A stable ternary inclusion complex comprising a host, an electron donor, and an electron acceptor with a long alkyl tail (see schematic representation) triggers the spontaneous formation of giant vesicles (see TEM image). The ternary complex behaves as a supramolecular amphiphile with a large polar head group and a single hydrophobic tail. Treatment of the complex with an oxidizing agent results in disruption of the vesicles.
A novel metal-organic framework, [{(Zn(0.25))(8)(O)}Zn(6)(L)(12)(H(2)O)(29)(DMF)(69)(NO(3))(2)](n) (1) {H(2)L = 1,3-bis(4-carboxyphenyl)imidazolium}, has been synthesized under solvothermal conditions in good yield. It shows a Zn(8)O cluster that is coordinated to six ligands and forms an overall three-dimensional structure with channels along the crystallographic a and b axes. The imidazolium groups of the ligand moiety are aligned in the channels. The channels are not empty but are occupied by a large number of DMF and water molecules. Upon heating, these solvent molecules can be removed without breakdown of the overall structure of the framework as shown by variable-temperature powder X-ray diffraction patterns. Of great interest is the fact that the compound exhibits high proton conductivity with a low activation energy that is comparable to those of Nafion presently used in fuel cells.
Three heteroditopic cryptands with different cavity
dimensions have been synthesized in high yields at
278 K without employing any templating metal ion. The three
secondary amino nitrogens in each cryptand could
be derivatized with anthryl groups to have a
fluorophore−spacer−receptor configuration. The fluorophores in
these
systems do not show any fluorescence due to an efficient photoinduced
intramolecular electron transfer (PET) from
nitrogen lone pairs. However, the fluorescence can be recovered to
different extents in the presence of different
metal ions and protons as well. On complexation by a transition
metal ion or on protonation in a solvent like dry
THF, each exhibits large fluorescence enhancement as the nitrogen lone
pairs responsible for PET are engaged in
bonding. Inner-transition-metal ions like Eu(III) or
Tb(III) show remarkable discrimination and give high
fluorescence
enhancement only in one case where the cavity size is smaller than that
of other two. Each system exhibits large
fluorescence enhancement with Pb(II) among the heavy metal ions
studied. The present study shows that transition
metal ions and Pb(II), which are known for quenching, can indeed
cause fluorescence enhancement in cryptand-based systems. It is also reported for the first time that
inner-transition-metal ions can also cause fluorescence.
The
enhancement in each case is interpreted in terms of a communication gap
between the metal ion and fluorophore.
Such cryptand-based fluorophores can be useful as potential
molecular photonic devices and metal ion sensors as
well.
Ce(NO3)3.6H2O or Pr(NO3)3.6H2O and pyridine-2,6-dicarboxylic acid form a linear coordination polymeric structure under hydrothermal conditions. Hexameric water clusters join these linear chains through bonding to the metal ions. Other coordinated water and the carboxylate oxygen form an intricate array of hydrogen bonding resulting in a 3D network where each metal ion shows 9-coordination with an approximate D3 symmetry. Dimeric water clusters are also located in the void spaces. In the structure containing Pr(III), the water dimers are hydrogen-bonded to the hexamers, whereas in the Ce(III) structure, the dimers and the hexamers are far apart.
The porous coordination polymer {[Mn(L)(H(2)O)](H(2)O)(1.5)(DMF)}(n) (1) containing a water molecule coordinated at the apical position of each distorted octahedral Mn(II) center has been synthesized using the solvothermal technique by reacting Mn(NO(3))(2) x 4 H(2)O with a new flexible ligand (LH(2)) having isophthalic fragment and pyridine donors at the two ends. The coordinated water molecule could be substituted by nitrile guest molecules such as acetonitrile, acrylonitrile, allylnitrile, and crotononitrile (affording compounds 2-5, respectively) without loss of crystallinity. Interestingly, compound 1 selectively captures cis-crotononitrile into its cavity from a mixture of cis and trans isomers. Hence, the cis isomer can be separated from the trans isomer. In each case, 1.5 lattice water molecules and a dimethylformamide (DMF) molecule are also simultaneously replaced by certain numbers of these guest molecules. When these first-generation compounds 2-5 are dipped in DMF at room temperature with the lid of the vial open to the atmosphere, the mother crystal 1 is regenerated in each case. Thus, all of these substitution reactions are completely reversible. Also, the first-generation compounds 2-5 can be interconverted among one another by dipping them in appropriate nitrile guests. All of these phenomena could be observed in single-crystal to single-crystal fashion.
Pyrazine-2,3,5,6-tetracarboxylic acid (pytcH(4)) reacts with Cu(NO(3))(2)x6H(2)O in 1:2 molar ratio in the presence of pyridine (py) vapor to form blue crystals of a coordination polymer with the empirical formula [Cu(2.5)(pytc)(py)(8)(NO(3)(-))x10H(2)O](n). Four such polymeric chains gather around a hexadecameric water cluster to form an overall 3D metal-organic framework structure. Once the water molecules are removed, the 3D structure breaks down. It presents a new mode of association of water molecules not predicted theoretically or found experimentally.
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