二元和三元复合物中阳离子硫键与磷键的理论研究

采用MP2/cc-pVDZ和cc-pVTZ基组分别对复合物XH₂S⁺…NCH₂P和NCH₂P…PyX(X=NH₂, CH₃, H, CN, F, Cl, Br)中的硫键和磷键进行了研究, 讨论了键长、 键临界点的电荷密度(ρ)、 拉普拉斯密度(▽²ρ)、 范德华表面穿透距离、 二阶稳定化能和电荷转移量对硫键和磷键相互作用能的影响. 结果表明, 当取代基X为吸电子基团时, 形成的硫键较强. 当X为给电子基团时, 形成的磷键较强. 利用能量分解方法分析了取代基—CN导致硫键稳定性反常的可能原因. 还进一步讨论了三元复合物H₃S⁺…NCH₂P…PyX(X=NH₂, CH₃, H, CN, F, Cl, Br)中硫键和磷键的协同相互作用以及取代基对复合物稳定性的影响. 并通过对比相同的2种单体在三元复合物和二元复合物中的二阶稳定化能和相互作用能的差值, 说明了硫键与磷键起到相互促进的正协同作用, 增强了三元复合物的稳定性.     

Vector and scalar correlations in the photodissociation of NCCN

The CN photofragments from the photodissociation of NCCN at 193 nm have been measured by high-resolution transient absorption spectroscopy. Doppler-broadened profiles of isolated rotational lines in the 2-0 and 3–1 vibrational bands of the CN A---X transition were observed under collisionless conditions with a tunable, single-frequency Ti:sapphire ring laser. Analysis of the Dopple profiles reveals a vector correlation between the translation and rotation of CN photoproducts, with the angular momentum of the high rotational states increasingly perpendicular to the recoil velocity. After correction for vector correlations, the laboratory-frame scalar speed distribution of state-selected photoproducts can be determined. The mean squared laboratory velocity is directly related to the average internal energy of coincident CN fragments. The wings of the Doppler profiles indicate that the available energy for a pair of ground state CN photoproducts following 193 nm dissociation of NCCN at 295 K is 5300±150 cm⁻¹, which includes the average vibrational energy of the parent molecules selected by the photolysis laser. Phase space theory with an optimized available energy of 5300 cm⁻¹ produces laboratory speed distributions that are in qualitatively reasonable agreement with the kinetic energy measurements, but overestimate the total internal energy of the photofragments. The measurements are good enough to warrant comparison with more sophisticated models of unimolecular decomposition.     

A theoretical study of the CX2N radicals (X = F, Cl, Br): the effect of halogen substitution on structure, isomerization, and energetics

Structural isomers of the CX(2)N radicals, where X = F, Cl, and Br, have been investigated at high level of theory, i.e., using the coupled-cluster method in conjunction with correlation-consistent basis sets ranging in size from triple- to sextuple-zeta. Extrapolation to the complete basis-set limit as well as core-correlation effects and inclusion of higher excitations in the cluster operator have been considered for accurately evaluating geometries and energies. The effect of halogen substitution on molecular structure, isomer stability, and dissociation energy is addressed; in particular, only the F(2)CN, Cl(2)CN, Br(2)CN, and F(2)NC radicals of C(2V) symmetry are predicted to be stable with respect to dissociation.     

Experimental and theoretical studies of the CN-Ar van der Waals complex

The CN-Ar van der Waals complex has been observed using the B (2)Sigma(+)-X (2)Sigma(+) and A (2)Pi-X (2)Sigma(+) electronic transitions. The spectra yield a dissociation energy of D(0")=102+/-2 cm(-1) and a zero-point rotational constant of B(0")=0.067+/-0.005 cm(-1) for CN(X)-Ar. The dissociation energy for CN(A)-Ar was found to be D(0')=125+/-2 cm(-1). Transitions to vibrationally excited levels of CN(B)-Ar dominated the B-X spectrum, indicative of substantial differences in the intermolecular potential energy surfaces (PESs) for the X and B states. Ab initio PESs were calculated for the X and B states. These were used to predict rovibrational energy levels and van der Waals bond energies (D(0")=115 and D(0')=183 cm(-1)). The results for the X state were in reasonably good agreement with the experimental data. Spectral simulations based on the ab initio potentials yielded qualitative insights concerning the B-X spectrum, but the level of agreement was not sufficient to permit vibronic assignment. Electronic predissociation was observed for both CN(A)-Ar and CN(B)-Ar. The process leading to the production of CN(A,nu=8,9) fragments from the predissociation of CN(B,nu=0)-Ar was characterized using time-resolved fluorescence and optical-optical double resonance measurements.     

Formation of CN(B2Σ+) by electron-impact dissociation of BrCN

Electron impact (8.4–20 eV) on BrCN resulted in the formation of polarized CN(B–X) emission, from which the polarization and the vibrational distribution of the CN(B) fragment were obtained as a function of impact energy. The data indicate that the dissociation process proceeds mainly via the states having ^I Σ⁺(0⁺) and/or ¹A′ symmetry in the energy range observed.     

RRKM理论研究N(4S)+CH2X(X=F,Cl)的反应通道

采用RRKM理论和疏松过渡态模型计算了N(4S)+CH2X(X=F,Cl)反应的微正则速率常数和通道分支比.计算结果表明,在较低的内能下(E=280.29 kJ/mol), N(4S)+CH2F的主要产物为NCHF+H,占总产物的59.2%,次要产物为H2CN+F,占37.4%.而N(4S)+CH2Cl反应在E＝267.78 kJ/mol时,主要产物是H2CN+Cl,占90.3%, NCHCl+H只占9.0%.在内能较高的时候(取E=500.00 kJ/mol), N(4S)+CH2F的主要通道并未变化,而N(4S)+CH2Cl的主要通道变为NCHCl+H,比例为51.5%, H2CN+Cl的比例降到40.4%.     

Energy disposal in the photodissociation HCN(Ã1A″) → H + CN(X 2Σ) at 193 nm

Rotational energy disposal has been measured in CN(X ²Σ, υ″ = 0, 1, 2) following 193 nm dissociation of HCN vapor at 295 K. The fractional populations for the three vibrational states are 0.56 ± 0.08, 0.33 ± 0.13, and 0.11 ± 0.03 for υ″ = 0, 1 and 2 respectively. This distribution is fit well by a Poisson distribution with an average vibrational quantum number of 0.55 corresponding to the average vibrational energy of 1128 ± 294 cm⁻¹. This energy represents (10 ± 3)% of the available energy. The rotational distributions in all three vibrational states can be represented by a single surprisal which depends linearly on N″/N″_max where N″_max is the maximum value of the rotational quantum number permitted by energy conservation and the prior distribution is similarly constrained. The average energy in rotation is 1055 ± 373 cm⁻¹ which represents (9 ± 3)% of that available for disposal. Time-dependence measurements indicate that product CN(X ²Σ, υ = 0) is formed in both a fast (τ < 80 ns) and a slow process. No evidence is found for the production of CN(A ²Π, υ ≈ 0).     

Are excimers formed along with hydrated electrons in the UV excitation of cyanocuprate(I) ions in aqueous solution?

The three cyanocuprate(I) complexes, Cu(CN)₂⁻, Cu(CN)₃²⁻, and Cu(CN)₄³⁻, photoeject electrons with high efficiency when excited in aqueous solution by 266 nm laser pulses of 7 ns duration with quantum yields of 0.37±0.06, 0.224±0.021, and 0.240±0.005, for Cu(CN)₂⁻ (at 2 M ionic strength), Cu(CN)₃²⁻, and Cu(CN)₄³⁻ (both measured at 1 M ionic strength). Along with hydrated electrons, two transient intermediates, absorbing at 460 and 340 nm, respectively, form consecutively after excitation through bimolecular reactions with ground-state Cu(I) in solutions of Cu(CN)₂⁻, and Cu(CN)₃²⁻, but not in Cu(CN)₄³⁻. All photoprocesses are essentially monophotonic. A mechanism is proposed that suggests the formation of a dinuclear excited-state complex such as an excimer.     

Valence band photoelectron spectra of transition-metal cyanides

X-ray photoelectron spectra of the valence bands of NaCN, Li₄Fe(CN)₆, Li₃Fe(CN)₆, Ni(CN)₂, Li₂Pt(CN)₄ and LiSCN have been measured and interpreted. Normalization of the valence-band intensities by equalization of the nitrogen is intensities made it possible to distinguish between cyanide and transition-metal bands. The spectrum of CN⁻ is similar to that of the iso-electronic molecules N₂ and CO. The transition-metal bands occur at a lower binding energy than the CN⁻ bands and do not show structure. From the intensities we conclude that much less mixing of the metal and ligand orbitals takes place than indicated by recent MO calculations.     

纤维素凝胶电解质及其在超级电容器中的应用

以纸浆为原料制备得到一种粘胶液,经静置水化交联,得到一种纤维素凝胶电解质(XWD-NaOH);添加亚铁氰化钾,使获得的新型纤维素凝胶电解质(XWD-NaOH-K 4[Fe(CN)6])呈现良好的氧化还原活性,电导率达15.3 mS/cm;与XWD-NaOH相比,XWD-NaOH-K 4[Fe(CN)6]电解质超级电容器,在0.5 A/g电流密度下,比电容、功率密度和能量密度分别提高了57%、111%和214%,并且体系具有更低的内阻、电荷转移电阻及高的循环稳定性。     

Photodissociation of NO2. Internal energy distribution and anisotropies in the fragments

The near-UV photodissociation of NO₂ has been investigated at excess energies from −600 up to 1700 cm⁻¹ above the NO X ν = 1 + O³P dissociation limit. A complete analysis of the NO X ν = 1 fragment, including internal and translational energy as well as the angular properties of its vectorial parameters, has been carried out using REMPI combined with TOF mass spectrometry. The high-precision state-selective measurements of the NO fragment velocity have been used to evaluate the internal energy of the O atoms formed in coincidence. Concerning the internal energy of the NO X ν = 1 fragment, two types of final state distributions of the fragments have been found; the difference depending upon the excess energy with respect to the NO X ν = 1 + O₃P dissociation limit. Above the threshold, statistical rotational behaviour with nonvanishing anisotropies has been observed. Below the threshold, an efficient R→V transfer, allowed by a significant molecular distortion, was detected. The influence of the parent rotation on the NO fragment rotational distribution is discussed.     

Tautomeric and conformational stabilities of methylphosphonic dicyanide, methoxydicyanophosphine, and their isocyano analogs: an ab initio calculation

The relative energies and structural parameters of the equilibrium forms and the potential functions of internal rotation of methylphosphonic dicyanide, CH₃(=O)(CN)₂, methoxydicyanophosphine, CH₃OP(CN)₂, and their isocyano analogs, CH₃P(=O)(NC)₂ and CH₃OP(NC)₂, have been calculated at the RHF/6-31G* level. The total energy of the more stable oxo forms CH₃P(=O)(CN)₂ and CH₃P(=O)(NC)₂ are 10–20 kcal mol⁻¹ lower than the energies of the aci forms CH₃OP(CN)₂ and CH₃OP(NC)₂. The relative stabilities of the cyano and isocyano isomers are almost the same in the case of the oxo forms, but for the aci forms the energies of the cyano isomers are 8 kcal mol⁻¹ lower than those of the isocyano isomers. The potential curves for internal rotation in the aci forms are characterized by a deep minimum corresponding to the trans arrangement of the methyl group and the lone pair of electrons on the phosphorus atom. Two less pronounced minima are symmetrically situated with respect to relative maximum corresponding to the transition cis form. The potential curves of internal rotation in the oxo form possess three minima corresponding to staggered configurations of the methyl group and phosphorus atom bonds. The energy characteristics and geometrical parameters of the studied molecules are compared with known data for similar compounds.     

Ultrafast photochemical dissociation of an equatorial CO ligand from trans(X,X)-[Ru(X)2(CO)2(bpy)] (X = Cl, Br, I): a picosecond time-resolved infrared spectroscopic and DFT computational study

Ultrafast photochemistry of the complexes trans(X,X)-[Ru(X)(2)(CO)(2)(bpy)] (X = Cl, Br, I) was studied in order to understand excited-state reactivity of equatorial CO ligands, coordinated trans to the 2,2'-bipyridine ligand (bpy). TD-DFT calculations have identified the lowest electronic transitions and singlet excited states as mixed X -->bpy/Ru --> bpy ligand to ligand/metal to ligand charge transfer (LLCT/MLCT). Picosecond time-resolved IR spectroscopy in the region of nu(CO) vibrations has revealed that, for X = Cl and Br, subpicosecond CO dissociation is accompanied by bending of the X-Ru-X moiety, producing a pentacoordinated intermediate trans(X,X)-[Ru(X)(2)(CO)(bpy)]. Final movement of an axial halide ligand to the vacant equatorial position and solvent (CH(3)CN) coordination follows with a time constant of 13-15 ps, forming the photoproduct cis(X,X)-[Ru(X)(2)(CO)(CH(3)CN)(bpy)]. For X = I, the optically populated (1)LLCT/MLCT excited state undergoes a simultaneous subpicosecond CO dissociation and relaxation to a triplet IRuI-localized excited state which involves population of an orbital that is sigma-antibonding with respect to the axial I-Ru-I bonds. Vibrationally relaxed photoproduct cis(I,I)-[Ru(I)(2)(CO)(CH(3)CN)(bpy)] is formed with a time constant of ca. 55 ps. The triplet excited state is unreactive, decaying to the ground state with a 155 ps lifetime. The experimentally observed photochemical intermediates and excited states were assigned by comparing calculated (DFT) and experimental IR spectra. The different behavior of the chloro and bromo complexes from that of the iodo complex is caused by different characters of the lowest triplet excited states.     

Computational I(III)—X BDEs for Benziodoxol(on)e‐based Hypervalent Iodine Reagents: Implications for Their Functional Group Transfer Abilities

The first comprehensive I(III)―X (X = F, Br, CN, N₃, CF₃, etc.) bond dissociation energy (BDE) scales for benziodoxol(on)e‐based hypervalent iodine reagents have been developed by virtue of DFT calculations. Excellent correlation is observed between the I(III)―X BDEs and the X―H BDEs, offering a powerful avenue to quickly estimate the group‐transfer ability of a novel benziodoxol(on)e‐based hypervalent reagent.     

OH (A Σ) fragment emission from reaction of electronically excited Xe(6p) with H2O under free jet and bulb conditions

The state-selective energy transfer from two-photon excited Xe(6p) to H₂O and the subsequent reaction has been studied by measured of emission spectra of OH (A ²Σ⁺ → X ²Π). The vibrational population ratios, N_v=1/N_v=0, are 0.52 ± 0.01 in a free jet and 0.37 ± 0.02 in a bulb. This reveals the difference in dissociation dynamics following the intra-complex and the intermolecular electronic energy transfers from Xe(6p) to H₂O.     

Internal energy distributions of tungsten hexacarbonyl ions after neutralization—Reionization

The internal energy distributions P(ε) transferred to W(CO)^+√₆ during the kiloelectronvolt collisions that occur upon neutralization-reionization (NR) have been estimated based on the relative abundances of the W(CO)^+√₀₋₆ products present in NR spectra (thermochemical method). The average internal energy of the incipient W(CO)^+√₆ ^* ions arising after near thermoneutral neutralization with trimethylamine followed by reionization with O₂ is −9 eV for 8-keV precursor ions and is mainly deposited during reionization. For comparison, the mean internal energy of W(CO)^+√₆* after electron ionization (EI) or collisionally activated dissociation (CAD) is −6 eV. Making the neutralization step endothermic slightly increases the overall excitation gained; however, a large increase in endothermicity ( > 16 eV) causes only a modest rise of the average internal energy (< 2 eV). The P(ε) curve for NR increases exponentially up to 6 eV and levels off at higher energies, showing that the probability of imparting large internal energies (6–17 eV) is high. In sharp contrast, the most probable excitation on CAD is ≤ 6 eV, and the probability of deposition of larger energies declines exponentially. The mean internal energies after CAD and NR decrease steadily when the kinetic energy is lowered. The structure (minima-maxima) observed in the P(ε) distribution for EI, which most likely originates from Franck-Condon factors, is not reproduced in the distributions for NR or high energy CAD, despite the fact that all three methods involve electronic excitation. Because of the large internal energies transferred upon NR, NR mass spectrometry could be particularly useful in the differentiation of ionic isomers with high dissociation but low isomerization thresholds. (J Am Soc Mass Spectrom 1994, 5, 1093-1101)     

The interaction between C28 (Td) and X (X=H and F)

Hydrogen and fluorine addition reactions with C₂₈(T_d) have been investigated by the density function theory method at B3LYP/6-31G level. The interaction potential between C₂₈(T_d) and atom X (X=H and F) shows that there are three possible stable isomers of C₂₈(T_d)X (X=H and F) and the average binding energy calculations suggest that C₂₈(T_d)H₄ is the most stable hydrogen adduct among C₂₈(T_d)H_n (n=1–28). Furthermore, by comparisons of the energy between C₂₈(T_d)H and C₂₈(C_s)H we found that the former are more stable than the later, and the structural and energy analysis further indicate that C₂₈(C_s)H is only with a small distortion of C₂₈(T_d)H symmetry. In addition, the transition states, as well as reaction pathways of X transfer reactions between different key points on C₂₈(T_d) representative patch are given to explore the possible reaction mechanism.     

Chemical bonding in phosphane and amine complexes of main group elements and transition metals

The geometries and bond dissociation energies of the main group complexes X3B-NX3, X3B-PX3, X3Al-NX3, and X3Al-PX3 (X = H, Me, Cl) and the transition metal complexes (CO)5M-NX3 and (CO)5M-PX3 (M = Cr, Mo, W) have been calculated using gradient-corrected density functional theory at the BP86/TZ2P level. The nature of the donor-acceptor bonds was investigated with an energy decomposition analysis. It is found that the bond dissociation energy is not a good measure for the intrinsic strength of Lewis acidity and basicity because the preparation energies of the fragments may significantly change the trend of the bond strength. The interaction energies between the frozen fragments of the borane complexes are in most cases larger than the interaction energies of the alane complexes. The bond dissociation energy of the alane complexes is sometimes higher than that of the borane analogues because the energy for distorting the planar equilibrium geometry of BX3 to the pyramidal from in the complexes is higher than for AlX3. Inspection of the three energy terms, DeltaE(Pauli), DeltaE(orb), and DeltaE(elstat), shows that all three of them must be considered to understand the trends of the Lewis acid and base strength. The orbital term of the donor-acceptor bonds with the Lewis bases NCl3 and PCl3 have a higher pi character than the bonds of EH3 and EMe3, but NCl3 and PCl3 are weaker Lewis bases because the lone-pair orbital at the donor atoms N and P has a high percent s character. The calculated DeltaE(int) values suggest that the trends of the intrinsic Lewis bases' strengths in the main-group complexes with BX3 and AlX3 are NMe3 > NH3 > NCl3 and PMe3 > PH3 > PCl3. The transition metal complexes exhibit a somewhat different order with NH3 > NMe3 > NCl3 and PMe3 > PH3 > PCl3. The slightly weaker bonding of NMe3 than that of NH3 comes from stronger Pauli repulsion. The bond length does not always correlate with the bond dissociation energy, nor does it always correlate with the intrinsic interaction energy.     

Ab initio study of hydrated sodium halides NaX(H2O)(1-6) (X=F, Cl, Br, and I)

We have studied the dissociation phenomena of sodium halides by water molecules. The structures, binding energies, electronic properties, and IR spectroscopic features have been investigated by using the density-functional theory, second-order Moller-Plesset perturbation theory, and coupled clusters theory with single, double, and perturbative triplet excitations. In the case that the sodium halides are hydrated by three water molecules, the most stable structures show the partial (or half) dissociation feature. The dissociated structures are first found for NaX(H2O)(n=5) for X=BrI, though these structures are slightly higher in energy than the global minimum-energy structure. In the case of hexahydrated sodium halides the global minimum-energy structures (which are different from the structures reported in any previous work) are found to be dissociated (X=F/I) or partially/half dissociated (X=Cl/Br), while other nearly isoenergetic structures are undissociated, and the dissociated cubical structures are higher in energy than the corresponding global minimum-energy structure.