Quantum-chemical calculations of the IR absorption spectra of modified polytetrafluoroethylene forms

DFT(B3LYP) (basis set 6–31 + G(d)) and HF (basis set 6–31G) calculations were performed to determine the geometric structure and vibrational spectra of the C_nF_2n and C_nF_2n O molecules (n = 3–13). The IR spectra of chain C_nF_2n O molecules with the terminal carbonyl group (-COF) were found to contain a band at 1885 cm^?1. The C=C and C=O stretching vibrations of the-CF=CF₂ and COF terminal groups were independent, and there was no mutual influence of their frequencies starting with the seven-fragment molecule. In the presence of chain branching, the sensitivity of the ν(C=C) and ν(C=O) frequencies in the olefin and carbonyl groups depended on where branching occurred. The chain configuration was found to be energetically favorable compared with branched structures.     

Synthesis and electronic spectra of dimeric phthalocyanines

Dimeric phthalocyanines of a new type with a bridging 9,9,10,10-tetramethyl-9,10-dihydroanthracene fragment were synthesized. On the basis of X-ray diffraction analysis and molecular modeling of 9,9,10,10-tetramethyl-9,10-dihydroanthracene, a nearly planar structure was assumed for these phthalocyanines. The electronic absorption spectra of the obtained phthalocyanines and their monomeric and conjugated dimeric analogs were compared. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1686–1692, October, 2006.     

Quantum-chemical calculations of the tautomeric forms of azo derivatives of acetylacetone and determination of the stability constants of their complexes with rare-earth metals

The effective atomic charges in the tautomeric forms (enol-azo, keto-azo, and hydrazo) of 3-(2-hydroxy-5-nitro-3-sulfophenylazo)pentane-2,4-dione (L¹), 3-(2-hydroxy-3,5-disulfophenylazo)pentane-2,4-dione (L²), 3-(5-chloro-2-hydroxy-3-sulfophenylazo)pentane-2,4-dione (L³), 3-(2-hydroxy-4-nitrophenylazo)pentane-2,4-dione (L⁴), and 3-(2-hydroxyphenylazo)pentane-2,4-dione (L⁵) were calculated by the Hückel method (MO LCAO). It was found that the hydrazo form is most reactive for meta- and meta’-substituted derivatives (L^1–3) and the keto-azo form is most reactive for para-substituted (L⁴) and unsubstituted ones (L⁵). The stability constants of complexes of rare-earth metals (La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) with L^1–5 determined by potentiometric titration decrease in the order: Lu > Yb > Tm > Er > Ho > Dy > Tb > Gd > Eu > Sm > Nd > Ce > La. Functionalization of the aromatic part of ligands L affected neither the rare-earth metal: L ratio (1: 2) nor the above order of the stability constants.     

Quantum-chemical calculations of the electronic structure and reactivity of silylenes

The origin of the different reactivities of carbenes and silylenes has been discussed. Molecular orbital calculations have been carried out in order to estimate the effects of substituents on the singlet-triplet splittings E _ST in these molecules. The data ofab initio calculations have been used to establish the linear correlation between E _ST values for carbenes and silylenes. Both qualitative and quantitative appraisals of the applicability of the semiempirical MNDO method to calculations of E _ST values for carbenes and silylenes have been derived. E _ST values for a large number of substituted carbenes and silylenes have been computed by the PM3 method, one of the latest versions of the MNDO approach (Ref. 14).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1006–1008, June, 1994.     

Quantum-chemical calculations of the electronic structures of polymethylidyne dyes

The energies of the transitions of unsubstituted and substituted thia-, thiazolo-, and thienothiazolocarbocyanines, as well as quinocyanines and carbocyanines with a condensed thiophene, furan, selenophene, or pyridine ring, to the excited singlet states and their electronic structures were calculated by the MO LCAO method within the Pariser—Parr—Pople approximation. The nature of the long-wave and short-wave absorption bands in the spectra of these dyes and the peculiarities of the color of thieno-, furo-, and selenophenothiazolo- and -pyridocyanines, as well as the effect of substituents on their electronic characteristics as a function of the position in the heteroresidues and the nature of the latter, are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 626–633, May, 1978.     

Density functional calculations on electronic circular dichroism spectra of chiral transition metal complexes

Time-dependent density functional theory (TD-DFT) has for the first time been applied to the computation of circular dichroism (CD) spectra of transition metal complexes, and a detailed comparison with experimental spectra has been made. Absorption spectra are also reported. Various Co(III) complexes as well as [Rh(en)(3)](3+) are studied in this work. The resulting simulated CD spectra are generally in good agreement with experimental spectra after corrections for systematic errors in a few of the lowest excitation energies are applied. This allows for an interpretation and assignment of the spectra for the whole experimentally accessible energy range (UV/vis). Solvent effects on the excitations are estimated via inclusion of a continuum solvent model. This significantly improves the computed excitation energies for charge-transfer bands for complexes of charge +3, but has only a small effect on those for neutral or singly charged complexes. The energies of the weak d-to-d transitions of the Co complexes are systematically overestimated due to deficiencies of the density functionals. These errors are much smaller for the 4d metal complex. Taking these systematic errors and the effect of a solvent into consideration, TD-DFT computations are demonstrated to be a reliable tool in order to assist with the assignment and interpretation of CD spectra of chiral transition metal complexes.     

Quantum-chemical gas-phase calculations on the protonation forms oftrans- andcis-urocanic acid

The neutral, cationic, and anionic structures of both prototropic tautomers oftrans- andcis-urocanic acid [(E)- and (Z)-3-(1H-imidazol-4(5)-yl)propenoic acid, respectively] were studied by using semiempirical andab initio gas-phase calculations. Potential energy surfaces of the structures were calculated by using the semiempirical AM1 method, and the geometries corresponding to global minima on these surfaces were optimized up to the MP2/6-31G^* level of theory. The calculated protonation forms of each urocanic acid isomer have a planar molecular structure due to a delocalized -electron system, and all of them prefer thes-trans conformation with respect to the bond between the imidazole and the propenoic acid moieties. Thecis-urocanic acid structures are stabilized by an intramolecular hydrogen bond. The chargedcis-urocanic acid isomers have a lower molecular energy than the correspondingtrans-isomers, whereas the neutral molecules have, after inclusion of thermodynamic corrections, approximately the same energy. The cationic urocanic acid structures have about 2500 kJ mol^–1 lower energy than the anionic ones and about 1000 kJ mol^–1 lower energy than the neutral ones. The nonzwitterionic forms of the neutral urocanic acid isomers have about 200 kJ mol^–1 lower energy than the zwitterionic ones. These energy differences are explained by the proton affinities of the imidazole and the propenoic acid moieties of the urocanic acid structures.     

Quantum-chemical calculations of elastic properties of crystalline fluorides of alkaline-earth metals

Institute of Chemistry and Chemical-Metallurgical Processes, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 6, pp. 31–35, November–December, 1992.     

Calculations of electronic spectra of Fe and Co porphyrins and their anionic forms

Energies and intensities of electronic transitions of a number of Co and Fe porphyrins and their anionic forms have been calculated by the INDO/S-CI method in the Zerner parametrization. The results from the theoretical analysis are consistent with the basic relationships observed in the change of electronic spectra within the limits of isoelectronic series of compounds characterized by identical total number of -electrons and identical filling of the pair of d orbitals. It has been established that in the spectra of compounds of an isoelectronic series corresponding to the neutral state of the porphyrin ligand, the allowed electronic transitions are described by superpositions of two ^* configurations (la_1u 4e_g) ) and (3a ^2u 4e_g ) , two configurations of intermolecular charge transfer 3 (d 2b_1u) and (d 3b_2u), and two types of doubly excited configurations (la_1u, d 4e_g, 4e_g) and (3a _2u, d 4e_g, 4e_g). Data have been obtained on the energies and orbital nature of the even electronic states that are responsible for rapid exchange of excitation energy of the porphyrin molecules with the transition metals.Leningrad. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 2, pp. 144–151, March–April, 1991. Original article submitted September 28, 1989.     

All-valence-electron and transition density matrix calculations of the electronic spectra of [2.2]paracyclophanequinones

The combined CNDO/S and transition density matrix methods reproduced well the UV-VIS spectra of the intramolecular charge-transfer complexes of double- and triple-layered [2.2]paracyclophanequinones in which benzene and p-benzoquinone represent the donor and acceptor layers: DA, DDA and DAD. Calculations pointed to the already known experimental bathochromic shifts of the longest wavelength absorption band for the DADDADAD transformations. The electronic transitions corresponding to this band are for DA and DDA the CT transitions of the ^* type; however, for DAD the band represents the n ^* transition localized on the acceptor ring.     

Theoretical investigation of the molecular, electronic structures and vibrational spectra of a series of first transition metal phthalocyanines

A theoretical investigation of the fully optimized geometries and electronic structures of metallophthalocyanines FePc, CoPc, NiPc, CuPc and ZnPc has been conducted with the density functional theory (DFT) method. A comparison between the different molecules for the geometry, molecular orbital, and atomic charge is made. The simulated order of the sizes of the central hole is FePc>CoPc>NiPcNiPc>CuPc>ZnPc, and the atomic charges of the central metal (M=Fe, Co, Ni, Cu, Zn) ions vary in the same order, FePc>CoPc>NiPcCoPc>FePc>CuPc>ZnPc, and the corresponding peaks predicted at 894, 896, 898, 882 and 871 cm(-1), respectively, also exhibit the same order as above-mentioned. Moreover, the lines of fit through plots of the experimental IR and Ra frequencies versus the calculated ones show very good correlations.     

Quantum-chemical calculations of solvent effects on the electronic structure and reactivity of molecules

Journal of Structural Chemistry -     

Catalytic reduction of nitric oxide over phthalocyanines of first transition metals

Catalytic activities of metal phthalocyanines for the reduction of nitric oxide with hydrogen were found to be in the order Mn < Fe < Co > Ni Cu > Zn. This order can be related to the number of d-electrons of the metal ions. Complexes of the first three metals adsorbed nitric oxide at 80 °C and produced molecular nitrogen as well as ammonia through the reduction of nitric oxide, whereas the others did not adsorb nitric oxide and formed ammonia almost exclusively. The activities of nickel and copper phthalocyanine were greatly increased by heat treatment at 340 °C. Catalytic activity and product distribution are discussed from the mechanistic viewpoint.     

Electronic absorption spectra for free hydrazyl radicals,their ionic forms and initial hydrazines

The results of the calculations of π–π^* transition energies of some free hydrazyl radicals, their ionic forms and initial hydrazines by the SCF –MO –LCAO method with restricted configuration interaction are presented. The comparison of the data obtained with the electronic spectra experimentally found, revealed that the absorption of radical solutions in the visible area was due to the electronic structure of radical molecules, the contribution of ionic forms to the absorption being negligible.     

Direct SCF direct static-exchange calculations of electronic spectra

Applications of the direct SCF direct static-exchange method are reviewed for three different types of systems (free molecules, polymers, and surface adsorbates) and for six types of spectroscopy (X-ray absorption-, -emission-, and -shake-up spectroscopy, ultraviolet photoelectron emission, X-ray Raman and circular dichroism spectroscopy. Received: 28 December 1996 / Accepted: 8 April 1997     

NMR spectra of some reduced symmetry peripheral fused-ring-substituted phthalocyanines: density functional calculations

Chemical shifts of some reduced symmetry peripheral fused-ring-substituted phthalocyanines, namely Zn3B1N, Zncis2B2N, Zntrans2B2N, Zn1B3N and Zn3B0N, have been calculated at density functional B3LYP level using the gauge-independent atomic orbital (GIAO) method. The geometries were optimized using the 6-31G(d) basis set and the following NMR calculations were performed using 6-31G(d) and 6-311G(d,p) basis sets, respectively. The calculated NMR shielding tensors and chemical shifts are compared with previous experimental results. The chemical shifts are assigned according to the calculated data and satisfying results are obtained. The NMR shielding tensor simulation of Zn3B0N has been raised as a significant theoretical topic.