Diruthenium compounds bearing equatorial fc-containing ligands: synthesis and electronic structure

Previously, the synthesis of compounds Ru(2)(D(3,5-Cl(2)Ph)F)(4-n)(O(2)CFc)(n)Cl (n = 1, 3a; 2, 4a), where D(3,5-Cl(2)Ph)F is N,N'-di(3,5-dichlorophenyl)formamidinate, from the carboxylate exchange reactions between Ru(2)(D(3,5-Cl(2)Ph)F)(4-n)(OAc)(n)Cl and ferrocene carboxylic acid was communicated. Reported herein is the preparation of analogous compounds Ru(2)(DmAniF)(4-n)(O(2)CFc)(n)Cl (n = 1, 3b; 2, 4b), where DmAniF is N,N'-di(3-methoxyphenyl)formamidinate, from Ru(2)(DmAniF)(4-n)(OAc)(n)Cl. Compounds 3 and 4 were characterized with various techniques including X-ray structural determinations of 3a and 4a. Voltammetric behaviors of compounds 3 and 4 were investigated, and stepwise one-electron ferrocene oxidations were observed for both compounds 4a and 4b. Spectral analysis of the monocations [4](+) indicated that they are the Robin-Day class II mixed valent [Fc···Fc](+) species. Measurement and fitting of magnetic data (χT) of 4a between 2 and 300 K revealed a typical zero-field splitting of a S = 3/2 center with D = 77 cm(-1), while those of [4a]BF(4) are consistent with the presence of S = 3/2 (Ru(2)) and S = 1/2 (Fc(+)) centers that are weakly coupled (zJ = -0.76 cm(-1)).     

Synthesis, structure and electroluminescent properties of cyclometalated iridium complexes possessing sterically hindered ligands

New CN donor ligands incorporating pyridine or benzoimidazole N donors and a sterically hindered cyclometalating aromatic core featuring a polyphenylenephenyl, fluoranthene, or triphenylene segment are prepared and successfully converted into heteroleptic iridium(III) cyclometalated complexes with acetylacetone auxiliary ligands. The X-ray structure of the complex, derived from a ligand containing a fluoranthene fragment, has been solved to unveil the corresponding structure. The results clearly demonstrate that the nature of the sigma-coordinating ligand segment plays a key role in dictating the emission profile and peak position, such that the emission hue has been successfully tuned ranging from green to red. Supplementary support of this viewpoint is also rendered by computational (DFT) approaches. Electroluminescent devices fabricated using a complex as dopant in the PVK matrix were found to exhibit bright greenish yellow emission with promising device characteristics (maximum brightness 26450 cd m(-2) at 30 V and a maximum current efficiency of 40 cd A(-1)).     

Assessment of the electronic structure of 2,2'-pyridylpyrrolides as ligands

The ligand class 2,2'-pyridylpyrrolide is surveyed, both for its structural features and its electronic structure, when attached to monovalent K, Cu, Ag, Au, and Rh. The influence of pyrrolide ring substituents is studied, as well as the question of push/pull interaction between the pyridyl and pyrrolide halves. The π donor ability of the pyrrolide is found to be less than that of an analogous phenyl. However, in contrast to the phenyl analog, the HOMO is pyrrolide π in character for pyridylpyrrolide complexes of copper and rhodium, while it is conventionally metal localized for planar, d(8) rhodium pyridylphenyl. Monovalent three-coordinate copper complexes show great deviations from Y-shaped toward T-shaped structures, including cases where the pyridyl ligand bonds only weakly.     

A novel series of iridium complexes with alkenylquinoline ligands: Theoretical study on electronic structure and spectroscopic property

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of a novel series of neutral iridium(III) complexes with cyclometalated alkenylquinoline ligands [(C^N)₂Ir(acac)] (acac = acetoylacetonate; C^N = 2-[(E)-2-phenyl-1-ethenyl]pyridine (pep) 1; 2-[(E)-2-phenyl-1-ethenyl]quinoline (peq) 2; 1-[(E)-2-phenyl-1-ethenyl]isoquinoline (peiq) 3; 2-[(E)-1-propenyl]pyridine (pp) 4; 2-[(E)-1-fluoro-1-ethenyl]pyridine (fpp) 5) were investigated by DFT and CIS methods. The highest occupied molecular orbital is composed of d(Ir) and π(C^N) orbital, while the lowest unoccupied molecular orbital is dominantly localized on C^N ligand. Under the TD-DFT with PCM model level, the absorption and phosphorescence in CH₂Cl₂ media were calculated based on the optimized ground and triplet excited state geometries, respectively. The calculated lowest-lying absorptions at 437 nm (1), 481 nm (2), 487 nm (3), 422 nm (4), and 389 nm (5) are attributed to a {[d_x²-y²(Ir) + d_xz(Ir) + π(C^N)] → [π∗(C^N)]} transition with metal-to-ligand/intra-ligand charge transfer (MLCT/ILCT) characters, and the calculated phosphorescence at 582 nm (1), 607 nm (2), 634 nm (3), 515 nm (4), and 491 nm (5) can be described as originating from the ³{[d_x²-y²(Ir) + d_xz(Ir) + π (C^N)] [π∗(C^N)]} excited state with the ³MLCT/³ILCT characters. The calculated results revealed that the phosphorescent color of these new Ir(III) complexes can be tuned by changing the π-conjugation effect strength of the C^N ligand.     

End-substitution effect on the geometry and electronic structure of oligoheterocyclics

The end-substitution effects on the geometric and electronic structures of oligoheterocyclics are systematically studied using the density functional theory. It is found that the influence of the end-substitution does not depend on the heteroatom. End-substitution plays a fine-tune effect on the geometry and the excitation state. While the influences on the conducting type (p-type or n-type) and the inter-chain charge carrier hoping channels are much different between the electron-donating –CH ₃ and electron–accepting –CN substitutions. Both molecular electrostatic potentials and charge carrier injection rates indicate that the –CH ₃/–CH ₃ substitution is beneficial to the p-type doping, while the –CN/–CN substitution is in favor of the n-type doping, which is in agreement with the experimental observations. The –CH ₃ substituted packing dimers exert similar intermolecular interactions to the unsubstituted ones. The –CN substituted packing dimers yield much stronger intermolecular interactions comparing to the –CH ₃ substituted ones. It could be anticipated that the –CN substitution would be helpful to the charge carrier hopings between chains and thereby enhance the conductivity.     

Complexes of manganese, iron and cobalt with sterically demanding indenyl ligands

A series of manganese, iron and cobalt complexes bearing sterically demanding 1,3-disubstituted indenyl ligands, 1,3-(Me(3)C)(2)C(9)H(5) (Ind(tBu)) (1) and 1,3-(C(6)H(11))(2)C(9)H(5) (Ind(cHexyl)) (2), has been prepared. These complexes have been fully characterised by various spectroscopic techniques, elemental analysis, and X-ray diffraction experiments. In addition the electronic and steric properties of these ligands have been evaluated. Although the cone angles and electronic properties are similar to 1,2,4-(Me(3)C)(3)C(5)H(2) (Cp'), indenyl iron half-sandwich complexes are only stable at low temperature. This has been demonstrated for 1-FeI using suitable trapping experiments such as CO or NaCp' addition to yield 1-Fe(CO)(2)I and 1-FeCp', respectively. Overall the metal-ligand bonds in these indenyl compounds are weaker than in the corresponding cyclopentadienyl derivatives. In addition, the bis(indenyl)manganese complexes, 1-Mn and 2-Mn, are high-spin, as established by solid state magnetic susceptibility studies in the temperature range 2-300 K.     

Synthesis of uranium complexes incorporating extended azo-imine ligands: Molecular and electronic structure

The new azo-imine ligands 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl)diazenyl) phenylimino)methyl)phenol, H₂L¹, 1a, and 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl) diazenyl)p-chlorophenylimino)phenol, H₂L², 1b, were prepared. Reaction of H₂L¹;1a, and H₂L²;1b, with uranyl nitrate hexahydrate afforded the mononuclear complexes of compositions [U(O)₂(L¹)(H₂O)]; 2a, and [U(O)₂(L²)(H₂O)]; 2b, complexes respectively. The newly synthesised ligands (1a and 1b) and the complexes (2a and 2b) were characterised unequivocally. The x-ray structure of 2a was determined. The tetradentate dianionic ligand (L¹)^2- coordinated the uranium ion equatorially with a water molecule in the same plane. Two axially coordinated oxo ligands completed the overall pentagonal bipyramid geometry around U(VI) ion. Structural pattern, electron transfer properties (oxidation near 1.32 ​V vs Ag/AgCl) and electronic transitions of [U(O)₂(L¹)(H₂O)]; 2a, and [U(O)₂(L²)(H₂O)]; 2b have been rationalized by DFT calculations.     

The effect of reduction on rhenium(I) complexes with binaphthyridine and biquinoline ligands: a spectroscopic and computational study

A number of rhenium complexes with binaphthyridine and biquinoline ligands have been synthesized and studied. These are [Re(L)(CO)3Cl] where L = 3,3'-dimethylene-2,2'-bi-1,8-naphthyridine (dbn), 2,2'-bi-1,8-naphthyridine (bn), 3,3'-dimethylene-2,2'-biquinoline (dbq), and 3,3'-dimethyl-2,2'-biquinoline (diq). This series represents ligands in which the electronic properties and steric preferences are tuned. These complexes are modeled using density functional theory (DFT). An analysis of the resonance Raman spectra for these complexes, in concert with the vibrational assignments, reveals that the accepting molecular orbital (MO) in the metal-to-ligand charge transfer (MLCT) transition is the LUMO and causes bonding changes at the inter-ring section of the ligand. The electronic absorption spectroelectrochemistry for the reduced complexes of [Re(dbn)(CO)3Cl], [Re(dbq)(CO)3Cl], and [Re(diq)(CO)3Cl] suggest that the singly occupied MO is delocalized over the entire ligand structure despite the nonplanar nature of the diq ligand in [Re(diq)(CO)3Cl]. The IR spectroelectrochemistry for [Re(dbn)(CO)3Cl], [Re(dbq)(CO)3Cl], and [Re(bn)(CO)3Cl] reveal that reduction lowers the CO ligand vibrational frequencies to a similar extent in all three complexes. The substitution of naphthyridine for quinoline has little effect on the nature of the singly occupied MO. These data are supported by DFT calculations on the reduced complexes, which reveal that the ligands are flattened out by reduction: This may explain the similarity in the properties of the reduced complexes.     

Hypercoordinate germanium complexes with phenanthrene-9,10-diolate ligands: synthesis,structure, and electronic properties

The synthesis, molecular structure, and electronic properties of sodium tris(phenanthrene-9,10-diolato)germanate(iv) are described. The germanate complex is readily oxidized in air to produce 9,10-phenanthrenequinone, and the resulting quinones and the ligands reveal intermolecular π-stacking interaction in the polymeric association in the solid state. Addition of phenanthroline to the germanate complex leads to a monomeric structure.     

Substitution effect on the geometry and electronic structure of the ferrocene

The substitution effects on the geometry and the electronic structure of the ferrocene are systematically and comparatively studied using the density functional theory. It is found that -NH(2) and -OH substituents exert different influence on the geometry from -CH(3), -SiH(3), -PH(2), and -SH substituents. The topological analysis shows that all the C-C bonds in a-g are typical opened-shell interactions while the Fe-C bonds are typical closed-shell interactions. NBO analysis indicates that the cooperated interaction of d --> pi* and feedback pi --> d + 4s enhances the Fe-ligand interaction. The energy partitioning analysis demonstrates that the substituents with the second row elements lead to stronger iron-ligand interactions than those with the third row elements. The molecular electrostatic potential predicts that the electrophiles are expected to attack preferably the N, O, P, or S atoms in Fer-NH(2), Fer-OH, Fer-PH(2), and Fer-SH, and attack the ring C atoms in Fer-SiH(3) and Fer-CH(3). In turn, the nucleophiles are supposed to interact predominantly by attacking the hydrogen atoms. The simulated theoretical excitation spectra show that the maximum absorption peaks are red-shifted when the substituents going from second row elements to the third row elements.     

Torsion potentials and electronic structure of trifluoromethoxy- and trifluoromethylthiobenzene: an ab initio study

Potential functions of internal rotation about the C_sp²X bonds in molecules C₆H₅XCF₃ (X=O, S) were calculated at the second-order Møller-Plesset perturbation level of theory with 6-31G(d) basis set. The profile of the potential function and the rotation barrier (ΔE^#=3.0 kJ/mol) found for C₆H₅OCF₃ suggest that, depending on experimental conditions, there can be either free rotation about the C_sp²O bond or the conformational equilibrium is shifted to the side of the orthogonal form. The rotational barrier for C₆H₅SCF₃ is 14.7 kJ/mol and the molecule exists in the stable orthogonal conformation. The nature of hybridization, energy and population of lone electron pairs (LPs) on the oxygen and sulfur atoms were considered by using the Natural Bond Orbital (NBO) method. The energy of interactions of the LPs with antibonding π^∗-orbitals of the aromatic moiety were estimated for different conformations. The distribution of electron density in the molecules was discussed. The results were compared with analogous calculations on the molecules C₆H₅XCH₃.     

Redox-active metal(II) complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c

The synthesis and physico-chemical characterization of Fe(II) and Mn(II) complexes of 4,6-di-tert-butyl-3[(2-hydroxyethyl)sulphanyl]-1,2-dihydroxybenzene (HL^I) and 2-amino-4,6-di-tert-butylphenol (HL^II) were carried out. Antibacterial activity of the Co(II), Fe(II) and Mn(II) complexes was evaluated in comparison with Cu(II) complexes and three common antibiotics; it was found to follow the order: (1) Сu(L^I)₂ > Сo(L^I)₂ > Fe(L^I)₂ ? Mn(L^I)₂ > HL^I; (2) Сu(L^II)₂ > Сo(L^II)₂ > HL^II > Fe(L^II)₂ ? Mn(L^II)₂; and their reducing ability (determined electrochemically) followed the same order. Spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart сytochrome c with the ligands and their metal(II) complexes. NADPH:cytochrome P450-reductase was found to increase the rate of сytochrome c reduction with HL^I and HL^II ligands, while adrenodoxin in couple with NAD(P)H: adrenodoxin reductase had no substantial effect thereon. It was shown that the reduction of сytochrome c with these compounds cannot be related solely to the facility of their oxidation оr ionization.     

Effects of peripheral substituents and axial ligands on the electronic structure and properties of iron phthalocyanine

The effects of peripheral substituents and axial ligands on the electronic structure and properties of iron phthalocyanine, H(16)PcFe, have been investigated using a DFT method. Substitution by electron-withdrawing fluorinated groups alters the ground state of H(16)PcFe and gives rise to large changes in the ionization potentials and electron affinity. For the six-coordinate adducts with acetone, H(2)O, and pyridine, the axial coordination of two weak-field ligands leads to an intermediate-spin ground state, while the strong-field ligands make the system diamagnetic. The electronic configuration of a ligated iron phthalocyanine is determined mainly by the axial ligand-field strength but can also be affected by peripheral substituents. Axial ligands also exert an effect on ionization potentials and electron affinity and can, as observed experimentally, even change the site of oxidation/reduction.     

Effects of peripheral substituents and axial ligands on the electronic structure and properties of cobalt porphyrins

The effects of peripheral substituents and axial ligands (L) on the electronic structure and properties of cobalt tetraphenylporphyrin (CoTPP) have been studied using DFT methods. Various density functionals were tested, and the ground state of each system was determined by considering several possible low-lying states. The ground states of the fully fluorinated CoTPPF28(L)2 complexes with L = THF, Py, and Im were identified to be high-spin (4E(g)) by the meta-GGA functional tau-HCTH, which contains the kinetic energy density tau, in agreement with experimental measurements. All the pure GGA functionals, including the recently developed mPBE, OPBE, and HCTH/407, show more or less overestimation of the relative energies of the high-spin states. The energy gap between the 2A(1g) and 4E(g) states is insignificant (approximately 0.1 eV) and varies in the order L = Py < L = THF < L = Im. The results and their trend are consistent with 19F NMR studies which show partial population of the 4E(g) state in CoTPPF28(THF)2 and CoTPPF28(Py)2 and a complete conversion to the high-spin state in CoTPPF28(1-MeIm)2. Upon coordination by two very strong field axial CO ligands, CoTPPF28(CO)2 becomes low-spin, as in unligated CoTPPF(x). The influence of the peripheral substituents and axial ligands on the ionization potentials, electron affinities, and CoTPPF(x)-(L)2 binding strength was also investigated in detail.     

Quantum-chemical modeling of the atomic and electronic structure of thin diamond-like nanocrystallites

The structural and electronic characteristics of thin diamond-like nanocrystallites (with cross-sectional areas 5 < S < 280 Ų) were investigated by the electron density functional tight binding (DFTB) method. A new type of extended “hybrid” (sp³ + sp²) nanostructures, in the form of monolithic diamond-like sp³ crystallites encapsulated in a graphite-like sp² shell, was discovered. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 199–203, July–August, 2006.     

Influence of multi-atom bridging ligands on the electronic structure and magnetic properties of homodinuclear titanium molecules

The electronic structure and magnetic properties of homodinuclear titanium(III) molecules with bridging ligands from groups 14, 15, and 16 are examined. Single- and multireference methods with triple-zeta plus polarization basis sets are employed. Dynamic electron correlation effects are included via second-order multireference perturbation theory. Isotropic interaction parameters are calculated, and two of the complexes studied are predicted to be ferromagnetic based on multireference second-order perturbation (MRMP2) theory, using the TZVP(fg) basis set. Zero-field splitting parameters are determined using spin-orbit coupling obtained from complete active space (CAS) self-consistent field (SCF) and multiconfigurational quasi-degenerate perturbation theory (MCQDPT) wave functions. Three Breit-Pauli-based spin coupling methods were employed: full Breit-Pauli (HSO2), the partial two-electron method (P2E), and the semiempirical one-electron method (HSO1).