Metallomacrocycle (MacM) complex with cyanide as bridged ligand: Electronic structures of [MacMCN]n

The electronic structures of complexes and one‐dimensional metallomacrocycles with cyanide as bridged ligand, such as [MacM(CN)₂]^? and [MacM(CN)]_n [Mac=phthalocyanine, tetrabenzoporphyrine; M=Co(III), Rh(III)] have been investigated using density functional theory. The results of this study show that the intrinsic semiconductivity properties depend on the frontier bands. The valence band is composed by the π‐macrocycle orbital. The conduction band for the cobalt polymers is a mixture of orbitals between this metal and the cyanide ligand along of the stacking direction. However, in the rhodium polymers such a band is exclusively composed of the π* system of the macrocycles. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Multi‐Field Effect on the Electronic Properties of Silicon Nanowires

The quantum confinement and electronic properties of silicon nanowires (SiNWs) under an external strain field ε and an electric field E —as well as both (ε plus E )—are systematically investigated using density functional theory. These two fields exist in working environments of integrated circuits. It is found that both ε and E lead to a drop of the band gap E_g(ε, E ) of the SiNWs. If both fields coexist, the interaction between ε and E causes that E_g(ε, E ) becomes orientation‐dependent, which results from variations of both the conduction‐band minimum and the valence‐band maximum. The interaction is further illustrated by the density of states near the Fermi level and the eigenvalue of the highest occupied molecular orbital.     

Lithiation of tricarbonylchromium complexes with polyaromatic carbo-and heterocyclic ligands. DFT study

The reactions of tricarbonylchromium complexes of polyaromatic carbo-and heterocyclic derivatives with BuⁿLi was studied by the density functional theory. The kinetic and thermodynamic factors for controlling the direction and selectivity of metallation were calculated for the model biphenylenetricarbonylchromium complex. Both approaches indicate that lithiation occurs exclusively at the aromatic ring bonded to the transition metal, which agrees with experimental data, while the selectivity inside this ring is determined more exactly by the thermodynamic factor. The solvation effects were simulated for the lithium salt of the tricarbonylnaphthalenechromium complex in which the lithium atom is localized in position 1 of the coordinated ring. The simulation showed the stable coordination of the lithium atom with two THF molecules, and the addition of the next THF molecule is thermodynamically unfavorable. The results of calculation of the relative energies for all possible THF-solvated lithium salts of the tricarbonylchromium complexes of biphenyl, naphthalene, biphenylene, and dibenzothiophene indicate that the difference in energies Δ E ≤ 1 kcal mol⁻¹ corresponds to the experimentally observed absence of selectivity, while the difference more than 2.5 kcal mol⁻¹ corresponds to the selectivity of the reaction. No additional coordination of the lithium atom to the free electron pair of the heteroatom was observed for the sulfur-containing dibenzothiophene complex. Similar calculations show that double metallation in the dibenzothiophene complex occurs at positions 1 and 4. The developed approach enables one to predict the direction and selectivity of metallation reactions of transition metal complexes with different arenes. Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1993–2003, September, 2005.     

Synthesis of sulfone-containing monomers and polymers using cationic cyclopentadienyliron complexes

The synthesis of sulfone-containing monomers with pendent cationic cyclopentadienyliron (CpFe⁺) moieties has been accomplished via nucleophilic aromatic substitution of dichloroarene complexes with a number aliphatic dithiols. These complexes were further oxidized using m-CPBA to give the sulfone-based monomers. Polymerization of the sulfone-based monomers with O-containing nucleophiles produced the sulfone-based polymers. Direct nucleophilic aromatic substitution of dichloroarene complexes with dinucleophiles allowed for the formation of organoiron sulfide-based polymers. Oxidation of these polymers led to the formation of sulfone polymers with the pendent iron moieties. The organometallic monomers and polymers were found to be more soluble in polar solvents in comparison to their organic analogues.     

Twisting of conjugated oligomers and polymers: case study of oligo- and polythiophene

Interring twisting (change in the dihedral angle between conjugated rings) of polythiophene was studied theoretically using periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level. We find that the band gap of polymers is strongly dependent on the interring twist angle; yet twisting requires very little energy. A twist of 30 degrees increases the band gap by 0.75 eV in polythiophene, while requiring only 0.41 kcal mol(-1) per monomer unit. Such a small energetic value is of the order of crystal packing or van der Waals forces. These results are compared with calculations performed on model oligomers. Sexithiophene, its radical cations, and its dication are optimized at 0-180 degrees end-to-end twist angles (which correspond to 0-36 degrees interring dihedral angles) using the B3LYP/6-31G(d) method. The theoretical results suggest that the HOMO-LUMO gap, ionization potential, and charge distribution of oligomers are strongly dependent on twisting, whereas, similar to the case of polythiophene, twisting of neutral oligothiophenes costs very little energy. In the case of the radical cation, the lowest energy transition is shifted to a longer wavelength region on twisting, while the second-lowest energy transition is shifted to a shorter wavelength region. This implies that twisted, doped conducting polymers (modeled here by an oligomer radical cation), in contrast to planar, doped polymers, should be transparent within a certain optical window (in the far-visible region, at approximately 1.5 eV). This observation is explained on the basis of changes in the shape and overlap of the frontier molecular orbitals.     

The Electronic Structure and Photochemistry of Group 6 Bimetallic (Fischer) Carbene Complexes: Beyond the Photocarbonylation Reaction

The UV spectra of Group 6 metal carbene complexes bearing a CpM(CO)₃ (Cp=cyclopentadienyl) moiety bonded to the carbene carbon atom exhibit a redshift of the absorption maxima at higher wavelengths with respect to the parent monometallic complexes. This redshift is partly due to a higher occupation on the p_z atomic orbital of the carbene carbon atom. Time‐dependent DFT calculations accurately assign this band to a metal‐to‐ligand charge‐transfer transition, thus showing that the presence of a second metal center does not affect the nature of the transition. However, the photochemical reactivity of Group 6 metal carbene complexes bearing a CpM(CO)₃ moiety strongly depends on the nature of this metal fragment. A new photoslippage reaction leading to fulvenes occurs when Mn‐derived products 11 a , 11 b , and 12 a are irradiated (both Cr and W derivatives), whereas Re‐derived product 11 c behaves like standard Fischer complexes and yields the usual photocarbonylation products. A new photoreduction process occurring in the metallacyclopropanone intermediate is also observed for these complexes. Both computational and deuteration experiments support this unprecedented photoslippage process. The key to this differential photoreactivity seems to be the M–Cp back‐donation, which hampers the slippage process for Re derivatives and favors the carbonylation reaction.     

Electronic structure,magnetic properties,and mixed valence character of Ce2Ni3Si5 from first principles calculations

Cerium intermetallic compounds exhibit anomalous physical properties such as heavy fermion and Kondo behaviors. Here, an ab initio study of the electronic structure, magnetic properties, and mixed valence character of Ce₂Ni₃Si₅ using density functional theory (DFT) is presented. Two theoretical methods, including pure Perdew–Burke–Ernzerhof (PBE) and PBE + U , are used. In this study, Ce³⁺ and Ce⁴⁺ are considered as two different constituents in the unit cell. The formation energy calculations on the DFT level propose that Ce is in a stable mixed valence of 3.379 at 0 K. The calculated electronic structure shows that Ce₂Ni₃Si₅ is a metallic compound with a contribution at the Fermi level from Ce 4f and Ni 3d states. With the inclusion of the effective Hubbard parameter (U _eff), the five valence electrons of 5 Ce³⁺ ions are distributed only on Ce³⁺ 4f orbitals. Therefore, the occupied Ce³⁺ 4f band is located in the valence band (VB) while Ce⁴⁺ 4f orbitals are empty and Located at the Fermi level. The calculated magnetic moment in Ce₂Ni₃Si₅ is only due to cerium (Ce³⁺) in good agreement with the experimental results. The U _eff value of 5.4 eV provides a reasonable magnetic moment of 0.981 for the unpaired electron per Ce³⁺ ion. These results may serve as a guide for studying present mixed valence cerium‐based compounds. © 2017 Wiley Periodicals, Inc.     

Magnetic Properties and Electronic Structure of Neptunyl(VI) Complexes: Wavefunctions,Orbitals, and Crystal‐Field Models

The electronic structure and magnetic properties of neptunyl(VI), NpO₂²⁺, and two neptunyl complexes, [NpO₂(NO₃)₃]^? and [NpO₂Cl₄]^2?, were studied with a combination of theoretical methods: ab initio relativistic wavefunction methods and density functional theory (DFT), as well as crystal‐field (CF) models with parameters extracted from the ab initio calculations. Natural orbitals for electron density and spin magnetization from wavefunctions including spin–orbit coupling were employed to analyze the connection between the electronic structure and magnetic properties, and to link the results from CF models to the ab initio data. Free complex ions and systems embedded in a crystal environment were studied. Of prime interest were the electron paramagnetic resonance g‐factors and their relation to the complex geometry, ligand coordination, and nature of the nonbonding 5f orbitals. The g‐factors were calculated for the ground and excited states. For [NpO₂Cl₄]^2?, a strong influence of the environment of the complex on its magnetic behavior was demonstrated. Kohn–Sham DFT with standard functionals can produce reasonable g‐factors as long as the calculation converges to a solution resembling the electronic state of interest. However, this is not always straightforward.     

Towards new organometallic wires: tetraruthenium complexes bridged by phenylenevinylene and vinylpyridine ligands

The tetranuclear complexes [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)Ru Cl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)- CH=CH-1,4)] (3 a) and [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (3b), which contain vinylpyridine ligands that connect peripheral Ru(PiPr(3))(2)(CO)Cl units to a central divinylphenylene-bridged diruthenium core, have been prepared and investigated. These complexes, in various oxidation states up to the tetracation level, have been characterized by standard electrochemical and spectroelectrochemical techniques, including IR, UV/Vis/NIR and ESR spectroscopy. A comparison with the results for the vinylpyridine-bridged dinuclear complex [PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)(CH=CHPh)] (6) and the divinylphenylene-bridged complexes [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,4)] (8a) and [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (8b), which represent the outer sections (6) or the inner core (8a,b) of complexes 3a,b, and with the mononuclear complex [(EtOOCpy)(CO)(PPh(3))(2)RuCl(CH=CHPh)] (7) indicate that every accessible oxidation process is primarily centred on one of the vinyl ligands, with smaller contributions from the metal centres. The experimental results and quantum chemical calculations indicate charge- and spin-delocalization across the central divinylphenylenediruthenium part of 3a,b or the styrylruthenium unit of 6, but not beyond. The energy gap between the higher lying styryl- or divinylphenylenediruthenium-based and the lower occupied vinylpyridineruthenium-based orbitals increases in the order 6<3 b<3 a and thus follows the conjugation within the non-heteroatom-substituted aromatic vinyl ligand.     

Elucidating the 2D Magnetic Topology of the ‘Metal–Radical’ TTTA⋅Cu(hfac)2 System

The TTTA ? Cu(hfac)₂ polymer ( 1 ; in which TTTA=1,3,5‐trithia‐2,4,6‐triazapentalenyl, and hfac=(1,1,1,5,5,5)‐hexafluoroacetylacetonate) is one of the most prominent examples of the rational use of the ‘metal–radical’ synthetic approach to achieve ferromagnetic interactions. Experimentally, the magnetic topology of 1 could not be fully deciphered. Herein, the first‐principles bottom‐up procedure was applied to elucidate the nature and strength of the magnetic J_AB exchange interactions present in 1 . The computed J_AB values give rise to a 2D magnetic topology of ferromagnetic dimers (+11.9 cm^?1) coupled through weaker antiferromagnetic interactions (?3.0 and ?3.2 cm^?1) in two different spatial directions. The hitherto unknown origin of the antiferromagnetic interdimer interactions is thus unveiled. By using the 2D magnetic topology, the agreement between calculated and experimental χT(T) data is extraordinary. In the metal–radical TTTA ? Cu(hfac)₂ compound, the computational model transcends the local dimer cluster model owing to strong interactions between metal centers and organic radicals, thereby creating a de facto biradical. In addition, it is shown that the magnetic topology cannot be inferred from the polymeric [TTTA ??? Cu(hfac)₂]_n crystal motif, that is, from its chemical coordination pattern. Instead, one should think in terms of magnetic building blocks, namely, the de facto biradicals.     

A novel hybrid inorganic-metalorganic compound based on a polymeric polyoxometalate and a copper complex: synthesis, crystal structure and topological studies

Reaction of monosubstituted Keggin polyoxometalates (POMs) and [Cu(ac)(pmdien)]+ generated in situ led to the formation of the hybrid metal organic-inorganic compound K5[Cu(ac)(pmdien)][SiW11CuO39].12H2O; its crystal structure and magnetic properties have also been determined. The packing of this compound can be viewed as a stacking of hydrogen-bonded chiral double chains, with the cationic complexes located between the two-dimensional arrangement of POM double chains. DFT calculations performed on [Cu(ac)(pmdien)]+ suggest that the distortion presented in this cationic copper complex is due to electronic effects. An AIM stability study of the cationic copper complex, in order to determine the relationship between the bond angle Cu-O-C and the denticity of the acetate ligand, has been carried out. Topological analyses over the polyhedral distortion, both of the monosubstituted polyanion and copper complexes, have been performed by means of continuous shape measures (CSM).     

DFT description of the electronic structure and spectromagnetic properties of strongly correlated electronic systems: NiII, CuII and ZnII o-dioxolene complexes

The spectroscopic and magnetic properties of dioxolene complexes of zinc, copper and nickel were studied by DFT calculations on model complexes of formulas [(NH(3))(4)M(II)(SQ)](+) (M=Zn, Ni; SQ=semiquinonato) and [(NH(3))(2)Cu(II)(SQ)](+). Standard approaches such as time-dependent DFT (TDDFT), the Slater transition state (STS), and broken symmetry (BS) were found to be unable to completely account for the physical properties of the systems, and complete active space-configuration interaction (CAS-CI) calculations based on the Kohn-Sham (KS) orbitals was applied. The CAS-CI energies, properly corrected with multireference perturbation theory (MR-PT), were found to be in good agreement with experimental data. We present here a calculation protocol that has a low CPU cost/accuracy ratio and seems to be very promising for interpreting the properties of strongly correlated electronic systems in complexes of real chemical size.     

Electronic spectra and electron structure of fullerene complex (η2-C60)Fe(CO)4

The electronic spectrum of the C₆₀Fe(CO)₄ complex was studied in a toluene solution. The more intense absorption of C₆₀Fe(CO)₄ in the visible region, relative to the free C₆₀, can be attributed to the effect of lower symmetry of the C₆₀ fullerene cage in C₆₀Fe(CO)₄ and, thus, relaxation of selection rules for forbidden internal electronic transitions of C₆₀. No bands of the charge transfer from 3d(Fe) to C₆₀ orbitals were observed in the visible region of the complex spectrum. Assignment of the bands was confirmed by semiempirical calculations of the electronic spectrum.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1453–1458, June, 1996     

Electronic structure of francium

This article presents the first calculations of the electronic structure of francium for the bcc, fcc, and hcp structures, using the linearized augmented plane wave (LAPW) method. Both the local density approximation (LDA) and generalized gradient approximation (GGA) were used to calculate the electronic structure and total energy of francium (Fr). The GGA and LDA both found the total energy of the hcp structure to be slightly below that of the fcc and bcc structures, respectively. This is in agreement with similar results for the other alkali metals where the bcc structure is found not to be the ground state in contradiction to experiment. The equilibrium lattice constant, bulk modulus, and superconductivity parameters were calculated. Calculations of the enthalpy of the system suggest a structural transition from hcp to bcc under a pressure of 0.57 GPa. Using the McMillan‐Gaspari‐Gyorffy theories, we found that under further pressures, in the range of 3–14 GPa, Fr could be a superconductor with critical temperature up to 7 K. This is consistent with the other alkali metals and originates from an increase of the d‐like density of states at the Fermi level, which makes the alkali metals behave like transition metals. © 2013 Wiley Periodicals, Inc.     

Electronic Structure and Interface Properties of a Model Molecule for Organic Solar Cells

We study the electronic structure of 4,7‐bis(5‐methylthiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (MTBT) and its interface properties with gold using X‐ray photoemission spectroscopy (XPS), valence‐band ultraviolet photoemission spectroscopy (UPS), X‐ray absorption spectroscopy (XAS), as well as resonant photoemission (ResPES). MTBT can be regarded as a model molecule for PCPDTBT, a promising candidate for efficient bulk heterojunction solar cells. Almost no contribution of sulfur and only a weak contribution of nitrogen to the HOMO level is found. At the interface with gold, a strong chemical interaction between the sulfur of the benzothiadiazole and gold occurs, which may have consequences for interface properties in devices.     

Decomposition of dinitrosyl iron complex with thioformaldehyde ligands in water: reaction mechanisms and the role of chemical hardness of ligands

The mechanisms of hydrolysis of a model cationic dinitrosyl iron complex with a prototypic thioformaldehyde ligand have been studied using the density functional theory and polarizable continuum water model. The free-energy calculations have predicted that the associative mechanism of the thioformaldehyde ligand removal has a ～34 kJ mol^-1 lower activation barrier in water than the dissociative mechanism. The additional estimates of chemical hardness have provided useful qualitative characterization of the thio ligands binding.     

Organic-inorganic hybrids based on novel bimolecular [Si2W22Cu2O78(H2O)]12- polyoxometalates and the polynuclear complex cations [Cu(ac)(phen)(H2O)]n n+ (n=2, 3)

The reaction of a monosubstituted Keggin polyoxometalate (POM) generated in situ with copper-phenanthroline complexes in excess ammonium or rubidium acetate led to the formation of the hybrid metal organic-inorganic compounds A7[Cu2(ac)2(phen)2(H2O)2][Cu3(ac)3(phen)3(H2O)3][Si2W22Cu2O78(H2O)].approximately 18 H2O (A=NH4+ (1), Rb+ (2); ac=acetate; phen=1,10-phenanthroline). These compounds are constructed from inorganic and metalorganic interpenetrated sublattices containing the novel bimolecular Keggin POM, [Si2W22Cu2O78(H2O)]12-, and Cu-ac-phen complexes, [Cu(ac)(phen)(H2O)]n n+ (n=2, 3). The packing of compound 1 can be viewed as a stacking of open-framework layers parallel to the xy plane built of hydrogen-bonded POMs, and zigzag columns of pi-stacked Cu-ac-phen complex cations running along the [111] direction. Magnetic and EPR results are discussed with respect to the crystal structure of the compounds. DFT calculations on [Cu(ac)(phen)(H2O)]n n+ cationic complexes have been performed, to check the influence of packing in the complex geometry and determine the magnetic exchange pathways.