Intramolecular Nonbonded Interactions Between Oxygen and Group VIA Elements: An Ab Initio Molecular Orbital and Density Functional Theory Investigation of the Structures of HX—CH2—COOH (X=S,Se, and Te)

Ab initio molecular orbital and density functional methods have been used to study the potential energy surfaces of the substituted acetic acids HX—CH₂—COOH, where X is one of the Group VIA Chalcophiles S, Se, or Te. The various conformers adopted by these compounds provide information regarding the energetic importance of nonbonded and hydrogen bonding interactions involving oxygen atoms with different hybridizations. Density functional and ab initio molecular orbital methods yield similar structural and energetic trends for these compounds. Calculations show that the structure of the lowest-energy conformer of each of these acids has the X—C—C—O backbone substantially twisted from planarity, similar to that previously observed for the corresponding aldehydes, HX—CH₂—CHO. In the twisted acid structures the shortest distance is within about 0.1 Å of the sum of the X and O van der Waals radii, which reduces overcrowding of the lone pairs of electrons on these atoms. In conformers where the heavy atom backbone is planar, one of the distances is significantly shorter than the sum of the van der Waals radii, and the total molecular energy of these conformers is higher than that of the twisted forms. The variation of X—H vibrational frequencies among conformers reflects the extent of X—H hydrogen bonding, and indicates that formation of this hydrogen bond is not the dominant factor in determining the lowest-energy conformation. When X is oxygen (HO—CH₂—COOH), the lowest-energy conformer is also nonplanar, whereas for the corresponding aldehyde, HO—CH₂—CHO, the lowest-energy conformer is a planar structure with C_S symmetry. The conformational preferences of these simple species provide reference points for inter- and intramolecular interactions in more complex systems of biological interest.     

一个新的噻二唑衍生物H2ADTZ与锰的二维聚合物的合成与晶体结构(英)

A new 1,3,4 thiadiazole-derivative ligand 2,5-(s-acetic acid) dimercapto-1,3,4 thiadiazole (H₂ADTZ) and its one-dimensional manganese polymer Mn(ADTZ)·4H₂O had been synthesized and structurally characterized by X-ray single crystal diffraction in this paper. The Mn(Ⅱ) ion is coordinated with a distorted octahedron by two oxygen atoms from neighboring two deprotonated ligands ADTZ^2- and other four oxygen atoms from four coordinated water molecules. The structural feature of the title compound is the formation of one-dimensional manganese chains polymer through the bridging of dioxygen O-O units. In the solid state structure of the complex, one-dimensional manganese chains are joined together by the weak intermolecular hydrogen bonds and vander Waals interactions forming a two-dimensional supramolecular compound. Furthermore, the UV spectra and electro-chemical properties of the title compound were also investigated. CCDC: 260532.     

Synthesis and Crystal Structur of (4,4''-H2bipy)[CdBr4]·H2O

The title compound (4,4'-H2bipy)[CdBr4]·H2O 1 has been synthesized via hydrothermal reaction and characterized by X-ray diffraction. The crystal belongs to monoelinic,space group P21/c with a=8.260(3), b=23.926(7), c=9.774(2) (A), β=106.777(9)°,C10H12Br4CdN2O, Mr=608.26, V=1849.4(9)(A)3, Z=4, Dc=2.185 g/cm3, S=1.005, μ(MoKα)=9.814 mm-1, F(000)=1128, R=0.0646 and wR=0.0989. The crystal structure analysis of 1reveals that the title compound features an isolated structure, based on discrete 4,4'-H2bipy moieties and lattice water molecules which are linked by hydrogen bonds together with tetrahedral cadmium atoms terminally coordinated by four bromine atoms.     

Dynamic covalent approach to [2]- and [3]roxtanes by utilizing a reversible thiol-disulfide interchange reaction

A dynamic covalent approach to disulfide-containing [2]- and [3]rotaxanes is described. Symmetrical dumbbell-shaped compounds with two secondary ammonium centers and a central located disulfide bond were synthesized as components of rotaxanes. The rotaxanes were synthesized from the dumbbell-shaped compounds and dibenzo-[24]crown-8 (DB24C8) with catalysis by benzenethiol. The yields of isolated rotaxanes reached about 90 % under optimized conditions. A kinetic study on the reaction forming [2]rotaxane 2 a and [3]rotaxane 3 a suggested a plausible reaction mechanism comprising several steps, including 1) initiation, 2) [2]rotaxane formation, and 3) [3]rotaxane formation. The whole reaction was found to be reversible in the presence of thiols, and thermodynamic control over product distribution was thus possible by varying the temperature, solvent, initial ratio of substrates, and concentration. The steric bulk of the end-capping groups had almost no influence on rotaxane yields, but the structure of the thiol was crucial for reaction rates. Amines and phosphines were also effective as catalysts. The structural characterization of the rotaxanes included an X-ray crystallographic study on [3]rotaxane 3 a.     

On the calculation of arbitrary multielectron molecular integrals over Slater‐type orbitals using recurrence relations for overlap integrals. III. Auxiliary functions \documentclass{article}\pagestyle{empty}\begin{document}$Q_{nn'}^{q}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$G_{-nn'}^{q}$\end{document}

The auxiliary functions $Q_{nn'}^{q}(p,pt)$ and $G_{-nn'}^{q}(p_{a},p,pt)$ which are used in our previous paper [Guseinov, I. I.; Mamedov, B. A. Int J Quantum Chem 2001, 81, 117] for the computation of multicenter electron‐repulsion integrals over Slater‐type orbitals (STOs) are discussed in detail, and the method is given for their numerical computation. The present method is suitable for all values of the parameters p_a, p, and pt. Three‐ and four‐center electron‐repulsion integrals are calculated for extremely large quantum numbers using relations for auxiliary functions obtained in this paper. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Thermotropic Liquid Crystals Formed by Intermolecular Hydrogen Bonding Interactions

The role of hydrogen bonding in the formation or stabilization of liquid crystalline phases has only recently been appreciated. Following the first, wellestablished examples of liquid crystal formation from the dimerization of aromatic carboxylic acids, through hydrogen bonding, several classes of compounds have recently been synthesized, the liquid crystalline behavior of which is also dependent on intermolecular hydrogen bonds between similar or dissimilar molecules. In this review the main classes of compounds exhibiting liquid crystallinity due to hydrogen bonding are presented to show the diversity of organic compounds that can be used as building elements in liquid crystals. The molecules are either of the rigid-rod anisotropic or amphiphilic types such as molecules appropriately functionalized with pyridyl and carboxyl groups, whose interaction leads to the formation of liquid crystals; amphiphilic carbohydrates and amphiphilic and bolaamphiphilic compounds with multiple hydroxyl groups whose dimerization or association is indispensable for the formation of liquid crystals; and certain amphiphilic carboxylic acids with monomeric or polymeric mesogens and amphiphilic-type compounds bearing different moieties, whose interaction may lead to the formation of mesomorphic compounds. Associated with the macroscopic display of liquid crystalline phases is the supramolecular structure, and therefore rather extended discussion of these structures are included in this review.     

Synthesis of the anionic fluororeceptors based on thiourea and amide groups and recognition property for α,ω-dicarboxylate

Three new neutral receptors (1, 2 and 3) containing thiourea and amide groups were synthesized by simple steps in good yields. The binding properties for anions of 1, 2 and 3 were examined by UV-vis, fluorescence, and ¹H NMR spectroscopy. Receptors 1, 2 and 3 all had a better adipate anion selectivity by comparison with other dicarboxylate anions. The association constants of 1, 2 and 3 with adipate were higher as compared to other anions (malonate, succinate, glutarate). In particular, a distinct color change was observed from light yellow to orange-red upon addition of adipate to the solution of 1 in DMSO. The UV-vis and fluorescence data indicate that a 1:1 stoichiometry complex is formed between compound 1, 2 or 3 and dicarboxylate anions through hydrogen bonding interactions.     

Synthesis, Crystal Structure, and IR Spectroscopic Characterization of 1,6-Hexanediammonium Dihydrogendecavanadate

Summary.  Anhydrous 1,6-hexanediammonium dihydrogendecavanadate ((HdaH₂)₂H₂V₁₀O₂₈, 1) was prepared by reaction of V₂O₅ with 1,6-hexanediamine in aqueous solution. The crystal structure of 1 was determined, and the proton positions in the H₂V₁₀O₂₈ ⁴⁻ anion were calculated by the bond length/bond number method. The protons are bound to the centrosymmetrically oriented μ–OV₃ groups of the decavanadate anion. Based on the analysis of IR spectra of 1 prepared from H₂O and D₂O, the absorption band at 871 cm⁻¹ can be attributed to δ(V–O_b–H) vibrations. Received August 3, 2001. Accepted (revised) October 8, 2001     

Elastic moduli and structure of low density polyethylene

Summary Low density polyethylene film is drawn at room temperature four times the original length and subjected to thermal annealing at 60, 80, and 100 °C keeping the film length constant. Long spacing measured by SAXS increased with increasing temperature of annealing; the increase of the long spacing is presumed to be due to the decrease of the number of micelles through relaxation during the annealing. Simultaneous measurement of the changes of the long spacing and the film length by stretching is carried out and stress-extension curves are obtained. The values of the initial moduli of the long spacingE ₁ and the film lengthY are very near to each other. Elastic modulus of the crystal latticeE _c is known to be 235 GN/m² and that of the amorphous regionE _a is found to be 0.15 GN/m². When higher stress is applied than in the case of the initial modulus, the percentage of extension of film is much greater than that of the long spacing. The discrepancy is explained by the increase of the number of micelles through stress crystallization.Dedicated to Professor Dr. K. Ueberreiter on the occasion of his 70th birthday.     

New organogermanium cations [RGe(OCH2CH2NME2)2]+ with intramolecular N→Ge coordination bonds

New organohalogermanes RGe(OCH₂CH₂NMe₂)₂X (R = Ph, X = I (5); R = Me, X = Cl (6) or I (7)) with an intramolecular N→Ge coordination bond were synthesized. According to the ¹H and ¹³C NMR spectroscopic data, iodides 5 and 7 exist in solution as ionic compounds with the pentacoordinated germanium atom. In solution of compound 4 (R = Ph, X = Cl), there is an equilibrium between the ionic and covalent forms. The equilibrium shifts toward the ionic form with increasing solvent polarity or temperature. In solution, chloride 6 is a covalent compound. The structures and relative stabilities of different isomers of compounds 4–7 were studied by quantum chemical calculations at the density functional level of theory. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 892–900, May, 2007.