Synthesis and dynamics of atropisomeric (S)-N-(α-phenylethyl)benzamides

The synthesis of atropisomeric 2-substituted benzamides 2a-e, 3a-e, and 4a-e, and characterization by X-ray structure analysis of 2d, 2e, 3c, 3e, 4c, and 4e are reported. Dynamic ¹H NMR spectroscopic studies of benzamides 2b-d, 3b-d, and 4b-d indicate that only two of the four possible rotamers are present in solution, with population ratios ranging between 1.5:1 and 4.1:1. The measured free energy of activation to interconversion of the rotamers ranged from 12.4 to 18.9 kcal mol⁻¹. Benzamides ArCON[(S)-phenethyl]₂ (2e, 3e, and 4e), exhibited atropisomer ratios between 1.7:1 and 1:1, and free energies of interconversion of the rotamers ranged from 11.5 to 17.6 kcal mol⁻¹. The highest rotation barriers were observed for the ortho-nitro derivatives 2a-e. Molecular calculations at the semiempirical level (PM3MM) gave free energies of activation for benzamides 2e and 3e of 23.6 and 12.4 kcal mol⁻¹, respectively, which are comparable to the experimental values.     

An unprecedented Cu–Schiff base complex existing as two different trinuclear units with strong antiferromagnetic couplings

A new tetradentate N₂O₂ donor Schiff base ligand [OHC₆H₄CHNCH₂CH₂CH(CH₂CH₃)NCHC₆H₄OH = H₂L ] was obtained by 1:2 condensation of 1,3-diaminopentane with salicylaldehyde and has been used to synthesise an unusual copper(II) complex whose asymmetric unit presents two structurally different almost linear trinuclear units [Cu₃(μ-L)₂(ClO₄)₂] [Cu₃(μ-L)₂(H₂O)(ClO₄)₂] (1). The ligand and the complex were characterised by elemental analysis, FT-IR, ¹H NMR and UV–Vis spectroscopy in addition electrochemical and single crystal X-ray diffraction studies were performed for the complex. The magnetic properties of 1 reveal the presence of strong intra-trimer (J₁ = −202(3) cm⁻¹ and J₂ = −233(3) cm⁻¹) as well as very weak inter-trimer (zJ′ = −0.11(1) cm⁻¹) antiferromagnetic interactions.     

Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.     

H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about CC bond

The rotational barriers between the configurational isomers of two structurally related push–pull 4-oxothiazolidines, differing in the number of exocyclic CC bonds, have been determined by dynamic ¹H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl₃ at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG^# 98.5 kJ/mol (at 298 K). The variable-temperature ¹H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d₆, possessing the two exocyclic CC bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG^# separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the SCCCO entity. The ¹³C NMR Δδ_C(2)C(2′) values, ranging from 58 to 69 ppm in 1a–d and 49-58 ppm in 2a–d, correlate with the degree of the push-pull character of the exocyclic C(2)C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh COEt > CONHPh > CONHCH₂CH₂Ph. The decrease of the Δδ_C(2)C(2′) values in 2a–d has been discussed for the first time in terms of an estimation of the electron donor capacity of the S fragment on the polarization of the CC bonds.     

Molecular miscible blend of poly(2-cyano-1,4-phenyleneterephthalamide) and polyvinylpyrrolidone characterized by two-dimensional correlation FTIR and solid state C NMR spectroscopy

Miscibility of blends of poly(2-cyano-1,4-phenyleneterephthalamide/polyvinylpyrrolidone) (CN-PPTA/PVP) was investigated by dilute solution viscometry, two-dimensional (2D) correlation Fourier transformed infrared (FTIR) spectroscopy and solid state ¹³C NMR spectroscopy. It was shown that a large proportion of the PVP, the water-soluble component, could not be removed from CN-PPTA by extraction with water, and even with boiling water for blend films, suggesting that the flexible aliphatic PVP chain forms a blend with the rigid aromatic CN-PPTA chain through strong intermolecular interaction making it too difficult to dissolve even in boiling water. Viscometry on a polymer mixture of dilute solution showed that [η]_exp exhibited larger value than [η]_theo in all mixtures used in this experiment, suggesting occurrence of a strong attractive interaction between the two polymers. 2D correlation FTIR spectroscopy revealed that the carbonyl absorption band of PVP at 1675 cm⁻¹ shifted to a new low frequency absorption band at 1640 cm⁻¹ with a change of 35 cm⁻¹, suggesting strong hydrogen bonding with NH (amide II) proton of CN-PPTA. Another new absorption band at 1685 cm⁻¹ was due to the carbonyl absorption band of CN-PPTA shifting to a higher frequency than that at 1662 cm⁻¹, indicating that some of the carbonyl groups in the CN-PPTA components of the blends were in a free state or in a non-hydrogen bonded state as a consequence of the participation of NH proton of CN-PPTA in hydrogen bonding, resulting in the absorption bands of NH bend deformation of CN-PPTA at 1542 and 1313 cm⁻¹ being shifted to higher wavenumber of 1556 and 1324 cm⁻¹, respectively. Solid state ¹³C NMR spectroscopy revealed a chemical shift for CO of the PVP component in the blend fiber changing down-field (shift to left) at 177.346 ppm with a difference of 1.812 ppm; this was due to a lower electron density around the carbon atom of CO of lactam via hydrogen bonding with NH proton of amide in the CN-PPTA component, suggesting that a homogeneous blend of the CN-PPTA and PVP was produced on a molecular scale via hydrogen bonding.     

Fourier transform infrared study of mercury interaction with carboxyl groups in humic acids

An interaction between humic acid, an organic part of soil and mercury was studied by Fourier transform infrared spectroscopy (FTIR) and by ICP-AES analysis under given pH and concentration conditions. First the spectroscopic model was validated on the interaction of simple molecules representing the structural components of humic acid such as benzoic acid, catechol and salicylic acid with mercury. The interaction of carboxylic parts of humic acid with mercury is very interesting and easily characterised by infrared spectroscopy, an ideal mean for molecular study. Under the salt form (commercial humic acid Fluka TM: FHA), humic acid reacts with mercury in a different way from its acid form (FHA purified noted PFHA) and the Leonardite (LHA). Because of the straightforward exchange between Na⁺, Ca²⁺ and Hg²⁺, fixation of the latter is much more important with the salt form (FHA). However, this reaction is reduced under the acid form (PFHA, LHA) because the exchange with protons is difficult. The effect of this exchange was studied by FTIR showing the intensity decrease of ν_CO (COOH), the carboxylic functional group band of the acid, and the shifting of ν_as (COO⁻), the carboxylate functional group band under given pH and mercury conditions. For the FHA salt form, the characteristic band ν_CO (COOH) represented by a shoulder did not evolute, whereas the corresponding band to ν_as (COO⁻) strongly shifted (40 cm⁻¹) for a maximum Hg²⁺ concentration (1 g l⁻¹). On the other hand, for the acid form (PFHA, LHA), the intense band of ν_CO (COOH) disappeared proportionally to the increase of Hg²⁺concentration and the ν_as (COO⁻) band moved for about 20 cm⁻¹. The same results were reached with pH variations. Our results were confirmed by ICP-AES mercury analysis. This study shows that humic acids react differently according to their chemical and structural state.     

Study on dynamic interfacial tension of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide at liquid/liquid interface

Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R₁₂HTAB) and n-hexane were measured using the spinning drop method. The effects of the R₁₂HTAB concentration (the concentration below the CMC) and temperature on the dynamic interfacial tension have been investigated; the reason of the change of dynamic interfacial tension with time has been discussed. The effective diffusion coefficient, D_a, and the adsorption barrier, _a, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while _a becomes higher with increasing R₁₂HTAB concentration in the bulk aqueous phase. D_a decreases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 0.87 × 10⁻¹² m⁻² s⁻¹ while _a increases from 5.41 kJ mol⁻¹ to 7.74 kJ mol⁻¹ with the increase of concentration in the bulk solution of R₁₂HTAB from 0.5 × 10⁻³ mol dm⁻³ to 4 × 10⁻³ mol dm⁻³. Change of temperature affects the adsorption rate through altering D_a and _a. The value of D_a increases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 13.98 × 10⁻¹² m⁻² s⁻¹ while that of _a decreases from 5.41 kJ mol⁻¹ to 5.07 kJ mol⁻¹ with temperature ascending from 303 K to 323 K. The adsorption of surfactant from the bulk phase into the interface follows a mixed diffusion–activation mechanism, which has been discussed in the light of interaction between surfactant molecules, diffusion and thermo-motion of molecules.     

Semi-empirically derived petrophysical and thermodynamical coefficients of permselective shales—Implications on ore mineralization

Phenomenological coefficients of shale–electrolyte systems may offer a glimpse into probable matrix-permeability and solute-exclusionary relationships. Shales from unexposed Upper Cretaceous Period Mancos Shale and from Permian Period Abo Formation were cut into thin wafers, placed in custom built osmometers and a chemical potential applied across them giving rise to induced osmotic flow. This in turn spawned matrix unique constants namely mechanical filtration coefficient L_P (m³ N⁻¹ s⁻¹), diffusional mobility per unit osmotic pressure L_PD (m³ N⁻¹ s⁻¹), osmotic flow coefficient; L_D (m³ N⁻¹ s⁻¹), reflection coefficient σ (dimensionless) at zero gradients of temperature and hydrostatic pressure. Considering intrinsic relationships between these constants where and L_PD = −σL_P, we have ascertained that the bentonitic fossiliferous Mancos shale had a lower L_P and a higher σ compared to the kaolinitic and siliceous shale from Abo Formation indicating a higher degree of compaction post-diagenesis (lower porosity) and higher filtration efficiency. Mechanistic processes involved in solute transport and matrix morphology indicate key multi-scale transformations, ionic- and atomic-exchange competitions on high energy sites like cation-exchange sites, isomorphic substitution at argillaceous mineral edges, atomic-clipping within basal spacing, preferential pathway migration, dead-end pores that give rise to localized solute exclusionary processes and solute attenuation giving rise to anomalous osmotic gradients.     

Investigations of molecular interactions in propionic acid–N,N-dimethyl formamide binary system—FTIR study

FTIR spectra of propionic acid (PA), N,N-dimethyl formamide (DMF) and its binary mixtures with varying molefractions of the PA were recorded in the region 500–3500 cm⁻¹, to investigate the formation of hydrogen bonded complexes in a mixed system. The observed features in ν(CO), δ(OC–N) and ν_as(CN) of DMF, ν(CO) and ν(CO) of PA have been explained in terms of the hydrogen bonding interactions between DMF and PA and dipole–dipole interaction. The intrinsic bandwidth for the vibrational modes ν_as(CN) and ν(CO) has been elucidated using Bondarev and Mardaeva model.     

Use of a graphite–polyurethane composite electrode for electroanalytical determination of indole-3-acetic acid in soil samples

A new electroanalytical methodology was developed for the quantification of the phytohormone indole-3-acetic acid (IAA), using a graphite–polyurethane composite electrode (GPU) and the square wave voltammetry (SWV), in 0.1 mol L^− 1 phosphoric acid solution (pH 1.6). Analytical curves were constructed under optimized conditions (f = 100 s^− 1, a = 50 mV, E_i = 5 mV) and the reached detection and quantification limits were 26 μg L^− 1 and 0.2 mg L^− 1, respectively. The developed methodology is simple and accurate for the routine determination of IAA. In order to verify the application of the electroanalytical methodology in fortified soil samples without previous treatment, an IAA assay was performed without serious interferences of the soil constituents.     

Theoretical study of the reaction of CF3O radicals with CO

The potential energy surface for the reaction of the CF₃O radicals with CO was investigated. The geometries and vibrational frequencies of the reactants, transition states, intermediates, and products were calculated at the UB3LYP/6-311+G(2d,p), UB3LYP/6-311+G(3df,2p) and UMP2/6-311+G(2d,p) levels of theory. The energies were improved by using the G2M(CC2) and G3B3 methods. The calculation suggests the reaction proceeds via either the fluorine abstraction of CF₃O by CO to produce FCO + CF₂O with a high energy barrier or the barrierless association of the reactants to form the trans-CF₃OCO intermediate. The trans-CF₃OCO is predicted to undergo subsequent isomerization to cis-CF₃OCO or dissociate directly to the products FCO + CF₂O and CF₃ + CO₂. The collisional stabilization of trans-CF₃OCO is dominant at room temperature, while trans-CF₃OCO isomerizing to cis-CF₃OCO followed by dissociating to CF₃ + CO₂ is accessible when temperature rises. The reason for only trans-CF₃OCO without cis-CF₃OCO observable in Ashen’s experiment [S.V. Ahsen, J. Hufen, H. Willner, J.S. Francisco, Chem. Eur. J. 8 (2002) 1189] is cis-CF₃OCO can be produced only via the isomerization of trans-CF₃OCO, and its yield is inappreciable at a low experimental temperature. The enthalpies of formation for the two conformations of CF₃OCO have been deduced: (trans-CF₃OCO) = −196.25 kcal mol⁻¹, (trans-CF₃OCO) = −197.46 kcal mol⁻¹, (cis-CF₃OCO) = −193.64 kcal mol⁻¹, and (cis-CF₃OCO) = −194.90 kcal mol⁻¹.     

Theoretical study of the interaction of a proton with the O, F and Cl atoms of enflurane (CHFCl–CF2–O–CHF2)

Ab initio MP2 and density functional B3LYP calculations were performed to investigate the interaction of a proton with the O, F and Cl atoms of enflurane (CHFCl–CF₂–O–CHF₂) in the gas phase. The study included the optimized structures, proton affinities, interactions energies and thermodynamic properties of protonated enflurane. The proton affinities (PAs) of the O and Cl atoms are 154.5 and 139.8 kcal mol⁻¹, respectively, whereas PAs of five of the fluorine atoms are between 143.6 and 165.5 kcal mol⁻¹ (MP2 results). In contrast to protonation at the O and Cl atoms, protonation at each of the F atoms of enflurane reveals a striking result, it leads to a cleavage of the C–F bond and formation of an ion–dipole complex between the enfluranyl cation and neutral hydrogen fluoride. The [(enfluranyl)⁺FH] complexes are weakly bound, the SAPT-calculated interaction energy varies between −12.5 and −11.7 kcal mol⁻¹. The long range attraction in these complexes is dominated by the electrostatic term (70%), whereas the induction and dispersion components contribute by about 15% each. Protonation at the chlorine atom of enflurane does not lead to a cleavage of the C–Cl bond. For the O-protonated enflurane the results from the natural bond orbital analysis (NBO) are discussed in details.     

Chemically modified oximato complexes of titanium(IV) isopropoxide as new precursors for the sol-gel preparation of nano-sized titania: Crystal and molecular structure of [Ti{ONC10H16}4·2CH2Cl2]

Reactions of [Ti(OPrⁱ)₄] with various oximes, in anhydrous refluxing benzene yielded complexes of the type [Ti{OPrⁱ}_4−n{L}_n], where, n = 1-4 and LH = (CH₃)₂CNOH (1-4), C₉H₁₆CNOH (5-8) and C₉H₁₈CNOH (9-12). The compounds were characterized by elemental analyses, molecular weight measurements, FAB-mass, FT-IR and NMR (¹H, ¹³C{¹H}) spectral studies. The FAB-mass spectra of mono- (1), and di- (2), (6), (10) substituted products indicate their dimeric nature and that of tri- (3) and tetra- (4), (8) substituted derivatives suggest their monomeric nature. Crystal and molecular structure of [Ti{ONC₁₀H₁₆}₄·2CH₂Cl₂] (8A) suggests that the oximato ligands bind the metal in a dihapto η²-(N, O) manner, leading to the formation of an eight coordinated species. Thermogravimetric curves of (3), (6) and (10) exhibit multi-step decomposition with the formation of TiO₂ as the final product in each case, at 900 °C. Low temperature (∼600 °C) sol-gel transformations of (2), (3), (4), (6), (7) and (8) yielded nano-sized titania (a), (b), (c), (d), (e) and (f), respectively. Formation of anatase phase in all the titania samples was confirmed by powder XRD patterns, FT-IR and Raman spectroscopy. SEM images of (a), (b), (c), (d), (e) and (f) exhibit formation of nano-grains with agglomer like surface morphologies. Compositions of all the titania samples were investigated by EDX analyses. The absorption spectra of the two representative samples, (a) and (f) indicate an energy band gap of 3.17 eV and 3.75 eV, respectively.     

Facile strategies for the synthesis and crystallization of linear trinuclear nickel(II)-Schiff base complexes with carboxylate bridges: Tuning of coordination geometry and magnetic properties

Three new linear trinuclear nickel(II) complexes, [Ni₃(salpen)₂(OAc)₂(H₂O)₂]·4H₂O (1) (OAc = acetate, CH₃COO⁻), [Ni₃(salpen)₂(OBz)₂] (2) (OBz = benzoate, PhCOO⁻) and [Ni₃(salpen)₂(OCn)₂(CH₃CN)₂] (4) (OCn = cinnamate, PhCHCHCOO⁻), H₂salpen = tetradentate ligand, N,N′-bis(salicylidene)-1,3-pentanediamine have been synthesized and characterized structurally and magnetically. The choice of solvent for growing single crystal was made by inspecting the morphology of the initially obtained solids with the help of SEM study. The magnetic properties of a closely related complex, [Ni₃(salpen)₂(OPh)₂(EtOH)] (3) (OPh = phenyl acetate, PhCH₂COO⁻) whose structure and solution properties have been reported recently, has also been studied here. The structural analyses reveal that both phenoxo and carboxylate bridging are present in all the complexes and the three Ni(II) atoms remain in linear disposition. Although the Schiff base ligand and the syn–syn bridging bidentate mode of the carboxylate group remain the same in complexes 1–4, the change of alkyl/aryl group of the carboxylates brings about systematic variations between six- and five-coordination in the geometry of the terminal Ni(II) centres of the trinuclear units. The steric demand as well as hydrophobic nature of the alkyl/aryl group of the carboxylate is found to play a crucial role in the tuning of the geometry. Variable-temperature (2–300 K) magnetic susceptibility measurements show that complexes 1–4 are antiferromagnetically coupled (J = −3.2(1), −4.6(1), −3.2(1) and −2.8(1) cm⁻¹ in 1–4, respectively). Calculations of the zero-field splitting parameter indicate that the values of D for complexes 1–4 are in the high range (D = +9.1(2), +14.2(2), +9.8(2) and +8.6(1) cm⁻¹ for 1–4, respectively). The highest D value of +14.2(2) and +9.8(2) cm⁻¹ for complexes 2 and 3, respectively, are consistent with the pentacoordinated geometry of the two terminal nickel(II) ions in 2 and one terminal nickel(II) ion in 3.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Synthesis and conformational analysis of 1,3,2-diazaphosphorino[6,1-a]isoquinolines, a new ring system

Through ring-closure reactions of N- or 1′-substituted 1-(2′-aminoethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines (5a-e) with phenylphosphonyl dichloride, 1- or 3-substituted 4-phenyl-1,3,4,6,7,11b-tetrahydro-2H-1,3,2-diazaphosphorino[6,1-a]isoquinolin-4-one diastereomers (7a-e and 8a-c,e), the first representatives of a new ring system, were prepared. The diastereomeric ratios in the cyclizations and the conformer (A-E) populations of the nitrogen-bridged tricyclic systems (7 and 8) were strongly influenced by the N- and 1′-substituents of the starting diamines. The conformational analysis of compounds 7 and 8 was performed by ¹H, ¹³C and ³¹P NMR methods.     

Anisotropic exchange interactions in dinuclear systems (Ln = Dy, Tm, Yb): Magnetometry and Dual Mode X-band Electron Paramagnetic Resonance spectroscopic study

A recently developed experimental and theoretical procedure is used in order to calculate the magnitude and anisotropy of interaction between a lanthanide and a 3d-metal ion. The general formula of the molecular compounds is [Ln(H₂O)₃(dmf)₄(μ-CN)Fe–(CN)₅] · nH₂O where 1  n  1,5 and dmf = N,N′-dimethylformamide, abbreviated as [LnFe] from now on. The main parts of this procedure are (a) the evaluation of the effective g-parameters of the lanthanide ion with the help of EPR measurements. (b) The use of dual mode EPR spectroscopy to define the anisotropic exchange interactions with the help of an anisotropic Hamiltonian model. (c) Use of the same magnetic model to fit magnetization and susceptibility data in order to verify the EPR findings.It was possible to define some trends concerning the exchange components of the [DyFe] dimer according to which the antiferromagnetic isotropic exchange constant is smaller than 4 cm⁻¹ and the anisotropic components are [D_exc, E_exc] = [6(1), 0.0] cm⁻¹. Also for the case of [TmFe] and [YbFe] dimers the antiferromagnetic isotropic exchange constant is smaller than 0.3 cm⁻¹ while the anisotropic components are [D_exc, E_exc] = [12.0, 0.0] cm⁻¹ and [D_exc, E_exc] = [0.4(1), 0.0] cm⁻¹, respectively.     

Study of ion–solvent interactions of some tetraalkylammonium halides in THF + CCl4 mixtures by conductance measurements

Conductivities of some tetraalkylammonium halides, viz. tetrapentylammonium chloride (Pen₄NCl), tetrahexylammonium chloride (Hex₄NCl), tetraheptylammonium chloride (Hep₄NCl), and tetraoctylammonium chloride (Oct₄NCl) were measured at 298.15 K in THF + CCl₄ mixtures with 40, 60 and 80 mass% of THF. A minimum in the conductometric curves (molar conductance, Λ vs. square root of concentration, √c) was observed at concentrations which is dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M⁺ + X⁻ ↔ MX, K_P) and triple-ions (2M⁺ + X⁻ ↔ M₂X⁺; M⁺ + 2X⁻ ↔ MX₂⁻, K_T). A linear relationship between the triple-ion formation constants [log(K_T/K_P)] and the salt concentrations at the minimum conductivity (log C_min) was given for all salts in THF + CCl₄ mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R₄N⁺X⁻).     

Design and synthesis of 2-substituted-8-hydroxyquinline zinc complexes with hole-transporting ability for highly effective yellow-light emitters

Four multifunctional 8-hydroxyquinoline derivatives were designed and synthesized, their structures were identified by FT-IR, ¹H NMR, MS and elemental analysis. Among them are (E)-2-(2-(9-(4-methoxyphenyl)-9H-carbazol-3-yl)vinyl) quinolato-zinc (1), (E)-2-(2-(9-p-tolyl-9H-carbazol-3-yl)vinyl)quinolato-zinc (2), (E)-2-(2-(9H-fluoren-2-yl)vinyl)quinolato-zinc (3), and (E)-2-(2-(phenanthren-9-yl)vinyl)quinolato-zinc (4). The electroluminescence (EL) and hole-transporting characteristics of these materials were investigated on four configurations: (A) ITO/2-TNATA/NPB/1, 2, 3 or 4/Alq₃/LiF/Al; (B) ITO/2-TNATA/NPB/1, 2, 3 or 4/LiF/Al; (C) ITO/2-TNATA/1, 2, 3 or 4/Alq₃/LiF/Al; and (D) ITO/2-TNATA/1 or 2/NPB/Alq₃/LiF/Al. The maximum luminescence and current efficiencies of are 3556 cd m⁻² (at 13 V) and 2.17 cd A⁻¹ (at 9 V) for compound 2, 4624 cd m⁻² (at 15 V) and 2.1 cd A⁻¹ (at 7 V) for compound 3, and 3164 cd m⁻² (at 14 V) and 1.83 cd A⁻¹ (at 13 V) for compound 4 in the configuration D, respectively, indicating that they are good multifunctional materials with strong hole-transporting abilities and luminescence properties.     

Synthesis and characterization of half-sandwich iridium(III) and rhodium(III) complexes bearing organochalcogen ligands

Reactions of [Cp*M(μ-Cl)Cl]₂ (M = Ir, Rh; Cp* = η⁵-pentamethylcyclopentadienyl) with bi- or tri-dentate organochalcogen ligands Mbit (L1), Mbpit (L2), Mbbit (L3) and [Tm^Me]⁻ (L4) (Mbit = 1,1′-methylenebis(3-methyl-imidazole-2-thione); Mbpit = 1,1′-methylene bis (3-iso-propyl-imidazole-2-thione), Mbbit = 1,1′-methylene bis (3-tert-butyl-imidazole-2-thione)) and [Tm^Me]⁻ (Tm^Me = tris (2-mercapto-1-methylimidazolyl) borate) result in the formation of the 18-electron half-sandwich complexes [Cp*M(Mbit)Cl]Cl (M = Ir, 1a; M = Rh, 1b), [Cp*M(Mbpit)Cl]Cl (M = Ir, 2a; M = Rh, 2b), [Cp*M(Mbbit)Cl]Cl (M = Ir, 3a; M = Rh, 3b) and [Cp*M(Tm^Me)]Cl (M = Ir, 4a; M = Rh, 4b), respectively. All complexes have been characterized by elemental analysis, NMR and IR spectra. The molecular structures of 1a, 2b and 4a have been determined by X-ray crystallography.