Complexes Of Donors Research Articles

About Possibility of Development Synergetic Processes in Semiconductors of Type AIIIBV

Possibility of development of processes of selforganization in the semiconductors of type AIIIBV grown up by Chohralsky method in which there are no single vacancies because all of them are combined in complexes of type shallow donor + vacancy has been shown. At small homogeneous heating of such samples these complexes break up and periodic distribution of vacancies along the sample appearances. Thus, internal isotype potential barriers are formed. Because of division of created by action of temperature the non-equilibrium carriers by these barriers synergetic current and (or) voltage generate. These theoretical ideas are confirmed by experiments on gallium arsenide doped by tellurium and gallium arsenide doped by tin.

Complexes of Donor–Acceptor Cyclopropanes with Tin, Titanium, and Gallium Chlorides — Mechanism Studies

Hitherto unknown complexes of dimethyl cyclopropane-1,1-dicarboxylate with Lewis acids (Sn, Ti, and Ga chlorides) have been isolated and characterized. Their structures, which were previously assumed from theoretical considerations, have been confirmed, and the activating effect of Lewis acids on the cyclopropane ring has been shown experimentally. A single crystal of the complex with SnCl4 has been obtained, and an X-ray diffraction study has been performed. Hitherto unknown complexes of donor–acceptor cyclopropanes with GaCl3 belonging to a new type and having a 1,2-dipole (ylide) structure have been obtained and characterized. 1D and 2D NMR spectroscopy on 1H, 13C, 35Cl, 71Ga, and 119Sn nuclei were used to study the structures of the complexes. Furthermore, DOSY diffusion NMR spectroscopy was used to determine the diffusion coefficient in solution and the molecular masses of the complexes. The data obtained enrich the picture of transformations of donor–acceptor cyclopropanes widely used in organic syn...

Mn(III) complexes of the monoprotic tridentate ONN donor 2-[2-(1H-(benzo[d]imidazol-2-yl)ethylimino)methyl]phenol as a functional mimic of haloperoxidase

The reaction of MnII(ClO4)2 with 2-[2-(1H-(benzo[d]imidazol-2-yl)ethylimino)methyl]phenol (Hsal-aebmz, I) under aerobic conditions results in the formation of [MnIII(sal-aebmz)2]·ClO4 (1). In the presence of triethylamine and using MnCl2 under aerobic conditions, I forms [MnIII(sal-aebmz-H)(sal-aebmz)] (2). These complexes are characterised on the basis of elemental and electrochemical analyses, spectroscopic (IR and UV–Vis) data and thermogravimetric studies. Single crystal X-ray analysis of 2 shows that it is stabilized in the solid state through intermolecular hydrogen bonding between the NH groups of the two benzimidazole moieties after losing one of the hydrogen atoms; the coordination sites of the ligand are the imine nitrogen of the benzimidazole ring, the azomethine nitrogen and the deprotonated phenolic oxygen. Complex 2 catalyses the oxidative bromination of styrene by H2O2, yielding 1,2-dibromo-1-phenylethane, 1-phenylethane-1,2-diol and 2-bromo-1-phenylethane-1-ol, acting as a functional mimic of haloperoxidases.

QSPR study of charge–transfer complexes of some organic donors with p-chloranil using PLSR and MLR

A quantitative structure–property relationship (QSPR) study was conducted to develop models to relate the structure of 46 donor compounds to their charge–transfer complex formation constants with chloranil for the first time. Donors were a diverse set of organic compounds having different functional groups. QSPR models were calculated using multiple linear regressions (MLR) and partial least squares regression (PLSR) to predict charge–transfer complex formation constants. Some important descriptors in charge–transfer complex formation were calculated and added to the descriptors taken from DRAGON software. After a reduction step using variable importance in projection, stepwise regression was employed to select the most relevant descriptors and develop the QSPR models. Results of the PLSR and MLR modeling by the selected descriptors were markedly similar. The results showed that descriptors related to nitrogen, carbonyl group, and polarizability strengthen the charge–transfer interactions.

Spectral investigations of multiple charge transfer complex of p-nitrophenol as an electron acceptor with donor p-dimethylaminobenzaldehyde

The convincing evidence have been given that both the interactions π-π and π-π* (between p-nitrophenol (p-NTP) and p-dimethylaminobenzaldehyde (p-DAB)) are simultaneously involved. This has been established by using IR spectrometry. Association constant K evaluated by the method of Foster under the condition [A]0 = [D]0 with apply in this equation, [A]0/A = 1/Kɛλ[D]0 + 2/ɛλ, where [A]0 is the initial concentration of acceptor equal to [D]0, A is the absorbance of the complex at λ, K is the association constant, and ɛλ is the molar absorptivity of the complex at λ. In the IR spectral studies of several related organic compounds, one comes to the conclusion that p-NTP shows a broad band centred at 1600 cm−1 and to nitro asymmetric stretching vibrations. In the complex while the 1500 cm−1 band remains without shift, the broad band localized at 1600 cm−1 shift to 1610 cm−1. A shift of 10 cm−1 shows weak interactions. Studies on molecular complexes of organ metallic donors and acceptors are of very recent origin. Though alkyl donors have been extensively studied, very few studies have appeared on aryl donors.

Synthesis, chemical, electrochemical, and structural characterization of binuclear dioxo-bridged molybdenum(VI) complexes of tridentate ONS donors

A number of dioxo-bridged binuclear molybdenum(VI) complexes with diprotic tridentate ONS donor Schiff bases (H2L1, H2L2, H2L3, and H2L4) obtained by the condensation of salicylaldehyde/2-hydroxyacetophenone with S-benzyl and S-methyl dithiocarbazates have been synthesized using the Mo(V) complex (NH4)2[MoVOCl5] as starting material. All these reactions are carried out in air and the MoVO center of the precursor complex undergoes spontaneous aerial oxidation leading to the formation and isolation of molybdenum(VI) complexes Mo2O4L2. The complexes were characterized by elemental analyses, various spectroscopic techniques (UV-Vis, infrared etc.), magnetic susceptibility at room temperature, molar conductivity, and cyclic voltammetry. One of the complexes, Mo2O4L2 1 (1), was structurally characterized by single-crystal X-ray crystallography.

Proton transfer complexes based on some π-acceptors having acidic protons with 3-amino-6-[2-(2-thienyl)vinyl]-1,2,4-triazin-5(4 H)-one donor: Synthesis and spectroscopic characterizations

Charge transfer complexes based on 3-amino-6-[2-(2-thienyl)vinyl]-1,2,4-triazin-5(4 H)-one (ArNH 2) organic basic donor and pi-acceptors having acidic protons such as picric acid (PiA), hydroquinone (Q(OH) 2) and 3,5-dinitrobenzene (DNB) have been synthesized and spectroscopically studied. The NH 3 + ammonium ion was formed under the acid–base theory through proton transfer from an acidic to basic centers in all charge transfer complexes resulted. The values of formation constant ( K CT) and molar extinction coefficient ( ε CT) which were estimated from the spectrophotometric studies have a dramatic effect for the charge transfer complexes with differentiation of pi-acceptors. For further studies the vibrational spectroscopy of the [( ArNH 3 + )(PiA –)] (1), [( ArNH 3 + )(Q ( OH ) 2 - )] (2) and [( ArNH 3 + )(DNB –)] (3) of (1:1) charge transfer complexes of (donor: acceptor) were characterized by elemental analysis, infrared spectra, Raman spectra, 1H and 13CNMR spectra. The experimental data of elemental analyses of the charge transfer complexes (1), (2) and (3) were in agreement with calculated data. The IR and Raman spectra of (1), (2) and (3) are indicated to the presence of bands around 3100 and 1600 cm –1 distinguish to NH 3 + . The thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) techniques were performed to give knowledge about thermal stability behavior of the synthesized charge transfer complexes. The morphological features of start materials and charge transfer complexes were investigated using scanning electron microscopy (SEM) and optical microscopy.

“Union is strength”: how weak hydrogen bonds become stronger

Recently reported rotational spectroscopic studies on small dimers and oligomers bound by weak hydrogen bonds show that the driving forces, the spatial arrangement and the dynamical features displayed are very different from those involved in stronger and conventional hydrogen bonds. The very small binding energies (similar to those of van der Waals interactions) imply that the stabilization of the dimer is often obtained by networks of weak hydrogen bonds. Even in the presence of multiple bonds the partner molecules show a high degree of internal freedom within the complex. This paper analyses several examples of molecular adducts bound by weak hydrogen bonds formed in free jet expansions and recently characterized by rotational spectroscopy. They include weakly bound complexes of weak donors with strong acceptors (C-H···O,N, S-H···O,N), strong donors (O-H, N-H) with weak acceptors such as the halogen atoms and π systems but also the elusive interactions between weak donors and weak acceptors (C-H···π and C-H···halogen). Examples are also given where rotational spectroscopy highlights that weak hydrogen bonds are extremely important in chiral recognition phenomena and as driving forces of the conformational landscape of important biomolecules.

Spectroscopy, structure, and electrochemistry of transition metal complexes having [M2N2OS2] coordination sphere

Binuclear transition metal complexes of bicompartmental SNONS donors were synthesized and characterized by various physico-chemical techniques. Two different precursors with chloromethyl/formyl functionality at the 2 and 6 positions of phenolate ring are used to construct the ligands. The quinoxaline scaffolds provide SN donors incorporated at the 2 and 6 positions. Copper and zinc complexes are square pyramidal, whereas nickel and cobalt complexes are octahedral. The influence of two metal centers in terms of cooperative effect on the electronic, magnetic, electrochemical, and structural properties was investigated.

Neutron transmutation doping effects in GaN

The effects of neutron transmutation doping were studied for undoped (residual donor concentrations <1015 cm−3) GaN films grown by metalorganic chemical vapor deposition. After irradiation with reactor neutrons (equal fluences of 1.5×1017 n/cm2 of thermal and fast neutrons) the sample became semi-insulating, with the Fermi level pinned near Ec−0.8 eV. Isochronal annealing from 100 to 1000 °C showed three stages—slight recovery of conductivity at 200–300 °C, reverse annealing at 300–500 °C, and a broad recovery stage from 600 to 1000 °C. After annealing at 1000 °C, the donor concentration in the sample was close to the expected concentration of Ge donors transformed from Ga atoms upon interaction with thermal neutrons (2×1016 cm−3). Admittance spectroscopy showed that the donors had ionization energies ∼Ea=0.2 eV, much deeper than substitutional Ge donors. For intermediate annealing temperatures of 800 °C the donors were deeper (Ea=0.47 eV), but the proximity of concentrations of all these different centers suggests that they are due to transformation of complexes of Ge donors with radiation defects.

Comparison in the complexes of oxygen-containing σ-electron donor with hydrogen halide and dihalogen molecules

Ab initio and “Atoms in Molecules” studies have been carried on the intermolecular interactions between oxygen-containing σ-electron donors B (B = H 2O, H 2CO, (CH 2) 2O) and hydrogen halide HY and dihalogen molecules XY (X, Y = F, Cl, Br). The geometries, energies and topological characteristics of hydrogen-bonded systems have been compared with those of halogen-bonded systems. In general, many properties of the halogen bond are analogous to those of the hydrogen bond. For the same electron acceptor H or X atom, the properties such as bond distance, binding energy, electron density and charge transfer decrease in the sequence of B···HF > B···HCl > B···HBr, B···ClF > B···Cl 2, B···BrF > B···BrCl > B···Br 2. The bond distance, frequency shift and electron density may be applied as the measure of strength of hydrogen and halogen bond. The decrease in the atomic dipolar polarization and the atomic volume are dependent of the strength of halogen-bonded interaction, while they are independent of the strength of hydrogen-bonded interaction.

Low-Dimensional Nanostructures of Molecular Conductors

Amphiphilic bis-tetrathiafulvalene (bis-TTF) annulated macrocycles (1) were designed from the viewpoints of supramolecular chemistry and surface science in order to construct a variety of nanostructures based on molecular conductors. Electrically active low-dimensional nanostructures such as molecular-assembly nanodots, nanowires and nanorings were fabricated from the charge-transfer (CT) complexes of donor 1 by spin-coating and Langmuir-Blodgett techniques. CT complex of bis (methylthio)-substituted derivative (1a) formed oriented molecular-assembly nanowires on mica surface, whose typical dimensions were 2.5×50×>1,000 nm. The nanowire growth directions were consistent with the directions of hexagonal lattice of K+ sites on the mica surface. Ethylenedithio-substituted derivative (1b) had an ability to form a new redox-active organogel. Chemical oxidation of donor 1b yielded size-controllable nanodot structures by applying spin-coating technique. The diameter of nanodots (20∼800 nm) depended on the rotation speed of the spinner. Conductance of carrier dopped nanodots was three or four orders of magnitude higher than those of neutral molecular-assembly nanostructures.

Molecular adducts between a few phenolic donors and π-acceptors in solid-state

Electron donor–acceptor molecular complexes of a few phenolic donors with some quinonoid and tetracyanoethylene acceptors have been prepared by two different methods, i.e., by simple grinding of the respective component pair in the solid-state and in solution. Both the methods yielded identical dark colored 1:1 stoichiometric complexes. Spectral studies revealed that the complexes are ionic in nature. The g values obtained in ESR spectral studies for all these molecular adducts vary between 2.000 and 2.022, confirming the free radical nature of the adducts. The electronic absorption spectral studies proved that the donor–acceptor complexes formed initially, exhibit new electronic transitions at longer wavelengths, are less stable and disassociate readily into ionic type of adducts. The absorption maximum at longer wavelengths, i.e. ≥550 nm, are assigned to the charge transfer complexes, while the new transition at around 410 ± 5 nm is attributed to the anion radical of the adducts. The ease of complexation not only depends on the ionization potential and electron affinities of the phenolic donors and the acceptors but is also structure sensitive. Complexation is confirmed by the shift in IR absorption of the phenolic hydroxyl group and the carbonyl group of quinone acceptors and the cyano group of tetracyanoethylene. Proton magnetic resonance studies indicate an interaction between the phenolic donors and acceptors on basis of the altered chemical shifts. Further, IR and NMR studies show that the stability of the adducts is governed not only by the charge transfer interaction but also by hydrogen bonding.

Mononuclear manganese(II) and manganese(III) complexes of N2O donors involving amine and phenolate ligands: absorption spectra, electrochemistry and crystal structure of [Mn(L3)2](ClO4)

A number of mononuclear manganese(II) and manganese(III) complexes have been synthesized from tridentate N2O aminophenol ligands (HL1–HL5) formed by reduction of corresponding Schiff bases with NaBH4. Three types of tridentate N2O aminophenols have been prepared by reducing with NaBH4which are (a) Schiff bases obtained by bromo salicylaldehyde reaction with N,N-dimethyl/N,N-diethyl ethylene diamine (HL1, HL2), (b) Schiff bases obtained by condensing salicylaldehyde/bromo salicylaldehyde and picolyl amine (HL3, HL4), (c) pyridine-2-aldehyde and 2-aminophenol (HL5). All the manganese complexes have been prepared by direct addition of manganese perchlorate to the corresponding ligands and were characterized by the combination of i.r., u.v.–vis spectroscopy, magnetic moments and electrochemical studies. The u.v.–vis spectra of all of the manganese(III) complexes show two weak d–d transitions in the 630–520 nm region, which support a distorted octahedral geometry. The electron transfer properties of all of the manganese(III) complexes (1–4 and 6) exhibit mostly similar characteristics consisting two redox couples corresponding to the Mn III → Mn II reductions and Mn III → Mn IV oxidations. The electronic effect on the potential has also been studied by changing different substituents in the ligands. In all cases, an electron-donating group stabilizes the higher oxidation state and electron withdrawing group prefers the lower oxidation state. The cyclic voltammogram of [Mn II (L5)2] shows an irreversible oxidation Mn II → Mn III at −0.88 V, followed by another quasi-reversible oxidation Mn III → Mn IV at +0.48 V. The manganese(III) complex (3) [Mn(L3)2]ClO4has been characterized by X-ray crystallography.

Copper(II) complexes of several monophosphono dipeptides: the role of phosphonic oxygen and thioether sulfur in complex stabilization

Potentiometric, UV–Vis, CD and EPR studies were performed on the copper(II) complexes of oxygen and nitrogen donor ligands (monophosphono dipeptides: 1-( N- l-leucylamino)methylphosphonic acid – Leu–Gly(P), 1-( N- l-leucylamino)valylphosphonic acid – Leu–Val(P)) and a thioether sulfur donor ligands (monophosphono dipeptides: 1- N-(glycyloamino)-2-( S-benzylthio)ethanephosphonic acid – Gly–(Bz)Cys(P), d(+) and Gly–(Bz)Cys(P), d(−)). Complex formation reaction between copper(II) and dipeptides were very similar to each other, [MLH −1] − being the major species in wide pH region. CD spectroscopy, however, was a very sensitive tool for the elucidation of small structural differences among peptide complexes, including the weak interaction in an axial and equatorial position of thioether residues. The complexes of the thioether donors have higher thermodynamic stability constants than the other ones.

Charge-Transfer Molecular Complexes of Guanazole and Some 1,2,4-Triazoles with σ- and π-Acceptors Involving a New Acceptor: Resulting In Situ; DDQH2

Abstract Charge-transfer complexes of 1,2,4-triazole (1T), 3-amino-1,2,4-triazole (2T), 4-amino-4H-1,2,4-triazole (3T), and guanazole (3,5-diamino-1,2,4-triazole) (4T) with iodine as a typical σ-type acceptor and with typical π-type acceptors (tetracyanoethene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)) have been synthesized and characterized. The spectral characteristics and thermodynamic properties of such CT complexes were investigated. The system triazoles/iodine is characterized by the formation of triiodide ions (I3−), which is proposed to occur via the initial formation of outer-sphere charge-transfer complexes. The systems (1T–4T)/TCNE and (1T–4T)/DDQ produced the corresponding anion radicals, TCNE•− and DDQ•−, respectively. The time dependency of the spectral bands due to the 4T/TCNE system is discussed in terms of the scope of transformation from outer-sphere CT complexes to inner-sphere ones. Meanwhile, for the system 4T/DDQ the time dependency is accounted for by the stepwise reduction of DDQ to its anion radicals, and then to the corresponding hydroquinone (2,3-dichloro-5,6-dicyanohydroquinone), DDQH2. However, because the resulting in situ (DDQH2) was an unconventional new acceptor, it formed a CT complex with the donor (4T). The results show that the formed complexes are strong kinds of n–σ and n–π types in a 1:2 and 1:1 stoichiometry for the complexes of triazoles donors with iodine and DDQ, respectively.

ODMR of the photoexcited triplet state of donor–acceptor complexes of naphthalene donor with pyromellitic dianhydride, 1,2,4,5-tetracyanobenzene, and 1,3,5-trinitrobenzene acceptors

Odmr measurements of photoexcited triplet state traps were carried out at 1.2 K on polycrystalline donor–acceptor complexes of naphthalene (N) with the acceptors pyromellitic dianhydride (PMDA), 1,2,4,5-tetracyanobenzene (TCNB), and 1,3,5-trinitrobenzene (TNB). The zero field splittings (zfs) are consistent with a locally excited N triplet state with considerable admixture of charge transfer character that increases in the order N/TNB<N/TCNB≈N/PMDA based on zfs. The complexes reveal sublevel-selective enhancements of decay rate constants that are similar for N/TCNB and N/PMDA, but the pattern differs in N/TNB, suggesting a different donor–acceptor interaction for the latter.

Physical properties of CT complexes of a new asymmetric donor: (EDOB)(EDT)TTF

We investigate physical properties of the CT complexes of a new asymmetric (EDOB)(EDT)TTF donor which consists of the parts of BEDO-DBTTF and BEDT-TTF. The conductivities of the CT complexes are measured. The crystal structure of the radical salt [(EDOB)(EDT)TTF] 2PF 6 is analyzed and the band structure is discussed.

Controlled vapor-pressure heat-treatment effect on deep levels in liquid-encapsulated czochralski-grown GaP crystals

Photocapacitance (PHCAP) measurements have been carried out on GaP crystals grown by the liquid-encapsulated Czochralski (LEC) method with heat treatment under various phosphorus-vapor pressures at different temperatures. Electron traps of Ec-1.1 eV, Ec-1.6 eV, Ec-1.9 eV, and a hole trap of Ev+2.26 eV are mainly detected. The phosphorus-vapor pressure dependence of the Ec-1.9 eV trap density and their diffusion behavior indicate that they are interstitial phosphorus atoms. The densities of both Ec-1.1 eV and Ec-1.6 eV traps are strongly dependent on the shallow impurity concentrations. Moreover, the density of Ec-1.1 eV traps increases with increasing phosphorus-vapor pressure. From these results, we suggest that Ec-1.1 eV traps are the complexes of shallow donors and antisite phosphorus atoms. Deep-level densities in GaP crystals after annealing at 860°C or 960°C for 60 min are decreased almost one order of magnitude lower than those in untreated substrate crystals, which should have occurred via out-diffusion of interstitial phosphorus atoms. However, such an effect is not prominent for 800°C treatment for 60 min.

The preorganization step in organic reaction mechanisms. Charge-transfer complexes as precursors to electrophilic aromatic substitutions.

Metastable (pre-reactive) intermediates, as commonplace transients in simple bimolecular reactions, are usually unobserved (and ignored)-though they provide vital mechanistic insight. Thus, the preequilibrium (charge-transfer) complexes of various aromatic donors with rather typical electron acceptors such as Br(2), NO(+), and NO(2)(+) are examined quantitatively (via their molecular and electronic structures) to reveal surprisingly unorthodox aspects of what is conventionally referred to in organic chemistry textbooks as electrophilic aromatic bromination, nitrosation, and nitration, respectively.