Infrared spectroscopy of gas-phase Cr+ coordination complexes: determination of binding sites and electronic states

Infrared spectra were recorded for a series of gas-phase Cr+ complexes using infrared multiphoton dissociation (IRMPD) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The functionalized aromatic ligands (acetophenone, anisole, aniline, and dimethyl aniline) offer a choice of either aromatic ring-pi or n-donor-base binding sites. Use of the FELIX free electron laser light source allowed convenient, rapid scanning of the chemically informative wavelength range from approximately 500 to 1800 cm(-1), which in many cases characterized the preferred site of metal binding, as well as the electronic spin state of the complex. Mono-complex ions, Cr+(ligand), for anisole, aniline, and dimethyl aniline and bis-complex ions, Cr+(ligand)(2), for anisole, aniline, and acetophenone were produced by ligand attachment to laser-desorbed Cr+ ions in the FT-ICR cell. The photodissociation yields plotted as a function of wavelength were interpreted as approximations to the infrared absorption spectra and were compared with computed spectra of different possible geometries and spin states. Clear-cut diagnostic features in the spectra of the acetophenone, anisole, and aniline complexes showed the sites of Cr+ attachment to be the carbonyl oxygen site for acetophenone (bis-complex) and the ring-pi site for anisole and aniline (both mono- and bis-complexes). The bis-complexes of aniline and anisole are low-spin (probably doublet) states, while the mono-complexes of these same ligands are high-spin (sextet) states. The dimethyl aniline complex gave a cluttered spectrum in poor agreement with calculations, which may reflect a mixture of binding-site isomers in this case.     

Theoretical study of solvent and substituent effects on the structure, <Superscript>14</Superscript>N NQR and electronic spectra of [Cr(CO)<Subscript>5</Subscript>py]

The structure, ¹⁴N NQR parameters, electronic spectra, and hyperplarizability of [Cr(CO)₅py] in seven different solvents were theoretically computed with MPW1PW91 method based on Polarizable Continuum Model (PCM). The substituent effects in para- substituted Cr(CO)⁵–pyridine complexes have been evaluated. The results indicate that both polarity of solvents and the substituents have played a significant role on the structures and properties of complexes. The study also shows that the structural and solvent modification change the NLO properties.     

Molecular structure and vibrational investigation of benzenesulfonic acid methyl ester using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) theory calculations

The FT-Raman and FT-IR spectra for benzenesulfonic acid methyl ester (BSAME) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) method by employing 6-311G (d, p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for sulfonic acid and some substituted sulfonic acids. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from DFT. The scaled vibrational frequencies at LSDA/B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the sulfonic acid are effected upon profusely with the methyl substitution in comparison to benzene sulfonamide and these differences are interpreted.     

Alkali Metal Complexes of the Dipeptides PheAla and AlaPhe: IRMPD Spectroscopy

Complexes of PheAla and AlaPhe with alkali metal ions Na⁺ and K⁺ are generated by electrospray ionization, isolated in the Fourier‐transform ion cyclotron resonance (FT–ICR) ion trapping mass spectrometer, and investigated by infrared multiple‐photon dissociation (IRMPD) using light from the FELIX free electron laser over the mid‐infrared range from 500 to 1900 cm^?1. Insight into structural features of the complexes is gained by comparing the obtained spectra with predicted spectra and relative free energies obtained from DFT calculations for candidate conformers. Combining spectroscopic and energetic results establishes that the metal ion is always chelated by the amide carbonyl oxygen, whilst the C‐terminal hydroxyl does not complex the metal ion and is in the endo conformation. It is also likely that the aromatic ring of Phe always chelates the metal ion in a cation‐π binding configuration. Along with the amide CO and ring chelation sites, a third Lewis‐basic group almost certainly chelates the metal ion, giving a threefold chelation geometry. This third site may be either the C‐terminal carbonyl oxygen, or the N‐terminal amino nitrogen. From the spectroscopic and computational evidence, a slight preference is given to the carbonyl group, in an RO_aO_t chelation pattern, but coordination by the amino group is almost equally likely (particularly for K⁺PheAla) in an RO_aN_t chelation pattern, and either of these conformations, or a mixture of them, would be consistent with the present evidence. (R represents the π ring site, O_a the amide oxygen, O_t the terminal carbonyl oxygen, and N_t the terminal nitrogen.) The spectroscopic findings are in better agreement with the MPW1PW91 DFT functional calculations of the thermochemistry compared with the B3LYP functional, which seems to underestimate the importance of the cation–π interaction.     

DFT study of the structural characteristics of the yttrium(3+) aqua ion

Density functional theory (DFT) using SVWN5, B3LYP, B3P86, O3LYP, B3PW91, B1LYP, B971, MPW1PW91, PBE1PBE, BHandH, and BHandHLYP density functionals was employed to study the structural characteristics of the Y(H₂O) ₈ ³⁺ yttrium aqua ion. The nonlocal hybrid GGA functionals show worse predictive ability in structural calculations of the Y(H₂O) ₈ ³⁺ aqua ion compared to the relatively simple combined functional BHandH and to the simplest SVWN5 functional in LSDA theory.     

Syntheses and characterization of the MF6- (M = As, Sb) salts of the simple trithietanylium PhCS3+ cation and the identity of PhCS3Cl

MF6- (M = As or Sb) salts of a simple derivative of the trithietanylium PhCSSS+, 1, were synthesized for the first time by the reaction of PhCS3Cl and AgMF6 in liquid SO2. 1SbF6 was characterized by IR, FT-Raman, and NMR spectroscopy, elemental analysis, and a preliminary X-ray crystal structure. 1AsF6 was characterized by 1H NMR and FT-Raman spectroscopy. The calculated (MPW1PW91/3-21G* or 6-31G*) geometries, 1H and 13C chemical shifts (MPW1PW91/6-311G(2DF)//MPW1PW91/3-21G*), and vibrational frequencies and intensities (MPW1PW91/6-31G*) were in satisfactory agreement with the observed values. The calculated pi type molecular orbitals of HCSSS+ (MPW1PW91/6-311+G*) and 1 (MPW1PW91/3-21G*) imply that the 6pi-CSSS+ ring has some aromatic character. 1SbF6 undergoes a metathesis reaction with NBu4Cl in liquid SO2 to give PhCS3Cl, which was characterized by vibrational spectroscopy and mass spectrometry. The evidence indicates that PhCS3Cl has the ionic formulation PhCSSS+ Cl- with significant cation-anion interactions in the solid state. ArCSSS+ SbF6- (Ar = 1-naphthyl), 14SbF6, was prepared from ArCS3Cl and AgSbF6, suggesting that the synthesis of MF6- (M = As or Sb) salts of RCSSS+ is potentially general for aryl derivatives. The structure of 14SbF6 was established by 1H and 13C NMR, IR, and FT-Raman spectroscopy, and theoretical calculations gave values in agreement with the experimental data.     

Theoretical calculations on the mechanisms of the gas‐phase elimination kinetics of 2‐chloro‐1‐phenylethane, 3‐chloro‐1‐phenylpropane, 4‐chloro‐1‐phenylbutane, 5‐chloro‐1‐phenylpentane,and their corresponding chloroalkanes: The effect of the phenyl ring

The kinetics and mechanisms of the dehydrochlorination of 2‐chloro‐1‐ phenylethane, 3‐chloro‐1‐phenylpropane, 4‐chloro‐1‐phenylbutane, 5‐chloro‐1‐phenylpentane, and their corresponding chloroalkanes were examined by means of electronic structure calculation using density functional theory methods B3LYP/6–31G(d,p), B3LYP/6–31++G(d,p), MPW1PW91/6–31G(d,p), MPW1PW91/6–31++G(d,p), PBEPBE/6–31G(d,p), and PBEPBE/6–31++G(d,p). The potential energy surface was investigated for the minimum energy path. Calculated enthalpies and energies of activation are in good agreement with experimental values using the MPW1PW91 and B3LYP methods. The transition state of these reactions is a four‐centered cyclic structure. The reported experimental results proposing neighboring group participation by the phenyl group was not supported by theoretical calculations. The rate‐determining process in these reactions is the breaking of Cl? C bond. The reactions are described as concerted moderately polar and nonsynchronous. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 292–302, 2011     

Platinum(II) complexes with thiourea derivatives containing oxygen,sulfur or selenium in a heterocyclic ring: computational studies and cytotoxic properties

Platinum(II) complexes with 1-(2-oxolanylmethyl)-2-thiourea, 1-(2-thiolanylmethyl)-2-thiourea and 1-(2-selenolanylmethyl)-2-thiourea were synthesized in order to compare their cytotoxic activities with those of the free thioureas. Their equilibrium geometries and bonding energies in the gas phase and in solution were calculated using density functional theory at the MPW1PW/LanL2DZ level. The IR spectra of the complexes and their free ligands were compared. Stability of the complexes in 0.9% saline aqueous solution was tested by means of HPLC. The cytotoxic activities of the species against five human cell lines were evaluated, as well as the antimicrobial activities against twelve bacterial strains.     

FT-IR and FT-Raman, UV spectroscopic investigation of 1-bromo-3-fluorobenzene using DFT (B3LYP, B3PW91 and MPW91PW91) calculations

The FT-IR and FT-Raman spectra of 1-bromo-3-fluorobenzene (C₆H₄FBr) molecule have been recorded using Bruker IFS 66 V spectrometer in the range of 4000–100 cm⁻¹. The molecular geometry and vibrational frequencies in the ground state are calculated using the DFT (B3LYP, B3PW91 and MPW91PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. The isotropic DFT (B3LYP, B3PW91 and MPW1PW91) analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by B3LYP methods. The complete data of this molecule provide the information for future development of substituted benzene. The influence of bromine and fluorine atom on the geometry of benzene and its normal modes of vibrations has also been discussed. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, was performed by time dependent DFT (TD-DFT) approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds were discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated in gas phase, revealing the correlations between standard heat capacities (C) standard entropies (S), standard enthalpy changes (H) and temperatures.     

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.     

Inclusion complexes of ortho-anisidine and β-cyclodextrin: A quantum mechanical calculation

The structural aspects for the complexation of ortho-anisidine (O-AN)/β-cyclodextrin were explored by using PM6, density function theory B3LYP/6-31G*, M05-2X/6-31G*, B3PW91/6-31G*, MPW1PW91/6-31G*, HF/6-31G* methods and several combinations of ONIOM2 hybrid calculations. Calculations were performed upon the inclusion complexation of β-cyclodextrin (β-CD) with neutral (O-AN1) and cationic (O-AN2) species of ortho-anisidine. The obtained results with PM6 method clearly indicate that the formed complexes are energetically favored, the complex of O-AN2/β-CD in B orientation is significantly more favorable than the others energetically. The structures show the presence of several intermolecular hydrogen bond interactions that were studied on the basis of natural bonding orbital (NBO) analysis, employed to quantify the donor–acceptor interactions between ortho-anisidine and β-CD.     

Theoretical study of the vibrational frequencies of carbon disulfide

A benchmark comparison for different computational methods and basis sets has been presented. In this study, five computational methods (Hartree–Fock (HF), MP2, B3LYP, MPW1MP91, and PBE1PBE) along with 18 basis sets have been applied to optimize the geometry of carbon disulfide (CS₂), and further calculate the vibrational frequencies of the optimized geometries. The differences between the calculated frequencies and corresponding experimental data are used to evaluate the efficiency of each combination of computational method and basis set. The comparison of frequency difference indicates that B3LYP generally gives the best prediction of frequencies for CS₂, whereas the other two density functional theory (DFT) methods, i.e., MPW1PW91 and PBE1PBE, often give parallel results. Although MP2 predicts the frequencies with accuracy almost as good as those from DFT methods, in a particular case, HF calculation outperforms MP2 as well as MPW1PW91 and PBE1PBE for prediction of the frequency of asymmetrical stretching for CS₂. © 2013 Wiley Periodicals, Inc.     

Study of metal ions (Na+, K+) interaction with different conformations of glycine molecule

Interaction of metal ions (Na⁺, K⁺) with different binding sites, such as amino nitrogen, hydroxyl oxygen, and carbonyl oxygen for all gaseous conformers of glycine molecule were investigated using Density Functional Theory (B3LYP/6‐311++G**, B3PW91/6‐311++G**) methods. It was found that the order of stability of the conformers was changed due to the binding of the metal ion. The relative energy values show that the 7p conformer is more stable than the 1p conformer when a metal ion binds with the carbonyl oxygen. The intensity of interaction on hydroxyl oxygen is very low due to the low basicity of hydroxyl oxygen. The binding affinities of the complexes were calculated using the thermochemical properties. The relative energy and chemical hardness values predicted the most stable complex. The calculated condensed Fukui functions predict the favorable reactive site among the three binding sites. It is concluded that the reactivity of each binding site varies for each conformation due to the presence of intramolecular hydrogen bonding. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

DRIFTS investigation and DFT calculation of the adsorption of CO on Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2

Molecular structures and vibrational spectra of the CO species adsorbed on the Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2 have been investigated by means of density functional theory (DFT) calculation and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The geometrical structures and vibrational frequencies were obtained at the MPW1PW91/SDD level. Theoretical calculation shows that the calculated IR spectra were in good agreement with the experimental results. The calculated results clarify the assignment of the adsorbed CO species on the surface of Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2.     

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 spectroscopic properties of rhenium (I) tricarbonyl photosensitizer: [Re(4,4'-(COOEt)2-2,2'-bpy)(CO)3py]PF6

The ground state and lowest triplet-state structures of [Re(4,4'-(COOEt)(2)-2,2'-bpy)(CO)(3)py]PF(6) photosensitizer (bpy=bipyridine, py=pyridine) have been studied with density functional theory (DFT). Time-dependent density functional theory (TD-DFT) was carried out to predict the photophysical properties of the photosensitizer. The effects of the solvents were evaluated using the conductor-like polarizable continuum (CPCM) method in dichloromethane, chloroform, acetonitrile, acetone, ethanol and dimethylsulfoxide. The electronic transition energies computed with BLYP, MPWPW91, B3LYP and MPW1PW91 functionals are compared with the experimental spectra. Based on the calculated excited energies, the experimental absorption maximum is assigned as metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) mixed transition, and the luminescence originates from the lowest triplet state that is ascribed as the mixed transition of MLCT/LLCT.     

双环金属铱(Ⅲ)异腈配合物的二阶非线性光学性质

采用密度泛函理论(DFT)方法对双环金属Ir(III)异腈配合物的非线性光学(NLO)性质进行计算研究。用B3PW91(UB3PW91)(金属原子采用LANL2DZ基组,非金属原子采用6-31G*基组)方法对配合物进行几何结构优化。在优化构型基础上,采用B3PW91(UB3PW91)和B3LYP(UB3LYP)方法计算了配合物的第一超极化率(βtot),并用CAM-B3LYP(UCAM-B3LYP)(金属原子采用LANL2DZ基组,非金属原子采用6-31G**基组)方法模拟配合物的吸收光谱。结果表明,主配体的取代基(R1)和副配体的取代基(R2)对第一超极化率值贡献不大。配合物发生氧化还原反应,电荷转移方式增多,电荷转移程度增大,使βtot值显著增加,其中1a+([(C∧N)2Ir(CNR)2]+(R=CH3))发生氧化反应和还原反应的βtot值分别增大了75倍和144倍。因此,这类双环金属铱(III)异腈配合物的氧化还原反应可以有效地调节其二阶NLO性质。     

Design of density functionals that are broadly accurate for thermochemistry, thermochemical kinetics, and nonbonded interactions

This paper develops two new hybrid meta exchange-correlation functionals for thermochemistry, thermochemical kinetics, and nonbonded interactions. The new functionals are called PW6B95 (6-parameter functional based on Perdew-Wang-91 exchange and Becke-95 correlation) and PWB6K (6-parameter functional for kinetics based on Perdew-Wang-91 exchange and Becke-95 correlation). The resulting methods were comparatively assessed against the MGAE109/3 main group atomization energy database, against the IP13/3 ionization potential database, against the EA13/3 electron affinity database, against the HTBH38/4 and NHTBH38/04 hydrogen-transfer and non-hydrogen-transfer barrier height databases, against the HB6/04 hydrogen bonding database, against the CT7/04 charge-transfer complex database, against the DI6/04 dipole interaction database, against the WI7/05 weak interaction database, and against the new PPS5/05 pi-pi stacking interaction database. From the assessment and comparison of methods, we draw the following conclusions, based on an analysis of mean unsigned errors: (i) The PW6B95, MPW1B95, B98, B97-1, and TPSS1KCIS methods give the best results for a combination of thermochemistry and nonbonded interactions. (ii) PWB6K, MPWB1K, BB1K, MPW1K, and MPW1B95 give the best results for a combination of thermochemical kinetics and nonbonded interactions. (iii) PWB6K outperforms the MP2 method for nonbonded interactions. (iv) PW6B95 gives errors for main group covalent bond energies that are only 0.41 kcal (as measured by mean unsigned error per bond (MUEPB) for the MGAE109 database), as compared to 0.56 kcal/mol for the second best method and 0.92 kcal/mol for B3LYP.     

Vibrational investigation, molecular orbital studies and molecular electrostatic potential map analysis on 3-chlorobenzoic acid using hybrid computational calculations

The FT-IR and FT-Raman spectra of 3-chlorobenzoic acid (3CBA) are recorded in the liquid state. The fundamental vibrational frequencies, intensity of vibrational bands and the optimized geometrical parameters of the compound are evaluated using HF and DFT (LSDA/B3LYP/B3PW91/MPW1PW91) methods with 6-311+G(d,p) basis set. The theoretical wave numbers are scaled down and compared with the experimental values which showed very good agreement. Comparison of stimulated spectra with the experimental spectra provides important information about the ability of the hybrid computational method to describe the vibrational modes. The HOMO, LUMO, chemical hardness (η), chemical potential (μ), electrophilicity values (ω) and maximum amount of electronic charge transfer (ΔN(max)) are calculated. The molecular electrostatic potential (MESP) is calculated and the corresponding graphs are drawn. Some thermodynamic parameters and physico-chemical properties are calculated and discussed.