In this article, we study the behavior of an ionic liquid (IL) derived from pyridinium, 1-butyl-3-methylpyridinium
tetrafluoroborate [b3mpy][BF4], in mixtures with water and with the first alkanols of the series from methanol to
butan-1-ol, at the temperatures of (298.15 and 318.15) K. First, the miscibility regions with the alkanols were
established at these two temperatures, determining experimentally the liquid−liquid equilibria and the upper critical
solution temperature (UCST) for each binary mixture, confirming the quasiexponential variation of the UCST
with the alkanol chain. The enthalpies
were determined experimentally with a newly designed calorimetric
cell, and the excess molar volumes
were determined from densities, at (298.15 and 318.15) K. In all cases, the
are positive with (d
/dT)p > 0, whereas the
are negative for mixtures with alkanols but positive for the
mixture of IL + water. The thermal coefficient (d
/dT)p > 0 was also positive in all cases. All data were
correlated with a suitable polynomial equation, and the area and volume parameters of [b3mpy][BF4] were
calculated. Finally, we give an interpretation of the results and of the behavior of the mixtures.
Calix[4]arenes at the upper rim substituted with two (thio)urea moieties, 2a-c and 4, or substituted with two acetamido groups, 5, adopt a pinched cone conformation in CDCl 3 solution. The pinched cone conformation is the result of diametrical, intramolecular hydrogen bonds and was studied by 1 H NMR dilution and variable-temperature experiments, NOESY spectroscopy, and FTIR experiments. The pinched cone conformation in these novel calix[4]arenes is stable in C 2 D 2 Cl 4 up to at least 120°C. The bis(ureido)calix[4]arenes 2b,c give a hydrogen-bonded dimer in the pinched cone conformation.
Calix[4]arenes diametrically substituted at the upper rim with two melamine units spontaneously form welldefined box-like assemblies in the presence of two equivalents of 5,5-diethylbarbituric acid. These assemblies, consisting of nine different components, are held together by 36 hydrogen bonds and are stable in apolar solvents at concentrations of up to 1 0 -4 M . This paper reports the first X-ray crystal structure, and the MALDI TOF mass spectra together with the complete 'H NMR spectroscopic characterization of these hydrogen-bonded assemblies. The crystal structure clearly shows that the assemblies are stereogenic, as a result of the antiparallel orientation of the two rosette motifs. Furthermore, the synthesis of twelve new l ,3-bis(melamine)calix[4]arenes carrying different numbers and types of functionalities at the upper rim is described. Detailed 'HNMR spectroscopic studies on the as-
The loss of anions takes place inside the mass spectrometer, generating the multiply charged ions needed for detection and calculation of the molecular weight. ["] Moleculqr mechanics were performed on Go -C3. The square-planar coordination environment of the Pd centers is well preserved. It is clear that after the second generation the structure of the dendrimer becomes quite entangled (Fig. 2). 5 nm Fig 2. Optimircd structures of G,, G ,We have shown that organometallic structures of nanometer dimensions can now be constructed in a very simple and controlled way. This method of controlled assembly provides a new and versatile tool for dendrimer synthesis. The method allows large variation in the metal in each generation, the coordinating ligands, and the structure of the nucleus. Received. December 29, 1995 [Z86901E] German version Arigeii . C/iern.
An upper-rim-substituted calix[4]arene tetracarboxylic acid forms hydrogen-bonded duplexes with lower-rim-substituted tetra(4-pyridyl)- and tetra(3-pyridyl)calix[4]arenes in chloroform. The formation of these adducts was studied by extraction experiments. The association constants determined via (1)H NMR dilution experiments in CDCl(3) are 7.6 x 10(3) and 1.3 x 10(3) M(-1) for the 4-pyridyl and the 3-pyridyl derivative, respectively. IR studies in the solid state and in solution indicate that the interaction is based on hydrogen bonding and that the degree of proton transfer is negligible. VPO measurements support the formation of 1:1 adducts.
A theoretical-experimental study for a set of 18 binary systems comprised of [bXmpy][BF(4)] (X=2-4) + 1,ω-Br(CH(2))(v)Br (v =ω=1-6) at a temperature of 298.15 K is presented. The solubility curves are determined for each binary system, establishing the intervals of measurement for the excess properties, H(E)(m) and V(E)(m). These properties are then determined for those systems that present a miscibility zone. Binary systems containing 1,ω-dibromoalkanes with ω=5,6 present reduced solubility intervals at the temperature of 298.15 K. However, the mixtures with 1,1-dibromomethane were totally miscible with the three isomers of 1-butyl-X-methylpyridinium tetrafluoroborate. Mixtures with dibromomethane present H(E)(m) <0, whereas H(E)(m) >0 for the other binary systems. Sigmoidal curves were observed for the V(E)(m) describing expansion and contraction processes for all the systems, except for the mixtures of [b2mpy][BF(4)] with the smaller dibromoalkanes, which present contraction effects. The COSMO-RS methodology was used to estimate the solubilities and the intermolecular interaction energies, giving an acceptable explanation of the behavioral structure of pure compounds and solutions.
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