Infrared spectroscopic studies of transition metal complexes and polarizability effect

The literature data on substituent influence on the CS, CN, NC, NN, and NO stretching frequencies (ν) in the IR spectra and in specific cases on their respective stretching force constants (k) have been analyzed for 28 series of the transition metal complexes. The ν and k values were first established to depend not only on the inductive and resonance effects but on the polarizability of substituents as well. The contribution of the polarizability effect varies from 0 to 57% with the type of series.     

Kernquadrupolkopplung in einigen Kobalt(III)-komplexen

Zusammenfassung Aus Messungen der magnetischen Kernresonanz (MKR) an Einkristallen von [Co (NH₃)₅ H₂O] (ClO₄)₃ (I) und NH₄ [Co (NO₂)₄ (NH₃)₂] (II) wurden die Quadrupolkopplungskonstanten e ² Qq/h von Co⁵⁹ gewonnen. Ferner wurden die Linienbreiten der MKR in wÄ\rigen Lösungen von I, II und trans-[Co en₂Cl₂] Cl (III) gemessen.Aus e ² Qq/h und wurden nach der Theorie der Quadrupolrelaxation in Flüssigkeiten die Korrelationszeiten _cder Komplexionen bestimmt. Diese wiederum wurden zusammen mit den ebenfalls gemessenen Linienbreiten der MKR von N¹⁴ in wÄ\rigen Lösungen von I, II und III benutzt, um e ² Qq/h von N¹⁴ zu erhalten.Darüber hinaus wurden mittels geschÄtzter Korrelationszeiten und gemessener Linienbreiten der MKR von Co⁵⁹ und N¹⁴ für eine grö\ere Zahl von Co(III)-Komplexen NÄherungswerte von e ² Qq/h erhalten. Auf Grund dieser Werte wird die Elektronenstruktur der Komplexionen diskutiert.Die chemischen Verschiebungen der untersuchten Kernresonanzlinien werden angegeben. In einem Einkristall von I wurde die Anisotropie der chemischen Verschiebung bestimmt.

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Nuclear quadrupole coupling constants e ² Qq/h of Co⁵⁹ resulted from nuclear magnetic resonance (NMR) measurements on single crystals of [Co (NH₃)⁵ H₂O] (ClO₄)₃ (I) and NH₄ [Co (NO₂)₄ (NH₃)₂] (II). NMR line-widths were measured in aq. solutions of I, II, and trans-[Co en₂Cl₂] Cl (III). The correlation times _c of the complex ions resulted from e ² Qq/h and with the theory of quadrupole relaxation in liquids. These _c-values were used to obtain e ²Qq/h of N¹⁴ from NMR ine-width measurements of N¹⁴ in aq. solutions of I, II, and III.Approximate values for e ²Qq/h were obtained from NMR line-width measurements of Co⁵⁹ and N¹⁴ in a number of Co(III)-complexes with estimated correlation times. The electronic structure of the complex ions is discussed on the basis of the e ² Qq/h-values.The measured chemical shifts of the NMR-lines are listed. In a single crystal of I the anisotropy of chemical shift has been determined.

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Résumé Les constantes de couplage quadripolaire e ² Qq/h du ⁵⁹Co ont été tirées des mesures de la résonance nucléaire magnétique de monocristaux de [Co (NH₃)₅ H₂O] (ClO₄)₃ (I) et NH₄ [Co (NO₂)₄ (NH₃)₂] (II). En outre, la largeur des raies a été mesurée dans les solutions aqueuses de I, II et trans-[Co en₂ Cl₂] Cl (III).Les périodes de corrélation _c en ont été déduites d'après la théorie de la relaxation quadripolaire dans les liquides. Des _cet des du ¹⁴N, mesurés dans les solutions de I, II et III, on calcule e ² Qq/h pour ¹⁴N.Des _cestimés et de ⁵⁹Co et ¹⁴N mesurés pour plusieurs complexes du Co³⁺ s'obtiennent des valeurs approximatives de e ² Qq/h. Sur base de ces valeurs la structure électronique des ions complexes est discutée.Les déplacements chimiques (chemical shift) des raies de résonance examinées sont données. L'anisotropie du déplacement dans un monocristal de I a été déterminée.

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Herrn Professor Dr. P. Royen zum 60. Geburtstag gewidmet.     

Preparation and characterization of PEPPSI-palladium N-heterocyclic carbene complexes using benzimidazolium salts catalyzed Suzuki–Miyaura cross coupling reaction and their antitumor and antimicrobial activities

New palladium complexes were efficiently synthesized from the reaction of benzimidazolium salts 2a–e, potassium carbonate (K₂CO₃) and palladium chloride (PdCl₂) in pyridine (for 3a–e). The catalytic activity of these complexes in a catalytic system including palladium complexes and K₂CO₃ in DMF-H₂O was evaluated in Suzuki–Miyaura cross-coupling reactions of aryl bromides and chlorides with phenylboronic acid. Our novel complexes show excellent catalytic activities with high turnover numbers (TON) and high turnover frequencies (TOF) (e.g. for the Suzuki–Miyaura reaction: TON up to 370 and TOF up to 123.3?h^?1). Both benzimidazolium salts 2a–e and complexes 3 have been characterized using spectroscopic data and elemental analysis. The antimicrobial activity of the N-heterocyclic carbene palladium complexes 3a–e varies with the nature of the ligands. Also, the IC₅₀ values of both, complexes (3a–e) and benzimidazoles 2a–e, have been determined. In addition, the new palladium complexes were screened for their antitumor activity. Complexes 3e and 3d exhibited the highest antitumor effect with IC₅₀ values 6.85?μg/mL against MCF-7 and 10.75?μg/mL against T47D, respectively.     

Interpnictogen Cations: Exploring New Vistas in Coordination Chemistry

Pnictine derivatives can behave as both 2e^? donors (Lewis bases) and 2e^? acceptors (Lewis acids). As prototypical ligands in the coordination chemistry of transition metals, amines and phosphines also form complexes with p‐block Lewis acids, including a variety of pnictogen‐centered acceptors. The inherent Lewis acidity of pnictogen centers can be enhanced by the introduction of a cationic charge, and this feature has been exploited in recent years in the development of compounds resulting from coordinate Pn–Pn and Pn–Pn′ interactions. These compounds offer the unusual opportunity for homoatomic coordinate bonding and the development of complexes that possess a lone pair of electrons at the acceptor center. This Review presents new directions in the systematic extension of coordination chemistry from the transition series into the p‐block.     

Nuclear quadrupole resonance of 14N in imidazole and related compounds

Using the technique of nuclear double resonance with spin mixing by level crossing, the nuclear quadrupole resonance of ¹⁴N has been measured in L-histidine, D-L-histidine, L-histidine hydrochloride monohydrate, sodium urocanate and urocanic acid at 77 K. The nuclear quadrupole resonance of both ¹⁴N and ²D has been measured in deuterated imidazole at 77 K. The previously measured spectra for normal imidazole have been positively assigned with the electric field gradient parameters for the tri-coordinated nitrogen site given by e²qQ/h = 1424 kHz and η = 0.980, and for the di-coordinated nitrogen site by e²qQ/h = 3267 kHz and η = 0.129.     

Simultaneous morphological stability and high charge carrier mobilities in donor–acceptor block copolymer/PCBM blends

Donor–acceptor block copolymers (BCP), incorporating poly(3‐hexylthiophene) (P3HT), and a polystyrene copolymer with pendant fullerenes (PPCBM) provide desired stable nanostructures, but mostly do not exhibit balanced charge carrier mobilities. This work presents an elegant approach to match hole and electron transport in BCP by blending with molecular PCBM without causing any macrophase separation. An insufficient electron mobility of PPCBM can be widely compensated by adding PCBM which is monitored by the space‐charge limited current method. Using X‐ray diffraction, atomic force microscopy, and differential scanning calorimetry, we verify the large miscibility of the PPCBM:PCBM blend up to 60 wt % PCBM load forming an amorphous, molecularly mixed fullerene phase without crystallization. Thus, blending BCP with PCBM substantially enhances charge transport achieving an electron mobility of μ_e=(3.2 ± 1.7) × 10^?4 cm²V^?1s^?1 and hole mobility of μ_h=(1.8 ± 0.6) × 10^?3 cm²V^?1s^?1 in organic field‐effect transistors (OFET). The BCP:PCBM blend provides a similarly high ambipolar charge transport compared to the established P3HT:PCBM system, but with the advantage of an exceptionally stable morphology even for prolonged thermal annealing. This work demonstrates the feasibility of high charge transport and stable morphology simultaneously in a donor–acceptor BCP by a blend approach. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1125–1136     

Calculation of the electric susceptibilities of the helium atom

We calculated the static and the dynamic dipole polarizabilities and the static quadrupole polarizability of the helium atom. The results are α = 0.2070 × 10^?24 cm³ for the static dipole polarizability and γ₄ = 0.1038 × 10^?40 cm⁵ for the static quadrupole polarizability.     

Experimental and Computational Probes of the Nature of Halogen Bonding: Complexes of Bromine‐Containing Molecules with Bromide Anions

The nature of halogen bonding is examined via experimental and computational characterizations of a series of associates between electrophilic bromocarbons R? Br (R? Br=CBr₃F, CBr₃NO₂, CBr₃COCBr₃, CBr₃CONH₂, CBr₃CN, etc.) and bromide anions. The [R? Br, Br^?] complexes show intense absorption bands in the 200–350 nm range which follow the same Mulliken correlation as those observed for the charge‐transfer associates of bromide anions with common organic π‐acceptors. For a wide range of the associates, intermolecular R? Br???Br^? separations decrease and intramolecular C? Br bond lengths increase proportionally to the Br^?→R? Br charge transfer; and the energies of R? Br???Br^? bonds are correlated with the linear combination of orbital (charge‐transfer) and electrostatic interactions. On the whole, spectral, structural and thermodynamic characteristics of the [R? Br, Br^?] complexes indicate that besides electrostatics, the orbital (charge‐transfer) interactions play a vital role in the R? Br???Br^? halogen bonding. This indicates that in addition to controlling the geometries of supramolecular assemblies, halogen bonding leads to electronic coupling between interacting species, and thus affects reactivity of halogenated molecules, as well as conducting and magnetic properties of their solid‐state materials.     

N-Heterocyclic carbene-Pd(II)-PPh3 complexes as a new highly efficient catalyst system for the Sonogashira cross-coupling reaction: Synthesis,characterization and biological activities

A novel series of N-heterocyclic carbene-phosphine palladium(II) complexes has been synthesized and fully characterized by IR, ¹H NMR, ¹³C NMR, and ³¹P NMR spectroscopies, and elemental analysis. The new N-heterocyclic carbene (NHC)-phosphine palladium(II) complexes 3a–h have been easily prepared by the reaction of the corresponding PEPPSI (pyridine-enhanced precatalyst preparation stabilization and initiation) complexes 2a–h and triphenylphosphine in dichloromethane in high yields. These complexes were applied as catalyst precursors which efficiently catalyzed Sonogashira reactions between aryl bromides and phenylacetylene to afford the corresponding products in good yields. The bulky NHC-Pd-PPh₃ complexes 3 were tested against Gram-positive and Gram-negative bacteria to study their biological activity. All the complexes exhibit antibacterial against these organisms. Investigation of the anti-acetylcholinesterase activity of the studied complexes showed that compounds 3a and 3b exhibited moderate activity at 100 μg mL^?1 and product 3b is the most active.     

NMR chemical shielding and spin–spin coupling constants across hydrogen bonds in uracil–α-hydroxy-N-nitrosamine complexes

One- and two bond spin–spin coupling constants, ¹ J, ^1h J , and ^2h J across X–H?O hydrogen bonds and shielding constants of bridging hydrogens have been computed for complexes formed from interaction between the α-hydroxy-N-nitrosamine (NP) and four preferential binding sites of the uracil (U) at B3LYP/6-311++G(2d,2p)//MP2/6-311++G(2d,2p) level of theory. All complexes are stabilized by two H_U?O_NP and H_NP?O_U hydrogen bonds. Very good correlations were found between NMR spin–spin coupling constant as well as isotropic shielding constant and the binding energy, H-bond distance, red-shift of vibration frequency, charge transfer energy, and electron density at H-bond critical point.     

14N quadrupole resonance in polyglycine

Using proton-nitrogen double resonance in the laboratory frame, the quadrupole coupling of the peptide nitrogens in polyglycine has been determined. At 77 K, e²qQ/h = 3.097 MHz and the asymmetry parameter equals η = 0.76.     

Polarization effect in radical cations and H-complexes

The effect of substituents X on the ionization potentials IP (process DX + hν ? D^+·X + e) and shifts in vibration frequencies Δν of ν(OH) in the IR spectra of phenol complexes PhO-H + DX ? PhO^δ?-H…D^δ+X for nine series of DX molecules were studied. On compiling with three conditions (a constant donor center D; the electron density donation only from D and not from X; a constant sampling size within each series) it was possible to compare the polarization effect in D^+·X and D^δ+X. In the radical cations D^+·X the polarization effect is on the average 2.2 times larger than in the systems D^δ+X. The systems D^+·X and D^δ+X are virtually indistinguishable with respect to the external delocalization of the positive charge.     

New advances in the synthesis of tripyridinophane macrocycles suitable to enhance the luminescence of Ln(III) ions in aqueous solution

A series of four new 18-membered hexaaza macrocyclic ligands bearing three endocyclic pyridine units and acetate or methylenephosphonate pendant arms has been prepared. The new synthetic procedure is based on the use of amine and diamine precursors incorporating masked carboxylate or phosphonate functions and on an efficient sodium template effect which controls the crucial macrocyclization step (yields of macrocyclization reactions: 62–88%). This procedure appears as a suitable alternative compared to the classical Richman-Atkins methodology generally used for the preparation of this class of macrocycles. As demonstrated with the Eu^III and Tb^III complexes derived from two ligands, these tripyridinophane chelators form luminescent and stable mononuclear Ln^III complexes in aqueous solution at physiological pH. In such a medium, Tb^III complexes exhibit a brightness of 1700 (λ_exc?=?279?nm) and 3000 (λ_exc?=?268?nm)?M^?1?cm^?1.     

Collisional ionization of highly excited neon atoms by nonpolar hydrocarbons

When benzene, acetylene and ethylene were allowed to collide with Ne Rydberg atoms (17?n?40), significant Ne⁺ ions were observed. Their cross sections were estimated, with reference to the ionization by H₂O, to be as large as 10^?14–10^?15 cm². However, no Ne⁺ signals were observed when ethane, methane and N₂ were used as targets. Theoretical estimates of the cross sections for ionization by interaction of the quadrupole moment and polarizability of the first three molecules are several orders of magnitude smaller than the experimental cross sections given above. A similarity of this phenomenon to the scattering of a thermal electron by benzene etc., observed by Christophorou et al., is suggested.     

Transition metal NMR chemical shifts and polarizability effect in organometallic complexes

The literature data on substituent influence on the ⁵¹V, ⁵⁵Mn, ⁵⁷Fe, ⁵⁹Co, ⁶¹Ni, ⁹⁵Mo, ¹⁰³Rh, ¹⁸³W, ¹⁸⁷Os and ¹⁹⁵Pt NMR chemical shifts (δ) and on J (M, P; M = Mn, Fe, Mo, Rh, W, Os) coupling constants have been analyzed for 30 series of the organometallic complexes. It has been established for the first time that the δ and J values depend on the inductive, resonance and polarizability effects of substituents. The polarizability effect is caused by the partial charge on the central M atom. The contribution of this effect ranges from 3 to 86%. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparison of carbon aerogel and carbide-derived carbon as electrode materials for non-aqueous supercapacitors with high performance

Two porous carbon materials, one synthesised by pyrolysis of an organic aerogel prepared using sol–gel method and the other synthesised from molybdenum carbide by high temperature chlorination method, were tested as supercapacitor electrode materials in a non-aqueous tetraalkylammonium salt-based electrolyte. The gravimetric capacitance values calculated for the carbon aerogel (CAG)-based system were almost two times smaller (~55?F?g^?1) compared to carbide-derived carbon (C(Mo₂C))-based system (~125?F?g^?1). However, due to the very wide region of ideal polarizability, 3.6?V for C(Mo₂C) and 3.8?V for CAG-based test cells, very high energy densities up to 63?Wh?kg^?1 (34?Wh?dm^?3) and power densities up to 757?kW?kg^?1 (314?kW?dm^?3) were estimated for these systems, respectively. CAG-based system shows very short characteristic charge/discharge time constant values (0.05?s).     

Polarizability effect in transition metal carbonyl complexes

The literature date on substituent influence on the carbonyl stretching frequencies (ν), CO stretching force constants (k), as well as ¹³C NMR carbonyl chemical shifts (δ) have been analyzed for 19 series of the transition metal carbonyl complexes. It was established for the first time that the ν, k and δ values depend not only on the inductive and resonance effects but also on the polarizability of substituents. The polarizability contribution ranges up to 37%.     

Characterization of photocatalytic performance of silver deposited TiO2 nanorods

Ag–TiO₂ nanorods were synthesized via gel–sol methods. Cyclic voltammetry results showed that surface modification of TiO₂ nanorods using Ag led better electrochemical activity involving fast electron transfer to electrode. Electrochemical impedance spectroscopy results revealed that the increase in aspect ratio of TiO₂ nanorods and surface modification resulted in synergetic effect of reduction of e^?/h⁺ recombination and charge transfer resistance. Consequently the use of Ag–TiO₂ nanorods as photocatalysts exhibited significant increase in photocatalytic decomposition rate of acid red 44.     

A theoretical structural analysis of the factors that affect 1JNH, 1hJNH and 2hJNN in N–H···N hydrogen‐bonded complexes

Calculations of ¹ J_NH, ^1h J_NH and ^2h J_NN spin–spin coupling constants of 27 complexes presenting N–H·N hydrogen bonds have allowed to analyze these through hydrogen‐bond coupling as a function of the hybridization of both nitrogen atoms and the charge (+1, 0, ? 1) of the complex. The main conclusions are that the hybridization of N atom of the hydrogen bond donor is much more important than that of the hydrogen bond acceptor. Positive and negative charges (cationic and anionic complexes) exert opposite effects while the effect of the transition states ‘proton‐in‐the‐middle’ is considerable. Copyright © 2008 John Wiley & Sons, Ltd.     

On the correlation between deuteron quadrupole coupling constants,O-H and O-D stretching frequencies and hydrogen-bond distances in solid hydrates

Correlation curves are reported relating deuteron quadrupole coupling constants (e²qQ/h) to O-H and O-D stretching frequencies (v_OH and v_OD) for isotopically-dilute HDO molecules. Correlation curves are also given relating these quantities to hydrogen-bond distances.The best correlations are found to be between (e²qQ/h) and v_OH andv_OD whereas the correlations involving intermolecular geometries show considerably greater scatter.Complications caused by the effects of anharmonicity on the stretching vibrations and of vibrational averaging of the quadrupole coupling and geometrical parameters are discussed in light of the observed correlations. It is concluded that, although these effects are large, their magnitude is also strongly correlated with the stretching frequencies, quadrupole couplings and geometrical parameters.