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⁺, thioether functionalized bis­(pirazolyl)­methane ligands and CF₃SO₃^–/PF₆^– 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^SNf, L^SPhOMe, L^SPhm‑Me, L^SPhp‑Me, and L^SPhF). Helicoidal coordination polymeric chains are formed with CF₃SO₃^– (general formula [Ag­(L)]_<i>n</i>(CF₃SO₃)_<i>n</i>), whereas macrocyclic hexamers are formed with PF₆^– (general formula [Ag­(L)]₆(PF₆)₆). The macrocycles self-assemble into ordered capsules with the shape of a tetrahedron, and the overall framework is sustained by Ag⁺···(PF₆^–)···Ag⁺ 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 CO₂ and N₂O over CH₄ and N₂. The modulation of the microporosity of the materials is achieved by the different thioether functionalization of the ligands L^SNf, L^SPhOMe, L^SPhm‑Me, and L^SPhF. The diffusion and localization of the gas molecules within the cavities were investigated by 2D ¹H–¹³C solid state NMR on samples loaded with enriched ¹³CO₂, 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>₄ 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 ²H 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 10³ to 10⁸ 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 architecture’s 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 ²H NMR experiments at higher temperatures (310–420 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), [Al­(OH)­(L)]_<i>n</i> (<b>1a</b>; L = 2,6-naphthalenedicarboxylate, channel size = 8.5 × 8.5 Ų, <b>1b</b>; L = 4,4′-biphenyldicarboxylate, channel size = 11.1 × 11.1 Ų). 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 PCP–polysilane 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 10⁸ Hz at 240 K, are exposed to the crystalline channels, which absorb CO₂ and I₂ vapors at low pressure. The rotor dynamics could be switched off and on by I₂ 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 10⁸ Hz at 240 K, are exposed to the crystalline channels, which absorb CO₂ and I₂ vapors at low pressure. The rotor dynamics could be switched off and on by I₂ 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, tris­(<i>o</i>-phenylenedioxy)­cyclotriphosphazene (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