Electronic structures and chemical bonding in 4d transition metal monohalides

Bond distances, vibrational frequencies, dipole moments, dissociation energies, electron affinities, and ionization potentials of MX (XM = Y-Cd, X = F, Cl, Br, I) molecules in neutral, positively, and negatively charged ions were studied by density functional method, B3LYP. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides ionic component, covalent bonds are formed between the 4d transition metal s, d orbitals, and the p orbital of halogen. For both neutral and charged molecules, the fluorides have the shortest bond distance, iodides the longest. Although the opposite situation is observed for vibrational frequency, that is, fluorides have the largest value, iodides the smallest. For neutral and anionic species, the dissociation energy tends to decrease with the increasing atomic number from Y to Cd, suggesting the decreasing or weakening of the bond strength. For cationic species, the trend is observed from Y to Ag.     

Chemical Bonding and Electronic Structure of 4d-Metal Monosulfides

Bond distances, vibrational frequencies, dissociation energies, electron affinities, ionization potentials and dipole moments of the title molecules in neutral and charged ions were studied by use of density functional method. Ground states for each molecule were assigned. The calculated bond distance decreases with the increasing of atomic number of 4d metals, reaches minimum at RhS, then increases. For cationic molecules, the calculated bond distance decreases to the minimum at MoS⁺, then increases. The calculated vibrational frequency decreases from YS(YS⁺) to PdS(PdS⁺) for both neutral and cationic molecules. The bond ionic character decreases from YS(YS⁺) to PdS(PdS⁺) for neutral and cationic molecules. The bonding patterns are discussed and compared with the available studies. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Electronic Structures of 5d Transition Metal Monoxides by Density Functional Theory

Bond distances, vibrational frequencies, electron affinities, ionization potentials, and dissociation energies of the diatomic 5d transition metal (except La) monoxides and their positively and negatively charged ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, MPW1PW91, PBE1PBE, and SVWN. Our calculation shows that for each individual species, the calculated properties are quite sensitive to the method used. Compared with hybrid density functional method B3PW91 (B3P86), pure density functional method BPW91 (BP86) gives longer bond distance (lower vibrational frequency) from HfO to PtO for neutral species, HfO⁺ to IrO⁺ for cationic species, and HfO⁻ to AuO⁻ for anionic species. While for B3LYP and BLYP, the trend was observed for cationic species from HfO⁺ to IrO⁺ and anionic species from HfO⁻ to AuO⁻ (except TaO⁻), but not for neutrals. Pure density function methods BLYP, BPW91, and BP86 give larger dissociation energy compared with hybrid density functional methods B3LYP, B3PW91, and B3P86. SVWN in most cases gives the smallest bond distance, while BLYP gives the largest value. MPW1PW91 and PBE1PBE show the same performance in predicting the spectroscopic constants. In addition, useful empirical criteria that one has obtained the ground states of a species and its ions are the spin multiplicities of a neutral and its single charged ions which differs by ±1.     

Electronic structures of 3d-metal mononitrides

Bond distances, vibrational frequencies, electron affinities, ionization potentials, and dissociation energies of the title molecules in neutral, positively, and negatively charged ions were studied by use of density functional methods B3LYP, BLYP, BHLYP, BPW91, and B3PW91. The calculated results are compared with experiments and previous theoretical studies. It was found that the calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy and vibrational frequency. For neutral species, pure density functional methods BLYP and BPW91 have relatively good performance in reproducing the experimental bond distance and vibrational frequency. For cations, hybrid exchange functional methods B3LYP and B3PW91 are good in predicting the dissociation energy. For both neutral and charged species, BHLYP tends to give smaller dissociation energy.     

Density Functional Studies of Diatomic LaO to LuO

Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies and dipole moments of the title molecules in neutral, positively and negatively charged ions were studied by use of density functional method. Ground electronic state was assigned for each molecule. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides ionic component, covalent bonds are formed between the metal s, d and f orbitals and oxygen p orbitals. Contrary to the well known lanthanide contraction, the bond distance is not regular from LaO to LuO for both neutral and charged molecules. An obvious population at 5d orbital was observed through the lanthanide series. 4f electrons also participate the chemical bonding for CeO to NdO and TbO to TmO. For EuO, GdO, YbO and LuO, 4f electrons tend to be localized. The spin multiplicity is regular for neutral and charged molecules. The spin multiplicity of the charged molecules can be obtained by −1 (or +1 for TbO⁺, DyO⁺, YbO⁻ and YbO⁺) compared with the corresponding neutral molecules.     

Electronic structures of 4d transition metal monoxides by density functional theory

Bond distances, dissociation energies, ionization potentials and electron affinities of 4d transition metal monoxides from YO to CdO and their positive and negative ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, SVWN, MPW1PW91 and PBE1PBE. It was found that calculated properties are highly dependent on the functionals employed, especially for dissociation energy. For most neutral species, pure density functionals BLYP, BPW91 and BP86 have good performance in predicting dissociation energy than hybrid density functionals B3LYP, B3PW91 and B3P86. In addition, BLYP gives the largest bond distance compared with other density functional methods, while SVWN gives shortest bond distance, largest dissociation energy and electron affinity. For the ground state, the spin multiplicity of the charged species can be obtained by ± 1 of their corresponding neutral species.     

Electronic structures and chemical bonding in transition metal monosilicides MSi (M = 3d, 4d, 5d elements)

Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies, and dipole moments of the title molecules in neutral, positively, and negatively charged ions were studied using the density functional method. Ground state was assigned for each species. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides an ionic component, covalent bonds are formed between the metal s,d orbitals and the silicon 3p orbital. The covalent character increases from ScSi (YSi) to NiSi (PdSi) for 3d (4d) metal monosilicides, then decreases. For 5d metal monosilicides, the covalent character increases from LaSi to OsSi, then decreases. For the dissociation of cations, the dissociation channel depends on the magnitude of the ionization potential between metal and silicon. If the ionization potential of the metal is smaller than that of silicon, channel MSi+ --> M+ + Si is favored. Otherwise, MSi+ --> M + Si+ will be favored. A similar behavior was observed for anions, in which the dissociation channel depends on the magnitude of electron affinity.     

Density functional study of small neutral and charged silver cluster hydrides

Small neutral, anionic, and cationic silver cluster hydrides AgnH and anionic HAgnH (n=1-7) have been studied using the PW91PW91 density functional method. It was found that the most stable structure of the AgnH complex (neutral or charged) does not always come from that of the lowest energy bare silver cluster plus an attached H atom. Among various possible adsorption sites, the bridge site is energetically preferred for the cationic and most cases of neutral Agn. For anionic Agn, the top site is preferred for smaller Agn within n相似文献   

Experimental IR and Raman spectra and quantum chemical studies of molecular structures, conformers and vibrational characteristics of L-ascorbic acid and its anion and cation

IR and spectra of the L-ascorbic acid (L-AA) also known as vitamin C have been recorded in the region 4000-50 cm(-1). In order to make vibrational assignments of the observed IR and Raman bands computations were carried out by employing the RHF and DFT methods to calculate the molecular geometries and harmonic vibrational frequencies along with other related parameters for the neutral L-AA and its singly charged anionic (L-AA(-)) and cationic (L-AA(+)) species. Significant changes have been found for different characteristics of a number of vibrational modes. The four ν(O-H) modes of the L-AA molecule are found in the order ν(O(9)-H(10))>ν(O(19)-H(20))>ν(O(7)-H(8))>ν(O(14)-H(15)) which could be due to complexity of hydrogen bonding in the lactone ring and the side chain. The CO stretching wavenumber (ν(46)) decreases by 151 cm(-1) in going from the neutral to the anionic species whereas it increases by 151 cm(-1) in going from the anionic to the cationic species. The anionic radicals have less kinetic stabilities and high chemical reactivity as compared to the neutral molecule. It is found that the cationic radical of L-AA is kinetically least stable and chemically most reactive as compared to its neutral and anionic species.     

Size and charge effects on the binding of CO to late transition metal clusters

We report on the size and charge dependence of the C-O stretching frequency, nu(CO), in complexes of CO with gas phase anionic, neutral, and cationic cobalt clusters (Co(n)CO(-0+)), anionic, neutral, and cationic rhodium clusters (Rh(n)CO(-0+)), and cationic nickel clusters (Ni(n)CO(+)) for n up to 37. We develop models, based on the established vibrational spectroscopy of organometallic carbonyl compounds, to understand how cluster size and charge relate to nu(CO) in these complexes. The dominating factor is the available electron density for backdonation from the metal to the CO pi* orbital. Electrostatic effects play a significant but minor role. For the charged clusters, the size trends are related to the dilution of the charge density at the binding site on the cluster as n increases. At large n, nu(CO) approaches asymptotes that are not the same as found for nu(CO) on the single crystal metal surfaces, reflecting differences between binding sites on medium sized clusters and the more highly coordinated metal surface sites.     

High-resolution electron spectroscopy, preferential metal-binding sites, and thermochemistry of lithium complexes of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons are model systems for studying the mechanisms of lithium storage in carbonaceous materials. In this work, Li complexes of naphthalene, pyrene, perylene, and coronene were synthesized in a supersonic metal-cluster beam source and studied by zero-electron-kinetic-energy (ZEKE) electron spectroscopy and density functional theory calculations. The adiabatic ionization energies of the neutral complexes and frequencies of up to nine vibrational modes in the singly charged cations were determined from the ZEKE spectra. The metal-ligand bond energies of the neutral complexes were obtained from a thermodynamic cycle. Preferred Li∕Li(+) binding sites with the aromatic molecules were determined by comparing the measured spectra with theoretical calculations. Li and Li(+) prefer the ring-over binding to the benzene ring with a higher π-electron content and aromaticity. Although the ionization energies of the Li complexes show no clear correlation with the size of the aromatic molecules, the metal-ligand bond energies increase with the extension of the π-electron network up to perylene, then decrease from perylene to coronene. The trends in the ionization and metal-ligand bond dissociation energies of the complexes are discussed in terms of the orbital energies, local quadrupole moments, and polarizabilities of the free ligands and the charge transfer between the metal atom and aromatic molecules.     

Structural and vibrational studies of molecular conductors using quantum mechanical methods: 1,3-Dithiole-2-thione, 1,3-dithiole-2-one, 1,3-dioxole-2-one and 1,3-dioxole-2-thione

Computations were carried out by employing the RHF and density functional theory (DFT) methods to investigate the geometries, atomic charges, harmonic vibrational frequencies for the 1,3-dithiole-2-thione (DTT), 1,3-dithiole-2-one (DTO), 1,3-dioxole-2-thione (DOT) and 1,3-dioxole-2-one (DOO) molecules and their radical cations. The geometrical parameters and atomic charges on various atomic sites of the DTT and DOT molecules and their radical cations suggest extended conjugation in these systems. Contrary to this, for the DOO⁺ and DTO⁺ ions there is no evidence in favour of such conjugation, however, the neutral molecules exhibit some conjugation. Harmonic forced field and vibrational mode calculations provided convincing theoretical evidence for the reassignment of some fundamental vibrational modes for all the four molecules. In going from the neutral species to the charged ions for all the four cases the CC stretching frequency is found to decrease drastically. The CS stretching frequency reduces drastically for the DTT and DOT molecules as compared to their radical cations whereas the CO stretching frequency is found to increase in going from the neutral molecule to its radical cation for the DOO and DTO molecules. The ring stretching mode with a₁ symmetry and CC and CO/S stretching modes in these molecules appear to help in conversion of neutral molecule into respective radical cation and neighbouring radical cation into respective neutral molecule. Thus, there appears the feasibility of stretching vibrational mode coupling with electron transfer.     

Excited state properties of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles: A quantum chemical characterization

Structure, electronic states, photoluminescence, and carries transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles for light-emitting diodes were investigated experimentally [G. Yu, et al, J. Am. Chem. Soc. 2005, 127, 6335], and the excellent electroluminescent (EL) properties of them have been found. In this paper, excited state properties of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles are studied with quantum chemistry method as well as the 3D real space analysis methods. The transition densities of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles show that the orientations and strengths of dipole moments the neutral, anionic and cationic ones are significantly different, where the neutral 1,1-disubstituted 2,3,4,5-tetraphenylsiloles show the Frenkel character; while the anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles show the plasmon character. The charge difference densities of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles reveal the important diversity of the orientations and the results of intramolecular charge transfer (ICT). The theoretical results also reveal the contribution of the substituents at the 1,1-position to the neutral and charged excited state properties of 2,3,4,5-tetraphenylsiloles. The calculated results are consistent with the experimental results, and further provide the insight of understanding to the excited state properties of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles.     

Density functional study of AuXq (X = O, S, Se, Te, q = +1, 0, -1) molecules

Bond distances, vibrational frequencies, electron affinity, ionization potential, and dissociation energies of the title molecules were studied by use of density functional methods B3LYP, B3P86, B3PW91, BHLYP, BLYP, BP86, mPW1PW91, and PBE1PBE. It was found that the ground electronic state is doublet for neutral species, singlet for the anion, and triplet for the cation, in agreement with experiments and previous theoretical studies. The calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy. The predicted bond distances and vibrational frequencies are in agreement with experiments and previous theoretical results. BP86 and BLYP have relatively good performance in reproducing the experimental results, while BHLYP is the worst functional method compared with the other density functional methods used for the title molecules.     

Molecular structures,bond energies,and bonding analysis of group 11 cyanides TM(CN) and isocyanides TM(NC) (TM = Cu,Ag, Au)

We report on quantum chemical calculations at the DFT (BP86/TZP) and ab initio (CCSD(T)/III+) levels of the title compounds. The geometries, vibrational spectra, heats of formation, and homolytic and heterolytic bond dissociation energies are given. The calculated bond length of Cu-CN is in reasonable agreement with experiment. The theoretical geometries for CuNC and the other group 11 cyanides and isocyanides which have not been measured as isolated species provide a good estimate for the exact values. The theoretical bond dissociation energies and heats of formation should be accurate with an error limit of +/-5 kcal/mol. The calculation of the vibrational spectra shows that the C-N stretching mode of the cyanides, which lies between 2170 and 2180 cm(-)(1), is IR inactive. The omega(1)(C-N) vibrations of the isocyanides are shifted by approximately 100 cm(-)(1) to lower wavenumbers. They are predicted to have a very large IR intensity. The nature of the metal-ligand interactions was investigated with the help of an energy partitioning analysis in two different ways using the charged fragments TM(+) + CN(-) (TM = transition metal) and the neutral fragments TM(*) + CN(*) as bonding partners. The calculations suggest that covalent interactions are the driving force for the formation of the TM-CN and TM-NC bonds, but the finally formed bonds are better described in terms of interactions between TM(+) and CN(-), which have between 73% and 80% electrostatic character. The contribution of the pi bonding is rather small. The lower energy of the metal cyanides than that of the isocyanides comes from the stronger electrostatic interaction between the more diffuse electron density at the carbon atom of the cyano ligand and the positively charged nucleus of the metal.     

Micelle-sequestered dissociation of cationic DNA-intercalated drugs: unexpected surfactant-induced rate enhancement

Detergent sequestration using micelles as a hydrophobic sink for dissociated drug molecules is an established technique for determination of dissociation rates. The anionic surfactant molecules are generally assumed not to interact with the anionic DNA and thereby not to affect the rate of dissociation. By contrast, we here demonstrate that the surfactant molecules sodium dodecyl sulfate (SDS), sodium decyl sulfate, and sodium octyl sulfate all induce substantial rate enhancements of the dissociation of intercalators from DNA. Four different cationic DNA intercalators are studied with respect to surfactant-induced dissociation. Except for the smallest intercalator, ethidium, the dissociation rate constants increase monotonically with surfactant concentration both below cmc and (more strongly) above cmc, much more than expected from electrostatic effects of increased counterion concentration. The rate enhancement, most pronounced for the bulky, multicationic, hydrophobic DNA ligands in this study, indicates a reduction of the activation energy for the ligand to pass out from a deeply penetrating intercalation site of DNA. The discovery that surfactants enhance the rate of dissociation of cationic DNA-intercalators implies that rate constants previously determined by micelle-sequestered dissociation may have been overestimated. As an alternative, more reliable method, we suggest instead the addition of excess of dummy DNA as an absorbent for dissociated ligand.     

Quantum chemical studies on 1 charged forms of nitroglycerine

Semiempirical quantum chemical calculations at the level of AM1 (UHF) method are performed on the neutral as well as 1 charged systems originated from nitroglycerine. The geometry optimized systems standing for 1 charged forms fragmented. All the neutral and charged systems are found to be stable and exothermic with the exception of cationic system which is endothermic in nature. The fragmentation occurs by the cleavage of ester O–N bond of the terminal ester group in the charged forms while in the cationic form also the rapture of C–C bond occurs.     

Vibrations and dissociation of molecules in strong electric fields: N2, NACl, H2O and SF6

The static deformations and vibrations of the title compounds with an applied static electric field have been studied by density functional theory calculations. It is found that for diatomic molecules, bond length and vibrational frequency as a function of the field can be fit very well all the way up to the dissociation limit by an analytical formula derived from a Morse potential model including an additional external field term. Polyatomic molecules show more complex behaviour with a single mode becoming soft at the dissociation limit. The frequency of the soft mode near the critical field is again described well by the analytical model. The vibrational analysis shows that in polyatomic molecules dissociation proceeds as a heterolytic fragmentation process, which can break the symmetry of the molecule in the applied field.     

The adsorption of CO on charged and neutral Au and Au2: a comparison between wave-function based and density functional theory

Quantum theoretical calculations are presented for CO attached to charged and neutral Au and Au(2) with the aim to test the performance of currently applied density functional theory (DFT) by comparison with accurate wave-function based results. For this, we developed a compact sized correlation-consistent valence basis set which accompanies a small-core energy-consistent scalar relativistic pseudopotential for gold. The properties analyzed are geometries, dissociation energies, vibrational frequencies, ionization potentials, and electron affinities. The important role of the basis-set superposition error is addressed which can be substantial for the negatively charged systems. The dissociation energies decrease along the series Au(+)-CO, Au-CO, and Au(-)-CO and as well as along the series Au(2)(+)-CO, Au(2)-CO, and Au(2)(-)-CO. As one expects, a negative charge on gold weakens the carbon oxygen bond considerably, with a consequent redshift in the CO stretching frequency when moving from the positively charged to the neutral and the negatively charged gold atom or dimer. We find that the different density functional approximations applied are not able to correctly describe the rather weak interaction between CO and gold, thus questioning the application of DFT to CO adsorption on larger gold clusters or surfaces.     

Theoretical study of nitric oxide adsorption on Au clusters

The adsorption properties of NO molecule on anionic, cationic, and neutral Au(n) clusters (n=1-6) are studied using the density functional theory with the generalized gradient approximation, and with the hybrid functional. For anionic and cationic clusters, the charge transfer between the Au clusters and NO molecule and the corresponding weakening and elongation of the N-O bond are essential factors of the adsorption. The neutral Au clusters have also remarkable adsorption ability to NO molecule. The adsorption energies of NO on the cationic clusters are generally greater than those on the neutral and anionic clusters.