Syntheses,Structures, and Reactivities of Two Chalcogen‐Stabilized Carbones

Electronic effects on the central carbon atom of carbone, generated by the replacement of the S^IV ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph₂E, E=S or Se), were investigated. The carbones Ph₂E→C←SPh₂(NMe) [E=S( 1 ) or Se( 2 )] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2 , which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2 > 1 >CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four‐electron donor.     

Syntheses,Structures, and Reactivities of Two Chalcogen‐Stabilized Carbones

Electronic effects on the central carbon atom of carbone, generated by the replacement of the S^IV ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph₂E, E=S or Se), were investigated. The carbones Ph₂E→C←SPh₂(NMe) [E=S( 1 ) or Se( 2 )] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2 , which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2 > 1 >CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four‐electron donor.     

Synthesis and coordination properties of the zinc complex of dimeric porphyrin in reactions with imidazole, 2-methylimidazole, and the pyridine in benzene

Dimeric porphyrin(2,6-bis[15′-(3″,5″-di-tert-butylphenol)-3′,7′,13′,17′-tetramethyl-2′,8′,12′,18-tetraethylporphin-5′-yl]-4-tert-buthylphenol) and its binuclear zinc complex were obtained from 4,4′-dimethyl-3,3′-diethyldipyrrolylmethane, 2,6-diformyl-4-tert-butylphenol and 3,5-di-tert-buthylbenzaldehyde. Coordina-tion properties of dimeric zincporphyrin in the intermolecular reaction with nitrogen-containing bases (imidazole, 2-methylimidazole, and pyridine) in benzene were studied. Geometry and electronic structure of the zincporphyrin and its molecular complexes were calculated by a quantum-chemical method. Energy characteristics of the intermolecular reaction of the dimeric zincporphyrin with bases were determined. The calculated energies of the central metal atom interaction with the nitrogen atom of an extra-ligand agree well with the stability of the Zn-porphyrin molecular complexes. The influence of the deformation distortions of the porphyrin ligand on the strength of the metal-extra-ligand σ-bond was established.     

Synthesis of terphenyl oligomers as molecular electronic device candidates

Six functionalized bis(phenylene ethynylene)-p,p-terphenyls (BPETs) have been synthesized as potential molecular electronic devices. The molecules containing mono- and dinitro terphenyl cores, were rationally designed based on the electronic properties recently found in oligo(phenylene ethynylene)s (OPEs). From our understanding of the conductance properties in OPEs, improvement of electronic properties may be possible by using BPETs due to a higher rotational barrier between the central aromatic rings of the compounds prepared here. BPETs cores were functionalized with nitro groups and with different metallic adhesion moieties (alligator clips) to provide new compounds for testing in the nanopore and planar testbed structures.     

Prediction of retention indices. VI: Isothermal and temperature-programmed retention indices,methylene value,functionality constant,electronic and steric effects

The Kováts retention index system with n-alkanes as reference standards has properties not fully explored when single, isolated or stand-alone analytes are analyzed by isothermal gas chromatography. When a homologous series of analytes are analyzed by either linear or non-linear temperature-programmed gas chromatography, the retention data of the entire series can be treated systematically to produce an I vs. Z plot that is linear, thereby giving insight into the relationship between chemical structure and retention index. Dead time t_M is both instrument and temperature dependent. With no dead time t_M adjustment, the retention indices of analytes calculated from experimental retention times by the method of either linear or logarithmic interpolation give statistically identical values. Linear regression analysis of the data shows the slope as methylene value (A) and intercept as functionality constant or group retention factor (GRF) of the homologous series. The A and (GRF) values vary with chemical structures, intermolecular electronic and steric interactions, and polarity of column liquid phases, and can link gas chromatographic retention index to chemical structure. Examples of the influence of molecular electronic effects and steric effects on retention index are given and discussed.     

Sensitizing activity of metal tetraphenylporphines toward diethylaminobenzaldehyde <Emphasis Type="Italic">N,N</Emphasis>-diphenylhydrazone and its dependence on the central metal atom

The sensitizing activity of metal (Cu, Co, Ni, Zn, and Ag) tetraphenylporhines (TPPs) toward N,N-diphenylhydrazone of diethylaminobenzaldehyde was studied. It was found that the sensitized photosensitivity essentially depends on the electronic structure of the central metal atom in the TPP molecule: porphyrin complexes with metals that have vacant d or f shells or unpaired electrons (Co, Cu, Ni, and Ag TPPs) do not act as spectral sensitizers for diethylaminobenzaldehyde N,N-diphenylhydrazone.     

Spectroscopic and electronic structure of the CuIn,AgIn, CuGa and AgGa diatomics

Electronic, geometrical and spectroscopic properties of heteronuclear CuIn, AgIn, CuGa and AgGa diatomics have been investigated employing LCGTO-MP-LSD method. For all the molecules the ground state has been found to be the¹Σ one followed by³Π,¹Π and³Σ low-lying electronic state respectively. The geometric and electronic parameters are in reasonable agreement with the available experimental data. The chemical bond in the molecules has a single bond character due to the valence bond couplings between the Cu 4s (or Ag 5s) and the Ga 4p (or In 5p) electrons.     

Theoretical investigations of the elastic,electronic, optical and thermodynamics properties of SrSi

The crystal structural, electronic, optical and thermodynamic properties of SrSi are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). We have calculated the ground states properties and they are in good agreement with the available experimental data and other theoretical results. We have obtained the electronic structure and density of states, and the results showed that both of Immm and Cmcm phases are metal material. The elastic properties such as elastic constants, shear modulus, Young's modulus and Poisson's ratio are obtained for the first time. Furthermore, the optical properties are reported for radiation up to 30 eV. Finally, the thermodynamic properties of Cmcm phase such as free energy, entropy, enthalpy, heat capacity and Debye temperature are given for reference.     

Substituent effects on the redox properties and structure of substituted triphenylamines. An experimental and computational study

The peak oxidation potentials of a series of polysubstituted triphenylamines were found to be highly linearly correlated (R=0.995) with their ionization potentials as computed by density functional theory. The computations, as well as confirming previous experiments demonstrating the planar geometry of such substances around the central nitrogen atom, also demonstrate substantial resonance interactions between the central nitrogen atom and a nitro group located para or ortho to it; no such interaction is involved in the corresponding amine cation radicals. On the other hand, a methoxy group located para to the central nitrogen atom interacts strongly with the central nitrogen in the cation radical, but not in the neutral amine.     

Effect of substituent position and lithium,sodium and potassium on the electronic structure of o-, m- and p-methoxybenzoic acids

We have studied the effect of the substituent position in the ring, and lithium, sodium and potassium ions on the electronic structure of o-, m- and p-methoxybenzoic acids (anisic acids) by the use of FT-IR, FT-Raman, Ar matrix FT-IR and ¹H NMR methods, and ab initio calculations at the B3LYP/6-311++G** level of theory. Characteristic shifts of the bands in the spectra and changes in the band intensities along the metal and ligand series were observed. On the basis of the obtained results we may answer the questions: (1) do the substituents in the benzene ring influence the electronic charge distribution in the carboxylic group of anisic acids and alkali metal anisates, (2) do the metal ions affect the electronic charge distribution in the methoxy group, (3) in what way do the alkali metals affect the electronic system of o-, m- and p-anisic acids? The substitution of lithium, sodium and potassium ions in the carboxylic group of o-, m- and p-anisic acids causes changes in the values of bond lengths and angles, and in the electronic charge distribution in the carboxylic group, methoxy group and aromatic ring. The influence of alkali metals on the electronic structure of the ligands is weaker than the effect of methoxy substituents. The effect of Li, Na and K ions on the aromatic ring of the ligands is mostly noticeable in the case of the ortho isomer. The carboxylic and methoxy groups situated in ortho positions in the ring weaken the effect of the alkali metals on the electronic charge distribution in the carboxylic anion and methoxy group.     

Design,synthesis and structure of novel dendritic G-2 melamines comprising piperidine motifs as key linkers and 4-(n-octyloxy)aniline as a peripheral unit

Starting from 4-amino-1-(tert-butoxycarbonyl)piperidine (Boc-PD-NH₂), we report the synthesis of three novel meta-tri- and dimeric tetravalent N-substituted melamines with piperidin-4-yl groups. These compounds were used as central building-blocks and successfully incorporated into three new G-2 melamine dendrimers containing 4-(n-octyloxy)aniline as a peripheral unit. From a structural point of view, the challenging reactivity of Boc-PD-NH₂ in comparison with 1-Boc-piperazine and cyclohexylamine, as S_N2-Ar amination reagents against cyanuric chloride, was interpreted in terms of DFT (Density Functional Theory) thermodynamic and electronic computed data. Two out of the three dendrimers self-assembled in the solid state as large homogeneously packed spherical nano-aggregates (average D values ranging between 2500 and 3200 nm, TEM (Transmission Electron Microscopy) data) as a result of their “shell-to-shell” pre-associations in solution (DMF and 1,4-dioxane), promoted by chiral self-organisation, “round”- or “oval”-vaulted shapes (DFT data).     

Thienyl—Appended porphyrins: Synthesis,photophysical and electrochemical properties,and their applications

This review focuses on the synthesis, photophysical and electrochemical properties of thienyl porphyrins where processes such as electron transfer, energy transfer and electropolymerisation are discussed. The purpose of this review is to examine the influence of the thienyl ring, whether it be directly connected (via meso and β positions) or indirectly connected (via a covalent linker or axial coordination) on the ground and excited state electronic properties of the porphyrin macrocycle. Additionally, the importance of the electronic properties of a bridging oligothiophene between the porphyrin and another centre in supramolecular systems is discussed. Also included are applications of thienyl porphyrins in such areas as catalysis, therapeutics, (opto)electronics and electron-transfer/light-harvesting systems.     

On the ordering in new low gap semiconductors: PtSnS, PtSnSe, PtSnTe. Experimental and DFT studies

The crystallographic and electronic structures of PtSnS, PtSnSe and PtSnTe were investigated by X-ray structure analysis and density functional theory (DFT) calculations. Conductivity measurements and diffraction patterns show semiconducting ordered pyrite type related compounds containing SnX (X=S, Se, Te) entities. A scheme is presented to model ordered variants according to the relative orientation of the XY dumbbells. It represents the ullmannite, the cobaltite and a new rhombohedral structure type. The scheme allows for a systematic investigation of ordering preferences from first principles. According to the total electronic energy PtSnTe and PtSnSe prefer the cobaltite, PtSnS the rhombohedral structure type. The structural and electronic properties agree with experimental results. The three compounds are predicted to be narrow gap indirect semiconductors from conductivity measurements and band structure calculations.     

Straightforward, racemization-free synthesis of peptides with fairly to very bulky di- and trisubstituted glycines

Several fully protected tri- and pentapeptides containing a central symmetrical α,α-dialkyl glycine residue, with the alkyl group varying from methyl or ethyl to benzyl, were synthesized in good yields by a strategy based on the Ugi-Passerini reaction. Each Ugi-Passerini adduct was selectively cleaved and the product submitted to an assisted N,N′-dicyclohehylcarbodiimide coupling to an amino acid or dipeptide ester, respectively. Tripeptides as the above but containing a 4-methoxybenzyl group at the nitrogen atom of the central residue were also synthesized in fair to good yields by N-[(1H-benzotriazol-1-yl)-(dimethylamino)methylene]-N-methylmethanaminium hexafluorophosphate N-oxide assisted couplings. The results reported here show that our strategy is appropriate for routine synthesis of peptides incorporating these moieties.     

Mixed-valence trinuclear cluster (2dn,dn+1); Influence of the electronic coupling on the magnetic properties

The influence of electronic processes on the magnetic behavior of the mixed-valence trinuclear clusters (2dⁿ, dⁿ⁺¹) is discussed. The problem is solved by means of a pseudoparticle formalism by assuming competing effects such as electronic transfer, and localization of the extra-particle due to different transfer pathways or different sites…. The magnetic susceptibility is derived for significant values of the characteristic parameters in the cases n = 1, 3, 5. Finally, the magnetic behavior of Fe₃O(CH₃COO)₆L₃, with L = H₂O or pyridine, is discussed on the basis of the proposed model.     

π-electron structure,reactivity, and absorption spectra of anthrapyridone

The π-electronic spectra, heats of atomization, and electronic indexes of the lactam and lactim forms of anthrapyridone were calculated by the Pariser-Parr-Pople method with allowance for 25 one-electron configurations. An examination of the π-bond orders and the charges on the atoms showed that a system with a π-electron distribution close to the distribution in anthraquinone and in α-pyridone for the lactam tautometer and in α-hydroxypyridine and anthraquinone for the lactim form is formed in the lactam and lactim of anthrapyridone. The electronic absorption bands were assigned. An analysis of the calculated values demonstrated that the long-wave band in the spectrum of the anthrapyridone is due to charge transfer from the amide group to the ketone group. The reactivity and localization energy indexes of aromatic substitution reactions calculated by the Hückel MO method are in satisfactory agreement with the experimental data.     

Fulleropyrrolidine end-capped molecular wires for molecular electronics--synthesis, spectroscopic, electrochemical, and theoretical characterization

In continuation of previous studies showing promising metal-molecule contact properties a variety of C(60) end-capped "molecular wires" for molecular electronics were prepared by variants of the Prato 1,3-dipolar cycloaddition reaction. Either benzene or fluorene was chosen as the central wire, and synthetic protocols for derivatives terminated with one or two fullero[c]pyrrolidine "electrode anchoring" groups were developed. An aryl-substituted aziridine could in some cases be employed directly as the azomethine ylide precursor for the Prato reaction without the need of having an electron-withdrawing ester group present. The effect of extending the π-system of the central wire from 1,4-phenylenediamine to 2,7-fluorenediamine was investigated by absorption, fluorescence, and electrochemical methods. The central wire and the C(60) end-groups were found not to electronically communicate in the ground state. However, the fluorescence of C(60) was quenched by charge transfer from the wire to C(60). Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires.     

Anisotropy of the triplet spin—lattice relaxation in molecular crystals at low temperatures and high magnetic fields

The anisotropy of the triplet relaxation rates in molecular crystals at low temperatures (T = 1.6 K) and very high magnetic fields (B = 5.2–10 T) is explained by a model, which assumes time dependent matrix elements of the electronic dipole tensor and of the electronic g-tensor. The time dependencies may be due, for instance, to librations of the molecule or to changes in the electronic configuration; they arise from a direct process. This fact is used in order to reduce the number of parameters. The relaxation rates are given as functions of the direction cosines of the magnetic field and of eight parameters which are determined in a least-squares fit for the system quinoxaline in perdeuterated naphthalene. Some uncertainties concerning the numerical values of the parameters would be reduced by measurements with the magnetic field directed along the principal axes of the electronic dipole tensor.     

Electro-structural correlations,elastic and optical properties among the nanolaminated ternary carbides Zr2AC

We have performed ab initio calculations for the nanolaminates Zr₂AC (A = Ti, In, Tl, Si, Ge, Sn, Pb, P, As, S) ceramics to study their electronic structure, elastic and optical properties. In this work, we used the accurate augmented plane wave plus local orbital method with density functional theory to find the equilibrium structural parameters, dielectric functions and to compute the full elastic tensors. The obtained elastic constants were used to quantify the stiffness of the Zr₂AC phases and to appraise their mechanical stability. The relationship between elastic, electronic and valence electron concentration is discussed. Our results show that the bulk modulus and shear modulus increase across the periodic table for Zr₂AC. Furthermore, trends in elastic stiffness are well explained in terms of electronic structure analysis, as occupation of valence electrons in states near the Fermi level of Zr₂AC. We show that increments of bulk moduli originate from additional valence electrons filling states involving Zr d–A p. We show also that Zr d–A p hybridizations are located just below the Fermi level and are weaker bonds than the Zr d–C p hybridizations, which are deeper in energy. As a function of the p-state filling of the A element the Zr d–A p bands are driven to deeper energy. The optical spectra were analyzed by means of the electronic structure, which provides theoretical understanding of the conduction mechanism of these ceramics.     

Bond lengthening and through-bond interactions in p,p'-dibenzene and related molecules

The structure of p,p'-dibenzene (PDB) has been investigated by full geometry optimizations using the empirical force field (EFF) and MINDO/3 methods. While other structural parameters are in good agreement, the central bond length calculated by MINDO/3 (1.595 Å), as confirmed by an ab initio (STO-3G basis set) optimization (1.596 Å), is in striking contrast to the corresponding length calculated by EFF (1.543 Å). A detailed analysis of the electronic structure of PDB based on a quantitative perturbational molecular orbital treatment reveals that through-bond coupling of the four π systems is responsible for an elongation of the σ bond which mediates this interaction. Further studies using the EFF and MINDO/3 approaches demonstrate that extended C-C single bonds can arise even in structures with fewer than four π systems. The effect of substituents on the central bond length in PDB has been briefly investigated. (MINDO/3). A variety of other structures have been identified in which bond lengthening may result from through-bond coupling.