7 research outputs found
Multifunctional Organosulfonate Anions Self-Assembled with Organic Cations by Charge-Assisted Hydrogen Bonds and the Cooperation of Water
The
present study focuses on the assembly of organo-cations with
organo-anions in water. The anions, characterized by symmetric moieties
(carbon-, adamantane-, or calixarene-based) functionalized with directional
hydrogen bond (HB) acceptor functions (tetra-sulfonate moieties),
are combined with planar guanidinium or terephtalimidamide cations
as hydrogen bond donors, the purpose being to integrate water molecules
into the lattice. The imbalance between the charge on the two components,
and the considerable number of HB donor and acceptor sites, promotes
the insertion of water into the structures. In the reported structures,
a part of the water molecules serves as a structural linker between
the anions and cations, while the remaining molecules cluster into
channels and cavities in a loose association with the supramolecular
matrix framework
Porous Molecular Crystals by Macrocyclic Coordination Supramolecules
In
this study, we show how the combination of metal ions, counter-anions
and opportunely functionalized and preorganized ligands gives rise
to two distinct supramolecular isomers, coordination polymeric chains
and hexameric macrocycles. The hexamers then aggregate to form a cubic
structure exhibiting permanent microporosity. The supramolecular assemblies
are formed with Ag<sup>+</sup>, thioether functionalized bisÂ(pirazolyl)Âmethane
ligands and CF<sub>3</sub>SO<sub>3</sub><sup>â</sup>/PF<sub>6</sub><sup>â</sup> as the counter-anions. Five different
ligands were prepared by modifying the peripheral thioether moiety
with naphthyl, methoxy, <i>m</i>-Me, <i>p</i>-Me
and F groups (L<sup>SNf</sup>, L<sup>SPhOMe</sup>, L<sup>SPhmâMe</sup>, L<sup>SPhpâMe</sup>, and L<sup>SPhF</sup>). Helicoidal coordination
polymeric chains are formed with CF<sub>3</sub>SO<sub>3</sub><sup>â</sup> (general formula [AgÂ(L)]<sub><i>n</i></sub>(CF<sub>3</sub>SO<sub>3</sub>)<sub><i>n</i></sub>), whereas
macrocyclic hexamers are formed with PF<sub>6</sub><sup>â</sup> (general formula [AgÂ(L)]<sub>6</sub>(PF<sub>6</sub>)<sub>6</sub>). The macrocycles self-assemble into ordered capsules with the shape
of a tetrahedron, and the overall framework is sustained by Ag<sup>+</sup>¡¡¡(PF<sub>6</sub><sup>â</sup>)¡¡¡Ag<sup>+</sup> contacts. The capsules generate a highly symmetric structural
arrangement, which is characterized by permanent microporosity arising
from two distinct types of microporous chambers in the structure.
The gas absorption isotherms show that the materials can selectively
adsorb CO<sub>2</sub> and N<sub>2</sub>O over CH<sub>4</sub> and N<sub>2</sub>. The modulation of the microporosity of the materials is
achieved by the different thioether functionalization of the ligands
L<sup>SNf</sup>, L<sup>SPhOMe</sup>, L<sup>SPhmâMe</sup>, and
L<sup>SPhF</sup>. The diffusion and localization of the gas molecules
within the cavities were investigated by 2D <sup>1</sup>Hâ<sup>13</sup>C solid state NMR on samples loaded with enriched <sup>13</sup>CO<sub>2</sub>, showing that both types of cavities are accessible
to guest molecules from the gas phase
Dynamics of Molecular Rotors Confined in Two Dimensions: Transition from a 2D Rotational Glass to a 2D Rotational Fluid in a Periodic Mesoporous Organosilica
The motional behavior of <i>p</i>-phenylene-<i>d</i><sub>4</sub> rotators confined within the 2D layers of
a hierarchically
ordered periodic mesoporous <i>p-</i>divinylbenzenesilica
has been elucidated to evaluate the effects of reduced dimensionality
on the engineered dynamics of artificial molecular machines. The hybrid
mesoporous material, characterized by a honeycomb lattice structure,
has arrays of alternating <i>p</i>-divinylbenzene rotors
and siloxane layers forming the molecularly ordered walls of the mesoscopic
channels. The <i>p</i>-divinylbenzene rotors are strongly
anchored between two adjacent siloxane sheets, so that the <i>p</i>-phenylene rotators are unable to experience translational
diffusion and are allowed to rotate about only one fixed axis. Variable-temperature <sup>2</sup>H NMR experiments revealed that the <i>p</i>-phenylene
rotators undergo an exchange process between sites related by 180°
and a non-Arrhenius temperature dependence of the dynamics, with reorientational
rates ranging from 10<sup>3</sup> to 10<sup>8</sup> Hz between 215
to 305 K. The regime of motion changes rapidly at about 280 K indicating
the occurrence of a dynamical transition. The transition was also
recognized by a steep change in the heat capacity at constant pressure.
As a result of the robust lamellar architecture comprising the pore
walls, the orientational dynamic disorder related to the phase transition
is only realized in two dimensions within the layers, that is in the
plane perpendicular to the channel axis. Thus, the aligned rotors
that form the organic layers exhibit unique anisotropic dynamical
properties as a result of the architectureâs reduced dimensionality.
The dynamical disorder restricted to two dimensions constitutes a
highly mobile fluidlike rotational phase at room temperature, which
upon cooling undergoes a transition to a more rigid glasslike phase.
Activation energies of 5.9 and 9.5 kcal/mol respectively have been
measured for the two dynamical regimes of rotation. Collectively,
our investigation has led to the discovery of an orientationally disordered
2D rotational glass and its transition from rigid to soft at increasing
temperature. The spectral narrowing observed in the <sup>2</sup>H
NMR experiments at higher temperatures (310â420 K) is consistent
with fast rotational dynamics, which remain anisotropic in nature
within the robust lamellar architecture. This study suggests that
exploiting reduced dimensionality in the design of solid-state artificial
molecular machines and functional materials may yield access to behavior
previously unrealized in 3D materials
Confinement of Single Polysilane Chains in Coordination Nanospaces
Understanding
the intrinsic properties of single conducting polymer chains is of
interest, largely for their applications in molecular devices. In
this study, we report the accommodation of single polysilane chains
with hole-transporting ability in porous coordination polymers (PCPs),
[AlÂ(OH)Â(L)]<sub><i>n</i></sub> (<b>1a</b>; L = 2,6-naphthalenedicarboxylate,
channel size = 8.5 Ă 8.5 Ă
<sup>2</sup>, <b>1b</b>;
L = 4,4â˛-biphenyldicarboxylate, channel size = 11.1 Ă
11.1 Ă
<sup>2</sup>). Interestingly, the isolation of single polysilane
chains increased the values of carrier mobility in comparison with
that in the bulk state due to the elimination of the slow interchain
hole hopping. Moreover, even when the chains are isolated one another,
the main chain conformation of polysilane could be controlled by changing
the pore environment of PCPs, as evidenced by Raman spectroscopy,
solid-state NMR measurements, and molecular dynamics simulation. Hence,
we succeeded in varying the conducting property of single polysilane
chains. Additionally, polysilanes have a drawback, photodegradation
under ultraviolet light, which should be overcome for the application
of polysilanes. It is noteworthy that the accommodation of polysilane
in the nanopores did not exhibit photodegradation. These results highlight
that PCPâpolysilane hybrids are promising candidates for further
use in the field of molecular electronics
Engineering Switchable Rotors in Molecular Crystals with Open Porosity
The first example of a porous molecular
crystal containing rotors
is presented. The permanently porous crystal architecture is sustained
by rotor-bearing molecular rods which are connected through charge-assisted
hydrogen bonds. The rotors, as fast as 10<sup>8</sup> Hz at 240 K,
are exposed to the crystalline channels, which absorb CO<sub>2</sub> and I<sub>2</sub> vapors at low pressure. The rotor dynamics could
be switched off and on by I<sub>2</sub> absorption/desorption, showing
remarkable change of material dynamics by the interaction with gaseous
species and suggesting the use of molecular crystals in sensing and
pollutant management
Engineering Switchable Rotors in Molecular Crystals with Open Porosity
The first example of a porous molecular
crystal containing rotors
is presented. The permanently porous crystal architecture is sustained
by rotor-bearing molecular rods which are connected through charge-assisted
hydrogen bonds. The rotors, as fast as 10<sup>8</sup> Hz at 240 K,
are exposed to the crystalline channels, which absorb CO<sub>2</sub> and I<sub>2</sub> vapors at low pressure. The rotor dynamics could
be switched off and on by I<sub>2</sub> absorption/desorption, showing
remarkable change of material dynamics by the interaction with gaseous
species and suggesting the use of molecular crystals in sensing and
pollutant management
Inclusion Compound Based Approach to Arrays of Artificial Dipolar Molecular Rotors. A Surface Inclusion
We describe an approach to regular triangular arrays
of dipolar molecular rotors based on insertion of dipolar rotator
carrying shafts as guests into channels of a host, trisÂ(<i>o</i>-phenylenedioxy)Âcyclotriphosphazene (TPP). The rotor guests can either
enter the bulk of the host or stay at or near the surface, if a suitable
stopper is installed at the end of the shaft. Differential scanning
calorimetry, solid-state NMR, and powder X-ray diffraction were used
to examine the insertion of a dipolar rotor synthesized for the purpose,
1-<i>n</i>-hexadecyl-12-(2,3-dichlorophenyl)-<i>p</i>-dicarba-<i>closo</i>-dodecaborane, and it was found that
it forms a surface inclusion compound. Rotational barriers from 1.2
to 9 kcal/mol were found by dielectric spectroscopy and were attributed
to rotors inserted into the surface to different degrees, some rubbing
the surface as they turn