15 research outputs found
Induced chirality-at-metal and diastereoselectivity at Delta/Delta-configured distorted square-planar copper complexes by enantiopure Schiff base ligands: combined circular dichroism, DFT and X-ray structural studies
No full textBidentate enantiopure Schiff base ligands, (R or S)-N-1-(Ar) ethyl-2-oxo-1-naphthaldiminato-kappa N-2,O, diastereoselectively yield Delta/Delta-chiral four-coordinated, non-planar Cu((NO)-O-boolean AND)(2) complexes [Ar = C6H5 R/S-L1, m-C6H4OMe R-L2, p-C6H4OMe R/S-L3, and p-C6H4Br R/S-L4]. Two N,O-chelate ligands coordinate to the copper(II) atom in distorted square-planar mode, and induce metal-centered Delta/Delta-chirality at the copper atom in the C-2-symmetric complexes. In the solid state, the R-L1 (or R-L4) ligand chirality diastereoselectively induces a Delta-Cu configuration in Delta-Cu-R-L1 (or Delta-Cu-R-L4), the S-L1 ligand a Delta-Cu configuration in Delta-Cu-S-L1, forming enantiopure crystals upon crystallization. Conversely, the R-L2 ligand combines both Delta/Delta-Cu-R-L2 as a diastereomeric pair in the crystals. In solution, electronic circular dichroism (CD) spectra show full or partial diastereoselectivity towards Delta-Cu for R ligands and towards Delta-Cu for S ligands. The electronic CD spectra measured on all complexes obtained from R ligands (or S ligands), e.g. Cu-R-L1, Cu-R-L2, Cu-R-L3, and Cu-R-L4 (or Cu-S-L1, Cu-S-L3, and Cu-S-L4), show consistent spectral features. TDDFT calculations of the electronic CD spectra for the diastereomers Delta-Cu-R-L1 and.-Cu-R-L1 suggest that the CD spectra are largely dominated by the configuration at the metal center (Delta vs. Delta). The experimental CD spectrum of Cu-R-L1 agrees well with the one calculated for the Delta-Cu-R-L1 configuration. Cyclic voltammetry of Cu-R-L1 reveals a quasi-reversible redox wave corresponding to one-electron transfer for the [(CuL2)-L-II](0)/[(CuL2)-L-I](-1) couple in acetonitrile. DSC analyses for the complexes show an exothermic peak between 377 and 478 K (Delta H = -12 to -43 kJ mol(-1)), corresponding to a phase transformation from distorted square-planar/tetrahedral to regular tetrahedral geometry on heating
Synthesis and Characterization of Bis[(RorS)-N-1-(X-C6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]-Λ/Δ-cobalt(II) (X = H,p-CH3O,p-Br) with Symmetry- And Distance-Dependent Vibrational Circular Dichroism Enhancement and Sign Inversion
No full textThe enantiopure Schiff bases (RorS)-N-1-(X-C6H4)ethyl-2-hydroxy-1-naphthaldimine {X = H [(RorS)-HL1],p-CH3O [(RorS)-HL2], andp-Br [(R- orS)-HL3]} react with cobalt(II) acetate to give bis[(RorS)-N-1-(X-C6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]-Λ/Δ-cobalt(II) {X = H [Λ/Δ-Co-(RorS)-L1],p-CH3O [Λ/Δ-Co-(RorS)-L2], andp-Br [Λ/Δ-Co-(RorS)-L3]} ( 1 - 3 ), respectively. Induced Λ and Δ chirality originates at the metal center of theC2-symmetric molecule in pseudotetrahedral geometry. Differential scanning calorimetry analyses explored the thermal stability of the complexes, which undergo reversible phase transformation from crystalline solid to isotropic liquid phase for 1 and 3 but irreversible phase transformation for 2 . Like other cobalt(II) complexes, compounds 1 - 3 exhibit a continuous ensemble of absorption and circular dichroism bands, which span from the UV to IR region and can be collected into a superspectrum. Infrared vibrational circular dichroism (IR-VCD) spectra witness the coupling between Co2+-centered low-lying electronic states and ligand-centered vibrations. The coupling produces enhanced and almost monosignate VCD spectra, with both effects being mode-dependent in terms of theAorBsymmetry (in theC2point group) and distance from the Co2+core
Synthesis, X-ray, and Spectroscopic Study of Dissymmetric Tetrahedral Zinc(II) Complexes from Chiral Schiff Base Naphthaldiminate Ligands with Apparent Exception to the ECD Exciton Chirality
No full textBidentate enantiopure Schiff base ligands, (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminate (R- or S-N^O), diastereoselectively provide λ- or δ-chiral-at-metal four-coordinated Zn(R- or S-N^O)2 Ar = C6H5; Zn-1R or Zn-1S and p-C6H4OMe; Zn-2R or Zn-2S. Two R- or S-N^O-chelate ligands coordinate to the zinc(II) in a tetrahedral mode and induce λ- or δ-configuration at the zinc metal center. In the solid state, the R- or S-ligand diastereoselectively gives λ- or δ-Zn configuration, respectively, and forms enantiopure crystals. Single crystal structure determinations show two symmetry-independent molecules (A and B) in each asymmetric unit to give Z′ = 2 structures. Electronic circular dichroism (ECD) spectra show the expected mirror image relationship resulting from diastereomeric excess toward the λ-Zn for R-ligands and δ-Zn for S-ligands in solution. ECD spectra are well reproduced by TDDFT calculations, while the application of the exciton chirality method, in the common point-dipole approximation, predicts the wrong sign for the long-wavelength couplet. A dynamic diastereomeric equilibrium (λ vs δ) prevails for both R- and S-ligand-metal complexes in solution, respectively, evidenced by 1H NMR spectroscopy. Variable temperature 1H NMR spectra show a temperature-dependent shift of the diastereomeric equilibrium and confirm δ-Zn configuration (for S-ligand) to be the most stable one and favored at low temperature. DSC analyses provide quantitative diastereomeric excess in the solid state for Zn-2R and Zn-2S, which is comparable to the results of solution studies
Chirality at metal and helical ligand folding in optical isomers of chiral bis(naphthaldiminato)nickel(II) complexes
No full textEnantiopure bis[(R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]nickel(ii) complexes Ar = C6H5 (1R or 1S), p-OMeC6H4 (2R or 2S), and p-BrC6H4 (3R or 3S) are synthesized from the reactions between (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldimine and nickel(ii) acetate. Circular-dichroism spectra and their density-functional theoretical simulation reveal the expected mirror image relationship between the enantiomeric pairs 1R/1S and 3R/3S in solution. CD spectra are dominated by the metal-centered Λ- or Δ-chirality of non-planar four-coordinated nickel, this latter being in turn dictated by the ligand chirality. Single crystal structure determination for 1R and 1S shows that there are two symmetry-independent molecules (A and B) in each asymmetric unit that give a Z′ = 2 structure. Two asymmetric and chiral bidentate N^O-chelate Schiff base ligands coordinate to the nickel atom in a distorted square planar N2O2-coordination sphere. The conformational difference between the symmetry-independent molecules arises from the "up-or-down" folding of the naphthaldiminato ligand with respect to the coordination plane, which creates right- (P) or left-handed (M) helical conformations. Overall, the combination of ligand chirality, chirality at the metal and ligand folding gives rise to discrete metal helicates of preferred helicity in a selective way. Cyclic voltammograms (CV) show an oxidation wave at ca. 1.30 V for the [Ni(L)2]/[Ni(L)2]+ couple, and a reduction wave at ca. -0.35 V for the [Ni(L)2]/[Ni(L)2]- couple in acetonitrile
The political philosophy of Muhammed Iqbal
No full textDoktora TeziÇalışmamız 20. yy. da İslam siyasi düşüncesine yeni bir dinamizm ve anlayış kazandıran M. İkbal'in siyaset felsefesini konu almaktadır. İkbal, İslam dünyasını içine düştüğü esaretten ve krizden kurtarmaya çalışarak Batı emperyalizmine karşı güçlü, gelişmiş, yüksek maneviyatlı, İslam ilkelerine bağlı, benliğini (şahsiyet) kazanmış bir ideal birlik toplum oluşturmak ister. Bu toplumu oluşturan bireyler Allah'a yaklaşarak özgürlüğe kavuşacak ve kendisini sınırlayan tüm maddi bağlardan kurtulacaktır. Bu bireylerin tek rehberi Kur'ân ve Hz. Peygamberin yüksek ahlakı ve şahsiyetidir. Böylece bireyler Kur'ân'ı içselleştirecek, Kâbe'yi manevi kardeşliğin sembolü ve yeryüzünü Müslümanların yurdu olarak benimseyecek, kaderciliği ve taklitçiliği kökten reddecektir. Ayrıca bu toplumun bireyleri güçlü, yaratıcı, özgür, dinamik, çalışkan, mücadeleci ve her türlü gelişmeye, değişmeye ve modernliğe açık bireyler olmalıdır. Bu sebeple İkbal, toplumdan ziyade toplumu oluşturan bireyler üzerine yoğunlaşır. İkbal'in öngördüğü insan modeli, kalbi ve ruhu diri, yüksek şahsiyet sahibi, vatan mefhumundan bağımsız, köleliği, ideolojik milliyetçiliği reddeden ve dünyada olup bitenlere karşı kayıtsız kalmayan bir insan modelidir. Söz konusu niteliklere sahip bireylerden oluşan topluluklar birleşerek ideal devleti meydana getirecektir. Bu devletin idaresi ise tek kişinin elinde değil, toplumun elindedir yani bu idare, Cumhuriyet sistemidir. Bu sistemde halk yönetime aktif olarak katılmalıdır. Bu Cumhuriyetler birleşerek İslam birliğini veya milli devleti oluşturmalıdırlar. Çünkü Müslümanlar parçalanamaz tek millettir. Bu millet şuuru ile hareket edilmeli, milli ahlak geliştirilmeli ve topluma sağlıklı nesiller yetiştiren kadınlar iyi bir eğitimle donatılmalıdır.Our study is about the political philosophy of Muhammed Iqbal who gave a new dynamism and understanding of Islamic political thought in the 20th century. Iqbal wants to create an ideal society that strong, developed, highly spiritualized, depended on the principles of Islam, and self-identity against Western imperialism by trying to free the Islamic world from its captivity and crisis. The individuals who make up this society will liberate themselves by getting close to Allah and get rid of all the material connection that limit themselves. The only guide for these people is the Qur'an and the moral superiority and personality of the Prophet. Thus, people will internalize the Qur'an and adopt the Kaaba as the symbol of spiritual brotherhood and the earth as the home of Muslims, and will radically reject fatalism and imitation. In addition, individuals of this society should be strong, creative, free, dynamic, hardworking, challenging, and open to all kinds of development, change and modernity. For this reason, Iqbal focuses on individuals who make society rather than society. The human model predicted by Iqbal is a model in which is alive heart and soul, has a strong personality, is independent of the notion of the motherland, denial of slavery and ideological nationalism, and not indifferent to what is happening in the world. The communities of individuals with these qualifications will form the ideal state by uniting. The administration of this state is not in the hands of a single person, but in the hands of society, that is, this administration is the Republic system. In this system, the public should actively participate in the administration. These republics should form the Islamic Union or the national state by uniting. Because Muslims are the only nation that cannot disintegrate. It should be acted with this national consciousness, national morality must be developed, and women who bring up reliable generations to society should be equipped with a good education
Bismuth based half-Heusler alloys with giant thermoelectric figures of merit
No full textHalf-Heusler thermoelectric materials have attracted extensive research interest over the last two decades owing to their thermal stability, mechanical strength, and moderate efficiency. This article presents an ab initio theoretical evaluation of the electrical and thermal transport properties of three bismuth-based most promising thermoelectric alloys, selected out of 54 stable half-Heusler compounds. These are brand new compounds which are recently proposed to be stable (Nature Chem. 7, 308 (2015)) and may have interesting properties. The calculated band structures of the three compounds, namely HfRhBi, ZrIrBi and ZrRhBi, served as a hint for their promising thermoelectric properties. HfRhBi and ZrIrBi turn out to be narrow band gap semiconductors while ZrRhBi is a moderate band gap semiconductor. A detailed study of the carrier concentration and temperature dependence of the Seebeck coefficient, power factor, lattice and electronic thermal conductivity and hence the figure of merit (ZT) is carried out. In contrast to most promising known thermoelectric materials, we found a high power factor for these materials (highest similar to 17.36 mW m(-1) K-2 for p-type ZrIrBi). All three systems (especially p-type) show high ZT values, as high as 0.45 for the ideal crystals. The maximum ZT and the corresponding optimal n- and p-type doping concentrations are calculated, which shall certainly provide guidance for future experimental work
Synthesis, spectroscopy, electrochemistry, and molecular structure of <i>tetrakis</i>{(E)-2-((pyridin-2-ylimino)methyl)phenolato}(hydroxido)<sub>0.5</sub>(nitrato)<sub>1.5</sub>-tetracopper(II) nitrate hydroxide
No full textReaction between (E)-2-((pyridin-2-ylimino)methyl)phenol (HL) and copper(II) nitrate provides tetrakis{(E)-2-((pyridin-2-ylimino)methyl)phenolato}(hydroxido)0.5(nitrato)1.5-tetracopper(II) nitrate hydroxide, [(CuL)4(NO3)1.5(OH)0.5](NO3)(OH) (1). ESI-mass spectra show the ion peaks for the dinuclear species at m/z 565 for [(CuL)2(HCO2)]+ and 521 for [(CuL)2+H]+ and the mononuclear species at m/z 260 for [(CuL)]+. Vibrational spectra show very strong bands at 1604/1546 cm−1 for ν(C = N/C = C) and at 1384, 1351 cm−1 for ν(NO3–). Cyclic voltammograms demonstrate an irreversible redox processes for the Cu(II)/Cu(I) and Cu(I)/Cu(0) couples in acetonitrile. X-ray molecular structure determination explores the formation of a cationic tetranuclear copper(II)-complex, in which a deprotonated ligand molecule chelates to one copper ion with the phenolate-O and imino-N atoms. In addition, a phenolate-O atom bridges between two neighboring copper ions and a pyridine-N atom coordinates to a third copper ion, so that each ligand bridges among three copper ions in a κ2N,O:κO:κN' coordination sphere. Thus, the four copper ions and four chelating-bridging ligands assemble primarily into a cationic [(CuL)4]4+ complex. The two copper ions are further coordinated by either a nitrate anion (75% occupancy) or a hydroxide anion (25% occupancy) and form the core of a tetranuclear [(CuL)4(NO3)1.5(OH)0.5]2+ cation.</p
Kinetics and mechanism of the nucleophilic substitution reactions of 2-chloro-1-methylpyridinium iodide with primary and secondary amines
No full text32-36Rate constants for the SN2Ar reactions
of 2-chloro-1-methylpyridinium iodide with MeNH2, EtNH2, PrNH2,
BuNH2, Me2NH and Et2NH in water, at 1mol dm-3
constant ionic strength and 25°C have been determined. The observed rate of reaction
is first order with respect to amine as well as the pyridinium iodide i.e., the
overall reaction is second order. The relative reactiv ity of the amines towards
the reactions is Me2NH >> MeNH2 > EtNH2
> BuNH2 > PrNH2 > Et2NH. The Bronsted
β coefficient
is 0.67 and the Taft's correlation coefficient ρ25* is 4.39 for the primary
amines. Two oppositely charged species seem to be involved in the transition-state
of the substitution reactions. A two-step reaction mechanism is consistent with
the observed results in which the formation of an intermediate is believed to be
the rate determining step
