Structural stabilities and electronic properties of planar C4 carbon sheet and nanoribbons

By means of first-principles calculations, we theoretically studied the structural stabilities and electronic properties of a pure-carbon 2D covalent metal named planar C(4) in P4/mmm (D(1)(4h)) symmetry. Planar C(4) is confirmed to be dynamically stable in the ground state based on phonon-mode analysis, and it is more stable than graphyne and the recently prepared graphdiyne. Moreover, it has a higher density of states (DOS) at the Fermi level than any plausible metallic carbon nanotube. Of particular interest, there exist two distinct types of planar C(4) nanoribbons (NRs): type I is predicted to be uniformly metallic regardless of the width change, while type II exhibits remarkable odd-even metal-semiconductor oscillating behavior depending on the width. The edge structure of type II NRs is revealed to be energetically more favored since its formation energy is about 0.45 eV per edge atom lower than that of type I NRs. Our work shows that planar C(4) carbon sheet and its NRs could serve as potential materials for future functional nanodevices.     

A model for the anomalous electronic properties in liquid silver chalcogenides

The electronic conductivity in liquids Ag–S and Ag–Se systems exhibits a maximum and a negative temperature derivative at the stoichiometric composition Ag₂S and Ag₂Se. In a similar alloy, Cu chalcogenides and other liquid semiconductors, such anomalies have not been observed. In the present paper, a model that explains the origin of the anomaly is presented. It is suggested that the anomalous behavior is controlled by the connection between the second nearest neighbor orbitals. Such connection depends on the electronegativity difference between the constituent elements of the system and is intimately related with the superionic behavior that these materials exhibit in the solid phase.     

一种锑桥连的四核铥嵌入锑钨酸盐及其发光性质（英文）

在酸性水溶液中Na_9[B-α-SbW_9O_(33)]·19.5H_2O, SbCl_3, Tm(NO_3)_3·6H_2O和盐酸二甲胺反应,合成一例锑桥连的四核铥嵌入四聚锑钨酸盐[H_2N(CH_3)_2]_8Na_6H_8{[Tm_4(H_2O)_6Sb_6O_4](B-α-SbW_(10)O_(37))_2(B-α-SbW_8O_(31))_2}·24H_2O (1).该簇合物的四聚阴离子是由两个二缺位[B-α-SbW_(10)O_(37)]~(11-)片段、两个四缺位[B-α-SbW_8O_(31)]~(11-)片段和两个[Tm_2(H_2O)_3Sb_3O_2]~(11+)簇组成.发光性质研究表明在353 nm紫外光激发下,1的发射光谱在450 nm处显示出一个特征发射峰,该发射峰归属于铥离子~1D_2→~3F_4跃迁.它相关的发光性能参数如色度坐标、色纯度、主波长和色温分别为(0.184 3, 0.135 0)、71.69%、470 nm和4 471 K.这些数据表明1有可能作为蓝色发光体应用于白光发光二极管领域.     

Effect of structural and electronic properties of substituents on the metal porphyrin formation kinetics

5,10,15-trinitro-2,3,7,8,12,13,17,18-octaethylporphyrin was synthesized and the kinetics of its coordination to zinc acetate was studied in comparison with previously studied β-octamethylporphyrin, β-octaphenylporphyrin, 5,10,15-triphenyl-2,3,7,8,12,13,17,18-octamethylporphyrin, and 5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18-octamethylporphine. The effect of structural and electronic properties of substituents on the kinetics of formation of metal porphyrins is analyzed. It is shown that the properties of 5,10,15-trinitro-2,3,7,8,12,13,17,18-octaethylporphyrin are determined by both strong electron-withdrawing influence of three nitro groups and by the distortion of the planar structure of the tetrapyrrole macrocycle.     

A theoretical study about the structural, electronic and spectroscopic properties of the ground and singlet excited states of curcuminoidic core

Curcumin, a well-known Indian spice, holds a variety of properties in many different fields from medicinal chemistry to dye industry. The peculiar electronic structure makes curcumin a valuable metal chelator. The principal aim of this work is a computational study of the structural and electronic properties of the ground and the first singlet excited states of the curcuminoidic core. Concerning the ground state, tautomeric equilibrium, vibrational and thermochemical analysis and electronic absorption spectra (with ab initio and semi-empirical methodologies) have been studied. A full geometry optimization of the first singlet excited states was obtained, with different computational methodologies. Solvent effects are also implicitly considered. An accurate comparison of the results is presented. Interesting aspects emerge, which suggest successive investigation about the nature of the excited states. The obtained results may be of large applicative interest. If curcuminoids are considered as potential ligands for complexes formation with metallic ions of pharmaceutical, medical–physical and technological interest, exciting the system with photons of appropriate frequencies, a photomodulated release of the metallic ion in the environment might be guessed, because of an important photoinduced geometrical modification.     

A relativistic study of the electronic and magnetic properties of cerocene and thorocene and its anions

In this study, we evaluated the importance of the relativistic effects on the optical and magnetic properties of cerocene and thorocene and its corresponding anions. The optimized molecular structures show D(8h) symmetry for all systems, in good agreement with the experimental data. Atomic charges were analyzed using different approaches (Mulliken, AIM, multipole, and NBO), and the results suggest that the net charge on the thorium is greater than on the cerium atom; however, none of the methodologies were able to predict the expected net charge Ce(III) and Th(IV) atoms. However, by an energy decomposition analysis, a significant electrostatic, ionic, interaction, ~58% and ~61%, was found between the metal and the COT(2-) rings, respectively. The calculated electronic excitations are underestimated in comparison with the experimental data, while the calculated EPR g-tensors are in agreement with previous theoretical and experimental data. Besides, the NICS analysis shows an increased ring electron delocalization due to the lanthanide and actinide metals.     

The impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of the fused thiophene semiconductors

The charge transport properties of 3 fused thiophene semiconductors, end-capped with diperfluorophenylthien-2-yl (DFPT) groups (DFPT-thieno[2′, 3′:4, 5]thieno[3, 2-b]thieno[2, 3-d]thiophene (TTA), DFPT-dithieno[2, 3-b:3′, 2′-d]thiophenes (DTT), and DFPT-thieno[3, 2-b]thiophene (TT)), are explored via density functional theory (DFT). To gain a better understanding of the impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of these molecules, the geometric structures, reorganization energy, frontier molecular orbitals, molecular ionization potentials and electron affinities, absorption spectra of the corresponding molecules including diperfluorophenyl (DFP)-TTA, DFP-DTT, DFP-TT, dithienyl (DT)-TTA, DT-DTT, DT-TT as well as their parent molecules (TTA, DTT and TT) are investigated for comparison. The calculated results show that introducing perfluorophenyl groups to the fused thiophenes could be a good strategy to promote electron transport, while the insertion of additional thiophene rings to DFP-end-capped derivatives could further extend the π-conjugation and enhance the charge transport properties of DFPT-end-capped analogs.     

A tetrameric sugar-based azobenzene that gels water at various pH values and in the presence of salts

A novel low-molecular mass tetrameric sugar derivative containing azobenzene core, 1, showed pronounced hydrogelation at micromolar concentration. Based on this observation, four related azobenzene based tetrameric sugar derivatives, 4-7, and three tetrameric sugar derivatives with a bis-terephthalamide core, 9-11, were also synthesized. However, none of these closely related analogues of the compound 1 showed effective gelation. The gel formed from 1 was characterized extensively using melting temperature analysis, UV-vis, FT-IR, circular dichroism spectroscopy, and scanning electron microscopy. The resultant gel exhibited impressive tolerance to the pH variation of the aqueous phase and gelated water in the pH range of 4-10. While UV-vis and CD spectroscopy indicated that pronounced aggregation of the azobenzene chromophores in 1 was responsible for gelation, FT-IR studies showed that hydrogen bonding is also a contributing factor in the gelation process. The melting of gel was found to depend on the pH of the aqueous medium in which gel was formed. The gel showed considerable photostability to UV irradiation, indicating tight intermolecular packing inside the gelated state that rendered azobenzene groups in the resultant aggregate refractory to photoisomerization. The electron micrographs of the aqueous gels of 1 showed the existence of spongy globular aggregates in such gelated materials. Addition of salts to the aqueous medium led to a delay in the gelation process and also caused remarkable morphological changes in the microstructure of the gel.     

On the electronic structures and spectroscopic properties of polyyne and its derivatives

We present a theoretical study on the electronic structure and spectroscopic properties of polyyne and its derivatives using periodic density functional theory study and semiempirical ZINDO/s methods. The electronic density of states were calculated, which indicates that polyyne behaves like a semiconductor and the insertion of aromatic groups into the polymer chain gives rise to significant metallic characters in the materials. The vibrational and UV–vis spectra of polyyne and its derivatives were simulated using a monomer or oligomer model. The effects of aromatic insertion into polyyne chain on their electronic and spectroscopic properties were discussed. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Comparison of the photophysical properties of a planar, PtOEP, and a nonplanar, PtOETPP, porphyrin in solution and doped films

The absorption and emission spectroscopic properties of planar (2,3,7,8,12,13,17,18-octaethylporphyrinato)platinum(II) (PtOEP) and nonplanar (2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrinato)platinum(II) (PtOETPP) complexes have been studied at room temperature. Liquid solutions and doped films, in polystyrene (PS) and epoxy (EPO) polymers, have been investigated. In dilute liquid solution, the photophysical properties of the nonplanar complex are substantially perturbed compared to the planar analogue. Strong ligating solvents further affect the photophysical behavior of both Pt(II) complexes via axial ligation to the central metal ion. At high concentrations, ground state aggregation and excimer formation is observed for PtOEP films in PS and EPO hosts. Incorporation of the nonplanar PtOETPP complex in PS results in enhanced coplanarity of the meso-phenyl groups, leading to a more extended conjugation between the meso-substituents and the π-conjugated system of the macrocycle. A more planar conformer for the nonplanar PtOETPP is present in the EPO host.     

From cyclic polyenes to carbohydrates: synthesis of the hexose sugar β-allose and its 2C-branched homologue from cyclooctatetraene

In an unconventional but interesting synthetic enterprise, the commercially available hydrocarbon cyclooctatetraene (COT) has been elaborated to the rare hexose sugar (dl)-β-allose and its 2C-branched analogue. The synthetic sequence delineated here is notable for its high regio- and stereoselectivity and is flexible enough to enable access to polyoxygenated systems, hexose sugars, and their siblings from a cyclic polyene precursor.     

A study of the ternary oxide LiVO2 and its anomalous behavior

Nonstoichiometric LiVO₂ and its unusual magnetic, electrical, and thermal phase transition near 200°C were studied using X-ray diffraction, IR and EPR spectroscopy, thermoanalytical methods, and measurements of electrical resistivity and magnetic susceptibility. The transition is semireversible, appearing to be noncooperative and of higher or multiple order. It has been concluded that the driving force for the transition is not a structural instability, but rather a critical distance phenomenon involving a change in the V³⁺V³⁺ bond type. The low-temperature data are interpreted in terms of a two-dimensional vanadium “metal cluster layer” formed via covalent-type metal-to-metal bonds; above T_t, narrow-band metallic behavior sets in within the vanadium planes. The phase transition in LiVO₂ is similar to that of TiCl₃, and is also very similar to the semiconducting-to-metallic transformations in VO₂ and V₂O₃.     

A carboxylate group modified the electrochemistry and photovoltaic properties of vanillin-substituted zinc porphyrin dye

Journal of Solid State Electrochemistry - A straightforward condensation method has been employed to introduce the potential alternative anchoring group of vanillin in porphyrins. Depending on the...     

Reinvestigation of the GaMn structure and theoretical studies of its electronic and magnetic properties

The crystal structure of the binary gallide compound GaMn is reinvestigated using X-ray diffraction. The structure is quite different from that proposed previously. Although GaMn is reported to crystallize with the Al₈Cr₅ structure type, space group R3m, we found that the centrosymmetric space group , with a=12.605(2) Å and c=8.0424(11) Å, was more accurate. Moreover, the atomic positions and the atomic displacement parameters, which are missing in the previous study, are now refined. Thereafter, band structure calculations have been performed using the TB-LMTO-ASA method to understand the electronic and magnetic properties of this compound. Analyses from the band structure, the density of states and the magnetic moments obtained using spin-polarized calculations show the stability of two different magnetic models relative to the nonmagnetic one.     

A tetranuclear heterobimetallic square formed from the cooperative ligand binding properties of square planar and tetrahedral metal centers

Reaction of Rh(I) and Zn(II) metal centers with a ligand containing salicylaldiminato and thioether-phosphine moieties resulted in the formation of a tetranuclear heterobimetallic molecular square. The directionality required to form these structures is imparted by both the tetrahedral and square planar metal centers acting in concert with one another.     

Spectroscopic properties and electronic structure of five- and six-coordinate iron(II) porphyrin NO complexes: Effect of the axial N-donor ligand

In this paper, the differences in the spectroscopic properties and electronic structures of five- and six-coordinate iron(II) porphyrin NO complexes are explored using [Fe(TPP)(NO)] (1; TPP = tetraphenylporphyrin) and [Fe(TPP)(MI)(NO)] (2; MI = 1-methylimidazole) type systems. Binding of N-donor ligands in axial position trans to NO to five-coordinate complexes of type 1 is investigated using UV-vis absorption and 1H NMR spectroscopies. This way, the corresponding binding constants Keq are determined and the 1H NMR spectra of 1 and 2 are assigned for the first time. In addition, 1H NMR allows for the determination of the degree of denitrosylation in solutions of 1 with excess base. The influence of the axial ligand on the properties of the coordinated NO is then investigated. Vibrational spectra (IR and Raman) of 1 and 2 are presented and assigned using isotope substitution and normal-coordinate analysis. Obtained force constants are 12.53 (N-O) and 2.98 mdyn/A (Fe-NO) for 1 compared to 11.55 (N-O) and 2.55 mdyn/A (Fe-NO) for 2. Together with the NMR results, this provides experimental evidence that binding of the trans ligand weakens the Fe-NO bond. The principal bonding schemes of 1 and 2 are very similar. In both cases, the Fe-N-O subunit is strongly bent. Donation from the singly occupied pi* orbital of NO into d(z2) of iron(II) leads to the formation of an Fe-NO sigma bond. In addition, a medium-strong pi back-bond is present in these complexes. The most important difference in the electronic structures of 1 and 2 occurs for the Fe-NO sigma bond, which is distinctively stronger for 1 in agreement with the experimental force constants. The increased sigma donation from NO in 1 also leads to a significant transfer of spin density from NO to iron, as has been shown by magnetic circular dichroism (MCD) spectroscopy in a preceding Communication (Praneeth, V. K. K.; Neese, F.; Lehnert, N. Inorg. Chem. 2005, 44, 2570-2572). This is confirmed by the 1H NMR results presented here. Hence, further experimental and computational evidence is provided that complex 1 has noticeable Fe(I)NO+ character relative to 2, which is an Fe(II)NO(radical) complex. Finally, using MCD theory and quantum chemical calculations, the absorption and MCD C-term spectra of 1 and 2 are assigned for the first time.     

A first-principles study of the electronic and structural properties of gamma-TaON

The geometric and electronic structure of the recently found new polymorph of tantalum oxynitride, gamma-TaON, and its structural stability were studied quantum-chemically at the density functional level. Results obtained by complementary quantum-chemical techniques with wavefunctions either expanded in atom-centered functions or in plane waves were compared, having employed pure density-functional functionals within the generalized gradient approximation as well as density-functional/Hartree-Fock hybrid methods. In particular, several plausible anion distributions were investigated and, in accordance with Pauling's second rule, it was found that the configuration in which nitrogen occupies crystallographic sites with highest coordination numbers is the most stable one. Theoretically generated local structural parameters were used to improve the accuracy of the experimentally derived information. The bonding situation in the most stable configuration was investigated by an analysis of the density of states.     

Theoretical studies on graphyne substructures: geometry, aromaticity, and electronic properties of the multiply fused dehydrobenzo[12]annulenes

The geometries of multiply fused dehydrobenzo[12]annulenes [12]DBAs 2-7 with various topologies, which are considered as graphyne fragments, have been optimized at the B3LYP/6-31G* level of theory. Most of the optimized geometries of fused DBAs have planar structures excluding a boomerang-shaped bisDBA 4, a trefoil-shaped trisDBA 6, and a wheel-shaped DBA 7. For the boomerang-shaped bisDBA 4 and the trefoil-shaped trisDBA 6, distortions originate from the steric repulsion between hydrogen atoms attached to adjacent benzene rings. The harmonic oscillator model of aromaticity (HOMA) values at the central benzene ring of multiply fused DBAs decrease as the number of fused 12-membered rings increases except for the closely related structures 4 and 5 and 6 and 7, because of bond length elongation due to conjugation with the phenylethynyl groups. Nucleus-independent chemical shifts (NICS) were computed at the individual ring centers of the fused DBAs. The fusion of the antiaromatic 12-membered rings results in increasing (more positive) NICS values at the central benzene ring, indicating the decrease of diatropic ring currents. Furthermore, HOMO-LUMO gaps of the DBAs 2-7 are strongly influenced by the molecular topology. The para-conjugation pathway of the bis(phenylethynyl)benzene unit plays a more important role in the determination of the electronic properties of multiply fused DBAs than the meta- and ortho-conjugation pathways.     

A study of the electronic structure and properties of the propargyl radical

By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH₂CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH₂CCH are studied at the qualitative level. Characteristics of the electronic structure of CH₂CCH and its parent molecules CH₃–C≡CH and CH₂=C=CH₂ are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH₂CCH is considered and its conjugation energy is calculated.