DFT and Raman spectroscopy of porphyrin derivatives: Tetraphenylporphine (TPP)

Raman spectrum of the meso tetraphenylporphine (TPP) deposited onto smooth copper surface as thin film were recorded in the region 200–1700 cm⁻¹. To investigate the effect of meso-phenyl substitution rings on the vibrational spectrum of free base porphyrin, we calculated Raman and infrared (IR) spectra of the meso-tetraphenylporphine (TPP), meso tetramethylporphine (TMP), copper (II)porphine (CuPr) and free base porphine (FBP) at the B3LYP/6-311+G(d,p) level of the density functional theory (DFT). The observed Raman spectrum of the TPP is assigned based on the calculated its Raman spectrum in connection with the calculated spectra of the TMP, CuPr and FBP by taking into account of their corresponding vibrational motions of the Raman modes of frequencies. Results of the calculations clearly indicated that the meso tetraphenyl substitution rings are totally responsible for the observed Raman bands at ∼1593, 1234 and 1002 cm⁻¹. The calculated and observed Raman spectra also suggested that the observed Raman band with a medium intense at 962 cm⁻¹ might result from the surface plasmon effect. Furthermore, the observed Raman bands with medium intense at ∼334 and ∼201 cm⁻¹ are as results of the dimerization or aggregation of the TPP or would be that related to intramolecular interaction. We also calculated IR spectra of these molecules at same level of the theory. To investigate the solvent effect on the vibrational spectrum of porphine, the Raman and IR spectra of the TPP and FBP are calculated in solution phase where water used as solvent. The results of these calculation indicated that there is no any significant effect on the vibrational spectrum of the TPP.     

Theoretical study of vibration spectra of sensitizing dyes for photoelectrical converters based on ruthenium(II) and iridium(III) complexes

Quantum-chemical method of the density functional theory was employed to calculate, with the use of a B3LYP hybrid exchange-correlation functional, the IR absorption and Raman spectra of [Ru(bpy)₂(CN)₂] and [Ir(bpy)₂(CN)₂]⁺ complexes. All the normal vibrational frequencies were analyzed and new assignments of a number of bands in the IR absorption and Raman spectra were made. The role of vibrational motions of metal atoms and ligands in the vibronic deformation of electron shells in the course of electron transfer was discussed. This was done using data on surface-enhanced Raman spectra of [Fe(bpy)₂(CN)₂] and [Ru(bpy)₃]²⁺ complexes adsorbed on the surface of colloid silver.     

IR and Raman investigations of structures and phase changes in scandium fluorides

Crystallographic data and IR Raman spectra are presented for a new series of compounds, M₃ScF₆ (M Na, K, Rb, Cs, T1). Spectral assignments are proposed and effects of the cation on vibrational modes is discussed. Preliminary temperature-dependant Raman spectra are presented and correlated with DSC and crystallographic data.     

Vibrational assignment of some X3MCo(CO)4 molecules (M = Si,Ge, Sn and X = Cl,Br, I)

The infrared and Raman vibrational spectra of X₃MCo(CO)₄ compounds (M = Si, Ge, Sn and X = Cl, Br, I) including depolarization measurements are presented. These spectra result in complete vibrational assignments which are different from those reported previously.     

Infrared and Raman multi-phonon spectra and structure of PbWO4

Improved Raman spectra of PbWO₄ show previously reported spectra contain large polarization and/or orientation errors. New spectroscopic information, obtained from polarized IR reflection and Raman spectra, allowed us to assign the IR and the previously unreported Raman multi-phonon bands. It was also used to show that it determines uniquely the C_4h factor group of PbWO₄. The use of IR reflection vs. infrared transmission spectra in the vibrational determination of crystal structures is also discussed.     

Vibrational spectra and analyses of MFe(CO)4 (M = Cd,Hg)

The IR and Raman spectra of the compounds CdFe(CO)₄ and HgFe(CO)₄, are reported and assigned using C_2v, local symmetry around the iron atom; vibrational analyses of the spectra have also been carried out. The spectroscopic data obtained indicate that the compounds are probably polymers with a centre of symmetry and an octahedral configuration about the iron atom in accordance with X-ray structural results.     

A new phosphate,KMgY(PO4)2, isostructural with xenotime

A new phosphate, KMgY(PO₄)₂, isostructural with xenotime, was firstly reported in detail. It crystallizes in tetragonal system with space group I4₁/amd (No. 141). The cell parameters were obtained from X-ray powder diffraction data with a=0.6886, c=0.6025 nm, Z=2. The proposed structure of KMgY(PO₄)₂ was further confirmed by its vibrational spectra, IR and Raman spectra, which were also compared with those of iso-structural YPO₄.     

Structural features of disubstituted polyacetylenes with bulky substituents at double bonds

The structural features of polyacetylenes carrying two substituents at double bonds with the general formula [-C(CH₃)=CR-] _n , where R = Si(CH₃)₃, -Ge(CH₃)₃, or CH(CH₃)₂, are studied. It is shown that the experimental IR and Raman spectra of the polymers and the theoretically calculated vibrational spectra for the model polymers consisting of three units coincide well with experimental data. All bands in the IR spectra are interpreted. The potential curves of internal rotation are calculated and constructed; high values of rotation barriers indicate a high rigidity of chains for all polymers of interest. The orthogonal arrangement of neighboring monomer units and, as a result, the absence of electron-density conjugation over the polymer chain are revealed. Charges on atoms and electron density on bonds of the monomer unit obtained from theoretical calculations indicate the presence of strong polarization of all bonds, including the -C=C- bond. This effect causes a shift in the frequencies of stretching vibrations due to double bonds in the IR spectra of polyacetylenes with Si- and Ge-containing side substituents toward the longwave region. For polyacetylene with hydrocarbon side substituents -CH(CH₃)₂, such polarization is absent.     

Experimental and theoretical study on vibrational spectra of nickel and zinc complexes of 5,10-diphenylporphyrin

The vibrational spectra of nickel and zinc 5,10-diphenylporphyrin (NiDaPP and ZnDaPP) have been studied by density functional theory (B3LYP/6-31G(d)) and experimental measurement. The assignment of observed Raman and IR bands are proposed based on theoretical calculation. Theoretical study indicates that 5,10-diphenyl substitution together with out-of-plane distortion diversify the structure of four pyrrole rings and the environment around C_m atoms, which lowers the symmetry of porphyrin skeleton and brings about some variation to vibrational spectra. The first is the activation of all normal modes both in Raman and IR spectra. The second is the lifting of original degenerate E_u representation and its splitting into two A modes in NiDaPP (C₁ group point) and A′/A″ presentation in ZnDaPP (C_s group point), respectively. Furthermore, one or both of the two split components, especially for some vibration involving the motion of C_m atom, undergoes further mixing with original non-degenerate mode (A_1g, A_2g, B_1g, or B_2g) of same vibration. This produces new modes involving only partial motion of original mode. Besides general increasing frequency of NiDaPP with respect to ZnDaPP, different vibrational structure is also indicated by calculation for some structure-sensitive bands, especially ν₈ mode that couples with γ₆ mode and split into two modes for NiDaPP but not for ZnDaPP.     

DFT predictions of vibrational spectra of titanium tetramethoxide oligomers and the structure of titanium tetraalkoxides in liquid and solid phases

Plausible structures of the titanium tetramethoxide trimer were optimized at the B3LYP/6-31+G^* level. From the four types of structures of the Ti₃O₁₂ cage found earlier for the Ti(OH)₄ trimer only two isomers were found as energy minima on the Ti₃(OMe)₁₂ potential energy surface. One isomer (I), belonging to the C_i point group, is built from three interconnected titanium oxide tetrahedra with a linear arrangement of titanium atoms. This structure have a titanium oxide skeleton similar to that of Ti₃(OH)₁₂. The other isomer (II), of C₂ symmetry, is built by edge sharing TiO₆ groups. Theoretical IR spectra of these isomers are compared with reported experimental IR spectra of solid titanium tetramethoxide and newly obtained Raman spectra of commercial powders. It was shown that the number and position of observed bands in the CO stretching region of the IR spectra of the so-called modification A of solid titanium tetramethoxide are in a good agreement with the predicted vibrational spectrum of trimer I. The equilibrium structure and IR and Raman spectra were also obtained for the Ti₄(OMe)₁₆ tetramer. The comparison of the predicted vibrational spectrum with the experimental IR spectra of modification B as well as of the Raman spectrum of solid titanium tetramethoxide allows us to confirm the tetrameric structure of this modification and to propose the similar structure for commercial samples.     

Semiempirical method for extracting electron molecule cross sections from experimental data: CF4 as an example

A semiempirical method is described for calculating electron-molecule interaction potential, electron density, and elastic and vibrational inelastic cross sections using experimental data.CF ₄ was considered as un example. Experimental data from IR and Raman spectra, molecular property calculations (dipole matrix elements, polarizability, distance between atoms in molecule), beam measurements of total, momentum transfer, and differential cross sections, and swarm data (diffusion and drift veolcity) are used for extracting the interaction potential, the molecule electron density, avid the differential cross sections. Electron energy distribution functions, drift velocity, and characteristic energy are calculated with the obtained differential e-CF ₄ cross sections lierAr/CF ₄ mixtures.     

Molecular structure and vibrational spectra of trimethylarsenite

The molecular structure and vibrational spectra of trimethylarsenite were studied by gas phase electron diffractometry and IR and Raman spectroscopv. The configuration of the O-methyl groups with respect to the lone electron pair of the arsenic atom is established to be close to gosh-gosh-trans. The main geometrical parameters are: bond lengths (r_a, Å) As-O 1.780, C-0 1.451, and C-H 1.101; bond angles (deg) As-O-C 115.0, O-As-0 99.5, and O-C-H 115.3. The experimental IR and Raman spectra were obtained for pure liquid and CCl₄ solution. The frequencies and forms of normal vibrations were calculated.     

Spectroscopic investigation of organosilicon polymers. I. Vibrational analysis of poly(tetramethyl-p-silphenylene-siloxane)

This article is a detailed, normal coordinate analysis of an isolated chain of poly(tetramethyl-p-silphenylene-siloxane), based on results obtained for the corresponding monomer and a recent x-ray structure. Predicted vibrational frequencies are compared with new experimental infrared (IR) and Raman data obtained from powder and well oriented films. Vibrational spectra were also obtained for a deuterio derivative in which all hydrogens in the benzene rings were replaced with deuterium atoms. The results indicate that an intermode mixing occurs between vibrations of the ring and the saturated part which lead to low frequency normal modes characteristic of the chain. The simplified valence force field obtained for this polymer should provide a useful tool for understanding the vibrational spectra of other members of the class of polysiloxanes.     

Polarized IR and Raman spectra of kdy(moo4)2 single crystals,and the 92MO-100MO isotope effect

Polarized IR and Raman spectra below 4000 cm^?1 for single crystals of KDy(MoO₄)₂ are presented and discussed in relation to molecular and crystal structures. The spectroscopic data indicate additional intermolecular interactions due to pair coupling of the molybdate tetrahedra. This effect, combined with the multilayer crystal structure, is found to restrict the vibrational degrees of freedom, disturbing the selection rules for vibrational transitions. The spectra of first and higher-order transitions are described on the basis of ⁹²Mo/¹⁰⁰Mo isotopic-exchange effects and Y/Dy and K/Na substitutions.     

The vibrational spectrum of (maleic anhydride)iron tetracarbonyl

On the basis of solid-phase IR and Raman spectra, with some solution data for the IR, a reasonably complete vibrational assignment has been made for the modes of maleic anhydride in (maleic anhydride)iron tetracarbonyl. Shifts in v(C=C) and δ(CH) are consistent with a strong interaction with the metal, but relatively little coupling between the modes. More restricted assignments were made for modes associated with the (maleic anhydride)iron and Fe(CO)₄ fragments.     

Effect of intermolecular =C–HO interaction on the crystal structure and vibrational properties of 2,6-dimethyl-4-nitropyridine N-oxide

The crystal structure of 2,6-dimethyl-4-nitropyridine N-oxide (DMNPO) has been determined at ambient temperature. The compound crystallizes as a monoclinic structure, space group P2/n, with 12 molecules per unit cell. The unit cell contains three non-equivalent formula units. The nitro group is not coplanar with the pyridine ring. Through a system of =C–HO hydrogen bonds the molecules are arranged into a two-dimensional network of layers parallel to the axc plane.The IR and Raman spectra, measured in the 3500–100 cm⁻¹ region at ambient temperature, are correlated with X-ray structural data. The assignment of IR and Raman bands is given. The appearance of characteristic vibrational features in the spectra of this compound and the observed shifts of the =C–H and N–O IR active stretching modes, when the sample is dissolved in CCl₄, is discussed in terms of the relatively strong =C–HO hydrogen bonds present in this crystal.     

Four-membered rings family in the Si–O extended rocking IR band from quantum chemistry calculations

We calculate the vibrational modes of four-membered rings family in the Si–O extended rocking infrared for vitreous SiO₂ materials. In particular these species are obtained in the early stages of the sol–gel process. We have performed high quality quantum-mechanical calculations based on cluster models and gradient corrected density functional theory, (GC-DFT). Three possible configurations were obtained, a regular planar, a slightly deformed or quasi-planar, and a deformed ring. According to our result, the more probable one is the slightly deformed configuration. The calculated vibrational frequencies are compared with experimental IR and Raman results obtaining very good agreement. Also, we calculated geometries and vibrational frecuencies for three-membered rings. We found that 3- and 4-fold rings show evidence of decoupled vibrational modes, those modes are compared with a Raman spectrum obtaining very good coincidence.     

Vibrational spectra and structure ofN,N-dinitromethylamine

The vibrational (IR and Raman) spectra ofN,N-dinitromethylamine were studied. The assignments of the bands were carried out using a comparison of spectra obtained in different aggregate states, invoking the results of normal coordinate analysis. The most probable symmetry of the molecule was shown to beC _s with a planar configuration of the N(NO₂)₂ moiety.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1503–1507, August, 1995.     

Spektroskopische Untersuchungen an R3MF-Verbindungen (M = Si,Ge, Sn)

Spectroscopical Investigations on R₃MF Compounds (M = Si, Ge, Sn) The IR and RAMAN spectra of a number of R₃MF compounds (M? Si, Ge, Sn) have been recorded. The frequencies of the vibrational spectra were almost completely assigned. The measurements of the IR-spectra were investigated (as for as possible) in all states of aggregations. The force of the intermolecular interactions were discussed by means of the spectroscopic data.     

Theoretical Simulation of Vibrational Sum‐Frequency Generation Spectra from Density Functional Theory: Application to p‐Nitrothiophenol and 2,4‐Dinitroaniline

The molecular orientation of adsorbed molecules forming self‐assembled monolayers can be determined by combining vibrational sum‐frequency generation (SFG) measurements with quantum chemical calculations. Herein, we present a theoretical methodology used to simulate the SFG spectra for different combinations of polarizations. These simulations are based on calculations of the IR vectors and Raman tensors, which are obtained from density functional theory computations. The dependency of the SFG vibrational signature with respect to the molecular orientation is presented for the molecules p‐nitrothiophenol and 2,4‐dinitroaniline. It is found that a suitable choice of basis set as well as of exchange‐correlation (XC) functional is mandatory to correctly simulate the SFG intensities and consequently provide an accurate estimation of the adsorbed molecule orientation. Comparison with experimental data shows that calculations performed at the B3LYP/6‐311++G(d,p) level of approximation provide good agreement with experimental frequencies, and with IR and Raman intensities. In particular, it is demonstrated that polarization and diffuse functions are compulsory for reproducing the IR and Raman spectra, and consequently vibrational SFG spectra, of systems such as p‐nitrothiophenol. Moreover, the investigated XC functionals reveal their influence on the relative intensities, which show rather systematic variations with the amount of Hartree–Fock exchange. Finally, further aspects of the modeling are revealed by considering the frequency dependence of the Raman tensors.