresponding penta-coordinate compounds. Dinitrogen displacement by CO affords trans-[ReCl(CO)(PTA)4].     

Tetravalent silicon connectors MenSi(p-C6H4CO2H)(4-n) (n = 0, 1, 2) for the construction of metal-organic frameworks

A series of silicon-centered connecting units, Me(n)Si(p-C6H4CO2H)(4-n) (n = 0, 1, 2), have been prepared and their coordination polymers with Zn(II) metal atoms studied. The tetra-acid L1 (n = 0) acts as a tetrahedral node and reacts with Zn(II) centers to give 1, a novel interpenetrating 3D network containing distorted tetrahedral bimetallic secondary building units (SBUs). The triacid L2 (n = 1) acts as a trigonal pyramidal node and forms an intercalated 2D layered network, 2, with Zn(II) ions, containing distorted octahedral tetranuclear SBUs. Last, the bent diacid L3 (n = 2) reacts with Zn(II) centers to give 3, a corrugated 2D layered structure containing 1D zinc hydroxo chains. Together these three new coordination polymers demonstrate the potential versatility of tetravalent silicon containing connecting ligands for metal-organic framework construction.     

Molecular orbital investigation of the protonated H2X2AlNHn(CH3)3-n+ (X = F, Cl, and Br; n = 0-3) complexes

Structures of protonated alane-Lewis base donor-acceptor complexes H2X2AlNHn(CH3)(3-n)+ (X = F, Cl, and Br; n = 0-3) as well as their neutral parents were investigated. All the monocations H2X2AlNHn(CH3)(3-n)+ are Al-H protonated involving hypercoordinated alane with a three-center two-electron bond and adopt the C(s) symmetry arrangement. The energetic results show that the protonated alane-Lewis complexes are more stable than the neutral ones. They also show that this stability decreases on descending in the corresponding periodic table column from fluorine to bromine atoms. The calculated protonation energies of HX2AlNHn(CH3)(3-n) to form H2X2AlNHn(CH3)(3-n)+ were found to be highly exothermic. The possible dissociation of the cations H2X2AlNHn(CH3)(3-n)+ into X2AlNHn(CH3)(3-n)+ and molecular H2 is calculated to be endothermic.     

Infrared spectra of HC2-.(C2H2)n and O2-.(C2H2)n clusters (n=2-5)

We study the solvation of HC2- and O2- with acetylene ligands by means of midinfrared photodissociation spectroscopy in the CH stretching region, monitoring C2H2 evaporation upon infrared photon absorption by the parent cluster ions. Our findings are interpreted with the help of density functional theory. The infrared spectra indicate that while the binding generally occurs through ionic H bonds, there are two different classes of ligands which differ in their binding strength. This holds true for both core ions, even though their electronic structures and charge distributions are very different.     

Syntheses of (C_5H_9C_5H_4)_2LnCl(THF)_n (Ln=Nd, Sm, Er, Yb) and crystal structure of [(C_5H_9C_5H_4)_2-LnCl(THF)_n]_2(Ln=Sm, n=1; Ln=Er, n=0)

Reactions of lanthanoid trichlorides with sodium cyclopentylcyclopentadienyl in THFafford bis(cyclopentylcyclopentadienyl) lanthanoid chloride complexes (C_5H_9C_5H_4)_2LnCl(THF)_n (Ln=Nd, Sm, n=1; Ln= Er, Yb, n= 0). The compound [CP'_2SmCl(THF)]_2 (2) (Cp' =cyclopentylcy-clopentadienyl) crystallizes from mixed solvent of hexane and THF in monoclinic space group P_2_1/cwith a = 11.583 (3), b = 23.019(6), c = 8.227 (2), β= 90.26 (2)°, V= 2194 (1)~3, D_c= 1.59 g/cm~3.μ= 28.6 cm~(-1), F(000) = 1060, Z= 2 (dimers). Its crystal molecule is a dimer with a crystallographicsymmetry center. The central metal atom Sm is coordinated to two Cp' rings, two bridging chlorineatoms and one THF forming a distorted trigonal bipyramid. The crystal of [Cp'_2ErCl]_2 (3) belongs tothe triclinic space group P with a = 11.264 (2), b= 13.296(5), c = 14.296(6), a = 96.99 (3), β=112.47(2), γ= 102.78(2)°, V= 1865(1)~3, D_c= 1.67 g /cm~3, μ= 48.0 cm~(-1), F(000) = 924, Z = 2 (dimers).The molecule is a dimer consisting of two Cp'_2 ErCl species bridged by two Cl atoms. The centralmetal atom Er is coordinated to two Cp' rings and two bridging chlorine atoms forming a pseudo-tetrahedron. All these complexes are soluble in THF, DME, Et_2O, toluene and hexane.     

Photoelectron spectroscopic study of the hydrated nucleoside anions: Uridine(-)(H(2)O)(n=0-2), cytidine(-)(H(2)O)(n=0-2), and thymidine(-)(H(2)O)(n=0,1)

The hydrated nucleoside anions, uridine(-)(H(2)O)(n=0-2), cytidine(-)(H(2)O)(n=0-2), and thymidine(-)(H(2)O)(n=0,1), have been prepared in beams and studied by anion photoelectron spectroscopy in order to investigate the effects of a microhydrated environment on parent nucleoside anions. Vertical detachment energies (VDEs) were measured for all eight anions, and from these, estimates were made for five sequential anion hydration energies. Excellent agreement was found between our measured VDE value for thymidine(-)(H(2)O)(1) and its calculated value in the companion article by S. Kim and H. F. Schaefer III.     

A family of octahedral rhenium cluster complexes [Re6Q8(H2O)n(OH)6-n]n-4 (Q=S, Se; n=0-6): structural and pH-dependent spectroscopic studies

The conversions of hexahydroxo rhenium cluster complexes [Re6Q8(OH)6]4- (Q=S, Se) in aqueous solutions in a wide pH range were investigated by chemical methods and spectroscopic measurements. Dependences of the spectroscopic and excited-state properties of the solutions on pH have been studied in detail. It has been found that a pH decrease of aqueous solutions of the potassium salts K4[Re6Q8(OH)6].8H2O (Q=S, Se) results in the formation of aquahydroxo and hexaaqua cluster complexes with the general formula [Re6Q8(H2O)n(OH)6-n]n-4 that could be considered as a result of the protonation of the terminal OH- ligands in the hexahydroxo complexes. The compounds K2[Re6S8(H2O)2(OH)4].2H2O (1), [Re6S8(H2O)4(OH)2].12H2O (2), [Re6S8(H2O)6][Re6S6Br8].10H2O (3), and [Re6Se8(H2O)4(OH)2] (4) have been isolated and characterized by X-ray single-crystal diffraction and elemental analyses and infrared (IR) spectroscopy. In crystal structures of the aquahydroxo complexes, the cluster units are connected to each other by an extensive system of very strong hydrogen bonds between terminal ligands.     

Thermochemistry of halomethanes CF(n)Br(4-n) (n = 0-3) based on iPEPICO experiments and quantum chemical computations

Internal energy selected bromofluoromethane cations were prepared and their internal energy dependent fragmentation pathways were recorded by imaging photoelectron photoion coincidence spectroscopy (iPEPICO). The first dissociation reaction is bromine atom loss, which is followed by fluorine atom loss in CF(3)Br and CF(2)Br(2) at higher energies. Accurate 0 K appearance energies have been obtained for these processes, which are complemented by ab initio isodesmic reaction energy calculations. A thermochemical network is set up to obtain updated heats of formation of the samples and their dissociative photoionization products. Several computational methods have been benchmarked against the well-known interhalogen heats of formation. As a corollary, we stumbled upon an assignment issue for the ClF heat of formation leading to a 5.7 kJ mol(-1) error, resolved some time ago, but still lacking closure because of outdated compilations. Our CF(3)(+) appearance energy from CF(3)Br confirms the measurements of Asher and Ruscic (J. Chem. Phys. 1997, 106, 210) and Garcia et al. (J. Phys. Chem. A 2001, 105, 8296) as opposed to the most recent result of Clay et al. (J. Phys. Chem. A 2005, 109, 1541). The ionization energy of CF(3) is determined to be 9.02-9.08 eV on the basis of a previous CF(3)-Br neutral bond energy and the CF(3) heat of formation, respectively. We also show that the breakdown diagram of CFBr(3)(+), a weakly bound parent ion, can be used to obtain the accurate adiabatic ionization energy of the neutral of 10.625 ± 0.010 eV. The updated 298 K enthalpies of formation Δ(f)H(o)(g) for CF(3)Br, CF(2)Br(2), CFBr(3), and CBr(4) are reported to be -647.0 ± 3.5, -361.0 ± 7.4, -111.6 ± 7.7, and 113.7 ± 4 kJ mol(-1), respectively.     

Microsolvation of N2H): the nature of interactions in N2H+-(H2)n (n = 1-14) complexes

Experimental studies of the consecutive growth of N2H + (H2)n clusters led to the discovery of an unusual bonding pattern for species with n = 2-4. Theoretical studies revealed that the ligands are located within five well-separated solvation shells that are visible in structures, values of successive enthalpies and entropies of clustering reactions, vibrational motions, the distribution of atomic charges, and interaction energy decomposition components. The pattern of consecutive enthalpy changes for the second shell (n = 2-5) is complicated. This pattern shows anomalous behavior, although its interpretation is not univocal. A large part of consecutive enthalpies for the clustering reactions is a contribution due to the rotational and vibrational properties of clusters which are difficult for adequate modeling in large systems. The structures of clusters are rationalized based on interaction energy contributions of a different nature. Geometries of complexes are determined by prevailing covalent forces.