Search results for "Hydrogen bond"
showing 10 items of 1310 documents
Recognition-Directed Supramolecular Assemblies of Metal Complexes of Terpyridine Derived Ligands with Self-Complementary Hydrogen Bonding Sites
2000
The synthesis and X-ray structures of three metal complexes with terpyridine-derived ligands that contain amino-pyrimidine and amino-pyrazine moieties are presented. They have been designed in view of directing their self-assembly into specific supramolecular arrays through molecular recognition interactions. The solid-state structures indeed reveal extensive hydrogen-bonded networks. The Co complex 4a with PF6- counterions builds a two-dimensional infinite interwoven grid through strong double hydrogen bonds (d(N-H-N) =2.918-3.018 A) between the amino groups and the N atoms of the rings, with all H-bonding sites saturated. Changing the anions to BF4- in 4b leads to a similar infinite but p…
Thermodynamics of binary mixtures: Volumes, heat capacities, and dilution enthalpies for then-pentanol+2-methyl-2-butanol system
1983
The densities, heat capacities, and dilution enthalpies ofn-pentanol+2-methyl-2-butanol mixtures have been measured, in many cases as a function of temperature, over the complete mole fraction range. Excesses thermodynamic properties, apparent and partial molar heat capacities, volumes and expansibilities were derived. The concentration and temperature dependences of these functions are discussed in terms of the variations of the structure of the system caused by the participation of the two alcohol molecules (with quite different steric hindrance of the alkyl chain around the-OH group) in the dynamic intermolecular association process through hydrogen bonding.
Cooperative Binding of Divalent Diamides by N-Alkyl Ammonium Resorcinarene Chlorides
2015
N-Alkyl ammonium resorcinarene chlorides, stabilized by an intricate array of hydrogen bonds leading to a cavitand-like structure, bind amides. The molecular recognition occurs through intermolecular hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the guests and the cation-anion circular hydrogen-bonded seam of the hosts, as well as through CH⋅⋅⋅π interactions. The N-alkyl ammonium resorcinarene chlorides cooperatively bind a series of di-acetamides of varying spacer lengths ranging from three to seven carbons. Titration data fit either a 1:1 or 2:1 binding isotherm depending on the spacer lengths. Considering all the guests possess similar binding motifs, the first bin…
Molecular self-assembly on an insulating surface: interplay between substrate templating and intermolecular interactions
2012
We report on molecular self-assembly of biphenyl-4,4'-dicarboxylic acid (BPDCA) on CaCO3(10 (1) over bar4) under ultra-high vacuum conditions. Two-dimensional, ordered islands are obtained upon deposition at room temperature, coexisting with a streaky structure that is ascribed to individual, mobile molecules forming a two-dimensional gas-like phase. High-resolution non-contact atomic force microscopy (NC-AFM) images of the molecular islands reveal an ordered inner structure that is dominated by rows of molecules aligned side by side running along the [(42) over bar 61] crystallographic direction. A detailed analysis of these rows exhibits inter-row distances that are multiples of the calci…
Ternary Polymer Solutions with Hydrogen Bonds, 1
2007
The Flory Huggins methodology coupled to AET has been extended to ternary polymer systems, in particular to solvent (A)/polymer 1 (B)/polymer 2 (C) systems, with the two polymers displaying H-bonding interactions. Because the H-bonding can perturb the randomness of polymeric conformations, the change in Gibbs free energy of mixing, AG, should arise from changes in combinatorial entropy as well as in interaction energy. The combinatorial part of AG is evaluated through AET as a function of the association constant η between B and C components, the autoassociation constant a between B components, and the independent number m of interaction sites of acceptor C. The enthalpic contribution is ev…
N-(tert-butoxycarbonylglycyl-alpha,beta-dehydrophenylalanylglycylphenylalanyl)-4-nitroaniline.
2000
In the crystal structure of the tetrapeptide Boc0–Gly1–ΔPhe2–Gly3–Phe4–p-NA (p-NA is para-nitroaniline), C33H36N6O8, there are two independent molecules differing in conformation in the asymmetric part of the unit cell. All the amino acids in the peptide are linked trans to each other. The torsion angles in the main chain of both molecules are close to the values of the type β-II turn. Two intramolecular and three intermolecular N—H⋯O hydrogen bonds stabilize the conformation of each of the molecules.
Thermogravimetric and calorimetric studies of water absorbed in polyaniline
1995
Abstract Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the behavior of residual water absorbed by an emeraldine base and a salt of chemically synthesized polyaniline (PANI—EB, PANI-ES). The matrix of PANI is shown to contain water molecules participating in both reversible and irreversible absorption. In its turn, the reversibly absorbed water consists of two components. The first component (WD 1 ) amounts to 5–7 wt.% and is removable from PANI-EB in a flow of dry nitrogen at room temperature. The second one (6–8 wt.%) of more strongly bonded water (WD 2 ) can be withdrawn from PANI-EB at temperatures from 70 to 150 °C depending on the measu…
Structural, spectral, and magnetic properties of end-to-end di-mu-thiocyanato-bridged polymeric complexes of Ni(II) and Co(II). X-ray crystal structu…
2002
Thiocyanatonickel(II) and thiocyanatocobalt(II) complexes of the composition Ni(NCS)(2)(HIm)(2) (1) and Co(NCS)(2)(HIm)(2) (2), where HIm = imidazole, were prepared and studied. In particular, the crystal structure of Ni(NCS)(2)(HIm)(2) was determined by X-ray methods. This compound crystallizes in the monoclinic system, space group P2(1)/n, with a = 7.720(1) A, b = 5.557(1) A, c = 13.774(3) A, beta = 102.54(3) degrees, and Z = 2. Its structure consists of a one-dimensional polymeric chain in which nickel(II) ions are bridged by two thiocyanate groups bonding in an end-to-end fashion in a trans arrangement. The Ni...Ni distance is 5.557(1) A. The crystal packing is determined by the intermo…
Synthesis, characterization and magnetic properties of mixed-valence iron complexes with 2-pyridyl oximes
2018
Two new mixed-valence iron complexes with 2-pyridyl oximes, [Fe(mpko)3Fe(H2O)2(NO3)](NO3)·2H2O (1) (mpko− = methyl(2-pyridyl)ketone oximate) and [{Fe(dpko)3}2Fe](ClO4)·4H2O (2) (dpko− = bis(2-pyridyl)ketone oximate), have been prepared by reaction of FeIII with mpkoH in methanol (1) and FeII with dpkoH in methanol/water (2). Dinuclear FeII(low-spin)FeIII(high-spin) and trinuclear FeII(low-spin)FeIII(high-spin)FeII(low-spin) cations are present in the crystal structure of 1 and 2, respectively. Intermolecular hydrogen bonds in 1 lead to weak antiferromagnetic interactions between pairs of neighboring FeIII centers, which allows observation of single-ion zero-field splitting effects.
Alkyl and diether bridged N,N,N′,N′-tetra(2-hydroxybenzyl)diamines: effects of hydrogen bonding on structure and solubility
2012
A solvent-free one-step method has been used to prepare two N,N,N′,N′-tetra(2-hydroxy-3,5-dimethylbenzyl)diaminoalkanes containing a long n-alkyl bridge (6 and 8 CH2 groups between N-atoms). In addition, three novel N,N,N′,N′-tetra(2-hydroxy-5-alkyl-3-alkylbenzyl)-diaminoalkane-ethers (alkyl = methyl or t-butyl) have been prepared using the same method. The compounds were studied in the solid state using single crystal X-ray diffraction and their solubility was studied using UV/Vis spectroscopy. In the solid state, hydrogen bonding plays a key role in controlling the crystal packing and conformations of the molecules, thus affecting the solubility and properties of the compounds.